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Endocannabinoids Activate Transient Receptor Potential Vanilloid 1 Receptors to Reduce Hyperdopaminergia-Related Hyperactivity: Therapeutic Implications
Abstract
Knockout (KO) mice invalidated for the dopamine transporter (DAT) constitute a powerful animal model of neurobiological alterations associated with hyperdopaminergia relevant to schizophrenia and attention-deficit/hyperactivity disorder (ADHD).
Because of continuously increasing evidence for a neuromodulatory role of endocannabinoids in dopamine-related pathophysiological responses, we assessed endocannabinoid signaling in DAT KO mice and evaluated the ability of endocannabinoid ligands to normalize behavioral deficits, namely spontaneous hyperlocomotion in these mice.
In DAT KO mice, we found markedly reduced anandamide levels, specifically in striatum, the dopamine nerve terminal region. Furthermore, three distinct indirect endocannabinoid agonists, the selective anandamide reuptake inhibitors AM404 and VDM11 and the fatty acid amidohydrolase inhibitor AA5HT, attenuated spontaneous hyperlocomotion in DAT KO mice. The hypolocomotor effects of AM404, VDM11, and AA5HT were significantly attenuated by co-administration of the transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine but not the selective cannabinoid type 1 (CB1)receptor antagonist AM251. Interestingly, TRPV1 binding was increased in the striatum of DAT KO mice, while CB1 receptor binding was unaffected.
These data indicate a dysregulated striatal endocannabinoid neurotransmission associated with hyperdopaminergic state. Restoring endocannabinoid homeostasis in active synapses might constitute an alternative therapeutic strategy for disorders associated with hyperdopaminergia. In this process, TRPV1 receptors seem to play a key role and represent a novel promising pharmacological target.
... Structurally, DAT-KO animals show a reduced volume of the striatum followed by a concurrent volume increase in other important regions, such as the PFC and cerebellum [49]. Striatal volume loss in mice is mainly caused by a decreased density of GABAergic interneurons and raised markers of neurodegeneration (e.g., hyperphosphorylated tau protein) [50][51][52][53]. Notably, this negative correlation between striatal and cerebellar volume areas points out a potential neurodevelopmental compensation [49]. ...
... In addition, the decreased DAT activity leads to biochemical and structural changes that also affect other neurotransmitter pathways. Indeed, DAT-KO animals showed a decreased density of GABAergic neurons, as well as decreased concentrations of anandamide and serotonin [30,52]. Moreover, elevated numbers of neurodegeneration markers, such as hyperphosphorylated tau protein, that are also associated with dyskinesia manifestation, have been revealed in DAT-KO mice striatal samples [50][51][52][53]. ...
... Indeed, DAT-KO animals showed a decreased density of GABAergic neurons, as well as decreased concentrations of anandamide and serotonin [30,52]. Moreover, elevated numbers of neurodegeneration markers, such as hyperphosphorylated tau protein, that are also associated with dyskinesia manifestation, have been revealed in DAT-KO mice striatal samples [50][51][52][53]. ...
The key element of dopamine (DA) neurotransmission is undoubtedly DA transporter (DAT), a transmembrane protein responsible for the synaptic reuptake of the mediator. Changes in DAT’s function can be a key mechanism of pathological conditions associated with hyperdopaminergia. The first strain of gene-modified rodents with a lack of DAT were created more than 25 years ago. Such animals are characterized by increased levels of striatal DA, resulting in locomotor hyperactivity, increased levels of motor stereotypes, cognitive deficits, and other behavioral abnormalities. The administration of dopaminergic and pharmacological agents affecting other neurotransmitter systems can mitigate those abnormalities. The main purpose of this review is to systematize and analyze (1) known data on the consequences of changes in DAT expression in experimental animals, (2) results of pharmacological studies in these animals, and (3) to estimate the validity of animals lacking DAT as models for discovering new treatments of DA-related disorders.
... Cannabinoid receptors can also be modulated with higher specificity using exocannabinoids, including CP-55940 and WIN 55,212-2 (CB 1 /CB 2 agonists), AM-251 and SR-141716A (Rimonabant, CB 1 inverse agonists), and resiniferatoxin (TRPV 1 antagonist). Lastly, eCB upregulation can be induced by metabolic inhibitors, like URB-597 (FAAH inhibitor), URB-602 (2-AG degradation blocker), and AM404 (anandamide reuptake inhibitor/TRPV 1 agonist) (Melis et al., 2004b;Tzavara et al., 2006;Lafourcade et al., 2007;Xing and Li, 2007;Dissanayake et al., 2008;Hajós et al., 2008;Aguilar et al., 2014;Raver and Keller, 2014). ...
... These findings, together with those from Marinelli et al. (2005) and Grueter et al. (2010), suggest that complex interactions exist between the eCB and endovanilloid systems across hippocampal and mesolimbic circuits. Psychopharmacology studies had already observed that TRPV 1 receptors modulate behavioral changes in schizophrenia models (Tzavara et al., 2006;Almeida et al., 2014). In addition, systemic capsaicin in hyperdopaminergic animals has been reported to suppress the hyperlocomotion associated with decreased nigrostriatal activity (De Lago et al., 2004;Lee et al., 2006;Tzavara et al., 2006). ...
... Psychopharmacology studies had already observed that TRPV 1 receptors modulate behavioral changes in schizophrenia models (Tzavara et al., 2006;Almeida et al., 2014). In addition, systemic capsaicin in hyperdopaminergic animals has been reported to suppress the hyperlocomotion associated with decreased nigrostriatal activity (De Lago et al., 2004;Lee et al., 2006;Tzavara et al., 2006). It seems clear, therefore, that exploring these same psychopharmacological issues using neurophysiological tools tends to detail the relationship between the endovanilloid system and schizophrenia. ...
Much of our knowledge of the endocannabinoid system in schizophrenia comes from behavioral measures in rodents, like prepulse inhibition of the acoustic startle and open-field locomotion, which are commonly used along with neurochemical approaches or drug challenge designs. Such methods continue to map fundamental mechanisms of sensorimotor gating, hyperlocomotion, social interaction, and underlying monoaminergic, glutamatergic, and GABAergic disturbances. These strategies will require, however, a greater use of neurophysiological tools to better inform clinical research. In this sense, electrophysiology and viral vector-based circuit dissection, like optogenetics, can further elucidate how exogenous cannabinoids worsen (e.g., tetrahydrocannabinol, THC) or ameliorate (e.g., cannabidiol, CBD) schizophrenia symptoms, like hallucinations, delusions, and cognitive deficits. Also, recent studies point to a complex endocannabinoid-endovanilloid interplay, including the influence of anandamide (endogenous CB 1 and TRPV 1 agonist) on cognitive variables, such as aversive memory extinction. In fact, growing interest has been devoted to TRPV 1 receptors as promising therapeutic targets. Here, these issues are reviewed with an emphasis on the neurophysiological evidence. First, we contextualize imaging and electrographic findings in humans. Then, we present a comprehensive review on rodent electrophysiology. Finally, we discuss how basic research will benefit from further combining psychopharmacological and neurophysiological tools.
... Recent studies have elucidated regulatory mechanisms exerted by CBs on the TRPV1R (e.g., AEA, AM404, or N-arachidonoyl-dopamine (NADA) (Iannotti et al., 2016). TRPV1Rs are located in intrinsic neurons of the dorsal striatum (Galan-Rodriguez et al., 2009), nigrostriatal terminals, and TH + cells in the SNc (de Lago et al., 2004;Lastres-Becker et al., 2005;Morera-Herreras et al., 2016;Tzavara et al., 2006) and pharmacological modulation of these channels has been reported to influence striatum-dependent functions (de Lago et al., 2004;Tzavara et al., 2006). The presence of TRPV1R and its agonist in the BG allow a direct action of these ECB/endovanilloid compounds on the excitability of nigrostriatal DAergic neurons (Marinelli et al., 2003). ...
... Recent studies have elucidated regulatory mechanisms exerted by CBs on the TRPV1R (e.g., AEA, AM404, or N-arachidonoyl-dopamine (NADA) (Iannotti et al., 2016). TRPV1Rs are located in intrinsic neurons of the dorsal striatum (Galan-Rodriguez et al., 2009), nigrostriatal terminals, and TH + cells in the SNc (de Lago et al., 2004;Lastres-Becker et al., 2005;Morera-Herreras et al., 2016;Tzavara et al., 2006) and pharmacological modulation of these channels has been reported to influence striatum-dependent functions (de Lago et al., 2004;Tzavara et al., 2006). The presence of TRPV1R and its agonist in the BG allow a direct action of these ECB/endovanilloid compounds on the excitability of nigrostriatal DAergic neurons (Marinelli et al., 2003). ...
Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic (DAergic) neurons of the substantia nigra pars compacta (SNc) by neurodegeneration. Recent findings in animal models of PD propose tonic inhibition of the remaining DA neurons through GABA release from reactive glial cells. Movement dysfunctions could be ameliorated by promotion of activity in dormant DA cells. The endocannabinoid system (ECS) is extensively present in basal ganglia (BG) and is known as an indirect modulator of DAergic neurotransmission, thus drugs designed to target this system have shown promising therapeutic potential in PD patients. Interestingly, down/up-regulation of cannabinoid receptors (CBRs) varies across the different stages of PD, suggesting that some of the motor/ non-motor deficits may be related to changes in CBRs. Determination of the profile of changes of these receptors across the different stages of PD as well as their neural distribution within the BG could improve understanding of PD and identify pathways important in disease pathobiology. In this review, we focus on temporal and spatial alterations of CBRs during PD in the BG. At present, as inconclusive, but suggestive results have been obtained, future investigations should be conducted to extend preclinical studies examining CBRs changes within each stage in controlled clinical trials in order to determine the potential of targeting CBRs in management of PD.
... In addition, genetic studies have found a correlation between the cannabinoid receptor gene and ADHD [21]. However, the link between endocannabinoids and ADHD comes often from preclinical models [22][23][24][25], which require further translation into clinical practice. This section does not seek to offer a complete picture of the ECS and the complex neurobiological and metabolic interactions involved, but rather seeks to offer some potential research directions and mechanisms of action for exogenous cannabinoids research as a potential pharmacological treatment for some of the main symptoms of ADHD. ...
... In addition to dopamine, the role of for instance glutamate, GABA, and other neurotransmitter systems need consideration, as well as N-methyl-D-aspartate and can-nabinoid 2 (CB2) receptors, which have been suggested to modulate, for instance, impulsivity in interaction with endocannabinoids [10,22,23,34,35]. Therefore, further preclinical and clinical studies are warranted to map the complex interactions involved with the ECS in various pathophysiologies [35]. ...
This paper presents a detailed patient case report of a male patient who was diagnosed in adulthood (aged 33) with attention deficit hyperactivity disorder (ADHD) and treated initially with immediate-release methylphenidate (Ritalin® 10 mg twice daily). After experiencing adverse effects from prolonged use of this medication and afterwards other medications that were prescribed as alternatives, the patient discovered that cannabinoid therapeutics (CT) had been experimented inside the EU area to treat patients with ADHD. Subsequently, he was evaluated by a physician in Germany (June 2010) who prescribed CT (Bedrocan®, Bediol®). A Finnish neurologist later confirmed the two prescribed medicines (Bedrocan®, October 2010; Bediol®, May 2011) in the patient’s own country of permanent residence (Finland). During a 5-year period of access, Bedrocan®, which mainly contains Δ9-tetrahydrocannabinol (Δ9-THC), was found to be helpful in alleviating the patient’s ADHD symptoms, in particular poor tolerance to frustration, outbursts of anger, boredom, and problems related to concentration. The second CT medication, Bediol®, which contains both Δ9-THC and the phytocannabinoid cannabidiol, was found to neutralize the excessive dronabinol effects of Bedrocan® as well as zo offer other medical benefits (e.g., improved sleep). In addition to the case report, this paper also offers a brief review of the literature surrounding the medical benefits of CT for AD(H)D, which includes observational studies, clinical case reports, and one randomized clinical experiment. This paper also briefly discusses the endocannabinoid system in relation to ADHD, although more preclinical and clinical research is warranted to establish the optimal levels of cannabinoids, terpenes, and dosing regimens, which vary between different ADHD patients.
... Biosensor imaging experiments were performed with 8-12 days old C57Bl/6J mice obtained from Janvier (Le Genest Saint Isle, France). Breeding and genotyping of DAT wildtype and knockout mice was done as previously described (Tzavara et al., 2006). The animals were treated according to the regulations of Sorbonne Université animal care committee and the French Ministry of Agriculture and Forestry guidelines for handling animals. ...
... Assessment of locomotor activity in DAT wild-type and knockout mice was performed as previously described (Tzavara et al., 2006). To assess pharmacological effects of cholinergic compounds injected intraperitoneally, mice were placed on the actimeter 20 min after injection and locomotor activity was measured for a total of 60 min. ...
The opposing action of dopamine and acetylcholine has long been known to play an important role in basal ganglia physiology. However, the quantitative analysis of dopamine and acetylcholine signal interaction has been difficult to perform in the native context because the striatum comprises mainly two subtypes of medium-sized spiny neurons (MSNs) on which these neuromodulators exert different actions. We used biosensor imaging in live brain slices of dorsomedial striatum to monitor changes in intracellular cAMP at the level of individual MSNs. We observed that the muscarinic agonist oxotremorine decreases cAMP selectively in the MSN subpopulation that also expresses D1 dopamine receptors, an action mediated by the M4 muscarinic receptor. This receptor has a high efficacy on cAMP signaling and can shut down the positive cAMP response induced by dopamine, at acetylcholine concentrations which are consistent with physiological levels. This supports our prediction based on theoretical modeling that acetylcholine could exert a tonic inhibition on striatal cAMP signaling, thus supporting the possibility that a pause in acetylcholine release is required for phasic dopamine to transduce a cAMP signal in D1 MSNs. In vivo experiments with acetylcholinesterase inhibitors donepezil and tacrine, as well as with the positive allosteric modulators of M4 receptor VU0152100 and VU0010010 show that this effect is sufficient to reverse the increased locomotor activity of DAT-knockout mice. This suggests that M4 receptors could be a novel therapeutic target to treat hyperactivity disorders.
... This study found markedly decreased anandamide levels in the striatum of DAT KO mice; they then used three different indirect endocannabinoid agonists to show that these could attenuate spontaneous hyperlocomotion in DAT KO mice, and that this hyperlocomotion was significantly attenuated by the TRPV1 antagonist CPZ. It is very important to note that TRPV1 receptor binding by [ 3 H]resiniferatoxin was greater in the striatum of DAT KO mice 34 . This finding is consistent with our results that attenuated DAT binding by MAP was recovered by pretreatment with CPZ. ...
... This finding is consistent with our results that attenuated DAT binding by MAP was recovered by pretreatment with CPZ. Collectively, these findings indicated a correlation between TRPV1 and DAT in MAP reward, as DAT KO mice were hyperdopaminergic, hyperactive, and display perturbed cognitive performance 34 , and these properties were very similar to MAP-induced behavioral changes. Conversely, to assess the original DAT level of TRPV1 KO mice brain, we have conducted preliminary [ 3 H]mazindol binding assay with TRPV1 null mice, however, male TRPV1 KO mice did not show any change in NAc and DSt regions (data are not shown). ...
Methamphetamine (MAP) is the most widely used psychostimulant in the world, but the exact mechanisms underlying MAP addiction are not yet fully understood. Recent studies have identified the distribution of TRPV1 in several brain regions that are related to drug addiction, including nucleus accumbens (NAc) and dorsal striatum (DSt). In the present study, we performed conditioned place preference (CPP) and self-administration tests to examine the effects of capsazepine (CPZ) and SB366791 (SB) on MAP reward. We found that both CPZ and SB significantly inhibited MAP-induced CPP and self-administration; in contrast, TRPV1 knock-out (KO) mice did not develop MAP-induced CPP. Real-time RT-PCR, Western blot and quantitative autoradiographic tests showed up-regulation of TRPV1 mRNA and protein expression in the NAc and/or DSt regions of mice exhibiting MAP-induced CPP. In addition, an in vivo microdialysis experiment showed that CPZ dramatically reduced dopamine (DA) levels in the NAc region of MAP-treated mice. Furthermore, attenuated dopamine transporter (DAT) binding levels in the NAc and DSt regions of MAP-induced CPP mice were reversed by CPZ. Together, these data suggest that TRPV1 plays an important role in MAP reward via the modulation of DA release and DAT density, thereby providing a novel therapeutic target for MAP addiction.
... The overall effect of CB1 stimulation on dopamine release in the caudate putamen remains controversial, as some studies have shown a decrease (Sidlo et al., 2008), an increase (Malone & Taylor, 1999), or no effect at all (Kofalvi et al., 2005;Szabo, Muller, & Koch, 1999). AEA-and EC-enhancing drugs, such as FAAH inhibitors, can also modulate nigrostriatal dopamine transmission by acting at TRPV1 (de Lago, de Miguel, Lastres-Becker, Ramos, & Fernández-Ruiz, 2004;Marinelli et al., , 2007Tzavara et al., 2006) or PPAR receptors (Melis et al., 2008). ...
... Inhibitors of endocannabinoid transport or degradation enhance endocannabinoid levels, reducing the spontaneous hyperlocomotion in these mice. This effect is prevented by antagonism of TRPV1, implicating this pathway (Tzavara et al., 2006). The nonpsychoactive cannabinoid CBD also reportedly exhibits antipsychotic activity, reversing disruptions in PPI, induced by an NMDA receptor antagonist, in a similar way to the antipsychotic clozapine, with evidence suggesting that this is also via a TRPV1 receptor mechanism (Long, Malone, & Taylor, 2006). ...
... Some studies have shown that TRPV1 induces or exacerbates schizophrenia-like behaviors. For example, three different indirect endocannabinoid agonists, AM404, VDM11, and AA5HT, respectively attenuated hypermotility in dopamine transporter (DAT) knockout mice, and this effect was reversed by the TRPV1 antagonist capsaepine 48 . Administration of TRPV1 agonist CAP (50 mg/kg s.c.) on day 2 of life resulted in hyperactive B Effects of capsaicin administration on the novel object recognition assay in different groups. ...
Early life stress (ELS) is associated with the later development of schizophrenia. In the rodent model, the maternal separation (MS) stress may induce neuronal apoptosis and schizophrenia-like behavior. Although the TRPV1 agonist capsaicin (CAP) has been reported to reduce apoptosis in the central nervous system, its effect in MS models is unclear. Twenty-four hours of MS of Wistar rat pups on postnatal day (PND9) was used as an ELS. Male rats in the adult stage were the subjects of the study. CAP (1 mg/kg/day) intraperitoneal injection pretreatment was undertaken before behavioral tests for 1 week and continued during the tests. Behavioral tests included open field, novel object recognition, Barnes maze test, and pre-pulse inhibition (PPI) test. MS rats showed behavioral deficits and cognitive impairments mimicking symptoms of schizophrenia compared with controls. MS decreased the expression of TRPV1 in the frontal association cortex (FrA) and in the hippocampal CA1, CA3, and dentate gyrus (DG) regions compared with the control group resulting in the increase of pro-apoptotic proteins (BAX, Caspase3, Cleaved-Caspase3) and the decrease of anti-apoptotic proteins (Bcl-2). The number of NeuN ⁺ +TUNEL ⁺ cells increased in the MS group in the FrA, CA1, CA3, and DG compared with the control group. Neuronal and behavioral impairments of MS were reversed by treatment with CAP. Exposure to ELS may lead to increased neuronal apoptosis and impaired cognitive function with decreased TRPV1 expression in the prefrontal cortex and hippocampus in adulthood. Sustained low-dose administration of CAP improved neuronal apoptosis and cognitive function. Our results provide evidence for future clinical trials of chili peppers or CAP as dietary supplements for the reversal treatment of schizophrenia.
... Several other mechanisms of CBD have been proposed including regulating the GPA axis through facilitating 5-HT1A neurotransmission [205] and inhibition of fatty acid amide hydrolase [206]. Other putative targets identified pre-clinically include GPR55 and transient receptor potential vanilloid type 1 [207,208], though further work is needed to understand the role of these receptors in psychosis. ...
Despite strong evidence of the neurodevelopmental origins of psychosis, current pharmacological treatment is not usually initiated until after a clinical diagnosis is made, and is focussed on antagonising striatal dopamine receptors. These drugs are only partially effective, have serious side effects, fail to alleviate the negative and cognitive symptoms of the disorder, and are not useful as a preventive treatment. In recent years, attention has turned to upstream brain regions that regulate striatal dopamine function, such as the hippocampus. This review draws together these recent data to discuss why the hippocampus may be especially vulnerable in the pathophysiology of psychosis. First, we describe the neurodevelopmental trajectory of the hippocampus and its susceptibility to dysfunction, exploring this region’s proneness to structural and functional imbalances, metabolic pressures, and oxidative stress. We then examine mechanisms of hippocampal dysfunction in psychosis and in individuals at high-risk for psychosis and discuss how and when hippocampal abnormalities may be targeted in these groups. We conclude with future directions for prospective studies to unlock the discovery of novel therapeutic strategies targeting hippocampal circuit imbalances to prevent or delay the onset of psychosis.
... AM404 attenuated the impaired contextual fear conditioning, increased social interaction, and decreased locomotion (Almeida et al. 2014(Almeida et al. , 2019. The hypolocomotor effect of AM404 was attenuated by a TRPV1 antagonist, but not by a CBr1 antagonist (Tzavara et al. 2006). In another study, AM404 acted as a psychodysleptic, altering prepulse inhibition through the stimulation of CBr1 (Fernandez-Espejo and Galan-Rodriguez 2004). ...
The endocannabinoid system (ECS) is composed of endogenous cannabinoids; components involved in their synthesis, transport, and degradation; and an expansive variety of cannabinoid receptors. Hypofunction or deregulation of the ECS is related to pathological conditions. Consequently, endogenous enhancement of endocannabinoid levels and/or regulation of their metabolism represent promising therapeutic approaches. Several major strategies have been suggested for the modulation of the ECS: (1) blocking endocannabinoids degradation, (2) inhibition of endocannabinoid cellular uptake, and (3) pharmacological modulation of cannabinoid receptors as potential therapeutic targets. Here, we focused in this review on degradation/reuptake inhibitors over cannabinoid receptor modulators in order to provide an updated synopsis of contemporary evidence advancing mechanisms of endocannabinoids as pharmacological tools with therapeutic properties for the treatment of several disorders. For this purpose, we revisited the available literature and reported the latest advances regarding the biomedical properties of fatty acid amide hydrolase and monoacylglycerol lipase inhibitors in pre-clinical and clinical studies. We also highlighted anandamide and 2-arachidonoylglycerol reuptake inhibitors with promising results in pre-clinical studies using in vitro and animal models as an outlook for future research in clinical trials.
... Δ 9 Tetrahydrocannabinol (Δ 9 -THC), the main psychoactive constituent in cannabis, is a partial agonist of CB1 receptors in the brain (Zou and Kumar, 2018). Other receptors that participate in endocannabinoid signaling include transient receptor potential vanilloid 1 (TRPV1) and peroxisome proliferator-activated receptor (PPAR), which are involved in membrane excitability and gene regulation, respectively; however, there is limited research on their function in the ECS (Tyagi et al., 2011;Tzavara et al., 2006). ...
Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social communication deficits and patterns of restrictive and repetitive behavior. Although the neurological underpinnings of ASD remain elusive, the endocannabinoid system (ECS) may play a role in modulating social behavior in ASD. Preclinical studies have suggested that alterations in the ECS result in ASD-like phenotypes, but currently no reviews have examined ECS abnormalities in human studies. This scoping review investigated any evidence of ECS alterations in humans with ASD. A comprehensive literature search was conducted and five studies were eligible for review. Three studies reported a significant reduction of anandamide in ASD compared to controls. Other alterations included decreased 2-arachidonoylglycerol, oleoylethanolamide and palmitoylethanolamide and elevated diacylglycerol lipase and monoacylglycerol lipase. Some discrepant findings were also noted, which included elevated or reduced CB2 receptor in three studies, and elevated or reduced N-acyl phosphatidyl-ethanolamine phospholipase D and fatty acid amide hydrolase in two studies. We conclude from this preliminary investigation that the ECS may be altered in humans with ASD. Potential limitations of the reviewed studies include medication use and psychiatric comorbidities. Further research, such as positron emission tomography studies, are necessary to fully understand the relationship between ECS markers and ASD.
... It has been suggested that the exact mechanism of action may be via interruption of the fatty acid-binding proteins which transport endocannabinoids intracellularly (Elmes et al. 2015). Other ligands, such as palmitoylethanolamine, and effects of CBD on other receptors, such as GPR55 and TRPV1 (which are related to the endocannabinoid system), could also have a role, but the evidence supporting these is relatively sparse and is still limited to data from pre-clinical studies (Tzavara et al. 2006;Ryberg et al. 2007;Long et al. 2009;Muller et al. 2020). ...
The pharmacological interventions available for individuals in the early stages of psychosis are extremely limited. For those at clinical high risk for psychosis, there is no licensed treatment available. For those with first-episode psychosis, all licensed antipsychotic medications act via dopamine D 2 receptors. While treatment with antipsychotics is transformative in some patients, in others, it is ineffective. In addition, these medications can often cause adverse effects which make patients reluctant to take them. This is a particular problem in the early phases of psychosis, when patients are being treated for the first time, as unpleasant experiences may colour their future attitude towards treatment. Recent research has suggested that cannabidiol (CBD), a compound found in the Cannabis sativa plant, may have antipsychotic effects and relatively few adverse effects and could therefore be an ideal treatment for the early phases of psychosis, when minimising adverse effects is a clinical priority. In this review, we consider CBD’s potential as a treatment in the clinical high risk and first-episode stages of psychosis. First, we describe the limitations of existing treatments at these two stages. We then describe what is known of CBD’s mechanisms of action, effectiveness as a treatment for psychosis, adverse effects and acceptability to patients. We discuss how some of the outstanding issues about the utility of CBD in the early phases of psychosis may be resolved through ongoing clinical trials. Finally, we consider the impact of recreational cannabis use and over-the-counter cannabinoids preparations and discuss the potential therapeutic role of other compounds that modulate the endocannabinoid system in psychosis.
... Dopaminergic firing within the ventral tegmental area has also been increased by CB1 agonists in rodents French 1997;Gessa et al. 1998;Melis et al. 2000). Furthermore, using the dopamine transporter (DAT) knockout model of schizophrenia in mice (Giros et al. 1996;Hill and Tasker 2012) characterised by hyperdopaminergia primarily within the striatum and nucleus accumbens (Kasahara et al. 2013), it has been shown that DAT knockout mice present with reduced levels of the endocannabinoid, anandamide within the striatum (Tzavara et al. 2006). In contrast, repeated THC administration, a known risk factor for psychosis, has been shown to downregulate anandamide in the striatum (Di Marzo et al. 2000). ...
Background
Evidence suggests that an overlap exists between the neurobiology of psychotic disorders and the effects of cannabinoids on neurocognitive and neurochemical substrates involved in reward processing.
Aims
We investigate whether the psychotomimetic effects of delta-9-tetrahydrocannabinol (THC) and the antipsychotic potential of cannabidiol (CBD) are underpinned by their effects on the reward system and dopamine.
Methods
This narrative review focuses on the overlap between altered dopamine signalling and reward processing induced by cannabinoids, pre-clinically and in humans. A systematic search was conducted of acute cannabinoid drug-challenge studies using neuroimaging in healthy subjects and those with psychosis
Results
There is evidence of increased striatal presynaptic dopamine synthesis and release in psychosis, as well as abnormal engagement of the striatum during reward processing. Although, acute THC challenges have elicited a modest effect on striatal dopamine, cannabis users generally indicate impaired presynaptic dopaminergic function. Functional MRI studies have identified that a single dose of THC may modulate regions involved in reward and salience processing such as the striatum, midbrain, insular, and anterior cingulate, with some effects correlating with the severity of THC-induced psychotic symptoms. CBD may modulate brain regions involved in reward/salience processing in an opposite direction to that of THC.
Conclusions
There is evidence to suggest modulation of reward processing and its neural substrates by THC and CBD. Whether such effects underlie the psychotomimetic/antipsychotic effects of these cannabinoids remains unclear. Future research should address these unanswered questions to understand the relationship between endocannabinoid dysfunction, reward processing abnormalities, and psychosis.
... As expected, DAT knock-out mice shows a robust phenotype of increased motor activity and high striatal levels of dopamine. Interesting, this phenotype could be rescued by administration of anandamide membrane transporter inhibitors, whose effects were prevented by TRPV1 blockade (Tzavara et al., 2006). In addition, prenatal exposure to cannabinoids, which has been associate with neurodevelopmental psychiatric disorders, decreases TRPV1 mRNA in the brain of females rats (Bara et al., 2018). ...
The transient receptor potential vanilloid-1 channel (TRPV1) is responsible for decoding physical and chemical stimuli. TRPV1 is activated by capsaicin (a compound from chili peppers), heat (above 43°C) and acid environment, playing a major role in pain, inflammation and body temperature. Molecular and histological studies have suggested TRPV1 expression in specific brain regions, where it can be activated primarily by the endocannabinoid anandamide, fostering studies on its potential role in psychiatric disorders. TRPV1 blockers are effective in various animal models predictive of anxiolytic and antipanic activities, in addition to reducing conditioned fear. In models of antidepressant activity, these compounds reduce behavioral despair and promote active stress-coping behavior. TRPV1 blockers also reduce the effects of certain drugs of abuse and revert behavioral changes in animal models of neurodevelopmental disorders. The main limiting factor in developing TRPV1 blockers as therapeutic agents concerns their effects on body temperature, particularly hyperthermia. New compounds, which block specific states of the channel, could represent an alternative. Moreover, compounds blocking both TRPV1 and the anandamide-hydrolyzing enzyme, fatty acid amide hydrolase (FAAH), termed dual TRPV1/FAAH blockers, have been investigated with promising results. Overall, preclinical studies yield favorable results with TRPV1 blockers in animal models of psychiatric disorders.
... Ãèïåðàêòèâíîñòü aeèâîòíûõ ñ âûðàaeåííîé DAT-ãèïîôóíêöèåé ñïîñîáíû ñíèaeàòü è äðóãèå âåùåñòâà. Ê íèì îòíîñÿòñÿ àíòàãîíèñòû ðàçëè÷íûõ ÄÀ-ðåöåïòîðîâ [5,38], èíãèáèòîðû îáðàòíîãî çàõâàòà ñåðîòîíèíà è íîðàäðåíàëèíà [5,20,53], àíòàãîíèñòû 1 è 2À ïîäòèïîâ ñåðîòîíèíîâûõ ðåöåïòîðîâ [4,23], àíòàãîíèñòû ìåòàáîòðîïíûõ ãëóòàìàòíûõ ðåöåïòîðîâ 2 ïîäòèïà è ïîçèòèâíûå àëëîñòåðè÷åñêèå ìîäóëÿòîðû AMPA ðåöåïòîðîâ [19,53], íåéðîñòåðîèäû (ïðåãíåíîëîí) [56], àãîíèñòû ðåöåïòîðîâ, àññîöèèðîâàííûõ ñî ñëåäîâûìè àìèíàìè 1 ïîäòèïà [28,39], âåùåñòâà, ñòèìóëèðóþùèå õîëèíåðãè÷åñêèå ïðîöåññû [34,55], èíãèáèòîðû îáðàòíîãî çàõâàòà àíàíäàìèäà [50], ïðîòèâîñóäîðîaeíûå ñðåäñòâà è ñîëè ëèòèÿ [7,37]. Ñëåäóåò òàêaeå îòìåòèòü, ÷òî íåìàëîâàaeíîé äåòàëüþ â àíàëèçå ãèïîëîêîìîòîðíîãî äåéñòâèÿ ôàðìàêîëîãè÷åñêèõ âåùåñòâ ÿâëÿåòñÿ èõ ñåëåêòèâíîñòü â îòíîøåíèè aeèâîòíûõ ñ äåôèöèòîì DAT. ...
Работа трансмембранного протеина дофаминового транспортёра (dopamine transporter, DAT) — одна из ключевых составляющих дофаминергических процессов. Предполагают, что изменение функции DAT может являться одним из основных механизмов развития патологических состояний, сопровождающихся гипердофаминергией. Первая линия генетически модифицированных мышей, у которых отсутствовал DAT (DAT-KO), была создана более 15 лет назад. Со временем спектр линий животных с изменённой экспрессией DAT расширился: была создана линия мышей со сниженной на 90 % экспрессией данного белка, две линии DAT-KO крыс. В исследованиях на данных линиях лабораторных животных было установлено, что повышение уровня дофамина в синаптической щели приводит к тому, что у животных формируется двигательная гиперактивность и выраженные двигательные стереотипические реакции, а также когнитивные нарушения. Эти и другие изменения, по-видимому, вызванные избытком дофамина, могут быть уменьшены введением различных фармакологически активных веществ, влияющих как на дофаминовую, так и на другие нейромедиаторные системы. Целью настоящего обзора является систематизация и анализ накопленных данных о последствиях изменения экспрессии DAT у лабораторных животных, результатов исследований эффектов фармакологических веществ на этих животных, а также общая оценка обоснованности использования животных с гипофункцией DAT для поиска новых средств терапии психических расстройств, сопровождающихся гиперфункцией дофаминовой системы.
... It has been suggested that dysfunction of the eCB system may lead to psychosis by increasing dopaminergic activity (Müller-Vahl and Emrich, 2008), the final common pathway in the pathophysiology of psychosis (Howes and Kapur, 2009). Preclinical studies have demonstrated that administration of a dopamine receptor agonist is associated with increase in AEA release in the dorsal striatum and hyperdopaminergia observed in dopamine transporter knockout mice (an animal model for schizophrenia) is associated with decrease in striatal AEA levels (Tzavara et al., 2006). ...
Background
Evidence has been accumulating regarding alterations in components of the endocannabinoid system in patients with psychosis. Of all the putative risk factors associated with psychosis, being at clinical high-risk for psychosis (CHR) has the strongest association with the onset of psychosis, and exposure to childhood trauma has been linked to an increased risk of development of psychotic disorder. We aimed to investigate whether being at-risk for psychosis and exposure to childhood trauma were associated with altered endocannabinoid levels.
Method
We compared 33 CHR participants with 58 healthy controls (HC) and collected information about previous exposure to childhood trauma as well as plasma samples to analyse endocannabinoid levels.
Results
Individuals with both CHR and experience of childhood trauma had higher N- palmitoylethanolamine ( p < 0.001) and anandamide ( p < 0.001) levels in peripheral blood compared to HC and those with no childhood trauma. There was also a significant correlation between N- palmitoylethanolamine levels and symptoms as well as childhood trauma.
Conclusions
Our results suggest an association between CHR and/or childhood maltreatment and elevated endocannabinoid levels in peripheral blood, with a greater alteration in those with both CHR status and history of childhood maltreatment compared to those with either of those risks alone. Furthermore, endocannabinoid levels increased linearly with the number of risk factors and elevated endocannabinoid levels correlated with the severity of CHR symptoms and extent of childhood maltreatment. Further studies in larger cohorts, employing longitudinal designs are needed to confirm these findings and delineate the precise role of endocannabinoid alterations in the pathophysiology of psychosis.
... An improvement in the symptom domains of ADHD was noticed; however, adverse events such as muscular seizures/spasms, feeling of lightheadedness, and sleep difficulties were also reported. Thus, in light of our new data, it might be tempting to speculate that the FAAH inhibition per se as well as FAAH inhibition with concomitant blockade of AEA uptake and/or TRPV1 channels might be a more efficient approach to improve cognitive dysfunctions in ADHD (Tzavara et al., 2006), with reduced side effects compared to those of cannabis or ∆ 9 -THC. ...
The maturation of attentional control during adolescence might influence later functional outcome or predisposition to psychiatric disorders. During adolescence, the cannabinoid system is particularly sensitive to pharmacological challenges, with potential impact on cognitive functions. Here, we used a recently validated five-choice serial reaction time task protocol to test adolescent C57BL/6J mice. We showed that the pharmacological inhibition (by URB597) of the fatty acid amide hydrolase (FAAH), the major enzyme implicated in anandamide degradation, prevented cognitive disruptions induced by distracting cues in adolescent mice. In particular, these protective effects were indicated by increased accuracy and correct responses and decreased premature responses selectively in the distractor trials. Notably, at the relatively low dose used, we detected no effects in other cognitive, motor, or incentive measures nor long-lasting or rebound effects of FAAH inhibition in cognitive functions. Overall, these data provide initial evidence of selective procognitive effects of FAAH inhibition in measures of attentional control in adolescent mice.
... This finding supports the potential benefits of enhancing the endocannabinoid tone in the treatment of schizophrenia. In this sense, several preclinical studies have tested FAAH and other endocannabinoid degradation inhibitors as potential therapeutic tools to treat schizophrenia (Matricon et al., 2016;Seillier et al., 2010;Tzavara et al., 2006). Interestingly, cannabidiol, the main non-psychoactive component of Cannabis sativa, has also been postulated as a new therapeutic candidate in schizophrenia treatment, due in part to its ability to increase AEA levels through a potential mechanism that impedes the FAAH hydrolytic action (Elmes et al., 2015). ...
Background
The endocannabinoid system – comprising cannabinoid receptors, endocannabinoid ligands and their synthesis and inactivation enzymes – has been widely implicated in the pathophysiology of schizophrenia. However, little is known regarding the status of the different elements of the endocannabinoid system in the brain of schizophrenic patients. We have previously reported altered endocannabinoid levels in the postmortem brain of subjects with schizophrenia compared with matched controls.
Aims
Our aim was to further examine the status of the main elements of the endocannabinoid system in the postmortem prefrontal cortex of the same cohort of subjects.
Methods
Gene expression and function of the cannabinoid receptor type-1 (CB1) and the endocannabinoid degrading enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) have been assessed.
Results
A significant decrease in CB1 mRNA levels in schizophrenia was found, without alteration of FAAH or MAGL mRNA expression. Moreover, positive correlations among mRNA expressions of the three genes studied were found in the prefrontal cortex of controls but not in schizophrenic subjects. No alteration was found in CB1 receptor mediated functional coupling to G-proteins, but a significant increase of FAAH activity was found in schizophrenic subjects compared with controls. 2-arachidonoylglycerol levels and MAGL activity were found to positively correlate in controls but not in schizophrenic subjects.
Conclusions
The present findings reveal an imbalance in the expression and function of different elements of the endocannabinoid system in schizophrenia. This outcome highlights the relevance of the endocannabinoid system in the pathophysiology of schizophrenia and emphasises its elements as potential targets in the search for new therapeutic strategies.
... There is growing evidence suggesting potential role of TRPV1 in schizophrenia (see [28,60,63] for review). Here, we will mention just some notable findings: the presence of TRPV1 in dopaminergic neurons and its functional role in the regulation of dopamine release together with antipsychotic efficacy of dopamine D 2 receptor antagonists [63]; results of psychopharmacological studies indicating that TRPV1 modulates behavioral changes in schizophrenia models [64,65]. ...
TRPV1 has been originally cloned as the heat and capsaicin receptor implicated in acute pain signalling, while further research has shifted the focus to its importance in chronic pain caused by inflammation and associated with this TRPV1 sensitization. However, accumulating evidence suggests that, apart from pain signalling, TRPV1 subserves many other unrelated to nociception functions in the nervous system. In the brain, TRPV1 can modulate synaptic transmission via both pre- and postsynaptic mechanisms and there is a functional crosstalk between GABA receptors and TRPV1. Other fundamental processes include TRPV1 role in plasticity, microglia-to-neuron communication, and brain development. Moreover, TRPV1 is widely expressed in the peripheral tissues, including the vasculature, gastrointestinal tract, urinary bladder, epithelial cells, and the cells of the immune system. TRPV1 can be activated by a large array of physical (heat, mechanical stimuli) and chemical factors (e.g., protons, capsaicin, resiniferatoxin, and endogenous ligands, such as endovanilloids). This causes two general cell effects, membrane depolarization and calcium influx, thus triggering depending on the cell-type diverse functional responses ranging from neuronal excitation to secretion and smooth muscle contraction. Here, we review recent research on the diverse TRPV1 functions with focus on the brain, vasculature, and some visceral systems as the basis of our better understanding of TRPV1 role in different human disorders.
... Because of continuously increasing evidence for a role of endocannabinoids in reward processes , endocannabinoid signaling was assessed in DAT-KO mice and the ability of endocannabinoid ligands to normalize behavioral deficits was evaluated, namely spontaneous hyperlocomotion (Tzavara et al. 2006). DAT-KO mice had reduced striatal anandamide levels and in these mice, anandamide reuptake inhibitors attenuated spontaneous hyperlocomotion. ...
Among the neurotransmitters involved in addiction, dopamine (DA) is clearly the best known. The critical role of DA in addiction is supported by converging evidence that has been accumulated in the last 40 years. In the present review, first we describe the dopaminergic system in terms of connectivity, functioning and involvement in reward processes. Second, we describe the functional, structural, and molecular changes induced by drugs within the DA system in terms of neuronal activity, synaptic plasticity and transcriptional and molecular adaptations. Third, we describe how genetic mouse models have helped characterizing the role of DA in addiction. Fourth, we describe the involvement of the DA system in the vulnerability to addiction and the interesting case of addiction DA replacement therapy in Parkinson’s disease. Finally, we describe how the DA system has been targeted to treat patients suffering from addiction and the result obtained in clinical settings and we discuss how these different lines of evidence have been instrumental in shaping our understanding of the physiopathology of drug addiction.
... Moreover, it has been observed that capsazepine potentiated a cannabidiol-induced increase of intracellular Ca 2+ levels in vitro [131]. Although TRPV 1 Rs may be indirectly involved in schizophrenia by influencing dopaminergic [132] and glutamatergic neurotransmission [133], there is currently no evidence for a role of TRPV 1 R activation in schizophrenia. ...
The term schizophrenia describes a group of multifaceted psychiatric conditions causing significant impairment of the quality of life of affected patients. Although multiple pharmacological treatment options exist, e.g. first- or second-generation antipsychotics, these therapeutics often cause disturbing side effects, such as extrapyramidal symptoms, prolactin increase, sexual dysfunction and/or metabolic syndrome. Furthermore, cognitive impairments and negative symptoms, two factors significantly influencing the course and outcome, are not sufficiently addressed by the available antipsychotics. Since its discovery, multiple clinical and preclinical studies have linked the endocannabinoid system to schizophrenia. Both the endocannabinoid anandamide and the cannabinoid CB1 receptor are deeply linked to underlying disease processes. Based hereon, clinical trials in schizophrenia have explored cannabidiol, a primary component of Cannabis sativa, and rimonabant, a partial antagonist to the CB1 receptor. While the latter did not reveal positive results, cannabidiol significantly ameliorated psychotic symptoms, which was associated with an increase in anandamide serum levels. However, the exact mechanisms of the antipsychotic effects of cannabidiol are not fully understood, and, furthermore, only a limited number of clinical trials in humans have been concluded to date. Thus, the level of proof of safety and efficacy required to approve the therapeutic use of cannabidiol in schizophrenia is currently lacking. However, cannabidiol is a promising candidate as an effective and mechanistically different antipsychotic treatment with a favourable side-effect profile. We therefore conclude that further studies are urgently needed to clarify the antipsychotic effects and safety profile of cannabidiol, and to fully explore its potential antipsychotic mechanism.
... Behavioral dimensions and cognitive functions were assessed through the TST 30,31 , the FST 48 , the elevated plus maze, and the light-dark test 49 as well as tests for novelty-induced hypophagia 50,51 , sucrose preference 19 , latent learning 32 and novel-object recognition 52 according to previously described protocols with minor modifications. Locomotor activity was assessed in an automated actimeter 53 . Procedures are described in detail in the Supplementary Note. ...
Depression, a devastating psychiatric disorder, is a leading cause of disability worldwide. Current antidepressants address specific symptoms of the disease, but there is vast room for improvement 1 . In this respect, new compounds that act beyond classical antidepressants to target signal transduction pathways governing synaptic plasticity and cellular resilience are highly warranted2-4. The extracellular signal-regulated kinase (ERK) pathway is implicated in mood regulation5-7, but its pleiotropic functions and lack of target specificity prohibit optimal drug development. Here, we identified the transcription factor ELK-1, an ERK downstream partner 8 , as a specific signaling module in the pathophysiology and treatment of depression that can be targeted independently of ERK. ELK1 mRNA was upregulated in postmortem hippocampal tissues from depressed suicides; in blood samples from depressed individuals, failure to reduce ELK1 expression was associated with resistance to treatment. In mice, hippocampal ELK-1 overexpression per se produced depressive behaviors; conversely, the selective inhibition of ELK-1 activation prevented depression-like molecular, plasticity and behavioral states induced by stress. Our work stresses the importance of target selectivity for a successful approach for signal-transduction-based antidepressants, singles out ELK-1 as a depression-relevant transducer downstream of ERK and brings proof-of-concept evidence for the druggability of ELK-1.
... 45 Although causality is unclear, as the influence of one on the other may in fact be bidirectional, irregularities in both the availability of this neurotransmitter and in the activity of the eCB system are very likely related. This may be inferred from the dysregulated neural levels of anandamide-an endogenous cannabinoid-observed in hyperdopaminergic rat models of schizophrenia, 46 and increases in dopamine in the nucleus accumbens of healthy rats following acute administration of anandamide. 47 Additionally, an accumulating body of evidence suggests that acute and chronic cannabis use in humans may affect dopamine release and synthesis differentially, as reviewed by Sami et al. ...
Accumulating evidence suggests that dysfunction within the endocannabinoid (eCB) system may play a role in psychosis. However, little is understood about how this may be related to the neurocognitive abnormalities and symptoms of psychosis. In this paper, we summarize some of the evidence supporting the role of eCB system in psychosis, as well as the current understanding of the neurocognitive underpinnings of psychosis. We particularly focus on neuroimaging evidence pertaining to alteration in the functional integration between different brain regions in patients with psychosis, and then relate this to evidence from neuroimaging studies of the effects of cannabis and its main ingredients, such as delta-9-tetrahydrocannainol and cannabidiol. Specifically, we explore this in the context of the hypothesis that psychosis is a disorder of dysconnectivity between different brain regions, focusing particularly on three large scale functional networks (the default mode, central executive, and salience networks), alterations in which have been implicated in psychosis, and we discuss the gaps in this research thus far. Finally, we propose that an approach to investigating the role of the eCB system in psychosis may be to employ a pharmacological cannabinoid challenge paradigm to examine how experimental perturbation of the eCB system may be related to abnormalities in the brain networks implicated in psychosis. We discuss challenges associated with this approach, and suggest safe and practical options to overcome the main issues involved with such an experimental approach. Studies employing such an approach have the potential of offering insight into the neurocognitive mechanisms underlying psychosis, and identifying novel therapeutic targets.
... Yet, this side effect has not been reported or observed in clinical trials so far (e.g., Leweke et al., 2000Leweke et al., , 2012. To date, evidence for a role of TRPV1R activation in schizophrenia is lacking, but TRPV1Rs may be indirectly involved in schizophrenia via its influence on dopaminergic (Tzavara et al., 2006) and glutamatergic neurotransmission (Fawley et al., 2014). Furthermore, it has been suggested that cannabidiol targets GPR55 and GPR18 receptors, further subtypes of transient receptor potential receptors (TRPV2, TRPM8, TRPA1), α3 glycine receptors, adenosine receptors, µ and δ opioid receptors, nicotinic acetylcholine receptors, enzymes of the arachidonic acid cascade, ion channels like voltage-gated calcium channels or mitochondrial Na + /Ca 2+ exchange, nitric oxide signaling and inflammatory cytokines (McPartland et al., 2014;Ibeas Bih et al., 2015). ...
There is urgent need for the development of mechanistically different and less side-effect prone antipsychotic compounds. The endocannabinoid system has been suggested to represent a potential new target in this indication. While the chronic use of cannabis itself has been considered a risk factor contributing to the development of schizophrenia, triggered by the phytocannabinoid delta-9-tetrahydrocannabinol (Δ9-THC), cannabidiol, the second most important phytocannabinoid, appears to have no psychotomimetic potential. Although, results from animal studies are inconsistent to a certain extent and seem to depend on behavioral paradigms, treatment duration and experimental conditions applied, cannabidiol has shown antipsychotic properties in both rodents and rhesus monkeys. After some individual treatment attempts, the first randomized, double-blind controlled clinical trial demonstrated that in acute schizophrenia cannabidiol exerts antipsychotic properties comparable to the antipsychotic drug amisulpride while being accompanied by a superior, placebo-like side effect profile. As the clinical improvement by cannabidiol was significantly associated with elevated anandamide levels, it appears likely that its antipsychotic action is based on mechanisms associated with increased anandamide concentrations. Although, a plethora of mechanisms of action has been suggested, their potential relevance for the antipsychotic effects of cannabidiol still needs to be investigated. The clarification of these mechanisms as well as the establishment of cannabidiol’s antipsychotic efficacy and its hopefully benign side-effect profile remains the subject of a number of previously started clinical trials.
... Previously, FAAH inhibitors have been shown to reduce hyperdopaminergia-related hyperactivity in mice [43,44]. The reduction of LID was seen when FAAH inhibition was combined with an antagonist of TRPV1 receptor [17]. ...
L-3,4-dihydroxyphenylalanine (L-DOPA) is the most common treatment for patients with Parkinson's disease (PD). However, long term use of L-DOPA for PD therapy lead to abnormal involuntary movements (AIMs) known as dyskinesia. Fatty acid amide hydrolase (FAAH) is enriched protein in basal ganglia, and inhibition of the protein reduces dyskinetic behavior of mice. Palmitoyl serotonin (PA-5HT) is a hybrid molecule patterned after arachidonoyl serotonin, antagonist of FAAH. However, the effect of PA-5HT on L-DOPA-induced dyskinesia (LID) in PD have not yet been elucidated. To investigate whether PA-5HT relieve LID in PD and decrease hyperactivation of dopamine D1 receptors, we used the 6-hydroxydopomine (6-OHDA)-lesioned mouse model of PD and treated the L-DOPA (20 mg/kg) for 10 days with PA-5HT (0.3 mg/kg/day). The number of wall contacts with the forelimb in the cylinder test was significantly decreased by 6-OHDA lesion in mice and the pharmacotherapeutic effect of L-DOPA was also revealed in PA-5HT-treated mice. Moreover, in AIMs test, PA-5HT-treated mice showed significant reduction of locomotive, axial, limb, and orofacial AIMs score compared to the vehicle-treated mice. LID-induced hyper-phosphorylation of ERK1/2 and overexpression of FosB/ΔFosB was markedly decreased in 6-OHDA-lesioned striatum of PA-5HT-treated mice, indicating that PA-5HT decreased the dopamine D1 receptor-hyperactivation induced by chronic treatment of L-DOPA in dopamine-denervated striatum. These results suggest that PA-5HT effectively attenuates the development of LID and enhance of ERK1/2 phosphorylation and FosB/ΔFosB expression in the hemi-parkinsonian mouse model. PA-5HT may have beneficial effect on the LID in PD.
... In support, treatment with TRPV1 agonist capsaicin decreases DA release in the striatum [53,68] and decreases motor activity [26,65]. Furthermore, pharmacological modulation of these receptors has been reported to influence striatum-dependent functions [21], and to modulate motor symptoms originating from striatal dysfunction [65,105]. In the striatum, TRPV1 receptors co-localize with CB1 receptors [20,27], suggesting a close functional interaction between these receptors. ...
... They are activated by so-called endovanilloids which include AEA (Van Der Stelt and Di and their roles in behavioural processes still being revealed. In the context of schizophrenia, Tzavara et al. (2006) have shown that hyperlocomotor activity in dopamine transporter knockout (DAT KO) mice was attenuated by treatment with AEA reuptake inhibitors, VDM11 and AM404, and the FAAH inhibitor, AA5HT. These effects were blocked by capsazepine. ...
Schizophrenia is a debilitating psychiatric disorder which places a significant emotional and economic strain on the individual and society-at-large. Unfortunately, currently available therapeutic strategies do not provide adequate relief and some patients are treatment-resistant. In this regard, cannabidiol (CBD), a non-psychoactive constituent of Cannabis sativa, has shown significant promise as a potential antipsychotic for the treatment of schizophrenia. However, there is still considerable uncertainty about the mechanism of action of CBD as well as the brain regions which are thought to mediate its putative antipsychotic effects. We argue that further research on CBD is required to fast-track its progress to the clinic and in doing so, we may generate novel insights into the neurobiology of schizophrenia.
... Additionally, anandamide negatively modulates glutamergic input to the striatum (Gerdeman, Ronesi, & Lovinger, 2002). Tzavara, et al. ( 2006) found that mice without the ability to produce dopamine transporter (DAT-null) exhibited striatal hyperdopaminergic activity, and the inhibition of anandamide degradation restored motor behavior to normal levels. Finally, Lee, Di Marzo, & Brotchie (2006) found that the inhibition of anandamide hydrolysis caused hypolocomotion in normal rats, but reversed hyperlocomotion in rats administered L-DOPA. ...
... Thus, evidence for a role of TRPV1-R activation in schizophrenia is lacking. However, the influence of TRPV1-R on dopaminergic (89) and glutamatergic neurotransmission (90) ) of 8-OH-DPAT at 100 nM. Interestingly, cannabidiol had no effect on E max of 8-OH-DPAT at 1, 10 or 31.6 nM or at 1 µM (92). ...
Over recent years, the interest in the endocannabinoid system (eCBs) as a new target for the treatment of schizophrenia has evolved. The eCBs represents one of the most relevant neurotransmitter systems in the brain and mainly fulfills a homeostatic role in terms of neurotransmission but also with respect to inflammatory processes. Two main approaches to the modulation of endocannabinoid functioning have been chosen so far. First, the selective blockade or inverse agonism of the cannabinoid CB1-receptor has been tested for the improvement of acute psychotic symptoms as well as for the improvement of cognitive functions in schizophrenia. This was not effective in either case. Second, the modulation of endocannabinoid levels by use of the phytocannabinoid cannabidiol and selective fatty acid amide hydrolase (FAAH) inhibitors has been proposed and the antipsychotic properties of cannabidiol are currently investigated in humans. Unfortunately, for most these trials that focused on psychopathological and cognitive effects of cannabidiol no published data is available. However, there is first evidence that cannabidiol may ameliorate psychotic symptoms with a superior side-effect profile compared to established antipsychotics. In conclusion, several clinical trials targeting the eCBs in acute schizophrenia have either been completed or are under way. Although publicly available results are limited by now, preliminary data indicate that selected compounds modulating the eCBs may be effective in acute schizophrenia. Nevertheless, sample sizes of patients investigated are not sufficient to come to a final judgment so far and no maintenance studies are available to ensure long-term efficacy and safety.
Transient receptor potential vanilloid 1 (TRPV1) is a transmembrane and non-selective cation channel protein, which can be activated by various physical and chemical stimuli. Recent studies have shown the strong pathogenetic associations of TRPV1 with neurodegenerative diseases (NDs), in particular Alzheimer’s disease (AD), Parkinson’s disease (PD) and multiple sclerosis (MS) via regulating neuroinflammation. Therapeutic effects of TRPV1 agonists and antagonists on the treatment of AD and PD in animal models also are emerging. We here summarize the current understanding of TRPV1’s effects and its agonists and antagonists as a therapeutic means in neurodegenerative diseases, and highlight future treatment strategies using natural TRPV1 agonists. Developing new targets and applying natural products are becoming a promising direction in the treatment of chronic disorders, especially neurodegenerative diseases.
Endocannabinoids (eCBs) and the expanded endocannabinoid system (ECS)-“endocannabinoidome”, consists of the endogenous ligands, eCBs, their canonical and non-canonical receptor subtypes, and their synthesizing and metabolizing enzymes. This system modulates a wide range of body functions and acts as a retrograde signaling system within the central nervous system (CNS) by inhibition of classical transmitters, and plays a vital modulatory function on dopamine, a major neurotransmitter in the CNS. Dopamine is involved in different behavioral processes and contributes to different brain disorders—including Parkinson’s disease, schizophrenia, and drug addiction. After synthesis in the neuronal cytosol, dopamine is packaged into synaptic vesicles until released by extracellular signals. Calcium dependent neuronal activation results in the vesicular release of dopamine and interacts with different neurotransmitter systems. The ECS, among others, is involved in the regulation of dopamine release and the interaction occurs either through direct or indirect mechanisms. The cross-talk between the ECS and the dopaminergic system has important influence in various dopamine-related neurobiological and pathologic conditions and investigating this interaction might help identify therapeutic targets and options in disorders of the CNS associated with dopamine dysregulation.
Cannabis use for cancer symptom management is increasing and is becoming part of polypharmacy that patients with advanced cancer are often subjected to. Drug-drug interactions depend in part on the schedule of administration, absorption, method of administration, the capacity of either the drug and cannabinoids to inhibit CYP enzymes (inhibitory constant) or the ability to upregulate CYP enzymes. Phytocannabinoids and endocannabinoids are both metabolized by CYP450 enzymes, though endocannabinoids also have their own specific metabolic pathways. In general, endocannabinoids influence responses to various drug classes such as antiseizure medications, antidepressants, and opioids. Both tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations in blood are dependent on dose, diet(fat), route of administration, vehicle, and disease state. The more important cannabis-induced drug interactions are largely inhibitory in nature and encountered through the CYP2C family. Other drug interactions via immunomodulatory mechanisms have been shown to reduce efficacy of check-point inhibitors and are a reminder that cannabis use should be closely monitored in cancer patients.KeywordsCytochromeCompetitiveInhibitionDrug interactionsEndocannabinoidsAnandamide2-AGFAAHMAGLCheckpoint inhibitor
The endocannabinoid system (ECS) was discovered in the early 1990s and is one of the most important neuroregulatory systems in the body. The ECS is responsible for homeostasis of most systems in the body. At a simplistic level, it is composed of endogenous ligands called endocannabinoids, cannabinoid receptors (CB1 and CB2 receptors), and enzymes that synthesize and degrade them. However, the ECS is actually more complex than this and there are other receptors and endocannabinoid-like substances involved in the ‘extended ECS’. CB1 receptors are particularly concentrated in the central nervous system and CB2 receptors are particularly concentrated in cells and tissues/organs of the immune system. However, cannabinoid receptors are also widely distributed throughout the body. In the nervous system, the classical understanding is that endocannabinoids are synthesized on demand in postsynaptic neurons and act as retrograde messengers, binding with cannabinoid receptors on presynaptic neurons to reduce neurotransmitter release from the presynaptic neuron. It is now known that there are also intracellular reservoirs and transporters of endocannabinoids. The ECS is critically involved in brain development, from the fetus through to adulthood. Dysfunction including deficiency of the ECS has been associated with a range of pathological disorders, including mental health conditions. The ECS plays a key role in the regulation of our mind and emotions and our reaction to stress. It is involved with the corticolimbic system and the HPA axis, both of which are key systems involved in regulation of stress and emotions. This chapter gives an overview of the ECS, as an understanding is necessary to later understand how medicinal cannabis may work in alleviating mental health disorders.
Background
Despite the lack of evidence on the use of cannabis for the treatment of attention-deficit/hyperactivity disorder (ADHD), the growing perception that cannabis is safe has led more patients and caregivers to self-medicate. Some psychiatrists now authorize medicinal cannabis for patients with ADHD with features of oppositional defiant disorder (ODD) to curtail the unregulated (ie, self-medicated) use of recreational cannabis or to offer a therapeutic option to those who continue to experience symptoms after exhausting all other treatment options.
Objective
This protocol aims to explore the perceived effectiveness and pharmacokinetics of cannabis in youth and young adults, who are currently taking it as part of their treatment plan for ADHD with features of ODD, under the supervision of a psychiatrist.
Methods
Patients between the ages of 12 and 25 years with a diagnosis of ADHD and features of ODD, who are currently taking cannabis herbal extract (at a Δ9-tetrahydrocannabinol [THC]:cannabidiol [CBD] ratio of 1:20) as a treatment adjunct to stimulant pharmacotherapy will be recruited. A sample size of 10-20 individuals is estimated. The study interview will consist of (1) validated symptom rating scales (Swanson, Nolan, and Pelham-IV Questionnaire [SNAP-IV], 90-item; Patient Health Questionnaire, 9-item [PHQ-9]; and Screen for Child Anxiety Related Emotional Disorders [SCARED] tool to measure symptoms of ADHD and ODD, depression, and anxiety, respectively); (2) a semistructured interview to probe the experiences of using cannabis; and (3) a cannabis side effects survey. A cannabis product sample as well as 2 blood samples (a trough level and 2-hour postdose level) will be collected to measure plasma concentrations of cannabinoids and relevant metabolites (THC, CBD, 11-hydroxy-THC, 7-hydroxy-CBD, cannabichromene, and 11-nor-9-carboxy-THB) using liquid chromatography–tandem mass spectrometry (LC–MS/MS). Self-report rating scales (SNAP-IV, SCARED, and PHQ-9) will be scored in accordance with standard protocols and compared to retrospective scores obtained from the participant’s chart. Demographic variables (age, weight, and race), symptom scores, and blood levels (peaks and troughs) of THC, CBD, cannabichromene (CBC), and metabolites will be summarized using descriptive statistics. Relationships between plasma concentrations and symptom scores will be determined using analysis of variance, and multiple regression analysis will be performed to determine associations between plasma concentrations and demographic variables (age, weight, and ethnicity). The qualitative data will be audio-recorded and transcribed and organized into themes.
Results
The protocol was approved by the Biomedical Research Ethics Board at the University of Saskatchewan (protocol #1726), and recruitment began in May 2021.
Conclusions
This proof-of-concept study will explore the potential treatment effectiveness of medical cannabis in participants with ADHD and ODD through a mixed methods approach to inform future research in this area.
International Registered Report Identifier (IRRID)
DERR1-10.2196/31281
Memory, defined as an alteration in behavior that follows as a consequence of experience, can form when a sensory stimulus is encountered at the same time that the animal experiences a negative or positive internal state. How this coincident detection of external and internal stimuli stably alters responses to the external stimulus is still not fully understood, especially in the context of an intact animal. One barrier to understanding how an intact biological circuit changes is knowing what molecular processes are required to establish and maintain the memory. The optically accessible and compact nervous system of C. elegans provides a unique opportunity to examine the molecular and cellular processes that promote memory formation. The C. elegans nematode can remember an odor such as butanone when it is paired with a single negative experience and the transient receptor potential (TRP) OSM-9/TRPV5/TRPV6 channel is known to be required for this memory. The multiple gating mechanisms of TRPV channels give them the potential to be the coincidence detectors required to integrate internal state and external stimuli. Here, we report that this TRPV channel is also required for acquisition and possibly consolidation of sleep-dependent, long-term memory of butanone. Using an endogenous CRISPR-based tag, we find that OSM-9 is expressed in the paired AWA olfactory neurons, the ASH nociceptive neuron pair, the mechanosensory OLQ tetrad, and the paired ADF and ADL sensory neurons. In these cells, OSM-9 protein is concentrated in the sensory endings, dendrites, and cell bodies, but excluded from the neurites in the nerve ring. In the tail, OSM-9 is expressed in the nociceptive phasmid neurons PHA and PHB, possibly PQR as well as PVP. In the midbody, it is possibly expressed in the mechanosensitive PVD neuron. Because OSM-9 is expressed in sensory neurons that do not participate in butanone chemosensory behavior, this indicates that cells extrinsic to the primary sensory circuit may participate in acquiring and consolidating memory.
Author summary
How organisms learn from their environment and keep these memories for the long term ensures their survival. There is much known about the regions of the brain and the various proteins that are essential for memory, yet the exact molecular mechanisms and dynamics required are not known. We aimed to understand the genetics that underlie memory formation. We tested a gene that encodes a transient potential receptor channel vanilloid channel, which is similar to the channels we have that sense spicy foods and other harmful cues. Our studies have shown that this gene is required specifically to acquire and perhaps consolidate memory. This protein is not expressed in the sensory neurons that respond to odor or in other downstream interneurons in this circuit, but it is expressed and possibly acts in a distinct set of sensory neurons. This indicates that long-term memory involves a wider array of sensory neurons than is required for the primary sensation. These channels are also implicated in neurological disorders where memory is affected, including Alzheimer’s disease. Thus, understanding how a circuit of sensory neurons memory formation involves a circuit could also help us learn how to treat these disorders.
Studies investigating alterations of the endocannabinoid system (ECS) in Alzheimer’s disease (AD) in humans have reported inconsistent findings so far. We performed a systematic review of studies examining alterations of the ECS specifically within humans with AD or mild cognitive impairment (MCI), including neuroimaging studies, studies of serum and cerebrospinal fluid biomarkers, and post-mortem studies. We attempted to identify reported changes in the expression and activity of: cannabinoid receptors 1 and 2; anandamide (AEA); 2-arachidonoylglycerol (2-AG); monoacylglycerol lipase (MAGL); fatty acid amide hydrolase (FAAH); and transient receptor potential cation channel V1 (TRPV1). Twenty-two studies were identified for inclusion. Mixed findings were reported for most aspects of the ECS in AD, making it difficult to identify a particular profile of ECS alterations characterising AD. The included studies tended to be small, methodologically heterogeneous, and frequently did not control for important potential confounders, such as pathological progression of AD. Eight studies correlated ECS alterations with neuropsychometric performance measures, though studies infrequently examined behavioural and neuropsychiatric correlates.
PROSPERO database identifier: CRD42018096249.
Anticholinergic organophosphate (OP) agents act on the diverse serine hydrolases, thereby revealing unexpected biological effects. Epidemiological studies indicate a relationship between OP exposure and development of attention-deficit/hyperactivity disorder (ADHD)-like symptoms, whereas no plausible mechanism for the OP-induced ADHD has been established. The present investigation employs ethyl octylphosphonofluoridate (EOPF) as an OP-probe which is an extremely potent inhibitor of endocannabinoid (EC, anandamide and 2-arachidonoylglycerol)-hydrolyzing enzymes: i.e., fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). Ex vivo experiment shows that EOPF treatment decreases FAAH and MAGL activities and conversely increases EC levels in rat brain. Subsequently, EOPF (treated intraperitoneally once at 0, 1, 2, or 3 mg/kg) clearly induces ADHD-like behaviors (in elevated plus-maze test) in both Wistar and spontaneously hypertensive rats. The EOPF-induced behaviors are reduced by a concomitant administration of cannabinoid receptor inverse agonist SLV-319. Accordingly, EC system is a feasible target for OP-caused ADHD-like behaviors in adolescent rats.
Objective: This review discusses the relationship between cannabis use and psychotic, bipolar, depressive, and anxiety disorders, as well as suicide. It summarizes epidemiological evidence from cross-sectional and long-term prospective studies and considers possible etiological mechanisms. Methods: Systematic reviews and methodologically robust studies in the field (from inception to February 2019) were identified using a comprehensive search of Medline, PsychINFO, and Embase and summarized using a narrative synthesis. Results: Consistent evidence, both from observational and experimental studies, has confirmed the important role of cannabis use in the initiation and persistence of psychotic disorders. The size of the effect is related to the extent of cannabis use, with greater risk for early cannabis use and use of high-potency varieties and synthetic cannabinoids. Accumulating evidence suggests that frequent cannabis use also increases the risk for mania as well as for suicide. However, the effect on depression is less clear and findings on anxiety are contradictory with only a few methodologically robust studies. Furthermore, the relationship with common mental disorders may involve reverse causality, as depression and anxiety are reported to lead to greater cannabis consumption in some studies. Pathogenetic mechanisms focus on the effect of tetrahydrocannabinol (THC, the main psychoactive ingredient of cannabis) interacting with genetic predisposition and perhaps other environmental risk factors. Cannabidiol (CBD), the other important ingredient of traditional cannabis, ameliorates the psychotogenic effects of THC but is absent from the high-potency varieties that are increasingly available. Conclusions: The evidence that heavy use of high-THC/low-CBD types of cannabis increases the risk of psychosis is sufficiently strong to merit public health education. Evidence of similar but smaller effects in mania and suicide is growing, but is not convincing for depression and anxiety. There is much current interest in the possibility that CBD may be therapeutically useful.
Parkinson’s disease (PD) and l-DOPA-induced dyskinesia (LID) are motor disorders with significant impact on the patient’s quality of life. Unfortunately, pharmacological treatments that improve these disorders without causing severe side effects are not yet available. Delay in initiating l-DOPA is no longer recommended as LID development is a function of disease duration rather than cumulative l-DOPA exposure. Manipulation of the endocannabinoid system could be a promising therapy to control PD and LID symptoms. In this way, phytocannabinoids and synthetic cannabinoids, such as cannabidiol (CBD), the principal non-psychotomimetic constituent of the Cannabis sativa plant, have received considerable attention in the last decade. In this review, we present clinical and preclinical evidence suggesting CBD and other cannabinoids have therapeutic effects in PD and LID. Here, we discuss CBD pharmacology, as well as its neuroprotective effects and those of other cannabinoids. Finally, we discuss the modulation of several pro- or anti-inflammatory factors as possible mechanisms responsible for the therapeutic/neuroprotective potential of Cannabis-derived/cannabinoid synthetic compounds in motor disorders.
Novel pharmacological treatments are needed for Tourette syndrome. Our goal was to examine the current evidence base and biological rationale for the use of cannabis-derived medications or medications that act on the cannabinoid system in Tourette syndrome. We conducted a comprehensive literature search of PubMed for randomized controlled trials or clinical trials of cannabis-derived medications in Tourette syndrome. Data regarding the population, intervention, safety profile, and outcomes for each trial were extracted and reported and the evidence supporting use of individual cannabis-derived medications was critiqued. There is a strong biological rationale regarding how cannabis-derived medications could affect tic severity. Anecdotal case reports and series have noted that many patients report that their tics improve after using cannabis. However, only two small randomized, placebo-controlled trials of Δ⁹-tetrahydrocannabinol have been published; these suggested possible benefits of cannabis-derived agents for the treatment of tics. Trials examining other agents active on the cannabinoid system for tic disorders are currently ongoing. Cannabinoid-based treatments are a promising avenue of new research for medications that may help the Tourette syndrome population. However, given the limited research available, the overall efficacy and safety of cannabinoid-based treatments is largely unknown. Further trials are needed to examine dosing, active ingredients, and optimal mode of administration of cannabis-derived compounds, assuming initial trials suggest efficacy. Clinical use for refractory patients should at the very least be restricted to adult populations, given the uncertain efficacy and risk of developmental adverse effects that cannabinoids may have in children. Even in adult populations, cannabis-derived medications are associated with significant issues such as the effects they have on driving safety and the fact that they cause positive urine drug screens that can affect employment.
Cannabinoids are the derivatives of the cannabis plant, the most potent bioactive component of which is tetrahydrocannabinol (THC). The most commonly used drugs containing cannabinoids are marijuana, hashish, and hashish oil. These compounds exert their effects via interaction with the cannabinoid receptors CB1 and CB2. Type 1 receptors (CB1) are localised mostly in the central nervous system and in the adipose tissue and many visceral organs, including most endocrine organs. Type 2 cannabinoid receptors (CB2) are positioned in the peripheral nervous system (peripheral nerve endings) and on the surface of the immune system cells. Recently, more and more attention has been paid to the role that endogenous ligands play for these receptors, as well as to the role of the receptors themselves. So far, endogenous cannabinoids have been confirmed to participate in the regulation of food intake and energy homeostasis of the body, and have a significant impact on the endocrine system, including the activity of the pituitary gland, adrenal cortex, thyroid gland, pancreas, and gonads. Interrelations between the endocannabinoid system and the activity of the endocrine system may be a therapeutic target for a number of drugs that have been proved effective in the treatment of infertility, obesity, diabetes, and even prevention of diseases associated with the cardiovascular system. � 2018 Endokrynologia Polska. All rights reserved.
The insular cortex (IC) is an important brain region involved in the processing of pain and emotion. Recent studies indicate that lesions in the IC induce pain asymbolia and reverse neuropathic pain. Endogenous cannabinoids (endocannabinoids, eCBs), which have been shown to attenuate pain, are simultaneously degraded by fatty acid amide hydrolase (FAAH) that halts the mechanisms of action. Selective inhibitor URB597 suppresses FAAH activity by conserving eCBs, which reduces pain. The present study examined the analgesic effects of URB597 treatment in the IC of an animal model of neuropathic pain. Under pentobarbital anesthesia, male Sprague-Dawley rats were subjected to nerve injury and cannula implantation. On postoperative day (POD) 14, rodents received microinjection of URB597 into the IC. In order to verify the analgesic mechanisms of URB597, cannabinoid 1 receptor (CB1R) antagonist AM251, peroxisome proliferator-activated receptor alpha (PPAR alpha) antagonist GW6471, and transient receptor potential vanilloid 1 (TRPV1) antagonist I-RTX were microinjected 15 minutes prior to URB597 injection. Changes in mechanical allodynia were measured using the von-Frey test. Expressions of CB1R, N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD), and TRPV1 significantly increased in the neuropathic pain group, compared to the sham-operated control group. Mechanical threshold and expression of NAPE-PLD significantly increased in groups treated with 2 nM and 4 nM URB597 compared with the vehicle-injected group. Blockages of CB1R and PPAR alpha diminished the analgesic effects of URB597. Inhibition of TRPV1 did not effectively reduce the effects of URB597 but attenuated expression of NAPE-PLD compared with the URB597-injected group. In addition, optical imaging demonstrated that neuronal activity of the IC was reduced following URB597 treatment. Our results suggest that microinjection of FAAH inhibitor into the IC causes analgesic effects by decreasing neural excitability and increasing signals related to the endogenous cannabinoid pathway in the IC.
Experimental evidence suggests that the transport of endocannabinoids might work bi-directionally. Accordingly, it is possible that pharmacological blockade of the latter affects not only the re-uptake, but also the release of endocannabinoids, thus preventing them from stimulating CB1 receptors. We used biochemical, pharmacological, and behavioral approaches to investigate the effects of the transporter inhibitor OMDM-2 on social interaction, a behavioral assay that requires activation of CB1 receptors. The underlying mechanisms of OMDM-2 were compared with those of the Fatty Acid Amide Hydrolase (FAAH) inhibitor URB597.
Systemic administration of OMDM-2 reduced social interaction, but in contrast to URB597-induced social deficit, this effect was not reversed by the TRPV1 antagonist capsazepine. The CB1 antagonist AM251, which did not affect URB597-induced social withdrawal, exacerbated OMDM-2 effect. In addition, the potent CB1 agonist CP55,940 reversed OMDM-2-, but not URB597-, induced social withdrawal. Blockade of CB1 receptor by AM251 reduced social interaction and the cholecystokinin CCK2 antagonist LY225910 reversed this effect. Similarly, OMDM-2-induced social withdrawal was reversed by LY225910, whereas URB597 effect was not. Elevation of endocannabinoid levels by URB597 or JZL184, an inhibitor of 2-AG degradation, failed to reverse OMDM-2-induced social withdrawal, and did not show additive effects on cannabinoid measurements when co-administered with OMDM-2.
Taken together, these findings indicate that OMDM-2 impaired social interaction in a manner that is consistent with reduced activation of presynaptic CB1 receptors. As cannabinoid reuptake inhibitors may impair endocannabinoid release, caution should be taken when using these drugs to enhance endocannabinoid tone in vivo.
The second edition of this critically acclaimed and award-winning text provides a comprehensive overview of the psychiatry and neuroscience of Cannabis sativa (marijuana). It outlines the very latest developments in our understanding of the human cannabinoid system, and links this knowledge to clinical and epidemiological facts about the impact of cannabis on mental health. Clinically focused chapters review not only the direct psychomimetic properties of cannabis, but also the impact consumption has on the courses of evolving or established mental illnesses such as schizophrenia. Effects of cannabis on mood are reviewed, as are its effects on cognition. This new edition has been extensively updated and expanded with 10 new chapters to incorporate major new research findings. This book will be of interest to all members of the mental health team, as well as to neuroscientists, epidemiologists, public health specialists and those involved in drug and alcohol research.
The endocannabinoid system modulates the release of excitatory and inhibitory neurotransmitters in several brain areas implicated in motor control. Cannabinoid and dopamine receptors are highly abundant and often co-expressed in the basal ganglia circuitry, and the cross talk between these two systems regulates short- and long-term synaptic plasticity in the striatum. Dysregulation of the endocannabinoid system has been reported in animal models of Parkinson’s disease and parkinsonian patients and is exacerbated in dyskinetic states, following chronic levodopa administration.
This chapter reviews recent investigations on the relationships between endocannabinoids and other neurotransmitter/neuromodulator systems in the basal ganglia, with the intent to underline their relevance for the pathophysiology of levodopa-induced dyskinesia and discuss new pharmacological approaches for their treatment.
There is considerable evidence that signaling through cannabinoid 1 receptors (CB1Rs) contributes to the effects of stress on the brain as well as stress-adaptation. Similarly, serotonin, norepinephrine, and dopamine are important modulators and effectors of stress. The purpose of this review is to present and discuss the results of studies that have investigated the interactions between endocannabinoid-CB1 receptor signaling and each of the biogenic amines in the context of stress. © 2013 Springer Science+Business Media New York. All rights are reserved.
The second edition of this critically acclaimed and award-winning text provides a comprehensive overview of the psychiatry and neuroscience of Cannabis sativa (marijuana). It outlines the very latest developments in our understanding of the human cannabinoid system, and links this knowledge to clinical and epidemiological facts about the impact of cannabis on mental health. Clinically focused chapters review not only the direct psychomimetic properties of cannabis, but also the impact consumption has on the courses of evolving or established mental illnesses such as schizophrenia. Effects of cannabis on mood are reviewed, as are its effects on cognition. This new edition has been extensively updated and expanded with 10 new chapters to incorporate major new research findings. This book will be of interest to all members of the mental health team, as well as to neuroscientists, epidemiologists, public health specialists and those involved in drug and alcohol research.
Amphetamine-type stimulants (ATSs) are a large family of substances of abuse, characterized by well-known mood- and performance-enhancing properties. This class encompasses several high-potency stimulants and entactogens, such as the precursor compound d-amphetamine (AMPH), its synthetic N-methylated derivatives methamphetamine (METH) and 3, 4-methylenedioxy-N-methylamphetamine (MDMA, or "ecstasy"), as well as novel designer drugs, based on substituted forms of the natural alkaloid cathinone. ATSs (and in particular METH) are among the most commonly abused substances worldwide, second only to Cannabis sativa; indeed, the rate of concurrent consumption of METH and cannabis has been increasing over the last decade, particularly among adolescents. Anecdotal evidence suggests that marijuana may offset some unpleasant subjective effects of ATSs, such as anxiety and paranoia. Both drugs have been shown to increase schizophrenia vulnerability in young vulnerable individuals, raising the possibility that their concurrent intake may have synergistic effects with respect to the development of psychotic manifestations. In addition, the combination of these two substances may affect their subjective effects and exacerbate their abuse liability. Although current evidence on the neurobiological interactions of cannabis and ATSs remains mostly elusive, initial studies in animal models suggest that the cannabinoid system may play a relevant role in the motivational and addictive properties of ATSs; furthermore, cannabinoids may modify the behavioral effects and even attenuate some untoward long-term consequences of ATSs. In this chapter we review the available evidence on these potential interactions and outline some key mechanisms that may account for the mutual modulatory influence of these substances.
The endocannabinoid system timely orchestrates a variety of cerebral physiological processes by modulating brain neurotransmitters, and in particular the dopamine system. Both endocannabinoid and dopamine receptors are highly abundant and often coexpressed in the basal ganglia and mesolimbic pathways, where they regulate motor functions and motivational aspects of behavior. Understanding the interrelationship between these two systems is crucial to gain new insight on the pathophysiology of brain disorders characterized by a dysregulation of dopamine, such as Parkinson’s disease and schizophrenia. This review aims at: (1) presenting the complex functional interactions between these two neurotransmitter systems at the anatomical, pharmacological, cellular and electrophysiological levels, and (2) addressing the contribution of disturbances of cannabinoid–dopamine interactions to neurodegenerative and psychiatric disorders.
Keywords
Endocannabinoid CB1 Signaling Dopamine Dyskinesia Parkinson’s disease Schizophrenia Social behavior
The aim of this article is to summarize current evidence regarding alterations in the neuroendocrine stress response system and endocannabinoid system and their relationship in psychotic disorders such as schizophrenia. Exposure to stress is linked to the development of a number of psychiatric disorders including psychosis. However, the precise role of stress in the development of psychosis and the possible mechanisms that might underlie this are not well understood. Recently the cannabinoid hypothesis of schizophrenia has emerged as a potential line of enquiry. Endocannabinoid levels are increased in patients with psychosis compared with healthy volunteers; furthermore, they increase in response to stress, which suggests another potential mechanism for how stress might be a causal factor in the development of psychosis. However, research regarding the links between stress and the endocannabinoid system is in its infancy. Evidence summarized here points to an alteration in the baseline tone and reactivity of the hypothalamic-pituitary-adrenal (HPA) axis as well as in various components of the endocannabinoid system in patients with psychosis. Moreover, the precise nature of the inter-relationship between these two systems is unclear in man, especially their biological relevance in the context of psychosis. Future studies need to simultaneously investigate HPA axis and endocannabinoid alterations both at baseline and following experimental perturbation in healthy individuals and those with psychosis to understand how they interact with each other in health and disease and obtain mechanistic insight as to their relevance to the pathophysiology of schizophrenia.
Disruption of the mouse dopamine transporter gene results in spontaneous hyperlocomotion despite major adaptive changes, such as decreases in neurotransmitter and receptor levels. In homozygote mice, dopamine persists at least 100 times longer in the extracellular space, explaining the biochemical basis of the hyperdopaminergic phenotype and demonstrating the critical role of the transporter in regulating neurotransmission. The dopamine transporter is an obligatory target of cocaine and amphetamine, as these psychostimulants have no effect on locomotor activity or dopamine release and uptake in mice lacking the transporter.
Anandamide is the newly discovered endogenous cannabinoid ligand that binds to brain cannabinoid receptors and shares most, but not all, of the pharmacological properties of delta 9-THC. Therefore, this study was undertaken to determine whether its interaction with the CB1 receptor in brain was identical to that of delta 9-THC. Anandamide depressed spontaneous activity and produced hypothermia, antinociception and immobility in mice after i.v. administration. However, none of these effects was blocked by pretreatment with the selective CB1 antagonist, SR 141716A. However, the metabolically stable analog 2-methyl-2'-fluoroethylanandamide produced reductions in motor activity and antinociception in mice, effects that were blocked by the antagonist. To determine whether anandamide's receptor binding mimicked that of other cannabinoids, an autoradiographic comparison of anandamide, SR 141716A and CP 55,940 competition for [3H]CP55,940 binding was conducted throughout rat brain. The receptor affinities for all three compounds did not change according to brain area. As expected, Bmax values differed dramatically among differ brain areas. However, the Bmax values for each brain area were similar regardless of the compound used for displacement. These data suggest that anandamide, SR 141716A and CP 55,940 compete for the same cannabinoid receptor throughout brain despite SR 141716A's failure to block anandamide's pharmacological effects. Although there is no question that anandamide binds to the cannabinoid receptor, failure of SR 141716A to block its pharmacological effects in mice poses a dilemma. The results presented herein raise the possibility that anandamide may not be producing all of its effects by a direct interaction with the CB1 receptor.
We measured endogenous cannabinoid release in dorsal striatum of freely moving rats by microdialysis and gas chromatography/mass spectrometry. Neural activity stimulated the release of anandamide, but not of other endogenous cannabinoids such as 2-arachidonylglycerol. Moreover, anandamide release was increased eightfold over baseline after local administration of the D2-like (D2, D3, D4) dopamine receptor agonist quinpirole, a response that was prevented by the D2-like receptor antagonist raclopride. Administration of the D1-like (D1, D5) receptor agonist SKF38393 had no such effect. These results suggest that functional interactions between endocannabinoid and dopaminergic systems may contribute to striatal signaling. In agreement with this hypothesis, pretreatment with the cannabinoid antagonist SR141716A enhanced the stimulation of motor behavior elicited by systemic administration of quinpirole. The endocannabinoid system therefore may act as an inhibitory feedback mechanism countering dopamine-induced facilitation of motor activity.
We characterized the pharmacological properties of the anandamide transport inhibitor N-(4-hydroxyphenyl)-arachidonamide (AM404) in rats and investigated the effects of this drug on behavioral responses associated with activation of dopamine D(2) family receptors. Rat brain slices accumulated [(3)H]anandamide via a high-affinity transport mechanism that was blocked by AM404. When administered alone in vivo, AM404 caused a mild and slow-developing hypokinesia that was significant 60 min after intracerebroventricular injection of the drug and was reversed by the CB1 cannabinoid receptor antagonist SR141716A. AM404 produced no significant catalepsy or analgesia, two typical effects of direct-acting cannabinoid agonists. However, AM404 prevented the stereotypic yawning produced by systemic administration of a low dose of apomorphine, an effect that was dose-dependent and blocked by SR141716A. Furthermore, AM404 reduced the stimulation of motor behaviors elicited by the selective D(2) family receptor agonist quinpirole. Finally, AM404 reduced hyperactivity in juvenile spontaneously hypertensive rats, a putative model of attention deficit hyperactivity disorder. The results support a primary role of the endocannabinoid system in the regulation of psychomotor activity and point to anandamide transport as a potential target for neuropsychiatric medicines.
The endogenous ligand of CB1cannabinoid receptors, anandamide, is also a full agonist at vanilloid VR1 receptors for capsaicin and resiniferatoxin, thereby
causing an increase in cytosolic Ca2+ concentration in human VR1-overexpressing (hVR1-HEK) cells. Two selective inhibitors of anandamide facilitated transport
into cells, VDM11 and VDM13, and two inhibitors of anandamide enzymatic hydrolysis, phenylmethylsulfonyl fluoride and methylarachidonoyl
fluorophosphonate, inhibited and enhanced, respectively, the VR1-mediated effect of anandamide, but not of resiniferatoxin
or capsaicin. The nitric oxide donor, sodium nitroprusside, known to stimulate anandamide transport, enhanced anandamide effect
on the cytosolic Ca2+ concentration. Accordingly, hVR1-HEK cells contain an anandamide membrane transporter inhibited by VDM11 and VDM13 and activated
by sodium nitroprusside, and an anandamide hydrolase activity sensitive to phenylmethylsulfonyl fluoride and methylarachidonoyl
fluorophosphonate, and a fatty acid amide hydrolase transcript. These findings suggest the following. (i) Anandamide activates
VR1 receptors by acting at an intracellular site. (ii) Degradation by fatty acid amide hydrolase limits anandamide activity
on VR1; and (iii) the anandamide membrane transporter inhibitors can be used to distinguish between CB1 or VR1 receptor-mediated actions of anandamide. By contrast, the CB1 receptor antagonist SR141716A inhibited also the VR1-mediated effect of anandamide and capsaicin on cytosolic Ca2+ concentration, although at concentrations higher than those required for CB1 antagonism.
Leptin is the primary signal through which the hypothalamus senses nutritional state and modulates food intake and energy balance. Leptin reduces food intake by upregulating anorexigenic (appetite-reducing) neuropeptides, such as alpha-melanocyte-stimulating hormone, and downregulating orexigenic (appetite-stimulating) factors, primarily neuropeptide Y. Genetic defects in anorexigenic signalling, such as mutations in the melanocortin-4 (ref. 5) or leptin receptors, cause obesity. However, alternative orexigenic pathways maintain food intake in mice deficient in neuropeptide Y. CB1 cannabinoid receptors and the endocannabinoids anandamide and 2-arachidonoyl glycerol are present in the hypothalamus, and marijuana and anandamide stimulate food intake. Here we show that following temporary food restriction, CB1 receptor knockout mice eat less than their wild-type littermates, and the CB1 antagonist SR141716A reduces food intake in wild-type but not knockout mice. Furthermore, defective leptin signalling is associated with elevated hypothalamic, but not cerebellar, levels of endocannabinoids in obese db/db and ob/ob mice and Zucker rats. Acute leptin treatment of normal rats and ob/ob mice reduces anandamide and 2-arachidonoyl glycerol in the hypothalamus. These findings indicate that endocannabinoids in the hypothalamus may tonically activate CB1 receptors to maintain food intake and form part of the neural circuitry regulated by leptin.
The vanilloid receptor VR1 is a nonselective cation channel that is most abundant in peripheral sensory fibers but also is found in several brain nuclei. VR1 is gated by protons, heat, and the pungent ingredient of "hot" chili peppers, capsaicin. To date, no endogenous compound with potency at this receptor comparable to that of capsaicin has been identified. Here we examined the hypothesis, based on previous structure-activity relationship studies and the availability of biosynthetic precursors, that N-arachidonoyl-dopamine (NADA) is an endogenous "capsaicin-like" substance in mammalian nervous tissues. We found that NADA occurs in nervous tissues, with the highest concentrations being found in the striatum, hippocampus, and cerebellum and the lowest concentrations in the dorsal root ganglion. We also gained evidence for the existence of two possible routes for NADA biosynthesis and mechanisms for its inactivation in rat brain. NADA activates both human and rat VR1 overexpressed in human embryonic kidney (HEK)293 cells, with potency (EC(50) approximately 50 nM) and efficacy similar to those of capsaicin. Furthermore, NADA potently activates native vanilloid receptors in neurons from rat dorsal root ganglion and hippocampus, thereby inducing the release of substance P and calcitonin gene-related peptide (CGRP) from dorsal spinal cord slices and enhancing hippocampal paired-pulse depression, respectively. Intradermal NADA also induces VR1-mediated thermal hyperalgesia (EC(50) = 1.5 +/- 0.3 microg). Our data demonstrate the existence of a brain substance similar to capsaicin not only with respect to its chemical structure but also to its potency at VR1 receptors.
Do endocannabinoids (eCBs) participate in long-term synaptic plasticity in the brain? Using pharmacological approaches and genetically altered mice, we show that stimulation of prelimbic cortex afferents at naturally occurring frequencies causes a long-term depression of nucleus accumbens glutamatergic synapses mediated by eCB release and presynaptic CB1 receptors. Translation of glutamate synaptic transmission into eCB retrograde signaling involved metabotropic glutamate receptors and postsynaptic intracellular Ca(2+) stores. These findings unveil the role of the eCB system in activity-dependent long-term synaptic plasticity and identify a mechanism by which marijuana can alter synaptic functions in the endogenous brain reward system.
Cannabinoid receptors and their endogenous ligands have been recently identified in the brain as potent inhibitors of neurotransmitter release. Here we show that, in a rat model of Parkinson's disease induced by unilateral nigral lesion with 6-hydroxydopamine (6-OHDA), the striatal levels of anandamide, but not that of the other endocannabinoid 2-arachidonoylglycerol, were increased. Moreover, we observed a decreased activity of the anandamide membrane transporter (AMT) and of the anandamide hydrolase [fatty acid amide hydrolase (FAAH)], whereas the binding of anandamide to cannabinoid receptors was unaffected. Spontaneous glutamatergic activity recorded from striatal spiny neurons was higher in 6-OHDA-lesioned rats. Inhibition of AMT by N-(4-hydroxyphenyl)-arachidonoylamide (AM-404) or by VDM11, or stimulation of the cannabinoid CB1 receptor by HU-210 reduced glutamatergic spontaneous activity in both naive and 6-OHDA-lesioned animals to a similar extent. Conversely, the FAAH inhibitors phenylmethylsulfonyl fluoride and methyl-arachidonoyl fluorophosphonate were much more effective in 6-OHDA-lesioned animals. The present study shows that inhibition of anandamide hydrolysis might represent a possible target to decrease the abnormal cortical glutamatergic drive in Parkinson's disease.
Modulation of fast neurotransmission by monoamines is critically involved in numerous physiological functions and pathological conditions. Plasma membrane monoamine transporters provide one of the most efficient mechanisms controlling functional extracellular monoamine concentrations. These transporters for dopamine (DAT), serotonin (SERT), and norepinephrine (NET), which are expressed selectively on the corresponding neurons, are established targets of many psychostimulants, antidepressants, and neurotoxins. Recently, genetic animal models with targeted disruption of these transporters have become available. These mice have provided opportunities to investigate the functional importance of transporters in homeostatic control of monoaminergic transmission and to evaluate, in an in vivo model system, their roles in physiology and pathology. The use of these mice as test subjects has been helpful in resolving several important issues on specificity and mechanisms of action of certain pharmacological agents. In the present review, we summarize recent advances in understanding the physiology and pharmacology of monoamine transporters gained in mice with targeted genetic deletion of DAT, SERT, and NET.
Glutamatergic synaptic transmission within the striatum and prefrontal cortex regulates the neuronal synthesis of endocannabinoids. Because a primary role of dopamine is to modulate this excitatory transmission, we tested the hypothesis that dopaminergic transmission modulates endocannabinoid content in the limbic forebrain. Liquid chromatography/mass spectrometry was used to determine endogenous anandamide and 2-arachidonylglycerol (2-AG) contents within the limbic forebrain of mice after pharmacological manipulation of dopaminergic transmission. Increasing synaptic dopamine concentrations with methylphenidate significantly and dose dependently decreased both anandamide and 2-AG content. The selective dopamine reuptake inhibitor 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (GBR 12909) also significantly decreased anandamide and tended to decrease 2-AG content. The D1 receptor antagonist R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390) increased and the D1 receptor agonist 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine (SKF 33939) decreased anandamide content. 2-AG content was unaffected by SCH 23390 but was significantly increased by the D2 receptor antagonist eticlopride, which had no effect on anandamide content. The D2 agonist quinpirole had a biphasic effect on anandamide content with low, autoreceptor-preferring doses increasing anandamide and higher doses decreasing it back toward control. Quinpirole did not significantly affect 2-AG content. Together, these data indicate that endogenous dopamine exerts a differential, net suppressive effect upon anandamide and 2-AG content via activation of D1 and D2 receptors, respectively. These data are consistent with the hypothesis that modulation of endocannabinoid content by dopamine is secondary to changes in glutamatergic transmission, and they provide a pharmacological framework for the rational development of endocannabinoid-based therapeutic interventions for dopamine-related neuropsychiatric disorders.
To test the hypothesis that schizophrenia might be associated with alterations of the endogenous cannabinoid system in human blood.
Blood from 20 healthy volunteers and 12 patients with schizophrenia, 5 of which both before and after a successful antipsychotic treatment, was analysed for: 1) the amounts of the endocannabinoid anandamide; 2) the levels of cannabinoid CB1 and CB2 receptor mRNAs, and 3) the levels of the mRNA encoding the enzyme fatty acid amide hydrolase (FAAH), responsible for anandamide degradation. The amounts of anandamide were significantly higher in the blood of patients with acute schizophrenia than in healthy volunteers (7.79 +/- 0.50 vs. 2.58 +/- 0.28 pmol/ml). Clinical remission was accompanied by a significant decrease of the levels of anandamide (3.88 +/- 0.72 pmol/ml) and of the mRNA transcripts for CB2 receptors and FAAH.
These findings indicate that endocannabinoid signalling might be altered during the acute phase of schizophrenia not only in the central nervous system but also in the blood. These changes might be related to the several immunological alterations described in schizophrenia.
Activation of the CB1 cannabinoid receptor inhibits neurotransmission at numerous synapses in the brain. Indeed, CB1 is essential for certain types of both short- and long-term synaptic depression. It was demonstrated recently that CB1 is critical for activity-dependent long-term depression (LTD) at glutamatergic corticostriatal synapses in acute brain slice preparations. Here, we show that CB1 activation is necessary, but not solely sufficient, for induction of LTD and that the requisite signaling by endocannabinoids (eCBs) occurs during a time window limited to the first few minutes after high-frequency stimulation delivery. In addition, we have applied intracellularly anandamide membrane transporter inhibitors to provide novel evidence that postsynaptic transport mechanisms are responsible for the release of eCBs from striatal medium spiny neurons. These findings shed new light on the mechanisms by which transient eCB formation participates in the induction of long-lasting changes in synaptic efficacy that could contribute to brain information storage.
Compelling evidence indicates that endocannabinoids are implicated in drug addiction. In the present study, we have addressed the interaction between cocaine and endocannabinoid system by means of neurochemical and neurophysiological experiments in rat brain slices. Using gas chromatography-electron impact mass spectrometry, we have found that cocaine increased the levels of the endocannabinoid anandamide in the striatum, a brain area primarily involved in the compulsive drug-seeking and drug-taking behaviors typical of addiction. This effect was attenuated by pharmacological inhibition of D2-like receptors but not D1-like receptors, and it was mimicked by D2-like but not D1-like receptor stimulation. The cocaine-induced increase in anandamide concentrations was attributable to both stimulation of its synthesis and inhibition of its degradation, as suggested by the ability of cocaine and quinpirole, a D2-like receptor agonist, to enhance the activity of NAPE-phospholipase D and to inhibit fatty acid amide hydrolase. By means of electrophysiological recordings from single striatal neurons, we have then observed that the ability of cocaine to inhibit, via D2-like receptors, GABA transmission was partially prevented following blockade of cannabinoid receptors, suggesting that endocannabinoids may act as downstream effectors in the action of cocaine in the striatum. Understanding the molecular and physiological effects of drugs of abuse in the brain is essential for the development of effective strategies against addiction.
The molecular basis of cannabinoid activity is better understood since the discovery of the CB1 receptor in the mammalian brain and the CB2 receptor in peripheral tissues. Subsequently, an endogenous CB1 receptor ligand, arachidonylethanolamide (anandamide), was isolated from porcine brain and shown to be metabolized by the enzyme arachidonylethanolamide amidohydrolase or fatty acid amide hydrolase. Recently, we have characterized a reuptake system for the transport of anandamide across the cell membrane, and have shown that selective inhibition of this transporter is associated with analgesia and peripheral vasodilation. The four cannabinoid system proteins, including the CB1 and CB2 receptors, fatty acid amide hydrolase, and the anandamide transporter, are excellent targets for the development of novel medications for various conditions, including pain, immunosuppression, peripheral vascular disease, appetite enhancement or suppression, and motor disorders. During the last decade, numerous selective ligands for each of these proteins were designed and synthesized. Many of these agents serve as important molecular probes, providing structural information about their binding sites, as well as pharmacological tools imparting information about the roles of their targets in physiological and disease states. All of the above compounds that modulate the functions of the endocannabinoid system can be collectively described under the term cannabinergics, regardless of chemical classification or type of resultant pharmacological action.
The endogenous cannabinoid system is a new signaling system composed by the central (CB1) and the peripheral (CB2) receptors, and several lipid transmitters including anandamide and 2-arachidonylg-lycerol. This system is the target of
natural cannabinoids, the psychoactive constituents ofCannabis sativa preparations (marijuana, hashish). Acute and chronic cannabis exposure has been associated with subjective feelings of pleasure
and relaxation, but also to the onset of psychiatric syndromes, a decrease of the efficacy of neuroleptics and alterations
in the extrapyramidal system regulation of motor activity. These actions points to a tight association of the cannabinoid
system with the brain dopaminergic circuits involved in addiction, the clinical manifestation of positive symptoms of schizophrenia
and Parkinson’s disease. The present work discuss anatomical, biochemical and pharmacological evidences supporting a role
for the endogenous cannabinoid system in the modulation of dopaminergic transmission. Cannabinoid CB1 receptors are present in dopamine projecting brain areas. In primates and certain rat strains it is also located in dopamine
cells of the A8, A9 and A10 mesencephalic cell groups, as well as in hypothalamic dopaminergic neurons controlling prolactin
secretion. CB1 receptors co-localize with dopamine D1/D2 receptors in dopamine projecting fields. Manipulation of dopaminergic transmission is able of altere the synthesis and release
of anandamide as well as the expression of CB1 receptors. Additionally, CB1receptors can switch its transduction mechanism to oppose to the ongoing dopamine signaling. Acute blockade of CB1 receptor potentiates the facilitatory role of dopamine D2 receptor agonists on movement. CB1 stimulation results in sensitization to the motor effects of indirect dopaminergic agonists. The dynamics of these changes
indicate that the cannabinoid system is an activity-dependent modulator of dopaminergic transmission, an hypothesis relevant
for the design of new therapeutic strategies for dopamine-related diseases such as the psychosis and Parkinson’s disease.
The possibility that the anandamide transport inhibitor N-(4-hydroxyphenyl)-5,8,11,14-eicosatetraenamide (AM404), structurally similar to the vanilloid receptor agonists anandamide and capsaicin, may also activate vanilloid receptors and cause vasodilation was examined. AM404 evoked concentration-dependent relaxations in segments of rat isolated hepatic artery contracted with phenylephrine. Relaxations were abolished in preparations pre-treated with capsaicin. The calcitonin-gene related peptide (CGRP) receptor antagonist CGRP-(8-37) also abolished relaxations. The vanilloid receptor antagonist capsazepine inhibited vasodilation by AM404 and blocked AM404-induced currents in patch-clamp experiments on Xenopus oocytes expressing the vanilloid subtype 1 receptor (VR1). In conclusion, AM404 activates native and cloned vanilloid receptors.
Capsaicin and its analogue N-arachidonoyl-vanillyl-amine (arvanil) are agonists of vanilloid VR1 receptors, and suppress spontaneous activity in mice through an unknown mechanism. Here, we tested in rats the effect on motor behavior of: (1) capsaicin; (2) N-linoleoyl-vanillyl-amine (livanil) and N-α-linolenoyl-vanillyl-amine (linvanil), which, unlike arvanil, have very little affinity for cannabinoid CB1 receptors; and (3) the endocannabinoid anandamide (N-arachidonoyl-ethanolamine), which is a full agonist at both cannabinoid CB1 and vanilloid VR1 receptors. All compounds, administered i.p., dose-dependently (0.1–10 mg/kg) inhibited ambulation and stereotypic behavior and increased inactivity in the open field test. The rank of potency observed in vivo (livanil>capsaicin>linvanil>anandamide) bore little resemblance with the relative potencies in a functional assay for rat vanilloid VR1 receptors (livanil=linvanil>capsaicin>anandamide) and even less with the relative affinities in rat CB1 receptor binding assays (anandamide>livanil>linvanil>capsaicin). The vanilloid VR1 receptor antagonist capsazepine (10 mg/kg, i.p.) blocked the effect of capsaicin but not of livanil or anandamide, whereas the CB1 receptor antagonist (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide.HCl (SR141716A, 3 mg/kg, i.p.) antagonized the actions of the CB1 receptor agonist Δ9-tetrahydrocannabinol, but not of livanil, anandamide or capsaicin. Anandamide occluded the effects of livanil on locomotion, possibly suggestive of a common mechanism of action for the two compounds. Finally, stimulation with capsaicin of cells expressing rat vanilloid VR1 receptors led to anandamide formation. These data suggest that motor behavior can be suppressed by the activation of: (1) vanilloid receptors, possibly via the intermediacy of anandamide; or (2) capsazepine- and SR141716A-insensitive sites of action for anandamide, livanil and linvanil, possibly the same that were previously suggested to mediate arvanil hypokinetic effects in mice.
Anandamide was the first endogenous ligand of cannabinoid receptors to be discovered in 1992. Yet, this compound also efficiently activates receptors specific for capsaicin, known as vanilloid type 1 receptors (VR1). Whether anandamide is a physiological VR1 ligand is controversial. However, very recent reports demonstrate that activation of VR1 by anandamide can be significantly enhanced by various regulatory factors, suggesting that this compound might act as an ‘endovanilloid’ under certain conditions.
The biological actions of the endogenous cannabinoid anandamide are terminated by carrier-mediated transport into neurons and astrocytes, followed by enzymatic hydrolysis. Anandamide transport is inhibited by the compound N-(4-hydroxyphenyl)arachidonylamide (AM404). AM404 potentiates several responses elicited by administration of exogenous anandamide, suggesting that it may also protect endogenous anandamide from inactivation. To test this hypothesis, we studied the effects of AM404 on the plasma levels of anandamide using high-performance liquid chromatography/mass spectrometry (HPLC/MS). Systemic administration of AM404 (10 mg kg−1 intraperitoneal, i.p.) caused a gradual increase of anandamide in rat plasma, which was significantly different from untreated controls at 60 and 120 min after drug injection. In plasma, both AM404 and anandamide were associated with a plasma protein, which we identified as albumin by non-denaturing polyacrylamide gel electrophoresis. AM404 (10 mg kg−1, i.p.) caused a time-dependent decrease of motor activity, which was reversed by the cannabinoid CB1 receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide·hydrochloride (SR141716A, 0.5 mg kg−1, i.p). These results are consistent with the hypothesis that AM404 inhibits anandamide inactivation in vivo.
The endogenous cannabinoid receptor agonist anandamide is a powerful vasodilator of isolated vascular preparations, but its mechanism of action is unclear. Here we show that the vasodilator response to anandamide in isolated arteries is capsaicin-sensitive and accompanied by release of calcitonin-gene-related peptide (CGRP). The selective CGRP-receptor antagonist 8-37 CGRP, but not the cannabinoid CB1 receptor blocker SR141716A, inhibited the vasodilator effect of anandamide. Other endogenous (2-arachidonylglycerol, palmitylethanolamide) and synthetic (HU 210, WIN 55,212-2, CP 55,940) CB1 and CB2 receptor agonists could not mimic the action of anandamide. The selective 'vanilloid receptor' antagonist capsazepine inhibited anandamide-induced vasodilation and release of CGRP. In patch-clamp experiments on cells expressing the cloned vanilloid receptor (VR1), anandamide induced a capsazepine-sensitive current in whole cells and isolated membrane patches. Our results indicate that anandamide induces vasodilation by activating vanilloid receptors on perivascular sensory nerves and causing release of CGRP. The vanilloid receptor may thus be another molecular target for endogenous anandamide, besides cannabinoid receptors, in the nervous and cardiovascular systems.
Clozapine and haloperidol produce different induction patterns of c-fos expression in the forebrain, with haloperidol increasing Fos-like immunoreactivity (FLI) in the striatum, nucleus accumbens, lateral septal nucleus and clozapine producing such effects in the nucleus accumbens, prefrontal cortex and lateral septal nucleus. Accordingly, it was deemed possible that this approach may be useful in characterizing compounds with known or suggested antipsychotic actions. We therefore examined the effects of 17 compounds considered to be either typical, or atypical, antipsychotics on FLI in the prefrontal cortex, medial and dorsolateral striatum, nucleus accumbens and the lateral septal nucleus. Consistent with the hypothesis that the prefrontal cortex may be a target for some antipsychotic actions, FLI was elevated in this structure by clozapine, ICI 204,636, fluperlapine, RMI-81,582, remoxipride, molindone, melperone and tiospirone. Likewise, the ability of all of the compounds, except for risperidone, to enhance FLI in the lateral septal nucleus suggests that this limbic region also may be an important locus of antipsychotic action. All of the compounds examined elevated FLI in the nucleus accumbens and medial striatum, indicating that potential antipsychotic activity is predicted most consistently on this basis. Neuroleptics with a clearly documented liability for producing extrapyramidal side effects (EPS) such as chlorpromazine, fluphenazine, haloperidol, loxapine, metoclopramide and molindone elevated FLI in the dorsolateral striatum. In contrast, compounds unlikely to produce EPS such as clozapine, thioridazine, risperidone, remoxipride, fluperlapine, sulpiride, melperone and RMI-81,582 either failed to increase or produced minor elevations in FLI in the dorsolateral striatum.(ABSTRACT TRUNCATED AT 250 WORDS)
SR141716A is the first selective and orally active antagonist of the brain cannabinoid receptor. This compound displays nanomolar affinity for the central cannabinoid receptor but is not active on the peripheral cannabinoid receptor. In vitro, SR141716A antagonises the inhibitory effects of cannabinoid receptor agonists on both mouse vas deferens contractions and adenylyl cyclase activity in rat brain membranes. After intraperitoneal or oral administration SR141716A antagonises classical pharmacological and behavioural effects of cannabinoid receptor agonists. This compound should prove to be a powerful tool for investigating the in vivo functions of the anandamide/cannabinoid system.
Anandamide (arachidonylethanolamide) is a novel lipid neurotransmitter first isolated from porcine brain which has been shown to be a functional agonist for the cannabinoid CB1 and CB2 receptors. Anandamide has never been isolated from human brain or peripheral tissues and its role in human physiology has not been examined. Anandamide was measured by LC/MS/MS and was found in human and rat hippocampus (and human parahippocampal cortex), striatum, and cerebellum, brain areas known to express high levels of CB1 cannabinoid receptors. Significant levels of anandamide were also found in the thalamus which expresses low levels of CB1 receptors. Anandamide was also found in human and rat spleen which expresses high levels of the CB2 cannabinoid receptor. Small amounts of anandamide were also detected in human heart and rat skin. Only trace quantities were detected in pooled human serum, plasma, and CSF. The distribution of anandamide in human brain and spleen supports its potential role as an endogenous agonist in central and peripheral tissues. The low levels found in serum, plasma, and CSF suggest that it is metabolized in tissues where it is synthesized, and that its action is probably not hormonal in nature.
We have investigated the binding of 123I-labeled N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methy l-1 H-pyrazole-3-carboxamide (AM251), an analog of the cannabinoid receptor antagonist SR141716A [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1 H-pyrazole-3-carboxamide] in the mouse brain. Following intravenous injection, the peak whole-brain uptake of about 1% of the administered activity occurred at about 2 h. By 8 h radioactivity in brain had declined to about half its peak value. High-performance liquid chromatographic analysis showed that > 70% of radioactivity extracted from brain at 2 h was still present as [123I]AM251. Co-injection of SR141716A inhibited the in vivo brain binding of [123I]AM251 dose dependently. At 2 mg/kg, the highest dose that could be tested, inhibition was 50% at 2 h post-administration. The ED50 value calculated assuming that 2 mg/kg gave near-maximal inhibition was about 0.1 mg/kg. In contrast to the brain, radioactivity in other major organs (blood, liver, kidney, heart and lung) was little affected by SR141716A. The regional binding of [123I]AM251 in the brain was consistent with the published distribution of cannabinoid receptors in rat brain, in that the order was hippocampus, striatum > cerebellum > brain stem. delta 9-Tetrahydrocannabinol co-administered intravenously at 10 mg/kg, a dose which induced catalepsy and decreased locomotor activity, decreased the 2 h brain uptake of [123I]AM251 by 10%, but this was not significant (P = 0.08). In in vitro binding assays with mouse hippocampal membranes, tetrahydrocannabinol inhibited binding of [123I]AM251 with an IC50 value of about 700 nM, compared with about 0.2 nM for SR141716A.
The SPECT ligand AM 281, a less lipophilic analog of the cannabinoid receptor antagonist SR 141716A, robustly potentiated electrically-evoked release of acetylcholine from superfused hippocampal slices and prevented the inhibition of acetylcholine release by the cannabimimetic drug WIN 55212-2. These results, similar to earlier observations with SR 141716A, indicate that AM 281 is either a cannabinoid receptor antagonist or inverse agonist. Despite showing lower affinity than SR 141716A in hippocampal membrane binding experiments, AM 281 had slightly greater potency than SR 141716A in the hippocampal slice experiments, perhaps because of reduced drug absorption to slice membranes and to the apparatus.
Capsaicin has been suggested to act not only on thin primary afferents but also on the hypothalamus, but the neurotransmitter(s) of central capsaicin-sensitive neurons are unknown. The present study was conducted to determine whether any central, especially hypothalamic, glutamatergic terminals were sensitive to capsaicin. Capsaicin evoked glutamate release from slices of hypothalamus and lumbar dorsal horn, but not cerebellum. Such capsaicin action was Ca2+ dependent and inhibited by the capsaicin antagonist capsazepine. Vanilloid receptor subtype 1 mRNA was widely distributed in the brain, with a marked level in the hypothalamus and cerebellum, but not in the spinal cord. The results suggest that there are glutamatergic terminals sensitive to capsaicin in the hypothalamus.
Fatty acid amide hydrolase (FAAH) catalyzes the hydrolysis of bioactive fatty acid amides and esters such as the endogenous cannabinoid receptor ligands, anandamide (N-arachidonoyl-ethanolamine) and 2-arachidonoylglycerol, and the putative sleep inducing factor cis-9-octadecenoamide (oleamide). Most FAAH blockers developed to date also inhibit cytosolic phospholipase A2 (cPLA2) and/or bind to the CB1 cannabinoid receptor subtype. Here we report the finding of four novel FAAH inhibitors, two of which, malhamensilipin A and grenadadiene, were screened out of a series of thirty-two different algal natural products, and two others, arachidonoylethylene glycol (AEG) and arachidonoyl-serotonin (AA-5-HT) were selected out of five artificially functionalized polyunsaturated fatty acids. When using FAAH preparations from mouse neuroblastoma N18TG2 cells and [14C]anandamide as a substrate, the IC50s for these compounds ranged from 12.0 to 26 microM, the most active compound being AA-5-HT. This substance was also active on FAAH from rat basophilic leukaemia (RBL-2H3) cells (IC50 = 5.6 microM), and inhibited [14C]anandamide hydrolysis by both N18TG2 and RBL-2H3 intact cells without affecting [14C]anandamide uptake. While AEG behaved as a competitive inhibitor and was hydrolyzed to arachidonic acid (AA) by FAAH preparations, AA-5-HT was resistant to FAAH-catalyzed hydrolysis and behaved as a tight-binding, albeit non-covalent, mixed inhibitor. AA-5-HT did not interfere with cPLA2-mediated, ionomycin or antigen-induced release of [3H]AA from RBL-2H3 cells, nor with cPLA2 activity in cell-free experiments. Finally, AA-5-HT did not activate CB1 cannabinoid receptors since it acted as a very weak ligand in in vitro binding assays, and, at 10-15 mg/kg body weight, it was not active in the 'open field', 'hot plate' and rectal hypothermia tests carried out in mice. Conversely AEG behaved as a cannabimimetic substance in these tests as well as in the 'ring' immobility test where AA-5-HT was also active. AA-5-HT is the first FAAH inhibitor reported to date which is inactive both against cPLA2 and at CB1 receptors, whereas AEG represents a new type of cannabinoid receptor agonist.
The present study investigated, in rats, whether blockade of cannabinoid CB1 receptors may alter Fos protein expression in a manner comparable to that observed with antipsychotic drugs. Intraperitoneal administration of the selective CB1 receptor antagonist, SR141716, dose-dependently (1.0, 3.0 and 10 mg/kg) increased Fos-like immunoreactivity in mesocorticolimbic areas (prefrontal cortex, ventrolateral septum, shell of the nucleus accumbens and dorsomedial caudate–putamen), while motor-related structures such as the core of the nucleus accumbens and the dorsolateral caudate–putamen were unaffected. In the ventrolateral septum, taken as a representative structure, the Fos-inducing effect of SR141716 (10 mg/kg) was maximal 2 h after injection and returned to near control levels by 4 h. Within the prefrontal cortex, SR141716 increased the number of Fos-positive cells predominantly in the infralimbic and prelimbic cortices, presumptive pyramidal cells being the major cell types in which Fos was induced.
A cannabinoid hypothesis of schizophrenia has been proposed according to which cognitive dysfunction could be associated with dysregulation of an endogenous cannabinoid system.
The present study investigated whether SR 141716, a selective CB1 receptor antagonist, was able to reduce the hyperactivity induced in gerbils by various stimulant drugs known to produce or exacerbate schizophrenic symptoms.
Cocaine, d-amphetamine, morphine, and Win 55212-2 were administered intraperitoneally (IP) either immediately before placing the animals in the test apparatus (non-habituated gerbils) or after a 2- to 3-h habituation period in the actimeter (habituated gerbils). SR 141716 was given IP 30 min before the injection of stimulant drugs. Horizontal activity was recorded every 10 min for 1 h in Digiscan activity monitor.
SR 141716 (0.3-3 mg/kg) dose-dependently suppressed the enhanced locomotor activity induced by each stimulant drug in habituated gerbils, but not in non-habituated animals. Clozapine, an atypical antipsychotic compound, but not haloperidol, shared with SR 141716, the ability to differentially affect drug-induced hyperactivity in habituated versus non-habituated gerbils.
The activation of cannabinoid systems is a required, permissive element in the ability of cocaine, d-amphetamine, morphine, and Win 55212-2 to reinstate behaviour, i.e., to override stimulus satiation.
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The intraperitoneal (i.p.) injection of apomorphine or d-amphetamine significantly increased locomotor activity in Sprague-Dawley rats. Prior administration of the cannabinoid receptor antagonist, SR 141716A, significantly enhanced the stimulant effect of both d-amphetamine and apomorphine in a dose-dependent manner. Administration of SR 141716A alone had no effect on locomotor activity. These data indicate that endogenous cannabinoids exert an inhibitory action on the increase in locomotor activity produced by amphetamine and apomorphine.
Cannabinoid receptors, the molecular targets of the cannabis constituent Delta9-tetrahydrocannabinol, are present throughout the body and are normally bound by a family of endogenous lipids - the endocannabinoids. Release of endocannabinoids is stimulated in a receptor-dependent manner by neurotransmitters and requires the enzymatic cleavage of phospholipid precursors present in the membranes of neurons and other cells. Once released, the endocannabinoids activate cannabinoid receptors on nearby cells and are rapidly inactivated by transport and subsequent enzymatic hydrolysis. These compounds might act near their site of synthesis to serve a variety of regulatory functions, some of which are now beginning to be understood. Recent advances in the biochemistry and pharmacology of the endocannabinoid system in relation to the opportunities that this system offers for the development of novel therapeutic agents will be discussed.
In recent years, cannabinoid receptors and their endogenous ligands (endocannabinoids) have been identified within the brain. The high density of CB1 cannabinoid receptors within the basal ganglia suggests a potential role for endocannabinoids in the control of voluntary movement and in basal ganglia-related movement disorders such as Parkinson's disease. However, whether endocannabinoids play a role in regulating motor behavior in health and disease is unknown. Here we report the presence in two regions of the basal ganglia, the globus pallidus and substantia nigra, of the endocannabinoids 2-arachidonoylglycerol (2AG) and anandamide. The levels of the latter compound are approximately threefold higher than those previously reported in any other brain region. In the reserpine-treated rat, an animal model of Parkinson's disease, suppression of locomotion is accompanied by a sevenfold increase in the levels of the 2AG in the globus pallidus, but not in the other five brain regions analyzed. Stimulation of locomotion in the reserpine-treated rat by either of the two selective agonists of D2 and D1 dopamine receptors, quinpirole and R-(+/-)-3-allyl-6-chloro-7, 8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (Cl-APB), respectively, results in the reduction of both anandamide and 2AG levels in the globus pallidus. Finally, full restoration of locomotion in the reserpine-treated rat is obtained by coadministration of quinpirole and the selective antagonist of the cannabinoid CB1 receptor subtype, SR141716A. These findings indicate a link between endocannabinoid signaling in the globus pallidus and symptoms of Parkinson's disease in the reserpine-treated rat, and suggest that modulation of the endocannabinoid signaling system might prove useful in treating this or other basal ganglia-related movement disorders.
Some synthetic agonists of the VR1 vanilloid (capsaicin) receptor also inhibit the facilitated transport into cells of the endogenous cannabinoid anandamide (arachidonoylethanolamide, AEA). Here we tested several AEA derivatives containing various derivatized phenyl groups or different alkyl chains as either inhibitors of the AEA membrane transporter (AMT) in intact cells or functional agonists of the VR1 vanilloid receptor in HEK cells transfected with the human VR1. We found that four known AMT inhibitors, AM404, arvanil, olvanil and linvanil, activate VR1 receptors at concentrations 400-10000-fold lower than those necessary to inhibit the AMT. However, we also found three novel AEA derivatives, named VDM11, VDM12 and VDM13, which inhibit the AMT as potently as AM404 but exhibit little or no agonist activity at hVR1. These compounds are weak inhibitors of AEA enzymatic hydrolysis and poor CB(1)/CB(2) receptor ligands. We show for the first time that, despite the overlap between the chemical moieties of AMT inhibitors and VR1 agonists, selective inhibitors of AEA uptake that do not activate VR1 (e.g. VDM11) can be developed.
Mice lacking the dopamine transporter (DAT-/-) are characterized by high extracellular dopamine levels and spontaneous hyperlocomotion. We performed a detailed analysis of the behavioural phenotype of DAT-/- mice in order to identify other behavioural impairments associated with the hyperdopaminergic tone of these mutant mice. In particular, we investigated locomotor activity, exploration, and social and maternal behaviours, which are known to be regulated by dopamine. DAT-/- mice were easily aroused by novelty and always responded with hyperlocomotion, which interfered with habituation to the testing environment, exploratory behaviour in an open field and the coping response to forced swimming stress. Social behaviours such as interaction with an unknown congener or aggressiveness were not modified in DAT-/- mice compared with DAT+/- and DAT+/+ mice, although the maternal behaviour of mutant females was severely disturbed. Haloperidol and clozapine reversed the hyperactivity in DAT-/- mice, with a rightward shift of the dose-response curve compared with control animals, suggesting a dopamine-mediated effect. These results emphasize the role of dopamine regulation in locomotion, exploration and maternal behaviours and suggest that mice with a genetic deletion of DAT may represent a useful model to elucidate the altered behavioural processes accompanying pathological conditions associated with hyperdopaminergic function.
Spasticity is a complicating sign in multiple sclerosis that also develops in a model of chronic relapsing experimental autoimmune encephalomyelitis (CREAE) in mice. In areas associated with nerve damage, increased levels of the endocannabinoids, anandamide (arachidonoylethanolamide, AEA) and 2-arachidonoyl glycerol (2-AG), and of the AEA congener, palmitoylethanolamide (PEA), were detected here, whereas comparable levels of these compounds were found in normal and non-spastic CREAE mice. While exogenously administered endocannabinoids and PEA ameliorate spasticity, selective inhibitors of endocannabinoid re-uptake and hydrolysis-probably through the enhancement of endogenous levels of AEA, and, possibly, 2-arachidonoyl glycerol-significantly ameliorated spasticity to an extent comparable with that observed previously with potent cannabinoid receptor agonists. These studies provide definitive evidence for the tonic control of spasticity by the endocannabinoid system and open new horizons to therapy of multiple sclerosis, and other neuromuscular diseases, based on agents modulating endocannabinoid levels and action, which exhibit little psychotropic activity.
Dose-effect curves were established for the effects of the antipsychotic drugs haloperidol, clozapine, olanzapine, risperidone and ziprasidone on extracellular levels of dopamine and noradrenaline in the medial prefrontal cortex, and of dopamine in the striatum. Haloperidol was more effective in stimulating the release of dopamine in the striatum, whereas clozapine was much more effective in the medial prefrontal cortex. The efficacy of risperidone, olanzapine and ziprasidone did not differ for the two brain areas. The benzamides sulpiride and raclopride increased dopamine release in the striatum but did not affect the release of dopamine and noradrenaline in the medial prefrontal cortex. In the presence of dopamine/noradrenaline reuptake inhibitors, the benzamides strongly increased the release of dopamine-but not of noradrenaline-in the medial prefrontal cortex. The 5-HT(2) receptor antagonist R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl)ethyl]-4-piperidinemethanol (MDL100,907) (800 nmol/kg) and the dopamine D(2) receptor antagonist raclopride (2 micromol/kg) displayed a clear synergism in increasing the release of dopamine in the medial prefrontal cortex. No such synergism was seen in the case of noradrenaline. Co-administration of the 5-HT(2) receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine HCl (DOI) (850 nmol/kg) with clozapine (10 micromol/kg) or haloperidol (800 nmol/kg) blocked the increase in dopamine as well as noradrenaline in the medial prefrontal cortex. It is concluded that typical and non-benzamide atypical antipsychotics increase extracellular dopamine in the medial prefrontal cortex via a synergistic interaction by blocking 5-HT(2) as well as dopamine D(2) receptors. The increase in extracellular noradrenaline in the medial prefrontal cortex that was observed after administration of antipsychotics is explained by inhibition of 5-HT(2) receptors and not dopamine D(2) receptors. Finally, the significance of the classification of antipsychotic drugs based on their selective action on the release of dopamine and noradrenaline in the medial prefrontal cortex is discussed. In particular, the position of the benzamides is discussed.
The endocannabinoids, a family of endogenous lipids that activate cannabinoid receptors, are released from cells in a stimulus-dependent manner by cleavage of membrane lipid precursors. After release, the endocannabinoids are rapidly deactivated by uptake into cells and enzymatic hydrolysis. Endocannabinoid reuptake occurs via a carrier-mediated mechanism, which has not yet been molecularly characterized. Endocannabinoid reuptake has been demonstrated in discrete brain regions and in various tissues and cells throughout the body. Inhibitors of endocannabinoid reuptake include N-(4-hydroxyphenyl)-arachidonylamide (AM404), which blocks transport with IC50 (concentration necessary to produce half-maximal inhibition) values in the low micromolar range. AM404 does not directly activate cannabinoid receptors or display cannabimimetic activity in vivo. Nevertheless, AM404 increases circulating anandamide levels and inhibits motor activity, an effect that is prevented by the CB1 cannabinoid antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR141716A). AM404 also reduces behavioral responses to dopamine agonists and normalizes motor activity in a rat model of attention deficit hyperactivity disorder. The endocannabinoids are hydrolyzed by an intracellular membrane-bound enzyme, termed anandamide amidohydrolase (AAH), which has been molecularly cloned. Several fatty acid sulfonyl fluorides inhibit AAH activity irreversibly with IC50 values in the low nanomolar range and protect anandamide from deactivation in vivo. alpha-Keto-oxazolopyridines inhibit AAH activity with high potency (IC50 values in the low picomolar range). A more thorough characterization of the roles of endocannabinoids in health and disease will be necessary to define the significance of endocannabinoid inactivation mechanisms as targets for therapeutic drugs.
Chili peppers produce the pungent vanilloid compound capsaicin, which offers protection from predatory mammals. Birds are indifferent to the pain-producing effects of capsaicin and therefore serve as vectors for seed dispersal. Here, we determine the molecular basis for this species-specific behavioral response by identifying a domain of the rat vanilloid receptor that confers sensitivity to capsaicin to the normally insensitive chicken ortholog. Like its mammalian counterpart, the chicken receptor is activated by heat or protons, consistent with the fact that both mammals and birds detect noxious heat and experience thermal hypersensitivity. Our findings provide a molecular basis for the ecological phenomenon of directed deterence and suggest that the capacity to detect capsaicin-like inflammatory substances is a recent acquisition of mammalian vanilloid receptors.
Cannabis use is associated with a wide range of pharmacological effects, some of which have potential therapeutic benefit while others result in negative outcomes. Acute cannabinoid intoxication has been well documented to produce deficits in cognitive functioning with concomitant changes in glutamatergic, GABAergic, and cholinergic neurochemical systems in the hippocampus, each of which has been implicated in memory. Additionally, cannabis-dependent individuals abstaining from this drug can undergo a constellation of mild withdrawal effects. The use of the CB(1) cannabinoid receptor antagonist SR141716A and transgenic mice lacking the CB(1) receptor are critical tools for investigating the role of the endocannabinoid system in cognition, drug dependence, and other physiological processes. Converging evidence in which performance in a variety of memory tasks is enhanced following either SR141716A treatment or in CB(1) receptor knockout mice indicates that this system may play an important role in modulating cognition. There are also indications that this system may function to modulate opioid dependence. The purpose of this review is to describe recent advances that have furthered our understanding of the roles that the endocannabinoid system play on both cognition and drug dependence.
In recent years, our knowledge on the cannabinoid pharmacology has shown a significant rise in terms of both quantity (more compounds and more targets) and quality (more selective compounds). This allows to consider cannabinoids and related compounds as a promising new line of research for therapeutic treatment of a variety of conditions, such as brain injury, chronic pain, glaucoma, asthma, cancer and AIDS-associated effects and other pathologies. Motor disorders are another promising field for the therapeutic application of cannabinoid-related compounds, since the control of movement is one of the more relevant physiological roles of the endocannabinoid transmission in the brain. There are two pathologies, Parkinson's disease and Huntington's chorea, which are particularly interesting from a clinical point of view due to the direct relationship of endocannabinoids and their receptors with neurons that degenerate in those disorders. However, other neurological pathologies, such as Alzheimer's disease or multiple sclerosis, which are not motor disorders in origin, but present a strong alteration in the control of movement, have also been a subject of interesting research for a cannabinoid therapy. This review will summarize our current knowledge on the role of these endogenous substances in the control of movement and, in particular, on the possible therapeutic usefulness of these compounds in the treatment of motor pathologies.
The endogenous cannabinoid anandamide (AEA) is transported into cells by a temperature-sensitive process of facilitated diffusion. This uptake process has been characterised both biochemically and pharmacologically, and shown to be regulated at least in part by the intracellular metabolism of the accumulated AEA by fatty acid amide hydrolase. In this review, the properties of this transport process are briefly reviewed together with the corresponding transport mechanisms for the related endogenous compounds 2-arachidonoylglycerol and palmitoylethanolamide. In addition, the possibility that these transport mechanisms can be targets for therapeutic strategies aimed at prolonging the effects of the endocannabinoids is discussed.
The molecular basis of cannabinoid activity is better understood since the discovery of the CB(1) receptor in the mammalian brain and the CB(2) receptor in peripheral tissues. Subsequently, an endogenous CB(1) receptor ligand, arachidonylethanolamide (anandamide), was isolated from porcine brain and shown to be metabolized by the enzyme arachidonylethanolamide amidohydrolase or fatty acid amide hydrolase. Recently, we have characterized a reuptake system for the transport of anandamide across the cell membrane, and have shown that selective inhibition of this transporter is associated with analgesia and peripheral vasodilation. The four cannabinoid system proteins, including the CB(1) and CB(2) receptors, fatty acid amide hydrolase, and the anandamide transporter, are excellent targets for the development of novel medications for various conditions, including pain, immunosuppression, peripheral vascular disease, appetite enhancement or suppression, and motor disorders. During the last decade, numerous selective ligands for each of these proteins were designed and synthesized. Many of these agents serve as important molecular probes, providing structural information about their binding sites, as well as pharmacological tools imparting information about the roles of their targets in physiological and disease states. All of the above compounds that modulate the functions of the endocannabinoid system can be collectively described under the term cannabinergics, regardless of chemical classification or type of resultant pharmacological action.
Monoamine transporters, such as the dopamine transporter, 5-HT transporter and noradrenaline transporter, in the plasma membrane provide effective control over the intensity of monoamine-mediated signaling by recapturing neurotransmitters released by presynaptic neurons. These proteins represent established targets for several psychotropic drugs, including psychostimulants and antidepressants; however, important issues regarding the selectivity and mechanisms of action of these drugs remain unresolved. Although monoamine transporter knockout mice have profound changes in neurotransmission, they provide useful in vivo models to analyze the effects of psychotropic drugs. In this review, we summarize recent insights into the pharmacology of psychotropic drugs using mice in which the genes encoding these transporters have been deleted.
In order to explore potential therapeutic implications of cannabinoid antagonists, the effects of the prototypical cannabinoid antagonist SR141716A on monoamine efflux from the medial prefrontal cortex and the nucleus accumbens of the rat were investigated by in vivo microdialysis.
SR141716A moderately increased serotonin efflux and concentrations of its metabolite 5-HIAA, both in the medial prefrontal cortex and the nucleus accumbens, and increased norepinephrine, dopamine and their metabolites in the medial prefrontal cortex. In contrast, it had no effect on norepinephrine, dopamine and their metabolites in the nucleus accumbens.
At the same doses, SR141716A increased acetylcholine efflux in the medial prefrontal cortex, in agreement with previous studies; contrary to the effects in cortex, SR141716A had no effect on acetylcholine efflux in the nucleus accumbens.
The efficacy of SR141716A in the psychostimulant-induced hyperlocomotion and the forced swimming paradigms was also explored in mice. SR141716A attenuated phenylcyclidine- and d-amphetamine-induced hyperlocomotion, without affecting locomotor activity when administered alone, and decreased immobility in the forced swimming test.
These results suggest that the cortical selectivity in the release of catecholamines, dopamine in particular, induced by the cannabinoid antagonist SR141716A, its procholinergic properties, together with its mild stimulatory effects on serotonin and norepinephrine efflux make similar compounds unique candidates for the treatment of psychosis, affective and cognitive disorders.
British Journal of Pharmacology (2003) 138, 544–553. doi:10.1038/sj.bjp.0705100
We have recently reported that the administration of AM404, an inhibitor of the endocannabinoid re-uptake process, which also has affinity for the vanilloid VR1 receptors, is able to reduce hyperkinesia, and causes recovery from neurochemical deficits, in a rat model of Huntington's disease (HD) generated by bilateral intrastriatal injections of 3-nitropropionic acid (3NP). In the present study, we wanted to explore the mechanism(s) by which AM404 produces its antihyperkinetic effect in 3NP-lesioned rats by employing several experimental approaches. First, we tried to block the effects of AM404 with selective antagonists for the CB1 or VR1 receptors, i.e. SR141716A and capsazepine, respectively. We found that the reduction caused by AM404 of the increased ambulation exhibited by 3NP-lesioned rats in the open-field test was reversed when the animals had been pre-treated with capsazepine but not with SR141716A, thus suggesting a major role of VR1 receptors in the antihyperkinetic effects of AM404. However, despite the lack of behavioral effects of the CB1 receptor antagonist, the pretreatment with this compound abolished the recovery of neurochemical [gamma-aminobutyric acid (GABA) and dopamine] deficits in the caudate- putamen caused by AM404, as also did capsazepine. In a second group of studies, we wanted to explore the potential antihyperkinetic effects of various compounds which, compared to AM404, exhibit more selectivity for either the endovanilloid or the endocannabinoid systems. First, we tested VDM11 or AM374, two selective inhibitors or the endocannabinoid re-uptake or hydrolysis, respectively. Both compounds were mostly unable to reduce hyperkinesia in 3NP-lesioned rats, although VDM11 produced a certain motor depression, and AM374 exhibited a trend to stimulate ambulation, in control rats. We also tested the effects of selective direct agonists for VR1 (capsaicin) or CB1 (CP55,940) receptors. Capsaicin exhibited a strong antihyperkinetic activity and, moreover, was able to attenuate the reductions in dopamine and GABA transmission provoked by the 3NP lesion, whereas CP55,940 had also antihyperkinetic activity but was unable to cause recovery of either dopamine or GABA deficits in the basal ganglia. In summary, our data indicate a major role for VR1 receptors, as compared to CB1 receptors, in the antihyperkinetic effects and the recovery of neurochemical deficits caused in 3NP-lesioned rats by compounds that activate both CB1 and VR1 receptors, either directly or via manipulation of the levels of endogenous agonists.
Several evidences suggest that endocannabinoids exert a neurotrophic effect on developing mesencephalic dopamine neurons. Since an altered mesocorticolimbic system seems to underlie hyperactivity and attention deficit in clinical and animal studies of attention deficit hyperactivity disorder (ADHD), prenatal elevation of anandamide has been induced in Naples high excitability (NHE) rats by inhibition of its reuptake. To this aim, pregnant NHE and random-bred females received a subcutaneous injection of AM-404 (1 mg/kg) or vehicle daily from E11 until E20. Young adult male offsprings were exposed to a spatial novelty (Làt-maze) for 30 min and the behavior was videotaped and analysed for indices of activity (travelled distance, rearing frequency) and attention (rearing duration). Moreover, morphological analysis of the brains was carried out that pertained to cytochrome oxydase as marker of metabolic activity and thyrosine hydroxylase as marker of the dopamine systems. The results indicate that prenatal AM-404 treatment significantly reduces activity by about 20% during the entire testing period and modifies the distribution of scanning times towards short duration episodes in the first part of the test only in NHE-treated rats. In addition, image analysis revealed a significant increase in relative optical density of TH+terminals in the dorsal striatum and substantia nigra of AM-404 treated NHE rats and minor changes in the dorsal cortex of AM-404 treated NRB rats. The data suggest a corrected unbalance between the two dopamine systems that apparently leads to reduced hyperactivity and modified scanning times in this animal model of ADHD. This, in turn, might open new strategies in the treatment of a subset of ADHD cases.
Knowledge of the distribution and function of the vanilloid receptor (VR-1 or TRPV1) in the CNS lacks the detailed appreciation of its role in the peripheral nervous system. The radiolabelled vanilloid agonist [3H]resiniferatoxin (RTX) has been used to indicate the presence of TRPV1 receptor protein in the brain but low specific binding has complicated interpretation of this data. Recently, support for a more widespread CNS distribution of TRPV1 mRNA and protein has been provided by RT-PCR and antibody data. We have exploited the availability of TRPV1 null mice and used [3H]RTX autoradiography in the CNS of TRPV1 wild-type and TRPV1 null mice to identify the component of [3H]RTX binding to TRPV1 receptor protein. In the brains of TRPV1+/+ mice, specific [3H]RTX binding was broadly localised with the greatest binding in the olfactory nuclei, the cerebral cortex, dentate gyrus, thalamus, hypothalamus, periaqueductal grey, superior colliculus, locus coeruleus and cerebellar cortex. Specific binding was also seen in the spinal cord and sensory (dorsal root and trigeminal) ganglia. This binding was much lower but not abolished in most regions in the TRPV1-/- mice. Nonspecific binding was low in all cases. The present study unequivocally demonstrates a widespread and discrete distribution pattern of the TRPV1 receptor protein in the rat central nervous system. The presence of TRPV1 receptors in several brain regions suggests that it may function as a cannabinoid-gated channel in the CNS.
The administration of the endocannabinoid anandamide to rats produces hypokinesia in parallel to a decrease in the activity of nigrostriatal dopaminergic neurons. It was earlier hypothesized that this effect was mediated through the activation of CB(1) receptors, although these receptors have not been found in dopaminergic neurons, but in striatal projection neurons connected with them. However, two recent discoveries: (i) that anandamide is also able to activate vanilloid VR(1) receptors, and (ii) that VR(1) receptors are located on nigrostriatal dopaminergic neurons, allow to re-evaluate this hypothesis and suggest that the activation of vanilloid-like receptors rather than CB(1) receptors might be responsible of anandamide-induced hypokinesia and decreased nigrostriatal dopaminergic activity. To validate this new hypothesis, we carried out two different experiments. First, we explored whether the inhibitory effects of anandamide on motor activity and dopaminergic transmission were reversed by capsazepine, an antagonist for vanilloid-like receptors. Our data demonstrated that anandamide reduced ambulation, stereotypies and exploration, measured in the open-field test, whereas it increased the time spent in inactivity. All these effects were completely reversed by capsazepine, which had no effect by itself. Anandamide also caused a significant decrease in nigrostriatal dopaminergic activity, reflected by a reduction in DOPAC contents in the caudate-putamen, which was also reversed by capsazepine. As a second objective, we explored whether anandamide is able to directly influence nigrostriatal dopaminergic function by examining its effects on in vitro dopamine (DA) release using perifused striatal fragments. Our data confirmed that anandamide significantly decreased K(+)-stimulated dopamine release from nigrostriatal terminals and that this effect was vanilloid-like receptor-mediated since it was prevented by capsazepine. This in vitro inhibitory effect was not seen with a classic cannabinoid agonist that does not bind vanilloid-like receptors. In summary, anandamide behaves as a hypokinetic substance, thus producing motor depression in the open-field test, presumably related to a decrease in nigrostriatal dopaminergic activity. These effects were completely reversed by the vanilloid-like receptor antagonist capsazepine, thus indicating a role of these receptors, which are located on dopaminergic neurons, in mediating hypokinetic effects of anandamide. In vitro studies, using perifused striatal fragments, support this vanilloid-like receptor-mediated direct action, which would not be available for classic cannabinoid agonists.