Previously, we have shown that systemic administration of the 5-HT(2C) receptor agonist Ro60-0175 reduces cocaine-induced locomotor activity and cocaine self-administration. Ro60-0175 also alters the activity of midbrain dopamine (DA) neurons of the ventral tegmental area (VTA), a region where 5-HT(2C) receptors are expressed. The present experiments investigated whether microinjections of Ro60-0175 into the VTA would alter the locomotor stimulant effect of cocaine and cocaine self-administration. In the tests for locomotor activity injection of 3 and 10, but not 1 microg, Ro60-0175 into the VTA reduced the locomotor stimulation resulting from injection of 10 mg/kg cocaine. In tests of cocaine self-administration, rats were trained to lever press for intravenous infusions of 0.25 mg cocaine delivered on either a fixed ratio 5 (FR5) or a progressive ratio schedule. Intra-VTA injection of Ro60-0175 at doses of 3 and 10 microg reduced responding for cocaine on both schedules without significantly altering the latency to initiate responding or the rate of responding. A subsequent experiment determined that the suppressant effect of intra-VTA Ro60-0175 (3 microg) on responding for cocaine was prevented by pretreatment with the selective 5-HT(2C) receptor antagonist SB242,084 (0.5 mg/kg). In a final experiment, intra-VTA injection of Ro60-0175 reduced responding for food reinforcement on the same progressive ratio schedule as used for cocaine self-administration. These results demonstrate that stimulation of 5-HT(2C) receptors in the VTA is sufficient to attenuate the stimulant and reinforcing effects of cocaine. These effects complement electrophysiological and neurochemical findings, and indicate that 5-HT(2C) receptors localized within the VTA modulate the activity of mesolimbic DA neurons.
Previously, we showed that the 5-HT2C receptor agonist Ro60-0175 reduces cocaine self-administration, and the ability of cocaine to reinstate responding after extinction of drug-seeking behavior. The present experiments extended these findings further by determining whether the effects of Ro60-0175 on self-administration were sustained with repeated treatment, and whether Ro60-0175 altered reinstatement induced by the pharmacological stressor yohimbine, or by the context in which self-administration occurred. In Experiment 1, Ro60-0175 (1 mg/kg, s.c.) reduced cocaine (0.25 mg/infusion) self-administration maintained by a progressive ratio schedule. This reduction was sustained over eight daily injections. In Experiment 2, rats self-administered cocaine in daily 2 h sessions for 15 days on a FR1 schedule. Following extinction, yohimbine (1 mg/kg, i.p.) reinstated responding, and this effect was reduced dose dependently by Ro60-0175 (0.3-3 mg/kg, s.c.). In Experiment 3, rats were trained to respond for cocaine on a FR1 schedule in a distinct environmental context (A); responding was then extinguished in a different context (B). Reinstatement tests occurred in either context A or B. Responding was reinstated only when rats were tested in the original self-administration context (A). This reinstatement was reduced dose dependently by Ro60-0175. All effects of Ro60-0175 were blocked by the 5-HT2C receptor antagonist SB242084. Thus, Ro60-0175, acting via 5-HT2C receptors, reduces cocaine self-administration and cocaine-seeking triggered by a stressor and by drug-associated cues. The effects of Ro60-0175 do not exhibit tolerance within the 8-day test period. These results indicate that selective 5-HT2C receptor agonists may be a useful pharmacological strategy for treatment of drug abuse.
A key feature of addiction to nicotine likely resides in its ability to produce subjective effects that, in turn, may be reflected in its discriminative-stimulus properties. Vaccination against such effects of nicotine offers an intriguing therapeutic approach for smoking cessation, but a reliably effective and immunologically safe vaccine remains to be identified. Here we report on the ability of SEL-068, a nanoparticle-based vaccine that targets nicotine, to modify the discriminative-stimulus effects of nicotine in a primate species. Results indicate that squirrel monkeys vaccinated with SEL-068 failed to acquire 0.1 mg/kg nicotine discrimination but readily learned to discriminate 0.001 mg/kg of the nicotinic full agonist (+)-epibatidine [(+)-EPI]. After (+)-EPI training, doses of nicotine≥0.32 mg/kg, which produced behaviorally adverse actions, still failed to substitute for the (+)-EPI training stimulus in immunized monkeys, whereas (+)-EPI and the partial agonist varenicline engendered, respectively, complete and partial substitution in all monkeys with potency comparable to their potency in non-immunized subjects. In other subjects, nicotine was trained as a discriminative-stimulus and then replaced by (+)-EPI. Subsequent vaccination with SEL-068 led to a 3-fold and long-lasting (>30 weeks) decrease in the potency of nicotine but not (+)-EPI or varenicline. Collectively, our results show that SEL-068 can block the development of nicotine discrimination and attenuate nicotine's effects in nicotine-experienced monkeys without altering the discriminative-stimulus properties of other nicotinic drugs. The difference in the vaccine's effects in naïve and nicotine-experienced subjects provides important insight into the conditions under which immunotherapy may be effective in combating nicotine addiction.Neuropsychopharmacology accepted article preview online, 06 March 2015. doi:10.1038/npp.2015.64.
The purpose of the present investigation was to explore further the hypothesis that the self-injurious behavior induced by L-dihydroxyphenylalanine (L-DOPA) in neonatal-6-hydroxydopamine (OHDA)-lesioned rats is associated with an action on D1 dopamine receptors. This was accomplished by examining the behavioral responses induced by SKF-38393, quinpirole, and L-DOPA after treatment with the D1 antagonist SCH-23390 and three new pharmacologic agents, SCH-39166, NO-0756, and A-69024, reported to be D1 antagonists. All putative D1 antagonists were found to antagonize the action of SKF-38393 without reducing the increased locomotion and behavioral responses induced by quinpirole, consistent with an in vivo action on D1 receptors. The potency hierarchy of the compounds against the action of SKF-38393 on activity, from strongest to weakest, was: SCH-39166 equaled SCH-23390 and these were greater than NO-0756, which was greater than A-69024. All compounds were found to antagonize L-DOPA-induced self-mutilatory behavior (SMB) in neonatal-6-OHDA-lesioned rats in a dose-related manner. The potency hierarchy against this behavior, from strongest to weakest, was: SCH-23390, SCH-39166, NO-0756, and A-69024. The correlation between the ED50 for the ability of these drugs to antagonize SKF-38393-induced activity and their ability to reduce SMB by L-DOPA was greater than 0.99. In conclusion, the present findings provide additional evidence in vivo that NO-0756, SCH-39166, and A-69024 are selective D1 receptor antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)
The administration of 1.0 mg SDZ 210-086, an orally acting muscarinic agonist, shortened rapid-eye movement (REM) latency, increased REM percent of sleep period time and the total duration of REM sleep, and decreased slow-wave sleep in 12 healthy male subjects. The administration of 0.5 mg SDZ 210-086 had no statistically significant effect on sleep variables. Although the tonic components of REM sleep (REM duration, the REM percent of sleep period time) were increased, REM density percent (total) was significantly decreased due to the prolongation of total REM duration (in minutes) and a parallel reduction of the total number of eye movements. This finding is in contrast to studies using other cholinomimetics (i.e., physostigmine, arecoline, and RS 86) and may implicate different generating systems of phasic and tonic REM sleep components.
Neuroleptic treatment of schizophrenia provides a reduction in psychotic episodes and is accompanied by unwanted extrapyramidal side effects. Clozapine is atypical in that it does not produce these side effects. Typical antipsychotics have high affinity for dopamine D2 receptors, whereas atypicals, such as Clozapine, have D4 selectivity. Location of mRNA in rat brain show that D2 message is highest in the nigrostriatal areas, whereas D4 is distributed in cortical and limbic regions. The D4 selectivity of Clozapine and mRNA location indicate that D4 receptor antagonism may provide antipsychotic efficacy without extrapyramidal side effects. This study identifies for the first time the D4 receptor protein in autoradiographic blocking studies with [(3)H]-YM-09151-2 ([(3)M]-YM), a D2, D3, and D4 ligand. Blocked studies demonstrated that Raclopride, a D2/D3 compound, and D4 selective compounds Clozapine and (+)Apomorphine showed inhibitions in similar brain regions of D2 and D4 mRNA distribution, respectively. The study also investigated [(3)H] - Raclopride ([(3)H]-RAC) autoradiography to further contrast D2 location from D4. [(3)H]-RAC showed similar binding in regions blocked by cold Raclopride in [(3)H]-YM autoradiography. These findings reveal that the D4 receptor is located in dopaminergic structures involved in cognition and emotional stability while avoiding extrapyramidal structures which affect motor functioning.
Disrupted-in-schizophrenia-1 (DISC1) is associated with mental disorders, including major depression. We previously showed that DISC1-Q31L mutant mice have depression-like behaviors and can therefore be used to study neurobiological mechanisms of depression and antidepressant (AD) medication action. First, we found reduced levels of dopamine, serotonin and norepinephrine in the nucleus accumbens (NAC) of DISC1-Q31L mutants. Next, we assessed social-conditioned place preference as a reward-dependent task and the capacity of distinct ADs to correct impaired social behavior in DISC1-Q31L mice. Bupropion, but not fluoxetine or desipramine, was able to correct deficient social facilitation, social reward, and social novelty in DISC1-Q31L mutants, whereas all three ADs were able to improve social motivation and behavioral despair in DISC1-Q31L mutants. Furthermore, we sought to correlate social anhedonia with molecular and cellular features including dendritic spine density, β-arrestin-1,2, and cAMP-response-element-binding protein (CREB) in the NAC as biomarkers related to depression and the DISC1 pathway. DISC1-Q31L mutants showed reduced levels of β-arrestin-1,2, CREB, and spine density in the NAC, further supporting the construct validity of the genetic model. Bupropion induced the greatest effect on CREB in DISC1-Q31L mutants, whereas all studied ADs corrected the reduced levels of β-arrestin-1,2 and modestly ameliorated deficient spine density in this brain region. Overall, we find neurobiological changes accompanying social anhedonia in the NAC of DISC1-Q31L mutant mice, consistent with a role for DISC1 in regulating social reward as an endophenotype of depression.Neuropsychopharmacology advance online publication, 26 September 2012; doi:10.1038/npp.2012.197.
Previous reports have demonstrated the anxiolytic effect of the potent and systemically active metabotropic glutamate subtype 5 (mGlu5) receptor antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) in rodents. Here, we present evidence for the anxiolytic activity of a novel mGlu5 receptor antagonist, 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP), in rats and compare its profile to the benzodiazepine receptor agonist diazepam. MTEP occupied mGlu5 receptors in a dose-dependent manner with essentially full receptor occupancy at the highest dose tested (10 mg/kg, i.p.). At doses appropriate for mGlu5 receptor-mediated effects, MTEP significantly reduced fear-potentiated startle and increased punished responding in a modified Geller-Seifter conflict model consistent with an anxiolytic-like profile. In both models, the magnitude of the anxiolytic-like response was similar to that seen with diazepam. In contrast, MTEP decreased unpunished responding to a lesser extent than diazepam and had no effect on rotarod performance when administered either alone or in combination with ethanol. Repeated dosing with MTEP in this model eliminated the increase in punished responding observed with acute dosing. The present results suggest that mGlu5 receptor antagonists lack the side effects seen with benzodiazepines, such as sedation and ethanol interaction, and provide insight into a possible role for mGlu5 receptor antagonists in the modulation of mood disorders.
Combined dopamine D(2) receptor antagonism and serotonin (5-HT)(1A) receptor agonism may improve efficacy and alleviate some side effects associated with classical antipsychotics. The present study describes the in vitro and in vivo characterization of 1-(2,3-dihydro-benzo[1,4]dioxin-5-yl)-4-[5-(4-fluoro-phenyl)-pyridin-3-ylmethyl]-piperazine monohydrochloride (SLV313), a D(2/3) antagonist and 5-HT(1A) agonist. SLV313 possessed high affinity at human recombinant D(2), D(3), D(4), 5-HT(2B), and 5-HT(1A) receptors, moderate affinity at 5-HT(7) and weak affinity at 5-HT(2A) receptors, with little-no affinity at 5-HT(4), 5-HT(6), alpha(1), and alpha(2) (rat), H(1) (guinea pig), M(1), M(4), 5-HT(3) receptors, and the 5-HT transporter. SLV313 had full agonist activity at cloned h5-HT(1A) receptors (pEC(50)=9.0) and full antagonist activity at hD(2) (pA(2)=9.3) and hD(3) (pA(2)=8.9) receptors. In vivo, SLV313 antagonized apomorphine-induced climbing and induced 5-HT(1A) syndrome behaviors and hypothermia, the latter behaviors being antagonized by the 5-HT(1A) antagonist WAY100635. In a drug discrimination procedure SLV313 induced full generalization to the training drug flesinoxan and was also antagonized by WAY100635. In the nucleus accumbens SLV313 reduced extracellular 5-HT and increased dopamine levels in the same dose range. Acetylcholine and dopamine were elevated in the hippocampus and mPFCx, the latter antagonized by WAY100635, suggesting possible 5-HT(1A)-dependent efficacy for the treatment of cognitive and attentional processes. SLV313 did not possess cataleptogenic potential (up to 60 mg/kg p.o.). The number of spontaneously active dopamine cells in the ventral tegmental area was reduced by SLV313 and clozapine, while no such changes were seen in the substantia nigra zona compacta following chronic administration. These results suggest that SLV313 is a full 5-HT(1A) receptor agonist and full D(2/3) receptor antagonist possessing characteristics of an atypical antipsychotic, representing a potential novel treatment for schizophrenia.
Numerous reports in both humans and animals have confirmed that benzodiazepines produce amnesia; however, mechanisms mediating this effect are not clear. In view of the important role of brain somatostatin (SRIF) in the cognitive function of rats, this study sought to determine if the benzodiazepine, diazepam, alters somatostatinergic system in the rat frontoparietal cortex. Intraperitoneal (i.p.) administration of diazepam (5 mg/kg/day) to male Wistar rats (200-250 g) for 3 or 7 days decreased the number of SRIF receptors (26 and 37%, respectively) in synaptosomes from the frontoparietal cortex, without influencing their apparent affinity. This decrease in the tracer binding was not attributable to a direct effect of diazepam on SRIF receptors, because no decrease of SRIF binding was induced by a large concentration of diazepam (10(-4) M) when the drug was added to a preparation of synaptosomes from frontoparietal cortex of untreated rats. To determine if the effect of diazepam on SRIF binding is related to the binding of diazepam to its recognition site on the GABA(A) receptor, a benzodiazepine antagonist, 2-phenylpyrazolo[3,4-c]quinolin-3(5H)-one (CGS 8216) was administered before the diazepam injection. Pretreatment with CGS 8216 (20 mg/kg/day, i.p.) blocked completely the diazepam-induced decrease in the number of SRIF receptors. CGS 8216 alone had no observable effect. The decrease in the number of 125I-Tyr11-SRIF receptor induced by diazepam was accompanied by a decrease in the effect of SRIF, after 15 seconds of stimulation, on inositol 1,4, 5-trisphosphate (IP3) mass accumulation in the rat frontoparietal cortex at 3 (64%) or 7 days (59%) after its administration. Diazepam alone had no observable effect on mass accumulation of IP3. After 14 days of daily diazepam injections, the levels of binding of 125I-Tyr11-SRIF in the frontoparietal cortex returned to control values, coinciding with the tolerance that develops to this benzodiazepine agonists when administered chronically. The decrease in IP3 levels was still observed after 14 days (57%) diazepam administration. Diazepam and CGS 8216 did not affect SRIF-like immunoreactivity levels in the frontoparietal cortex at the three time intervals studied (3, 7 or 14 days). The alteration of frontoparietal cortex SRIF receptor-effector system after 3 or 7 days of diazepam treatment suggests that somatostatinergic neurotransmission plays a role in the mechanism of diazepam action on memory.
The neuropharmacological profile of Y-931, 8-fluoro-12- (4-methylpiperazin-1-yl)- 6H-benzothieno [2,3-b][1,5]benzodiazepine maleate, was investigated in comparison with those of typical and claimed atypical antipsychotic drugs. Similar to clozapine and olanzapine, Y-931 interacted with multiple neurotransmitter receptors such as dopaminergic, serotonergic, alpha-adrenergic, muscarinic and histaminergic receptors. Y-931, as well as the other antipsychotics, was active in a dose-dependent manner in established tests which are indicative of potential antipsychotic activity such as inhibition of apomorphine-induced hyperactivity and suppression of conditioned avoidance responses, however, only Y-931 and clozapine were devoid of cataleptogenic potential. In models of N-methyl-D-aspartate (NMDA) receptor hypofunction, Y-931 demonstrated the most potent protective action against the dizocilpine-induced neurotoxicity (neuronal vacuolization) in the rat retrosplenial cortex ([Y-931 (ED(50); 0.20 mg/kg, p.o.), olanzapine (1.1), clozapine (5.7), risperidone (6.9), haloperidol (19)). Furthermore, Y-931 and clozapine, unlike the other antipsychotics used, reversed the dizocilpine-induced social deficits at the same doses at which their neuroprotective action was exhibited. The present results suggest that Y-931 may be a novel potential atypical antipsychotic drug with a low risk of extrapyramidal syndrome (EPS) and the property to ameliorate NMDA receptor hypofunction.
(+/-)3,4-Methylenedioxymethamphetamine (MDMA) releases dopamine and serotonin in vivo and stimulates locomotor activity. Previous work demonstrated that MDMA-stimulated dopamine release could be reduced by the selective 5-HT2A receptor antagonist [R-(+)-a- (2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidinem ethanol] (MDL 100,907). In the present study MDL 100,907 significantly reduced MDMA-stimulated locomotion without affecting basal levels of locomotion. Other agents with 5-HT2A antagonist activity (ritanserin, clozapine, MDL 28,133A, or methiothepin), as well as agents that block 5-HT1A-(propranolol), D2-(haloperidol), or D1 receptors (SCH 23390) also reduced MDMA-stimulated locomotion. Intraventricularly administered 5,7-dihydroxytryptamine decreased regional 5-HT levels and attenuated MDMA-stimulated locomotion. These data support the conclusion that serotonin released onto 5-HT2A receptors contributes to MDMA-stimulated locomotion and suggest that MDMA-stimulated locomotion may be useful as an in vivo behavioral measure of 5-HT2A antagonism. The data also support previous reports of contributions of 5-HT1A, D1 and D2 receptors to MDMA-stimulated locomotion. A preliminary time-course analysis indicating time-dependent contributions of different receptors to MDMA-stimulated locomotion suggests the potential utility of this model for characterizing potential atypical antipsychotic compounds.
Genomic and pharmacologic data have suggested the involvement of the α3β4 subtype of nicotinic acetylcholine receptors (nAChRs) in drug seeking to nicotine and other drugs of abuse. In order to better examine this receptor subtype, we have identified and characterized the first high affinity and selective α3β4 nAChR antagonist, AT-1001, both in vitro and in vivo. This is the first reported compound with a Ki below 10 nM at α3β4 nAChR and >90-fold selectivity over the other major subtypes, the α4β2 and α7 nAChR. AT-1001 competes with epibatidine, allowing for [³H]epibatidine binding to be used for structure-activity studies, however, both receptor binding and ligand-induced Ca²⁺ flux are not strictly competitive because increasing ligand concentration produces an apparent decrease in receptor number and maximal Ca²⁺ fluorescence. AT-1001 also potently and reversibly blocks epibatidine-induced inward currents in HEK cells transfected with α3β4 nAChR. Importantly, AT-1001 potently and dose-dependently blocks nicotine self-administration in rats, without affecting food responding. When tested in a nucleus accumbens (NAcs) synaptosomal preparation, AT-1001 inhibits nicotine-induced [³H]dopamine release poorly and at significantly higher concentrations compared with mecamylamine and conotoxin MII. These results suggest that its inhibition of nicotine self-administration in rats is not directly due to a decrease in dopamine release from the NAc, and most likely involves an indirect pathway requiring α3β4 nAChR. In conclusion, our studies provide further evidence for the involvement of α3β4 nAChR in nicotine self-administration. These findings suggest the utility of this receptor as a target for smoking cessation medications, and highlight the potential of AT-1001 and congeners as clinically useful compounds.
In the present study, we investigated whether the antagonist of 5-HT1A receptors, WAY 100135, was capable of modifying the psychostimulant and psychotomimetic effects of MK-801, a non-competitive antagonist of NMDA receptors. It was found that: 1) WAY 100135 (10 and 20 mg/kg, but not 1.25, 2.5, and 5 mg/kg) transiently, in a dose dependent manner, attenuated the locomotor stimulant effects of MK-801 (0.4 mg/kg). Given alone, WAY 100135 had no effect on the locomotor activity of rats; 2) WAY 100135 (1.25 and 2.5 mg/kg, but not 10 or 20 mg/kg), attenuated or abolished the disruptive effects of MK-801 on the sensorimotor gating measured in a prepulse-induced inhibition of the acoustic startle response paradigm. WAY 100135 in all tested doses had no effect on the sensorimotor gating or amplitude of the acoustic startle response; 3) WAY 100135 (1.25, 2.5 mg/kg, but not 5 mg/kg) attenuated the detrimental effects of MK-801 on working memory and selective attention, measured in a delayed alternation task. Again, given alone, WAY 100135 did not influence the behavior of rats in that experimental paradigm; and 4) MK-801 (0.4 mg/kg) had no effect on the 5-HT1A receptor mRNA level in rat hippocampus, measured 2 and 24 hours after MK-801 administration. These data indicate that 5-HT1A receptors might be involved in the psychotomimetic effects of non-competitive NMDA receptor antagonists. In addition, 5-HT1A serotonin receptor antagonists and partial agonists may have potential antipsychotic properties.
We recently found that in rats trained to self-administer a heroin-cocaine mixture, exposure to the drug self-administration environment, after extinction of the drug-reinforced behavior in a different context, leads to renewal of drug seeking. Here we further explored the role of contextual stimuli in drug seeking by characterizing the effect of drug-associated environmental stimuli on renewal of cocaine seeking. We also investigated whether activation of dopamine receptors contributes to context-induced renewal of cocaine seeking by testing the effects of selective D1-like (SCH 23390) and D2-like (raclopride) receptor antagonists. Rats were trained for 10 days to self-administer cocaine by pressing a lever. Next, lever pressing was extinguished in the presence of the discrete cues associated with cocaine infusions for 10 days in a context that was distinctively different from the drug-taking context. On the test days, rats were pretreated with SCH 23390 (0, 5 or 10 microg/kg) or raclopride (0, 50 or 100 microg/kg) and non-reinforced lever-pressing behavior was determined either in the extinction context (Control group) or the cocaine-associated context (Renewal group). Consistent with our previous report, cocaine seeking was renewed when rats were exposed to the drug-associated context after extinction in a different context. Furthermore, pretreatment with the D1-like or the D2-like receptor antagonists attenuated context-induced renewal of cocaine seeking. These data suggest that activation of dopamine receptors is involved in reinstatement of cocaine seeking induced by exposure to the drug self-administration context.
Positron emission tomography (PET) and [11C]WAY-100635 were used to examine the effect of age on serotonin-1A (5-HT1A) receptor binding potential (BP) in 19 healthy subjects. Regions of interest (ROI) were drawn on the co-registered magnetic resonance imaging (MRI) in orbitofrontal (OFC), dorsolateral prefrontal (DLPFC), anterior cingulate (ACC), lateral (LTC), and mediotemporal (MTC), parietal, occipital and cerebellar cortex, and the raphe nuclei. BP values were calculated using a simplified reference tissue method. In addition, a voxelwise analysis was performed using SPM99. Voxelwise analysis revealed a significant global decrease of 5-HT(1A) BP with age (set level <.001). ROI analysis revealed significant age-related 5-HT(1A) BP decreases in DLPFC (r = -0.56), ACC (r = -0.44), OFC (r = -0.42), LTC (r = -0.40), parietal (r = -0.65), and occipital cortex (r = -0.43), but not in MTC or raphe nuclei. Overall, cortical 5-HT(1A) BP declined by approximately 10% per decade, except for the MTC, where we did not find a significant age effect. Hence, careful age matching may be recommended for future studies using PET and [11C]WAY-100635 to examine 5-HT1A receptors.
Augmentation of selective serotonin reuptake inhibitors (SSRIs) therapy by the 5-HT(1A) receptor agent pindolol may reduce the delay between initiation of antidepressant treatment and clinical response. This hypothesis is based on the ability of pindolol to block 5-HT(1A) autoreceptors in the dorsal raphe nuclei (DRN) and to potentiate the increase in 5-HT transmission induced by SSRIs. However, placebo-controlled clinical studies of pindolol augmentation of antidepressant therapy have reported inconsistent results. Here, we evaluated the occupancy of 5-HT(1A) receptors during treatment with pindolol controlled release (CR) in nine healthy volunteers with Positron Emission Tomography and [11C]WAY 100635. Subjects were studied four times: at baseline, following one week of pindolol CR 7.5 mg/day (4 and 10 hrs post dose), and following one dose of pindolol CR 30 mg(4 hrs post dose). Occupancy of the DRN was 40 +/- 29% on scan 2, 38 +/- 26% on scan 3, and 64 +/- 15% on scan 4. The average occupancy in all other regions was significantly lower at each doses (18 +/- 5% on scan 2, 12 +/- 3% on scan 3, and 42 +/- 4% on scan 4). These results suggest that the blockade in the DRN reached in clinical studies (7.5 mg/day) might be too low and variable to consistently augment the therapeutic effect of SSRIs. However, these data indicate that pindolol exhibits in vivo selectivity for the DRN 5-HT(1A) autoreceptors. As DRN selectivity is desirable for potentiation of 5-HT function, this observation represents an important proof of concept for the development of 5-HT(1A) agents in this application.
Systemic administration of the muscarinic-receptor antagonists atropine and scopolamine produces cognitive deficits in humans, nonhuman primates and rodents. In humans, these deficits resemble symptoms of dementia seen in Alzheimer's disease. The passive avoidance (PA) task has been one of the most frequently used animal models for studying cholinergic mechanisms in learning and memory. The present study examined the ability of two selective 5-HT(1A) receptor antagonists WAY 100635 and NAD-299 (robalzotan) and two acetylcholinesterase (AChE) inhibitors tacrine and donepezil to attenuate the impairment of PA retention caused by the nonselective muscarinic receptor antagonist scopolamine in the rat. Although demonstrating differences in their temporal kinetics, both WAY 100635 and NAD-299 attenuated the impairment of PA caused by scopolamine (0.3 mg/kg s.c.). Donepezil did not block the PA deficit caused by the 0.3 mg/kg dose of scopolamine, but it prevented the inhibitory effects of the 0.2 mg/kg dose of scopolamine. In contrast, tacrine was effective vs both the 0.2 and 0.3 mg/kg doses of scopolamine. These results indicate that (1). a functional 5-HT(1A) receptor antagonism can attenuate the anterograde amnesia produced by muscarinic-receptor blockade, and (2). the AChE inhibitors tacrine and donepezil differ in their ability to modify muscarinic-receptor-mediated function in vivo. These results suggest that 5-HT(1A) receptor antagonists may have a potential in the treatment of cognitive symptoms in psychopathologies characterized by reduced ACh transmission such as Alzheimer's disease.
To elucidate the relative contribution of somatodendritic 5-HT(1A) autoreceptors and postsynaptic 5-HT(1A) receptors in the specific anti-aggressive properties of 5-HT(1A) receptor agonists, the influence of the novel benzodioxopiperazine compound S-15535, which behaves in vivo as a competitive antagonist at postsynaptic 5-HT(1A) receptors and as an agonist at 5-HT(1A) autoreceptors, upon offensive and defensive aggression was investigated in wild-type rats using a resident-intruder paradigm. S-15535 exerted a potent dose-dependent decrease in offensive, but not defensive, aggressive behavior (inhibitory dose (ID)(50) = 1.11 mg/kg). This anti-aggressive profile was roughly similar to that of the potent pre- and postsynaptic 5-HT(1A) full agonist alnespirone (ID(50) = 1. 24). The drug's profound anti-aggressive actions were not accompanied by sedative side effects or signs of the "5-HT(1A) receptor-mediated behavioral syndrome," which are characteristically induced by prototypical 5-HT(1A) receptor agonists like 8-OH-DPAT and buspirone. The selective pre- and postsynaptic 5-HT(1A) antagonist WAY-100635, which was inactive given alone, abolished the anti-aggressive effects of S-15535 and alnespirone, thereby confirming the involvement of 5-HT(1A) receptors. Furthermore, combined administration of S-15535 and alnespirone elicited an additive anti-aggressive effect, providing further support for somatodendritic 5-HT(1A) receptor involvement. Finally, the postsynaptic 5-HT(1A) antagonistic properties of S-15535 were confirmed by showing blockade of the alnespirone-induced hypothermia, a postsynaptic 5-HT(1A) mediated response in the rat. These data provide extensive evidence that the anti-aggressive effects of 5-HT(1A) receptor agonists are expressed via their action on somatodendritic 5-HT(1A) autoreceptors, thereby most likely attenuating intruder-activated serotonergic neurotransmission.
Using microdialysis, receptor autoradiography and in situ hybridization, we examined the effects of fluoxetine alone or with WAY-100635 on: (a) extracellular 5-HT in frontal cortex; and (b) density and sensitivity of 5-HT(1A) autoreceptors in rat brain. WAY-100635 (0.3 mg/kg, s.c.) doubled the increase in extracellular 5-HT produced by fluoxetine (3 mg/kg, i.p.) in frontal cortex. Two-week minipump treatments with these daily doses significantly raised extracellular 5-HT to 275 +/- 33% (fluoxetine) and 245 +/- 10% (fluoxetine plus WAY-100635) of controls. Fluoxetine 3 mg/kg.day desensitized dorsal raphe 5-HT(1A) autoreceptors, an effect prevented by the concurrent WAY-100635 administration. However, WAY-100635 (alone or with fluoxetine) did not change 5-HT(1A) autoreceptor sensitivity. The density of 5-HT(1A) receptors and its encoding mRNA, was unaffected by these treatments. These results suggest that prolonged blockade of 5-HT(1A) receptors in vivo prevents the autoreceptor desensitization induced by fluoxetine but does not result in receptor sensitization.
3,4-Methylenedioxymethamphetamine (MDMA), the main psychoactive component of the recreational drug ecstasy, is a potent serotonin (5-HT) releaser. In animals, MDMA induces 5-HT depletion and toxicity in 5-HT neurons. The aim of this study was to investigate both presynaptic (5-HT transporter, SERT) and postsynaptic (5-HT(2A) receptor) markers of 5-HT transmission in recently abstinent chronic MDMA users compared with matched healthy controls. We hypothesized that MDMA use is associated with lower SERT density and concomitant upregulation of 5-HT(2A) receptors. Positron emission tomography studies using the SERT ligand [¹¹C]DASB and the 5-HT(2A) receptor ligand [¹¹C]MDL 100907 were evaluated in 13 current and recently detoxified MDMA users and 13 matched healthy controls. MDMA users reported a mean duration of ecstasy use of 8 years, regular exposure, and at least 2 weeks of abstinence before the scans. SERT and 5-HT(2A) receptor availability (binding potential, BP(ND)) were analyzed with a two-tissue compartment model with arterial input function. Current recreational MDMA use was significantly associated with lower SERT BP(ND) and higher 5-HT(2A) receptor BP(ND) in cortical, but not subcortical regions. Decreased SERT BP(ND) was regionally associated with upregulated 5-HT(2A) receptor BP(ND). In light of the animal literature, the most parsimonious interpretation is that repeated exposure to MDMA in humans, even in moderate amounts, leads to damage in 5-HT neuron terminals innervating the cortex. Alterations in mood, cognition, and impulse control associated with these changes might contribute to sustain MDMA use. The reversibility of these changes upon abstinence remains to be firmly established.
The rate of serotonin (5-HT) synthesis was measured in the discrete regions of the rat brain utilizing an autoradiographic method and alpha[14C]methyl-L-tryptophan as a tracer after an acute treatment with reserpine (10 mg/kg IP) or NSD-1015 (m-hydroxybenzylhydrazine) (100 mg/kg IP). Controls were injected with the same volume of solvent in place of reserpine or NSD-1015. Our results showed that reserpine induced a statistically significant (except for medial geniculate body) decrease in the rate of 5-HT synthesis in a large number of discrete brain structures. Reserpine had no influence on the plasma concentration of amino acids sharing the same carrier with tryptophan nor on the fraction of plasma-free tryptophan. NSD-1015 induced a statistically significant increase (p < .05) in the rate of 5-HT synthesis in 20 out of 28 brain regions but produced a pronounced decrease in the rate of 5-HT synthesis in the pineal body. This decrease in the pineal body serotonin synthesis rate is most likely the result of the loss of the label in the form of 5-hydroxy-alpha[14C]methyl-L-tryptophan [5-OHMTrp] that is not metabolized further because aromatic amino acid decarboxylase was inhibited. The data showing that there was no loss of the 5-OHMTrp from other brain structures as result of reserpine are also given. NSD-1015 treatment also induced a time-dependent increase in the plasma concentration of free tryptophan that becomes significant 30 minutes after NSD-1015 injection. Our results suggest that reserpine induces a decrease in 5-HT synthesis probably via direct or indirect inhibition of tryptophan hydroxylase activity. Since NSD-1015 alone increased the rate of 5-HT synthesis, the measurement of 5-HT synthesis in previous experiments using NSD-1015 and measuring the rate of 5-hydroxytryptophan accumulation after NSD-1015 induced inhibition of decarboxylase activity should be interpreted with reservation.
Eight healthy men underwent two positron emission tomography (PET) [11C]raclopride scans, one following placebo, the second following d-amphetamine (0.30 mg/kg, p.o.). PET data were analyzed using: (1) brain parametric maps to statistically generate regions of significant change; and (2) a priori identified regions of interest (ROI) manually drawn on each individual's co-registered magnetic resonance (MR) images. Compared with placebo, d-amphetamine decreased [11C]raclopride binding potential (BP) with significant effects in ventral but not dorsal striatum. Change in BP in the statistically generated cluster correlated with self-reported drug-induced 'drug wanting' (r = 0.83, p =.01) and the personality trait of Novelty Seeking-Exploratory Excitability (r = 0.79, p =.02). The same associations were seen in the manually drawn ROI in ventral striatum but not in dorsal putamen or caudate. Changes in extracellular dopamine (DA) did not correlate with mood. Mesolimbic DA might mediate interest in obtaining reward rather than reward, per se. Individual differences in amphetamine-induced DA release might be related to predispositions to drug and novelty seeking.
Rapid advances in modern gene seeking techniques and the sequence data evolving from related genome research should provide both new targets for drug discovery and new insights into risk factors for many neurological and psychiatric disorders. Coupled with the high speed synthetic capabilities available in many companies, high-throughput screening is identifying potential novel drug candidates at extraordinary rates. This enables the drug discoverer to be more precise in the biological specificity of drugs taken to human trials thereby reducing the potential side-effect profile of clinical candidates. The ability to create large libraries of compounds also allows researchers to focus on metabolism and pharmacokinetics at an earlier stage in the drug development process to minimize drug-drug interactions via common sites of metabolism and optimize duration of action for particular indications. An emerging bottleneck in psychopharmacological drug discovery is the relative paucity of preclinical behavioral models predictive of clinical efficacy and the need to carry out early clinical trials to demonstrate therapeutic utility. However, through the use of recently developed chip technology, coupled with data bases of information about single nucleotide polymorphisms in potential candidate genes or risk factors for psychiatric disorders, it should be possible in the near future to stratify clinical populations genetically for inclusion in specific drug treatment trials. The ultimate goal of this research is to obtain homogeneous populations for trials and to predict risk before the phenotype of the disorder is manifest.
Previous studies have shown that repeated exposures to phencyclidine (PCP) induces prefrontal cortical dopaminergic and cognitive deficits in rats and monkeys, producing a possible model of schizophrenic frontal cortical dysfunction. In the current study, the effects of subchronic PCP exposure on forebrain dopaminergic function and behavior were further explored. Prefrontal cortical dopamine utilization was reduced 3 weeks after subchronic PCP administration, and the cortical dopaminergic deficit was mimicked by repeated dizocilpine exposure. In contrast, stress- and amphetamine-induced hyperlocomotion, behavior believed to be mediated by activation of mesolimbic dopamine transmission, was enhanced after PCP exposures. Furthermore, haloperidol-induced increases in nucleus accumbens dopamine utilization were larger in magnitude in PCP-treated rats relative to control subjects. These data are the first to demonstrate that repeated exposures to PCP causes prefrontal cortical dopaminergic hypoactivity and subcortical dopaminergic hyper-responsivity in rats, perhaps mimicking alterations in dopaminergic transmission that underlie the behavioral pathology of schizophrenia.
The effects of the selective glucocorticoid receptor (GR) antagonists ORG 34850, ORG 34116, and ORG 34517 on the rat hypothalamic-pituitary-adrenocortical (HPA) system were investigated. To assess the potency of the compounds to occupy GR in the brain and pituitary, we applied a single acute subcutaneous (s.c.) injection (10 mg/kg). ORG 34517 was most potent to occupy GR in the anterior pituitary and distinct brain areas, whereas all compounds were unable to occupy mineralocorticoid receptor (MR). Chronic administration of ORG 34850, ORG 34116, and ORG 34517 (20 mg/kg/day) for 1, 3, and 5 weeks resulted only in minor changes in brain GR levels. However, profound increases of hippocampal MR were observed virtually at all time points. Treatment with ORG 34850 and ORG 34116 elicited episodic increases in HPA axis activity, whereas ORG 34517 did not cause any changes in HPA activity. Thus, the GR antagonists exert distinct effects on the HPA axis, which may be pertinent for the proposed antidepressant activity of these compounds.
Sigma-Receptors (SigRs) have been implicated in behavioral and appetitive effects of psychostimulants and may also modulate the motivating properties of ethanol. This study tested the hypothesis that SigRs modulate ethanol reinforcement and contribute to excessive ethanol intake. The effects of subcutaneous treatment with the potent, selective Sig-1R antagonist BD-1063 on operant ethanol self-administration were studied in two models of excessive drinking-Sardinian alcohol-preferring (sP) rats and acutely withdrawn ethanol-dependent Wistar rats-and compared to ethanol self-administration in nondependent Wistar controls. To assess the specificity of action, the effects of BD-1063 on self-administration of an equally reinforcing saccharin solution were determined in Wistar and sP rats. Gene expression of Sig-1R in reward-related brain areas implicated in ethanol reinforcement was compared between ethanol-naive sP and Wistar rats and withdrawn ethanol-dependent Wistar rats. BD-1063 dose dependently reduced ethanol self-administration in sP rats (3.3-11 mg/kg) and withdrawn, dependent Wistar rats (4-11 mg/kg) at doses that did not modify mean ethanol self-administration in nondependent Wistar controls. BD-1063 did not reduce concurrent water self-administration and did not comparably suppress saccharin self-administration, suggesting selectivity of action. BD-1063 also reduced the breakpoints of sP rats to work for ethanol under a progressive-ratio reinforcement schedule. Ethanol-naive sP rats and 24-h withdrawn, dependent Wistar rats showed reduced Sig-1R mRNA expression in the nucleus accumbens. The results suggest that SigR systems may contribute to innate or ethanol-induced increases in susceptibility to self-administer high ethanol levels, identifying a potential neuroadaptive mechanism contributing to excessive drinking and a therapeutic target for alcohol abuse and dependence.
A history of stress produces increases in rodent relapse-like alcohol self-administration behavior and regional brain gene expression of phosphodiesterase 10A (PDE10A), a dual-specificity cyclic adenosine monophosphate/cyclic guanosine monophosphate-inhibiting enzyme. Here, we tested the hypothesis that administration of TP-10, a specific PDE10A inhibitor, would reduce alcohol self-administration in conditions predisposing to elevated self-administration. TP-10 administration dose-dependently (0.562, 1.0 mg/kg; subcutaneously) reduced relapse-like alcohol self-administration regardless of stress history enhancement of relapse-like behavior. TP-10 also reduced alcohol self-administration in genetically alcohol-preferring rats, as well as in alcohol-non-dependent and -dependent rats. Effective systemic TP-10 doses did not alter alcohol pharmacokinetics, significantly reduce motor activity or intrabout operant response speed, or promote a conditioned place aversion. TP-10 also reduced saccharin self-administration, suggesting a general role for PDE10A in the self-administration of reinforcing substances. PDE10A inhibition in the dorsolateral striatum, but not the nucleus accumbens, reduced alcohol self-administration. Taken together, the results implicate dorsolateral striatum PDE10A in facilitating alcohol intake and support further investigation of PDE10A systems in the pathophysiology and potential treatment of substance use disorders.Neuropsychopharmacology advance online publication, 19 February 2014; doi:10.1038/npp.2014.20.
Several genome scans on alcohol dependence (AD) and AD-related traits have been published. In this article, we present the results of a genome-wide linkage scan on AD and several related traits in 322 European-American (EA) families, and results of additional analysis in 335 African-American (AA) families that were the subject of a previous report. All families were initially ascertained for cocaine and/or opioid dependence. Non-parametric linkage analysis in the EA sample revealed suggestive linkages on chromosomes 7 (LOD=2.1 at 82.8 cM, p=0.0009) and 10 (LOD=3.0 at 137.7 cM, p=0.0001). The chromosome 10 linkage peak is 20 cM distal from a genome-wide significant linkage peak we observed previously in the AA sample. Parametric linkage analysis on chromosome 10 (assuming a recessive model, 80% penetrance, disease allele frequency=0.3) resulted in LOD scores of 2.7 at 136.7 cM and 1.9 at 121.7 cM in the EA and AA samples, respectively, with a combined sample genome-wide significant LOD score of 4.1 at 131.7 cM. To reduce heterogeneity of the AD phenotype, we also assessed linkage of chromosome 10 markers with the presence of alcohol withdrawal symptoms, one of the seven components of the DSM-IV diagnosis of AD. Suggestive evidence for linkage was observed in both populations with only 5 cM separating the location of the peak LOD scores despite a loss of power due to a smaller number of families informative for this trait. Results of our study confirm a chromosome 10 risk locus for AD in two genetically distinct populations and suggest that this locus may correspond more precisely to a specific component of the disorder.
Sibutramine is a centrally acting monoamine reuptake inhibitor prescribed as an appetite suppressant in the management of obesity. Its effects are mostly attributable to serotonin and norepinephrine transporter (SERT and NET, respectively) inhibition by its potent metabolites mono-desmethylsibutramine (M1) and di-desmethylsibutramine (M2). However, there is a paucity of in vivo data in humans about mechanisms underlying both clinical efficacy and the dose-independent non-response observed in a minority of patients. Twelve healthy male patients (mean age 41 years) completed a double-blind, placebo-controlled, within-subject crossover investigation of brain SERT occupancy by sibutramine 15 mg daily at steady state. Correlations were measured between occupancy and (i) plasma concentrations of sibutramine, M1 and M2; (ii) appetite suppression. (11)C-DASB PET scans were performed on the HRRT camera. Binding potentials (BP(ND)) were calculated by the Logan reference tissue (cerebellum) method. SERT occupancy was modest (mean 30+/-10%), was similar across brain regions, but varied widely across subjects (15-46%). Occupancy was correlated positively (p=0.09) with M2 concentration, but not with sibutramine or M1. No significant appetite suppression was seen at <25% occupancy and greatest suppression was associated with highest occupancy (25-46%). However, several subjects with occupancy (36-39%) in the higher range had no appetite suppression. SERT occupancy by clinical doses of sibutramine is of modest magnitude and may be mediated predominantly by M2 in humans. 5-HT reuptake inhibition may be necessary but is not sufficient for sibutramine's efficacy in humans, supporting preclinical data suggesting that the hypophagic effect requires the co-inhibition of both SERT and NET.
(+/-)3,4-Methylenedioxymethamphetamine (MDMA, 'Ecstasy') is a widely used illicit drug that produces toxic effects on brain serotonin axons and axon terminals in animals. The results of clinical studies addressing MDMA's serotonin neurotoxic potential in humans have been inconclusive. In the present study, 23 abstinent MDMA users and 19 non-MDMA controls underwent quantitative positron emission tomography (PET) studies using [11C]McN5652 and [11C]DASB, first- and second-generation serotonin transporter (SERT) ligands previously validated in baboons for detecting MDMA-induced brain serotonin neurotoxicity. Global and regional distribution volumes (DVs) and two additional SERT-binding parameters (DV(spec) and DVR) were compared in the two subject populations using parametric statistical analyses. Data from PET studies revealed excellent correlations between the various binding parameters of [11C]McN5652 and [11C]DASB, both in individual brain regions and individual subjects. Global SERT reductions were found in MDMA users with both PET ligands, using all three of the above-mentioned SERT-binding parameters. Preplanned comparisons in 15 regions of interest demonstrated reductions in selected cortical and subcortical structures. Exploratory correlational analyses suggested that SERT measures recover with time, and that loss of the SERT is directly associated with MDMA use intensity. These quantitative PET data, obtained using validated first- and second-generation SERT PET ligands, provide strong evidence of reduced SERT density in some recreational MDMA users.
The early postpartum period is associated with increased risk for affective and psychotic disorders. Because maternal dopaminergic reward system function is altered with perinatal status, dopaminergic system dysregulation may be an important mechanism of postpartum psychiatric disorders. Subjects included were non-postpartum healthy (n=13), postpartum healthy (n=13), non-postpartum unipolar depressed (n=10), non-postpartum bipolar depressed (n=7), postpartum unipolar (n=13), and postpartum bipolar depressed (n=7) women. Subjects underwent 60 min of [¹¹C]raclopride-positron emission tomography imaging to determine the nondisplaceable striatal D₂/₃ receptor binding potential (BP(ND)). Postpartum status and unipolar depression were associated with lower striatal D₂/₃ receptor BP(ND) in the whole striatum (p=0.05 and p=0.02, respectively) that reached a maximum of 7-8% in anteroventral striatum for postpartum status (p=0.02). Unipolar depression showed a nonsignificant trend toward being associated with 5% lower BP(ND) in dorsal striatum (p=0.06). D₂/₃ receptor BP(ND) did not differ significantly between unipolar depressed and healthy postpartum women or between bipolar and healthy subjects; however, D₂/₃ receptor BP(ND) was higher in dorsal striatal regions in bipolar relative to unipolar depressives (p=0.02). In conclusion, lower striatal D₂/₃ receptor BP(ND) in postpartum and unipolar depressed women, primarily in ventral striatum, and higher dorsal striatal D₂/₃ receptor BP(ND) in bipolar relative to unipolar depressives reveal a potential role for the dopamine (DA) system in the physiology of these states. Further studies delineating the mechanisms underlying these differences in D₂/₃ receptor BP(ND), including study of DA system responsivity to rewarding stimuli, and increasing power to assess unipolar vs bipolar-related differences, are needed to better understand the affective role of the DA system in postpartum and depressed women.
Chromosome 11 is a region of great interest in the search for genes for bipolar disorder. Although an initial report of linkage to 11p15 was not replicated in numerous subsequent studies, the remainder of the chromosome contains a variety of interesting candidate genes and regions. These include the D2 dopamine receptor and the site of a chromosomal translocation that has been reported to be associated with bipolar disorder. As part of a systematic survey of the genome for markers linked to bipolar disorder, we have examined 13 markers on chromosome 11 in three large Icelandic families and Amish pedigree 110. No clear evidence of linkage was obtained. The highest lod score was found at D11S29 (lod = 1.63 at theta = 0.1), which is in the general region of the reported translocation breakpoints. However, this lod is not statistically significant, and its meaning is further mitigated by strongly negative lods in two nearby flanking markers. Linkage to the D2 dopamine receptor locus was strongly excluded (lod = -4.02 at theta = 0.0). In two-point analyses, linkage to bipolar disorder could be excluded to eight of the 13 markers. Multipoint analyses, similarly, failed to reveal any evidence of linkage.
Bipolar disorder (BPD) is characterized by recurrent episodes of disturbed affect including mania and depression as well as changes in psychovegetative function, cognitive performance, and general health. A growing body of data suggests that BPD arises from abnormalities in synaptic and neuronal plasticity cascades, leading to aberrant information processing in critical synapses and circuits. Thus, these illnesses can best be conceptualized as genetically influenced disorders of synapses and circuits rather than simply as deficits or excesses in individual neurotransmitters. In addition, commonly used mood-stabilizing drugs that are effective in treating BPD have been shown to target intracellular signaling pathways that control synaptic plasticity and cellular resilience. In this article we draw on clinical, preclinical, neuroimaging, and post-mortem data to discuss the neurobiology of BPD within a conceptual framework while highlighting the role of neuroplasticity in the pathophysiology and treatment of this disorder.
Biologically active n-acylprolyl-dipeptides were described by us recently. GVS-111 was shown to be one of the more active substances of this series.The effects of the GVS-111 on diazepam withdrawal were studied in male Wistar rats treated for 21 days with diazepam 4 mg/kg/day (i.p.). The withdrawal syndrome was assessed 24 hours after the last diazepam injection. Withdrawal signs recorded were: anxiogenic - like behavior in the elevated plus maze (EPM), suppression of exploratory behavior in the open field and the intensification of seizures, precipitated by pentylentetrazol. Two regimes of administration of GVS-111 (0.5 mg/kg, i.p) were used: a) during withdrawal 15 minutes before testing in above mentioned paradigms, b) during last 7 days of diazepam administration and during withdrawal. GVS-111 was demonstrated to be able to attenuate the degree of anxiogenic state in EPM, dramatically increasing time spent in open arms. GVS-111 decreased the degree of pentylentetrazol precipitated seizures. There was no significant effects upon the activity in open field. All these effects of GVS-111 were more pronounced in case of long-term administration. These findings suggest that GVS-111 may have potential as a treatment for withdrawal from sedative/hypnotics.
Design of piracetam peptide analogues was proposed as a new approach to the creation of cognitive enchancers (Gudasheva et al, 1985). Dipeptides containing pyroglutamic acid with various natural amino acids were shown to be able to restore cognition damaged by a number of noxious influences in doses 0.001-1.0 mg/kg (Ostrovskaya et al, 1987, Gudasheva et al, 1988). Recently we showed antiamnestic effects in acyl prolyl containing dipeptides, in particular in phenylacetylprolyl derivatives. GVS-111 was chosen as one of the most active substances of this series. It was studied in the passive avoidance paradigm in rats. The substance was demonstrated to be able to facilitate acquisition per se. Administered before testing it facilitated retrieval processes as well. GVS-111 attenuated the amnestic effect of electroshock, scopolamine & proline cethylester (lypophylic prodrug of proline, designed by Skoldinov et al.). GVS-111 increased the degree of acute habituation of exploratory behavior in grouped (n= 10) mice without effect on baseline locomotion. GVS-111 showed all above listed mnemotropic effects in doses 0,1-1.0 mg/kg (i.p),LD 50 for mice is 5000 mg/kg. GVS-111 possesses much higher biological stability than TRH & AVP.GVS-111 preserved effectiveness in peroral administration. These studies demonstrate that GVS-111 may encance memory under range of condition.
The dopamine-type-1 receptor has been implicated in major depressive disorder (MDD) by clinical and preclinical evidence from neuroimaging, post-mortem and behavioral studies. To date, however, selective in vivo assessment of D1-receptors has been limited to the striatum in MDD-samples manifesting anger attacks. We employed the PET radioligand, [11C]NNC-112, to selectively assess D1-receptor binding in extrastriatal and striatal regions in a more generalized sample of MDD-subjects.
The [11C]NNC-112 nondisplaceable binding-potential (BPND) was assessed using PET in 18 unmedicated, currently-depressed subjects with MDD and 19 healthy controls, and compared between groups using MRI-based region-of-interest analysis.
The mean D1-receptor BPND was reduced (14%) in the left middle caudate of the MDD group relative to control group (p<0.05). Among the MDD-subjects D1-receptor BPND in this region correlated negatively with illness duration (r= −0.53; p=0.02), and the left-to-right BPND ratio correlated inversely with anhedonia ratings (r=−0.65, p=0.0040). The D1receptor BPND was strongly lateralized in striatal regions (p<0.002 for main effects of hemisphere in accumbens area, putamen and caudate). In post hoc analyses, a group-by-hemisphere-by-gender interaction was detected in the dorsal putamen, which was accounted for by a loss of the normal asymmetry in depressed females (F=7.33,p=0.01).
These data extended a previous finding of decreased striatal D1-receptor binding in an MDD-sample manifesting anger attacks to a sample selected more generally according to MDD criteria. Our data also more specifically localized this abnormality in MDD to the left middle caudate, which is the target of afferent neural projections from the orbitofrontal and anterior cingulate cortices where neuropathological changes have been reported in MDD. Finally, D1-receptor binding was asymmetrical across hemispheres in healthy humans, compatible with evidence that dopaminergic function in the striatum is lateralized during reward processing, voluntary movement and self-stimulation behavior.
This study was designed to evaluate the role of different serotonin (5-HT) receptor subtypes in mediating the effects of 3,4-methylenedioxymethamphetamine (MDMA) on rat exploration of a novel environment. The active enantiomer of MDMA, S-MDMA increases forward locomotion and suppresses investigatory behaviors and local movements. Previous studies indicate that S-MDMA-induced hyperactivity depends upon drug-induced 5-HT release. Propranolol and pindolol, beta-noradrenergic antagonists with affinity for 5-HT1 receptors, antagonized the S-MDMA-induced locomotor hyperactivity. The antagonism by propranolol was stereoselective. In contrast, a beta-noradrenergic antagonist that is a weaker antagonist of 5-HT receptors, betaxolol, was much less effective at blocking the behavioral response to S-MDMA. Among nonselective 5-HT antagonists, methiothepin was effective and methysergide and cyproheptadine were ineffective as antagonists of S-MDMA-induced hypermotility. In other systems, methiothepin has been found to be a good antagonist at 5-HT1B receptors where methysergide and cyproheptadine are ineffective. The 5-HT2 antagonist ritanserin was ineffective in blocking S-MDMA-induced hypermotility. However, ritanserin, methysergide, and cyproheptadine partially reversed the S-MDMA-induced suppression of investigatory responding, suggesting a contribution of 5-HT2 receptor activation to this component of the behavioral response to S-MDMA. This study indicates that S-MDMA produces a characteristic form of locomotor hyperactivity in rats that depends upon activation of 5-HT1-like receptors, possibly of the 5-HT1B subtype.
We investigated the effects of lithium ion (Li+) on muscarinic receptor-mediated nitric oxide (NO) generation, and guanylate cyclase (GCase) activation using the mouse neuroblastoma clone, N1E-115. The levels of released NO were determined by measuring the levels of nitrite/nitrate in the incubation medium, and the activity of GCase was measured with an assay for cellular cyclic [3H] GMP levels. We determined that Li+ had no effects on muscarinic receptor-activated elevation of nitrite/nitrate levels, which were significantly inhibited by 100 microM L-NG-monomethylarginine, although it has been reported that Li+ inhibits muscarinic receptor-activated cyclic GMP formation in the cells. In addition, Li+ inhibited the cyclic GMP formation induced by an NO donor, sodium nitroprusside (SNP), in both intact cells and a crude cellular homogenate; thus, the inhibition by Li+ of muscarinic receptor-mediated cyclic GMP synthesis appeared to be at the level of GCase, but not NO synthase.
The mu opioid receptor is centrally involved in the development of the addictive diseases. It also modulates the stress responsive hypothalamic-pituitary-adrenal axis. Receptors encoded by the variant 118G polymorphism in exon 1 of the mu opioid receptor gene have a threefold increase in beta-endorphin binding and beta-endorphin is three times more potent in receptor-mediated activation of G protein-coupled inwardly rectifying potassium channels. Humans with this variant have increased stress response following opioid antagonism. Here, we study basal levels of adrenocorticotropic hormone and cortisol in subjects with this variant. In all, 59 healthy adults were genotyped and had morning levels of adrenocorticotropic hormone and cortisol measured following intravenous administration of saline placebo. Subjects with a 118G allele had significantly greater levels of cortisol than subjects with the prototype gene. Groups did not differ in levels of adrenocorticotropic hormone. A planned comparison revealed significantly greater cortisol in females with at least one copy of the 118G allele compared to females with the prototype gene. There was no significant effect of gender alone, nor was there a significant interaction between gender and genotype, on ACTH or cortisol. Subjects with at least one copy of the 118G allele have increased basal levels of cortisol, which may influence the susceptibility to and treatment of the stress responsive dyscrasia.
The effects of cellular mediators that contribute to ischemia-induced neuronal degeneration on gamma-aminobutyric acid (GABAA)-receptor function were studied. In vitro, phospholipase A2 (PLA2) inhibited muscimol-induced 36Cl- uptake in cerebral cortical synaptoneurosomes. The major hydrolysis product of PLA2 activity, arachidonic acid, also inhibited GABA-mediated 36Cl- uptake. The unsaturated nature of arachidonic acid makes it (and its metabolites) highly susceptible to peroxidation by oxygen radicals. Incubation of synaptoneurosomes with the superoxide radical-generating system, xanthine and xanthine oxidase, decreased muscimol-induced 36Cl- uptake, suggesting that the peroxidation of arachidonic acid and/or its metabolites interferes with GABAA-receptor function. Another factor involved in ischemia-induced neuronal degeneration is an increase in intracellular Ca2+. Calcium also inhibited GABA-mediated 36Cl- flux, consistent with its ability to activate PLA2. In contrast, Mg2+, which blocks Ca2+ channels, enhanced muscimol-induced 36Cl- uptake, consistent with its neuroprotective effects. Each of these cellular processes is activated during cerebral ischemia and can lead to neuronal degeneration. We used a model of transient forebrain ischemia in gerbils to determine if GABAA-receptor regulation is altered in vivo at a time when CA1 hippocampal cells have degenerated. Four days after a 5 minute bilateral carotid artery occlusion, receptor autoradiography was performed to measure the binding of [35S]t-butylbicyclophosphorothionate (TBPS) to the GABA-gated chloride channel. Significant decreases in TBPS binding were observed only in the dendritic layers (stratum oriens and lacunosem moleculare) of the CA1 hippocampus. The results suggest that ischemia-induced cellular processes that contribute to cell death can decrease GABA-gated chloride channels on dendrites of CA1 pyramidal cells, and that GABAA receptors may also reside on neurons afferent to or intrinsic to the dendritic layers of CA1 hippocampus.
11192U90 was submitted to receptor binding and monoamine uptake assays. It bound potently at serotonin 5-HT2, dopaminergic D2, serotonin 5-HT1A, and adrenergic alpha 1 and alpha 2 receptors. It also bound to dopaminergic D1, serotonin 5-HT3, serotonin 5-HT4, and sigma sites, albeit with lower affinity. It was essentially inactive at 22 other sites, including those for cholinergic M1 and M2. It weakly inhibited uptake of 3H-norepinephrine, 3H-serotonin and 3H-dopamine. Acute doses of 1192U90 (5 and 20 mg/kg P.O.) increased whole-brain levels of dopamine metabolites but did not affect levels of norepinephrine, dopamine, and serotonin. Subcutaneous injection of 1192U90 (0.8 mg/kg/day) and clozapine (20 mg/kg/day) for 28 days preferentially decreased the number of spontaneously active dopamine cells in the ventral tegmental area (VTA) but not the substantia nigra (SN) of rats, as measured by population sampling. This outcome is characteristics of atypical antipsychotics like clozapine. Acute injections of 1192U90 reversed the rate-inhibiting effects of microiontophoretically applied dopamine and intravenously injected apomorphine and d-amphetamine on dopamine cell firing. Intravenous injection or iontophoretic application of 1192U90 or the 5-HT1A agonist (+/-)8-OH-DPAT inhibited the firing rates of dorsal raphe nucleus (DRN) neurons in rats, and the effects of both compounds were blocked by iontophoretically applied S(-) propranolol, a 5-HT1A antagonist. The results suggest that 1192U90 is a preferential dopamine D2 antagonist as well as a 5-HT1A agonist that may prove to be an atypical antipsychotic.
1192U90 was developed on the assumption that antagonism of 5-HT2 receptors efficacy yields more potently than D2 receptors against positive and negative symptoms of schizophrenia with minimal liability for extrapyramidal side effects (EPSs), and that 5-HT1A agonism further reduces EPSs and provides anxiolytic and antidepressant activity. 1192U90 was submitted to four tests that predict antipsychotic efficacy (antagonism of apomorphine-induced climbing in mouse, antagonism of apomorphine-induced circling in rats with unilateral 6-OHDA lesions, antagonism of amphetamine-induced hyperlocomotion in rat, and inhibition of conditioned avoidance in rat), two tests of 5-HT2 function (antagonism of 5-MeODMT-induced head twitches in mouse and antagonism of 5-HTP-induced wet dog shakes in rat), and three tests that predict EPS liability (antagonism of apomorphine-induced stereotypy in mouse and rat and induction of catalepsy in mouse). ED50s (mg/kg PO) were as follows: climbing 10.1, circling 7.9, hyperlocomotion 6.6, and avoidance 5.7; head twitches 5 and wet dog shakes 4.6; stereotypy in mouse 91.1, stereotypy in rat 133.4, and catalepsy 192.4. The ratio of ED50 for stereotypy antagonism to ED50 for climbing antagonism was 9 (compared to 4, 3, and 4 for clozapine, risperidone, and haloperidol). The ratio of ED50 for catalepsy induction to ED50 for climbing antagonism was 19 (compared to 7, 2, and 17 for clozapine, risperidone, and haloperidol). 1192U90 was also submitted to three tests that predict anxiolysis: It produced only a small increase in punished lever pressing for food in rat (Geller-Seifter conflict test), which is specific for rapid-onset efficacy, but produced large increases in punished key pecking for food in pigeon and cork gnawing in rat, which identify the delayed onset 5-HT1A agonists such as buspirone. The results suggest that 1192U90 would be effective for positive and negative symptoms of schizophrenia, with minimal liability for EPSs, and may also have anxiolytic properties.
The dopamine D(2) receptors exist in two states: a high-affinity state (D(2)(high)) that is linked to second messenger systems, is responsible for functional effects, and exhibits high affinity for agonists; and a low-affinity state that is functionally inert and exhibits lower affinity for agonists. The dopamine D(3) receptors have high-affinity for agonist (eg dopamine) and the existence of the two affinity states is controversial. Although preclinical studies in animal models of psychosis have shown a selective increase of D(2)(high) as the common pathway to psychosis, the D(3) has been suggested to be involved in the pathophysiology of psychosis. We report the first study of the D(2)(high) and D(3) in schizophrenia using the novel PET radiotracer, [(11)C]-(+)-PHNO. We recruited 13 patients with schizophrenia-spectrum disorder amidst an acute psychotic episode, drug free for at least 2 weeks, and 13 age-sex-matched healthy controls. The binding potential no-displaceable (BP(ND)) was examine in the main regions of interest (caudate, putamen, ventral striatum, globus pallidus, substantia nigra, and anterior thalamus) and in a voxel-wise analysis. The BP(ND) between patients and controls was not different in any of the regions. The voxel-wise analysis did not reveal any difference and no correlations were found between the BP(ND) and positive and negative syndrome scale subscales. Our results do not find support for the hypothesis linking psychosis to a selective increase in D(2)(high) and/or D(3) in schizophrenia. It is possible that receptors with high affinity are not accessible by [(11)C]-(+)-PHNO because they are occupied by endogenous dopamine, a possibility that can be ruled out in future experiments.
A number of addictions have been linked with decreased striatal dopamine (DA) receptor availability and DA release. Stress has a key role in cannabis craving, as well as in modulation of dopaminergic signaling. The present study aimed to assess DA release in response to a laboratory stress task with [(11)C]-(+)-PHNO positron emission tomography in cannabis users (CU). Thirteen healthy CU and 12 healthy volunteers (HV) were scanned during a sensorimotor control task (SMCT) and under a stress condition using the validated Montreal imaging stress task (MIST). The simplified reference tissue model (SRTM) was used to obtain binding potential (BP(ND)) in striatal subdivisions: limbic striatum (LST), associative striatum (AST), and sensorimotor striatum (SMST). Stress-induced DA release (indexed as a percentage of reduction in [(11)C]-(+)-PHNO BP (ND)) between CU and HV was tested with analysis of variance. SMCT BP(ND) was significantly higher in CU compared with HV in the AST (F=10.38, p=0.003), LST (F=4.95, p=0.036), SMST (F=4.33, p=0.048), and whole striatum (F=9.02, p=0.006). Percentage of displacement (change in BP(ND) between SMCT and MIST PET scans) was not significantly different across groups in any brain region, except in the GP (-5.03±14.6 in CU, compared with 6.15±12.1 in HV; F=4.39, p=0.049). Duration of cannabis use was significantly associated with stress-induced [(11)C]-(+)-PHNO displacement by endogenous DA in the LST (r=0.566, p=0.044), with no effect in any other brain region. In conclusion, despite an increase in striatal BP(ND) observed during the control task, chronic cannabis use is not associated with alterations in stress-induced DA release.Neuropsychopharmacology advance online publication, 5 December 2012; doi:10.1038/npp.2012.232.
Imaging the competition between D(2/3) radioligands and endogenous dopamine is so far the only way to measure dopamine release in the living human brain. The dopamine D(2) receptor exists in a high (D(2)(high)) and a low-affinity state for dopamine. Under physiological conditions, dopamine is expected to bind to D(2)(high) only. [(11)C]-(+)-4-propyl-9-hydroxynaphthoxazine ((+)-PHNO) is the first D(2/3) agonist radioligand for positron emission tomography (PET) imaging in humans. Since [(11)C]-(+)-PHNO is expected to bind preferentially to D(2)(high), it should be particularly vulnerable to competition with endogenous dopamine. Nine healthy subjects participated in two PET scans, one after administration of d-amphetamine and one after placebo. [(11)C]-(+)-PHNO PET test re-test variability was determined in 11 healthy subjects. Binding potentials (BPs) were calculated for caudate, putamen, ventral striatum, and globus pallidus. d-Amphetamine led to a significant decrease of [(11)C]-(+)-PHNO BPs in caudate (-13.2%), putamen (-20.8%), and ventral striatum (-24.9%), but not in globus pallidus (-6.5%). d-Amphetamine-induced displacement correlated with serum d-amphetamine levels in all regions but caudate. This is the first report on competition between endogenous dopamine and a D(2/3) agonist radioligand in humans. [(11)C]-(+)-PHNO PET might be a superior measure for release of endogenous dopamine than PET employing conventional D(2/3) antagonist radioligands.
The modulating effects of serotonin on dopamine neurotransmission are not well understood, particularly in acute psychotic states. Positron emission tomography was used to examine the effect of psilocybin on the in vivo binding of [11C]raclopride to D2-dopamine receptors in the striatum in healthy volunteers after placebo and a psychotomimetic dose of psilocybin (n = 7). Psilocybin is a potent indoleamine hallucinogen and a mixed 5-HT2A and 5-HT1A receptor agonist. Psilocybin administration (0.25 mg/kg p.o.) produced changes in mood, disturbances in thinking, illusions, elementary and complex visual hallucinations and impaired ego-functioning. Psilocybin significantly decreased [11C]raclopride receptor binding potential (BP) bilaterally in the caudate nucleus (19%) and putamen (20%) consistent with an increase in endogenous dopamine. Changes in [11C]raclopride BP in the ventral striatum correlated with depersonalization associated with euphoria. Together with previous reports of 5-HT receptor involvement in striatal dopamine release, it is concluded that stimulation of both 5-HT2A and 5-HT1A receptors may be important for the modulation of striatal dopamine release in acute psychoses. The present results indirectly support the hypothesis of a serotonin-dopamine dysbalance in schizophrenia and suggest that psilocybin is a valuable tool in the analysis of serotonin-dopamine interactions in acute psychotic states.
Drugs that increase dopamine levels in the brain can cause psychotic symptoms in healthy individuals and worsen them in schizophrenic patients. Psychological stress also increases dopamine release and is thought to play a role in susceptibility to psychotic illness. We hypothesized that healthy individuals at elevated risk of developing psychosis would show greater striatal dopamine release than controls in response to stress. Using positron emission tomography and [(11)C]raclopride, we measured changes in synaptic dopamine concentrations in 10 controls and 16 psychometric schizotypes; 9 with perceptual aberrations (PerAb, ie positive schizotypy) and 7 with physical anhedonia (PhysAn, ie negative schizotypy). [(11)C]Raclopride binding potential was measured during a psychological stress task and a sensory-motor control. All three groups showed significant increases in self-reported stress and cortisol levels between the stress and control conditions. However, only the PhysAn group showed significant stress-induced dopamine release. Dopamine release in the entire sample was significantly negatively correlated with smooth pursuit gain, an endophenotype linked to frontal lobe function. Our findings suggest the presence of abnormalities in the dopamine response to stress in negative symptom schizotypy, and provide indirect evidence of a link to frontal function.
The pharmacologic treatment of many neuropsychiatric disorders (Alzheimer's disease, schizophrenia, depressive illness) has been targeted at the central hypothesis that defects in a single neurotransmitter system underlie the pathophysiology of the disease state. With the recognition that such treatments have not been efficacious consistently, recent drug development has been directed at altering other functionally linked neurotransmitters involved in these diseases. Using positron emission tomography, we have noninvasively investigated the effects of two noncholinergic drugs on the release of acetylcholine. By examining the effects of gamma-vinyl gamma-aminobutyric acid (GABA) (a GABA transaminase inhibitor) or altanserin (a serotonergic antagonist) on the regional binding of 11C-benztropine in the primate brain (Papio anubis), we demonstrated that drugs acting upon either GABAergic or serotonergic neurons produce profound regional changes in acetylcholine release. These findings indicate that the mechanisms of action and the subsequent therapeutic efficacy of these centrally acting drugs may be linked to their multitransmitter effects. This application of positron emission tomography represents an extremely promising experimental approach that can be directed towards elucidating abnormalities in neurotransmitter modulation relevant to disease progression and pharmacologic treatment.
The muscarinic cholinergic receptor (mAChR) antagonist scopolamine was used to induce transient cognitive impairment in monkeys trained in a delayed matching to sample task. The temporal relationship between the occupancy level of central mAChRs and cognitive impairment was determined. Three conscious monkeys (Macaca mulatta) were subjected to positron emission tomography (PET) scans with the mAChR radioligand N-[(11)C]methyl-3-piperidyl benzilate ([(11)C](+)3-MPB). The scan sequence was pre-, 2, 6, 24, and 48 h post-intramuscular administration of scopolamine in doses of 0.01 and 0.03 mg/kg. Occupancy levels of mAChR were maximal 2 h post-scopolamine in cortical regions innervated primarily by the basal forebrain, thalamus, and brainstem, showing that mAChR occupancy levels were 43-59 and 65-89% in doses of 0.01 and 0.03 mg/kg, respectively. In addition, dose-dependent impairment of working memory performance was measured 2 h after scopolamine. A positive correlation between the mAChR occupancy and cognitive impairment 2 and 6 h post-scopolamine was the greatest in the brainstem (P<0.00001). Although cognitive impairment was not observed 24 h post-scopolamine, sustained mAChR occupancy (11-24%) was found with both doses in the basal forebrain and thalamus, but not in the brainstem. These results indicate that a significant degree of mAChRs occupancy is needed to produce cognitive impairment by scopolamine. Furthermore, the importance of the brainstem cholinergic system in working memory in monkey is described.