Neuropharmacology

Published by Elsevier
Online ISSN: 0028-3908
Publications
Article
Behavioral and electrophysiological comparative analyses of the effects of 2-o-chlorobenzoyl-4-chloro-N-methyl-N alpha-glycylglycinanilide hydrate (45-0088-S) and diazepam on the CNS were performed with cats and monkeys. No essential difference between 45-0088-S and diazepam on the effects in the CNS was observed, although the "taming" effect in wild cats and the hypnotic effect in monkeys caused by 45-0088-S were stronger than those of diazepam. The sleep-wakefulness cycles in both cats and monkeys were modified by 45-0088-S. The activity of the reticular formation, hypothalamus and amygdala in cats was inhibited by 45-0088-S and by diazepam.
 
Article
IK(SO) is a standing-outward potassium current found in cerebellar granule neurons which is inhibited by the activation of muscarinic M(3) receptors. However the pathway between muscarinic receptor activation and current inhibition is unknown. Using two structurally distinct inhibitors of the activation of MEK1 (mitogen activated protein (MAP) kinase kinase 1), PD 98059 and U 0126, we have shown that the MAP kinase signalling cascade does not appear to underlie muscarinic inhibition of IK(SO), recorded using whole-cell patch-clamp methods. Nevertheless, both PD 98059 and U 0126 caused an inhibition of IK(SO) when applied acutely with 30 microM of each compound producing around 50% inhibition of the current. In addition, U 0125, which is structurally related to U 0126 but has a much lower potency for inhibiting MEK1 activation, was also able to inhibit IK(SO) to a similar degree. Neither the inhibition by PD 98059 nor that by U 0126 was found to be voltage dependent. This was true whether the IK(SO) current was outward or inward. Block of IK(SO) by these two compounds may compromise interpretation of studies in intact neuronal preparations when they are used as MEK1 inhibitors.
 
Article
Employing a Fixed-Ratio 10, food-reinforced protocol, rats were trained to recognize the discriminative stimulus (DS) properties of the novel, potent, 5-HT2C agonist, Ro 60-0175 (2.5 mg/kg, i.p.). This schedule generated appropriate drug versus vehicle responding after 50 + 5 training sessions and Ro 60-0175 elicited full (100%) drug selection with an effective dose50 (ED50) of 0.6 mg/kg, i.p.. The 5-HT2C receptor agonists, mCPP and MK 212, fully generalized to Ro 60-0175 with ED50s of 0.8 and 0.4 mg/kg, s.c., respectively, whereas the preferential 5-HT2B agonist, BW 723C86 ( > 10.0 mg/kg, s.c.) and the 5-HT2A agonist, DOI ( > 2.5 mg/kg, s.c.), were ineffective. The 5-HT2A/2B/2C receptor antagonist, mianserin, dose-dependently blocked the DS properties of Ro 60-0175 with an ED50 of 0.7 mg/kg, s.c. This action was mimicked by the novel, 5-HT2B/2C antagonist, SB 206,553 (ED50 = 0.3 mg/kg, s.c.), whereas the selective 5-HT2A antagonist, MDL 100,907 ( > 0.63 mg/kg, s.c.), was ineffective. Further, the selective 5-HT2C antagonist, SB 242,084, dose-dependently and fully blocked drug selection (ED50 = 0.2 mg/kg, i.p.), whereas the selective 5-HT2B antagonist, SB 204,741, was not active ( > 0.63 mg/kg, i.p.). In conclusion, these data demonstrate that Ro 60-0175 generates a robust DS and suggest that activation of 5-HT2C receptors is the principal mechanism underlying its DS properties.
 
Article
The 5-HT1A receptor agonist, 8-OH-DPAT ((+/-)-8-dihydroxy-2-(di-n-propylamino) tetralin), (0.63 mg/kg, s.c.) elicited spontaneous tail-flicks (STFs) in rats. This response was potentiated by the selective 5-HT2C receptor agonist, RO 60-0175 ((S)-2-(6-chloro-5-fluoroindol-1-yl)-1-methylethylamine) fumarate) (0.16 mg/kg, s.c.), the action of which was abolished by the novel 5-HT2C antagonist, SB 206,553 (5 methyl-1-(3-pyridil-carbamoyl)-1,2,3,5-tetrahydropyrrolo[2,3 -f]indole) (0.16 mg/kg, s.c.). These data show that 5-HT1A receptor-mediated STFs in rats are facilitated by activation of 5-HT2C receptors supporting the existence of functional interactions between these sites.
 
Article
The reinforcing effects of nicotine are mediated in part by brain dopamine systems. Serotonin, acting via 5-HT(2A) and 5-HT(2C) receptors, modulates dopamine function. In these experiments we examined the effects of the 5-HT(2C) receptor agonist Ro60-0175 and the 5-HT(2A) receptor antagonist (M100907, volinanserin) on nicotine self-administration and reinstatement of nicotine-seeking. Male Long-Evans rats self-administered nicotine (0.03 mg/kg/infusion, IV) on either a FR5 or a progressive ratio schedule of reinforcement. Ro60-0175 reduced responding for nicotine on both schedules. While Ro60-0175 also reduced responding for food reinforcement, response rates under drug treatment were several-fold higher than in animals responding for nicotine. M100907 did not alter responding for nicotine, or food, on either schedule. In tests of reinstatement of nicotine-seeking, rats were first trained to lever press for IV infusions of nicotine; each infusion was also accompanied by a compound cue consisting of a light and tone. This response was then extinguished over multiple sessions. Injecting rats with a nicotine prime (0.15 mg/kg) reinstated responding; reinstatement was also observed when responses were accompanied by the nicotine associated cue. Ro60-0175 attenuated reinstatement of responding induced by nicotine and by the cue. The effects of Ro60-0175 on both forms of reinstatement were blocked by the 5-HT(2C) receptor antagonist SB242084. M100907 also reduced reinstatement induced by either the nicotine prime or by the nicotine associated cue. The results indicate that 5-HT(2C) and 5-HT(2A) receptors may be potential targets for therapies to treat some aspects of nicotine dependence.
 
Article
JWH-018 is a synthetic CB1 and CB2 agonist illegally marketed as products named "Spice" or "herbal blend" for its psychoactive effects which are much higher than those produced by cannabis. In the last year, the European Monitoring Centre for Drugs and Drug Addiction reported to the Italian National Early Warning System the seizure of plant material containing new halogenated derivatives of JWH-018 (JWH-018 Cl and JWH-018 Br). The present study aimed to investigate the in vitro and in vivo activity of these two new synthetic cannabinoids in mice. In vitro competition binding experiments performed on mouse and human CB1 receptors revealed a high affinity and potency of the halogenated compounds. Synthetic cannabinoids (0.01-6 mg/Kg i.p.) impaired motor activity and induced catalepsy in mice and their effects were more severe with respect to those evoked by Δ(9)-THC. Moreover, they increased the mechanical and thermal pain threshold and induced a marked hypothermia. It is interesting to note that whereas high doses of JWH-018 cause seizures, myoclonia and hyperreflexia, the halogenated compounds, in particular JWH-018Br, were less effective. Behavioral and neurological changes were prevented by the selective CB1 receptor antagonist AM 251. These data demonstrate for the first time that JWH-018 Cl and JWH-018 Br act similarly to JWH-018 while inducing less convulsive episodes and myoclonias. These data support the hypothesis that the halogenated compounds may have been introduced onto market to produce similar intoxicating effects as JWH-018 while causing less side effects. Copyright © 2015. Published by Elsevier Ltd.
 
Article
Numerous preclinical studies have reported neuroprotective effects of new agents in animal studies. None of these agents has yet translated into a successful clinical trial and therefore to a new therapy. There are many possible reasons for this failure, including poor design of clinical trials, mismatch between preclinical and clinical protocols, and insufficient preclinical data. The enzyme caspase-1 has been implicated in neuronal death. Deletion of the caspase-1 gene, or administration of partially selective inhibitors, reduces neuronal injury induced by cerebral ischemia in rodents. We report here, for the first time, that VRT-018858, the non-peptide, active metabolite of the selective caspase-1 inhibitor pro-drug, pralnacasan, markedly reduced ischemic injury in rats. VRT-018858 was neuroprotective when delivered at 1 and 3h (42% and 58% neuroprotection, respectively) but not 6h after injury, and protection was sustained 7 days after the induction of ischemia (66% neuroprotection). These data confirm caspase-1 as an important target for intervention in acute CNS injury, and propose a new class of caspase-1 inhibitors as highly effective neuroprotective agents.
 
Effect of VRX-03011 treatment on hippocampal ACh efflux during delayed spontaneous alternation testing and resting conditions (a) Effect of VRX-03011 (1 and 5 mg/kg) treatment on ACh release during delayed spontaneous alternation testing. VRX-03011 at 1 and 5 significantly enhanced efflux compared to that of vehicle controls during maze testing, *P < 0.05 vs. vehicle controls. No significant differences were found during baseline, pre-test or post-test periods. (b) ACh efflux during resting condition. VRX-03011 treatment did not affect ACh efflux at any point.
Effects of treatment with VRX-03011 (0.03 mg/kg), galanthamine (0.3 and 2.5 mg/kg), and combination of the galanthamine (0.3 mg/kg) and VRX-03011 (0.03 mg/kg) on delayed spontaneous alternation performance in a four arm cross-maze. (a) VRX-03011 at 0.03 mg/kg or galanthamine 0.3 mg/kg alone did not significantly enhance performance compared to that of vehicle controls. In contrast, VRX-03011 0.03 mg/kg and galanthamine 0.3 mg/kg significantly enhanced performance in a manner similar to that of galanthamine 2.5 mg/kg, *P < 0.05 vs. vehicle. (b) Mean number of arm entries in the delayed spontaneous alternation test. Galanthamine 2.5 mg/kg, VRX-03011 0.03 mg/kg, and the combination of galanthamine 0.3 mg/kg and VRX-03011 0.03 significantly increased arm entries, *P < 0.05 vs. vehicle.
Effects of treatment with VRX-03011 on secretion levels of non-amyloidogenic sAPPa and Ab. Representative immunoblot showing the effects of increasing concentrations of VRX-03011 on the cellular release of sAPPa in (a) CHO cells stably expressing the h5-HT 4(e) receptor isoform and (b) IMR32 neuroblastoma cells.
Serotonin receptor binding profile for VRX-03011
Stimulation of cAMP production by VRX-03011 in COS-7 cells expressing recombinant 5-HT 4 receptors
Article
Recent evidence suggests that 5-hydroxytryptamine (5-HT)(4) receptor activity enhances cognition and provides neuroprotection. Here we report the effects of VRX-03011, a novel partial 5-HT(4) agonist, that is both potent (K(i) approximately 30 nM) and highly selective (K(i) > 5 microM for all other 5-HT receptors tested). In separate experiments, rats received VRX-03011 (0.1-10 mg/kg i.p.) 30 min prior to spontaneous alternation testing in a no-delay or a 30-s delay condition. VRX-03011 (1, 5 and 10 mg/kg, but not 0.1 mg/kg) significantly enhanced delayed spontaneous alternation performance while none of the doses enhanced performance in the no-delay test. VRX-03011 (1 and 5 mg/kg) concomitantly enhanced hippocampal acetylcholine output and delayed spontaneous alternation scores compared to that of vehicle controls, but had no effect on hippocampal acetylcholine release under a resting condition. Moreover, suboptimal doses of VRX-03011 and the acetylcholinesterase inhibitor galanthamine combined to enhance memory. VRX-03011 also regulated amyloid precursor protein (APP) metabolism by inducing a concentration-dependent increase in the non-amyloidogenic soluble form of APP (sAPPalpha) with an EC(50) approximately 1--10 nM. VRX-03011 had no effect on contractile properties in guinea pig ileum or colon preparations with an EC(50) > 10 microM and did not alter rat intestinal transit at doses up to 10 mg/kg. These findings suggest that VRX-03011 may represent a novel treatment for Alzheimer's disease that reduces cognitive impairments and provides neuroprotection without gastrointestinal side effects.
 
Article
Dopamine, acting at a D1-like receptor, depresses the release of glutamate in the nucleus accumbens (NAcc) in brain slices, thereby reducing the amplitude of the excitatory postsynaptic current (EPSC). This effect depends upon an inhibitory feedback action of adenosine, liberated following facilitation of postsynaptic NMDA receptors by D1 receptor activation, an action independent of adenylyl cyclase stimulation or cyclic AMP-dependent protein kinase (PKA; Harvey, J., Lacey, M.G., 1997. J. Neurosci. 17, 5271). Using whole-cell recording from NAcc neurones, the dopamine depression of the EPSC was blocked by pre-treatment of brain slices with the selective protein kinase C (PKC) inhibitor Ro 32-0432, but only minimally attenuated by intracellular dialysis of single cells with Ro 32-0432 in the recording pipette. With synaptic transmission blocked by tetrodotoxin, inward currents caused by application of NMDA were enhanced by the D1 receptor agonist SKF 81297A in half the cells tested. In a separate population of cells dialysed intracellularly with Ro 32-0432, SKF 81297A was without effect on NMDA current amplitude. These findings indicate a functional role for phospholipase C-coupled D1-like receptors in both modulating synaptic transmission in NAcc and potentiating NMDA receptors on a subset of NAcc neurones, via PKC activation.
 
Article
Inhibition of phosphodiesterase 9 (PDE9) has been reported to enhance rodent cognitive function and may represent a potential novel approach to improving cognitive dysfunction in Alzheimer's disease. PF-04447943, (6-[(3S,4S)-4-methyl-1-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl]-1-(tetrahydro-2H-pyran-4-yl)-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one), a recently described PDE9 inhibitor, was found to have high affinity (Ki of 2.8, 4.5 and 18 nM) for human, rhesus and rat recombinant PDE9 respectively and high selectivity for PDE9 versus PDEs1-8 and 10-11. PF-04447943 significantly increased neurite outgrowth and synapse formation (as indicated by increased synapsin 1 expression) in cultured hippocampal neurons at low (30-100 nM) but not high (300-1000 nM) concentrations. PF-04447943 significantly facilitated hippocampal slice LTP evoked by a weak tetanic stimulus at a concentration of 100 nM but failed to affect response to the weak tetanus at either 30 or 300 nM, or the LTP produced by a theta burst stimulus. Systemic administration of PF-04447943 (1-30 mg/kg p.o.) dose-dependently increased cGMP in the cerebrospinal fluid 30 min after administration indicating target engagement in the CNS of rats. PF-04447943 (1-3 mg/kg p.o.) significantly improved cognitive performance in three rodent cognition assays (mouse Y maze spatial recognition memory model of natural forgetting, mouse social recognition memory model of natural forgetting and rat novel object recognition with a scopolamine deficit). When administered at a dose of 3 mg/kg p.o., which improved performance in novel object recognition, PF-04447943 significantly increased phosphorylated but not total GluR1 expression in rat hippocampal membranes. Collectively these data indicate that PF-04447943 is a potent, selective brain penetrant PDE9 inhibitor that increased indicators of hippocampal synaptic plasticity and improved cognitive function in a variety of cognition models in both rats and mice. Results with PF-04447943 are consistent with previously published findings using a structurally diverse PDE9 inhibitor, BAY73-6199, and further support the suggestion that PDE9 inhibition may represent a novel approach to the palliative remediation of cognitive dysfunction.
 
Article
Because free radical mechanisms may contribute to brain injury in hemorrhagic stroke, the effect of the free radical trapping agent disodium 4-[(tert-butylimino)methyl]benzene-1,3-disulfonate N-oxide (NXY-059) was investigated on outcome following intracerebral hemorrhage (ICH) in rat. ICH was induced in 20 adult rats by infusion of collagenase into the caudate-putamen. Thirty minutes later rats were treated with NXY-059 (50 mg/kg subcutaneous plus 8.8 mg/kg/h for 3 days subcutaneous delivered via implanted osmotic pumps) or saline (equivalent volumes). Magnetic resonance imaging 24 h after ICH confirmed that the hemorrhage was uniform in the two groups, and subsequent imaging at 7 and 42 days post-ICH showed that the hematoma resolved similarly in the two groups. Behavioral testing on days 1, 3, 7, 14, and 21 after ICH showed that rats treated with NXY-059 had significantly decreased neurological impairment at all times. Deficits in skilled forelimb use 4-5 weeks post-ICH, and in striatal function 6 weeks post-ICH, were not reduced by treatment with NXY-059. Treatment with NXY-059 significantly reduced the neutrophil infiltrate observed 48 h post-hemorrhage in the vicinity of the hematoma, and the number of TUNEL-positive cells 48 h post-hemorrhage at the hematoma margin. However, by 6 weeks there were no differences in neuronal densities in treated and control rats.
 
Article
The in vitro and in vivo effects of the novel acetylcholinesterase inhibitors donepezil and NXX-066 have been compared to tacrine. Using purified acetylcholinesterase from electric eel both tacrine and donepezil were shown to be reversible mixed type inhibitors, binding to a similar site on the enzyme. In contrast, NXX-066 was an irreversible non-competitive inhibitor. All three compounds were potent inhibitors of rat brain acetylcholinesterase (IC50 [nM]; tacrine: 125 +/- 23; NXX-066: 148 +/- 15; donepezil: 33 +/- 12). Tacrine was also a potent butyrylcholinesterase inhibitor. Donepezil and tacrine displaced [3H]pirenzepine binding in rat brain homogenates (IC50 values [microM]; tacrine: 0.7; donepezil: 0.5) but NXX-066 was around 80 times less potent at this M1-muscarinic site. Studies of carbachol stimulated increases in [Ca2+]i in neuroblastoma cells demonstrated that both donepezil and tacrine were M1 antagonists. Ligand binding suggested little activity of likely pharmacological significance with any of the drugs at other neurotransmitter sites. Intraperitoneal administration of the compounds to rats produced dose dependent increases in salivation and tremor (ED50 [micromol/kg]; tacrine: 15, NXX-066: 35, donepezil: 6) with NXX-066 having the most sustained effect on tremor. Following oral administration, NXX-066 had the slowest onset but the greatest duration of action. The relative potency also changed, tacrine having low potency (ED50 [micromol/kg]; tacrine: 200, NXX-066: 30, donepezil: 50). Salivation was severe only in tacrine treated animals. Using in vivo microdialysis in cerebral cortex, both NXX-066 and tacrine were found to produce a marked (at least 30-fold) increase in extracellular acetylcholine which remained elevated for more than 2 h after tacrine and 4 h after NXX-066.
 
Article
The anti-emetic profile of the novel brain penetrant tachykinin NK1 receptor antagonist MK-0869 (L-754,030) 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenylethoxy)-3-(S)-(4-fluor o)phenyl-4-(3-oxo-1,2,4-triazol-5-yl)methylmorpholine and its water soluble prodrug, L-758,298, has been examined against emesis induced by cisplatin in ferrets. In a 4 h observation period, MK-0869 and L-758,298 (3 mg/kg i.v. or p.o.) inhibited the emetic response to cisplatin (10 mg/kg i.v.). The anti-emetic protection afforded by MK-0869 (0.1 mg/kg i.v.) was enhanced by combined treatment with either dexamethasone (20 mg/kg i.v.) or the 5-HT3 receptor antagonist ondansetron (0.1 mg/kg i.v.). In a model of acute and delayed emesis, ferrets were dosed with cisplatin (5 mg/kg i.p.) and the retching and vomiting response recorded for 72 h. Pretreatment with MK-0869 (4-16 mg/kg p.o.) dose-dependently inhibited the emetic response to cisplatin. Once daily treatment with MK-0869 (2 and 4 mg/kg p.o.) completely prevented retching and vomiting in all ferrets tested. Further when daily dosing began at 24 h after cisplatin injection, when the acute phase of emesis had already become established, MK-0869 (4 mg/kg p.o. at 24 and 48 h after cisplatin) prevented retching and vomiting in three out of four ferrets. These data show that MK-0869 and its prodrug, L-758,298, have good activity against cisplatin-induced emesis in ferrets and provided a basis for the clinical testing of these agents for the treatment of emesis associated with cancer chemotherapy.
 
Article
Effects of TA-0910 (1-methyl-(S)-4,5-dihydroorotyl-L-histidyl-L-prolinamide), a new thyrotropin releasing hormone (TRH) analog, on spinal reflex potentials and flexor reflexes were compared with those of TRH in C1-spinal rats. Intravenously administered TA-0910 and TRH produced dose-dependent increases in the amplitudes of mono- and polysynaptic reflex potentials and withdrawal flexor reflexes. TA-0910 was more potent and more long-lasting than TRH. The stimulating actions of TA-0910 and TRH on the monosynaptic reflex potential were not antagonized by pretreatment with atropine, cyproheptadine, haloperidol or prazosin, suggesting no involvement of the cholinergic, serotonergic, dopaminergic or noradrenergic system. Intraduodenally administered TA-0910 also produced a lasting potentiation of the withdrawal flexor reflex, but intraduodenally administered TRH showed no effect. These results suggest that TA-0910 may be a more useful drug than TRH for spinal functional disorders.
 
Article
The electrophysiological properties and cataleptogenicity of YM-09151-2 (N-[(2RS, 3RS)-1-benzyl-2-methyl-3-pyrrolidinyl]-5-chloro-2-methoxy-4-methylaminobenzamide) were studied in the cat. This drug inhibited the EEG arousal response to electrical stimulation of the mesencephalic reticular formation with the same potency as that of haloperidol, whereas chlorpromazine revealed a more potent central depressant action. The duration of the afterdischarge induced by electrical stimulation of the amygdaloid nucleus was initially shortened and thereafter prolonged by both YM-09151-2 and haloperidol. However, YM-09151-2 was less effective than haloperidol and chlorpromazine in both augmenting the spindle bursts produced by electrical stimulation of the caudate nucleus and antagonizing the inhibitory effect of L-DOPA on the caudate spindle, indicating a smaller effect of YM-09151-2 on the extrapyramidal dopaminergic system than that of the two neuroleptic drugs. In fact, YM-09151-2 produced no cataleptic behaviour in the cat even at a dose of 5 mg/kg (s.c.), although haloperidol and chlorpromazine caused catalepsy in doses of 0.5 and 5 mg/kg (s.c.), respectively. Sulpiride, chemically related to YM-09151-2, showed much weaker central actions than YM-09151-2. The results indicate that a new benzamide, YM-09151-2, has a potent neuroleptic effect with a slight central depressant activity and that the cataleptogenicity of the compound is weaker than that of haloperidol and of chlorpromazine.
 
Article
The objective of this study was to examine the effect of neuronal impulse flow on the acetylcholine-dcpleting action of hemicholinium-3 (HC-3). We utilized electrolytic interruption of cholinergic axons and administration of pentobarbital as means to stop or slow impulse flow or release in cholinergic scptal-hippocampal neurones. It has been reported previously that placement of lesions in the septum results in a large rise in acetylcholine (ACh) levels in the hippocampus at short times post-lesion (0.5 3 hr). Administration of pentobarbital has a similar effect. When HC-3 was injected immediately prior to the placement of septal lesion, the post-lesion increase in ACh levels in the hippocampus were blocked. However, if HC-3 was administered 30 min after the placement of lesion, a time at which the post-lesion increases have already occurred, then HC-3 appeared to have no effect. In the striatum, a region which does not receive the cholinergic input from the septum and which should not be effected by placement of septal lesions, there was a depletion of acetylcholine caused by the administration of HC-3.The finding that HC-3 administration blocks the post-lesion rise in ACh levels, suggests that this post-lesion rise requires new synthesis of ACh and hence a supply of extracellular choline which is blocked by HC-3. Our finding that the HC-3 depleting effect was blocked 30 min after lesion, is consistent with the notion that the action of HC-3 is dependent on neuronal impulse flow. However it can be more broadly stated that HC-3 will have a reduced depleting action after any treatment resulting in a depression of acetylcholine synthesis rate.
 
Representative locations of microdialysis probe placements in the NAcc core and shell and core combined (A) and shell alone (B). Overlapping placements are not shown; therefore, the figure does not indicate the total distribution of the placements for the sake of clarity of presentation. Lines indicate the active area of the dialysis membrane used in this study, verified by perfusion with 1% bromphenol blue dye. Numbers to the right indicate distance in mm from bregma (Paxinos and Watson, 1986). 
(A) Effects of saline (SAL) and systemic acute nicotine (NIC, 0.4 mg/kg, sc) alone or in combination with mecamylamine (MEC, 4 mg/kg, sc) or bPiDDB (1 or 3 mg/kg, sc) on extracellular DA levels in NAcc (core and shell combined). On the test day, after collection of basal samples, the animals were given SAL, MEC or bPiDDB (left arrow) 15 min before SAL or NIC injection (right arrow). Data represent the mean AE SEM of 4e6 animals. Data (without transformation) were analyzed by two-way ANOVA with repeated measures which revealed a significant interaction ( p < 0.05) of treatment  time. The average basal extracellular level of DA in these groups was 0.8 AE 0.2 nM. (B) Effects of saline (SAL) and systemic acute nicotine (NIC, 0.4 mg/kg, sc) alone or in combination with bPiDDB (3 mg/kg, sc) on extracellular DA levels in NAcc shell. On the test day, after collection of basal samples, the animals were given SAL or bPiDDB (left arrow) 15 min before SAL or NIC injection (right arrow). Data represent the mean AE SEM of 5e6 animals. Data (without transformation) were analyzed by two-way ANOVA with repeated measures which revealed a significant interaction ( p < 0.05) of treatment  time. The average basal extracellular level of DA in these groups was 1.15 AE 0.2 nM.
Article
The present study examined the effects of the novel nicotinic acetylcholine receptor (nAChR) antagonist, N,N'-dodecane-1,12-diyl-bis-3-picolinium dibromide (bPiDDB), after acute and repeated nicotine treatment on extracellular dopamine (DA) levels in rat nucleus accumbens (NAcc), using in vivo microdialysis. Acute nicotine (0.4mg/kg, sc) injection produced an increase (232% of basal) in extracellular DA, which was attenuated by pretreatment with the nAChR antagonist mecamylamine (4mg/kg, sc). Pretreatment with bPiDDB (1 or 3mg/kg, sc) dose-dependently reduced the increase in extracellular DA produced by nicotine (0.4mg/kg, sc), but not by amphetamine (0.5mg/kg, sc). Basal levels of NAcc DA increased in animals that had been pretreated with nicotine (0.4mg/kg, sc) for 5 days compared to saline. In addition, nicotine challenge further increased extracellular DA (237% of basal). The increase in DA in NAcc following repeated nicotine was blocked by pretreatment with mecamylamine (4mg/kg, sc) and bPiDDB (1 or 3mg/kg, sc). These results indicate that bPiDDB likely acts as an antagonist at neuronal nAChRs to inhibit DA release in NAcc after acute or repeated nicotine administration. The ability of bPiDDB to inhibit the effect of nicotine in NAcc, combined with previous studies showing decreased nicotine self-administration in rats provides support for bPiDDB as a potential lead compound for the development of a novel pharmacotherapy for nicotine dependence.
 
Article
It is presently unclear whether the antiseizure effects exerted by NSAIDs are totally dependent on COX inhibition or not. To clarify this point we investigated whether 7-methyl-2-phenylimidazo[1,2-b]pyridazine-3-carboxylic acid (DM1) and 6-methoxy-2-phenylimidazo[1,2-b]pyridazine-3-carboxylic acid (DM2), two imidazo[1,2-b]pyridazines structurally related to indomethacin (IDM) but ineffective in blocking COXs, retain IDM antiabsence activity. When administered by intraperitoneal injection in WAG/Rij rats, a rat strain which spontaneously develops SWDs, both DM1 and DM2 dose-dependently suppressed the occurrence of these seizures. Importantly, these compounds were both more potent in suppressing SWD occurrence than IDM. As T-type channel blockade is considered a mechanism of action common to many antiabsence drugs we explored by whole cell patch clamp electrophysiology in stably transfected HEK-293 the effect of DM1 and DM2 on Ca(V)3.1 channels, the T-type channel subtype preferentially expressed in ventrobasal thalamic nuclei. Both these compounds dose-dependently suppressed the currents elicited by membrane depolarization in these cells. A similar T-type blocking effect was also observed when the cells were exposed to IDM. In conclusion, DM1 and DM2 whilst inactive on COXs, are potent antiabsence drugs. This suggests that compounds with structural features typical of NSAIDs may exert antiepileptic activity independently from COX inhibition and possibly by a direct interaction with T-type voltage-dependent Ca(2+) channels.
 
Article
The effect of in vivo administration of the alkylating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) on striatal and extrastriatal D-1 and D-2 dopamine (DA) receptors was investigated in the rat. N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline treatment reduced specific [3H]SCH 23390 (7-chloro-8-hydroxy-2,3,4,5-tetrahydro-3-methyl-1-phenyl-1H-3-benzaze pin e) binding to D-1 DA receptors in the striatum (42-46% of saline-treated controls), entopeduncular nucleus (20%) and substantia nigra pars reticulata (23%). Similarly, specific [3H]spiperone binding to D-2 DA receptors was decreased in the striatum (28-37% of saline-treated controls). However, [3H]spiperone binding in the substantia nigra pars compacta (67%) was much less affected. In vivo pretreatment with the D-1 DA antagonist SCH 23390 selectively and dose dependently protected [3H]SCH 23390 binding against the effects of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline in the striatal/extrastriatal regions. Pretreatment with the D-2 DA antagonist raclopride or the D-2 DA agonist quinpirole selectively protected [3H]spiperone binding. In contrast, pretreatment with the D-1 DA agonist SKF 38393 (7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine) not only protected [3H]-SCH 23390 binding but at very high doses protected striatal [3H]spiperone binding. The differential alkylating effects of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline on striatal vs extrastriatal D-1 and D-2 DA receptors may be related to their post- (striatal DA receptors) and pre-synaptic (extrastriatal DA receptors) localizations, respectively. The present results further demonstrate that in vivo, SCH 23390 and raclopride/quinpirole retain their D-1 and D-2 DA receptor selectivity.
 
Article
The effects of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), an alkylating agent producing irreversible blockade of various membrane bound receptors in brain, were investigated on four different types of serotonin receptors, 5-HT1A, 5-HT1B, 5-HT2A and 5-HT3, in various brain regions in the rat. In addition, the fate of central benzodiazepine- and "R"-zacopride-specific binding sites was also examined in rats treated with EEDQ. Membrane binding assays and/or quantitative autoradiography with appropriate radioligands indicated that EEDQ inactivated 5-HT1A, 5-HT1B and 5-HT2A sites, but was poorly active on 5-HT3, benzodiazepine and "R" sites. Among the receptors affected by EEDQ, hippocampal 5-HT1A sites were the most sensitive to the alkylating agent (ID50 approximately 1 mg/kg i.p.), followed by the cortical 5-HT2A (ID50 approximately 3 mg/kg i.p.) and the striatal 5-HT1B (ID50 approximately 6 mg/kg i.p.) sites. Pretreatment by selective ligands partially protected hippocampal 5-HT1A sites from irreversible inactivation by EEDQ (10 mg/kg i.p.) with the following order of efficacy: WAY 100635 > spiperone > BMY 7378 > ipsapirone. Similarly, pretreatment by spiperone (5 mg/kg i.p.) also reduced the ability of EEDQ to inactivated cortical 5-HT2A receptors. Analyses of the time-course recovery of respective binding sites after EEDQ administration showed that the turnover rate of 5-HT1A sites did not significantly differ in the dorsal raphe nucleus and in various forebrain areas (hippocampus, septum, cerebral cortex; half-life: approximately 4 days), but was lower than that of cortical 5-HT2A sites (half-life: 2.9 days).
 
Article
Intrapritoneal injection of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) to rats significantly reduced the density of alpha 1- and alpha 2-adrenoceptors in the cerebral cortex, without affecting beta-adrenoceptors. A single dose of EEDQ markedly accelerated the development of downregulation of beta-adrenoceptors induced by a short series of electroshocks. The accumulation of cAMP, induced by isoproterenol, was unchanged in rats treated with EEDQ, while the effect of noradrenaline was reduced, to the level observed after isoproterenol alone, indicating the attenuation of alpha-adrenoceptor function. The isoproterenol-induced accumulation of cAMP was not changed by EEDQ nor electroshock, not by the combined treatment. The stimulatory action of noradrenaline was reduced after EEDQ alone or in combination with electroshock, but the effect of electroshock alone was insignificant. The results suggest that the acceleration of downregulation of beta-adrenoceptors after combined treatment with an alpha-adrenoceptor blocking agent is related to elimination of the alpha-adrenergic potentiation of accumulation of cAMP mediated by beta-adrenoceptors.
 
Article
The 6-methoxy-2-phenylimidazo[1,2-b]pyridazine-3-carboxylic acid, DM2, exerts anti-absence activity and blocks Cav3.1 channel, a T-type voltage-dependent Ca(2+) channel subtype, in vitro. The current study investigated the effect of intra-ventrolateral periaqueductal grey (VLPAG) administration of DM2 on formalin-induced nocifensive responses in rats. In addition, the effect of intra-VLPAG microinjection of DM2 on the ongoing and tail flick-related activities of rostral ventromedial medulla (RVM) cell population was also investigated. Formalin was injected subcutaneously into the dorsal surface of the hind paws of awake rats. We found that DM2 reduced nocifensive responses in the late phase of the formalin test. Moreover, in the RVM, the intra-VLPAG microinjection of DM2 reduced the ongoing and tail flick-related activity of the nociceptive ON cells, whereas it increased the ongoing activity and reduced the tail flick-induced pause of the antinociceptive OFF cells, consistent with antinociception. Behavioural and electrophysiological effects were reproduced by intra-VLPAG microinjection of ethosuximide, a conventional T-type Ca(2+) channel blocker. Finally, DM2 administration did not produce any adverse cardiovascular effects as blood pressure and heart rate remained unchanged. In conclusion, DM2 plays an analgesic role in vivo and changes RVM cell activity, consistent with antinociception. These effects were even more potent than those elicited by ethosuximide treatments.
 
Article
SB-616234-A possesses high affinity for human 5-HT1B receptors stably expressed in Chinese hamster ovary (CHO) cells (pKi 8.3+/-0.2), and is over 100-fold selective for a range of molecular targets except h5-HT1) receptors (pKi 6.6+/-0.1). Similarly, affinity (pKi) for rat and guinea pig striatal 5-HT1B receptors is 9.2+/-0.1. In [35S]-GTPgammaS binding studies in the human recombinant cell line, SB-616234-A acted as a high affinity antagonist with a pA2 value of 8.6+/-0.2 whilst providing no evidence of agonist activity in this system. In [35S]-GTPgammaS binding studies in rat striatal membranes, SB-616234-A acted as a high affinity antagonist with an apparent pKB of 8.4+/-0.5, again whilst providing no evidence of agonist activity in this system. SB-616234-A (1 microM) potentiated electrically stimulated [3H]-5-HT release from guinea pig and rat cortical slices (S2/S1) ratios of 1.8 and 1.6, respectively). SB-616234-A (0.3-30 mg kg(-1) p.o.) caused a dose-dependent inhibition of ex vivo [3H]-GR125743 binding to rat striatal 5-HT1B receptors with an ED50 of 2.83+/-0.39 mg kg(-1) p.o. Taken together these data suggest that SB-616234-A is a potent and selective 5-HT(1B) autoreceptor antagonist that occupies central 5-HT1B receptors in vivo following oral administration.
 
Article
The (R)- and (S)-enantiomers of salsolinol, the dopamine-derived tetrahydroisoquinolines, were found to inhibit the activity of tryptophan hydroxylase (TPH), prepared from serotonin-producing murine mastocytoma P-815 cells. Inhibition of TPH by salsolinols was found to be non-competitive with the substrate L-tryptophan. Tryptophan hydroxylase is composed of two elements with different kinetic properties in terms of cofactor (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin and these two elements were inhibited by salsolinols in competitive and uncompetitive ways, respectively. Stereoselectivity of salsolinol was not observed, concerning the potency and the type of inhibition on PTH. These data indicate that salsolinols might be naturally occurring inhibitors of indoleamine metabolism.
 
Article
The mechanism by which 9-amino-1,2,3,4-tetrahydroacridine (THA) inhibits beta-adrenoceptor linked cyclic AMP formation and its possible relationship with the cholinergic system were studied. In addition, the effect of THA on alpha 1-adrenoceptor coupled transduction systems was also investigated. THA was not able to influence the concentration-response curve for forskolin indicating that it is not acting on the catalytic subunit of the adenylate cyclase complex. On the other hand a cholinergic component seems to participate in the action of THA on beta-adrenoceptor stimulated adenylate cyclase activity since the blockade of muscarinic receptors with atropine (10 microM) partially prevented the reduction in cyclic AMP formation attained by THA in the hippocampus, in isoprenaline-stimulated conditions. This effect is not reproducible by another potent anticholinesterase physostigmine. Moreover, THA at concentrations up to micromolar did not affect alpha 1-adrenoceptor stimulated cyclic AMP formation or phosphoinositide hydrolysis. In conclusion, the neuropharmacological profile of THA is not to be restricted to the cholinergic system and its effectiveness in improving age-associated cognitive deterioration may involve an action on the beta-adrenoceptor coupled signal transduction system. Moreover, the action of THA on the beta-adrenergic and cholinergic systems in the brain could be relevant to the amelioration of cognitive deterioration and could lead to the development of new therapeutic strategies.
 
Article
1-Methyl-1,2,3,4-tetrahydroisoquinoline (1-MeTHIQ - an endogenous parkinsonism-preventing substance) administered intraperitoneally at a dose of 20 mg/kg considerably elevated the threshold for electroconvulsions in mice from 6.4 to 8.4 mA (P < 0.05). In contrast, the agent administered at 5 and 10 mg/kg had no significant impact on the electroconvulsive threshold in mice. Moreover, 1-MeTHIQ (at a subthreshold dose of 10 mg/kg) potentiated the anticonvulsant action of valproate (VPA) against maximal electroshock (MES)-induced seizures in mice, reducing its median effective dose (ED50) from 232 to 170 mg/kg (P < 0.001). Similarly, 1-MeTHIQ (at 10 mg/kg) enhanced the antielectroshock activity of carbamazepine (CBZ) in mice, decreasing its ED50 from 10.8 to 7.8 mg/kg (P < 0.05). In contrast, 1-MeTHIQ (at 10 mg/kg) did not affect the anticonvulsant action of phenytoin and phenobarbital against MES-induced seizures in mice. The evaluation of acute neurotoxic effects of the studied antiepileptic drugs (AEDs) in combination with 1-MeTHIQ, as regards motor coordination impairment in the chimney test, revealed no significant changes in median toxic doses (TD50) of conventional AEDs after systemic administration of 1-MeTHIQ (up to 10 mg/kg). Pharmacokinetic characterization of interactions between 1-MeTHIQ (10 mg/kg) and VPA (170 mg/kg) or CBZ (7.8 mg/kg) revealed no significant changes in total brain concentrations of CBZ and VPA, indicating that the observed enhancement of antiseizure effects of CBZ and VPA by 1-MeTHIQ was pharmacodynamic in nature. Based on our preclinical study, it may be concluded that 1-MeTHIQ exerts the anticonvulsant effects increasing the threshold for electroconvulsions and potentiating the antiseizure action of CBZ and VPA against maximal electroshock. The antiseizure properties of 1-MeTHIQ (an endogenous parkinsonism-preventing substance) and its exact physiological role in the brain need extensive examination in further neuropharmacological studies.
 
Article
4-Phenyl-1,2,3,4-tetrahydroisoquinoline (4-PTIQ) has previously been shown to have antagonistic properties to methamphetamine in the spinal cord. Administration of 4-PTIQ (5 mg/kg, s.c.) reduced the ambulation induced by methamphetamine (0.5 mg/kg, s.c.) in rats. Methamphetamine (3 micrograms), injected unilaterally into the nucleus accumbens, increased ambulation. Alone, 4-PTIQ (10 micrograms) failed to elicit ambulation; however, it inhibited the methamphetamine-induced increase in ambulation. The alpha 1-antagonist prazosin (0.5 micrograms) or the beta-antagonist propranolol (3 micrograms) showed no effect on ambulation induced by methamphetamine. Haloperidol (5 ng), which possesses strong dopamine-blocking activity, abolished the ambulation induced by methamphetamine. The drug 4-PTIQ had weak affinity for dopamine D1 and D2 receptors. These results support the possibility that the inhibitory effects of 4-PTIQ on the ambulation-stimulating effects of methamphetamine, are due to blocking of the dopamine-releasing effect of methamphetamine but not due to dopamine blocking effects.
 
Article
Mitragynine is a major indole alkaloid isolated from the Thai medicinal plant Mitragyna speciosa that has opium-like properties, although its chemical structure is quite different from that of morphine. We attempted to develop novel analgesics derived from mitragynine, and thus synthesized the ethylene glycol-bridged and C10-fluorinated derivative of mitragynine, MGM-9 [(E)-methyl 2-(3-ethyl-7a,12a-(epoxyethanoxy)-9-fluoro-1,2,3,4,6,7,12,12b-octahydro-8-methoxyindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate]. We hypothesized that a dual-acting mu- and kappa-opioid agonist could produce potent antinociceptive effects with fewer rewarding effects compared with mu agonists. In this study, MGM-9 exhibited high affinity for mu- and kappa-opioid receptors with Ki values of 7.3 and 18 nM, respectively. MGM-9 showed a potent opioid agonistic effect, and its effects were meditated by mu- and kappa-opioid receptor mechanisms in in vitro assays. Subcutaneous and oral administration of MGM-9 produced potent antinociceptive effects in mouse tail-flick, hot-plate, and writhing tests. When administered orally, the antinociceptive effect of MGM-9 was seven to 22 times more potent than that of morphine. The antinociceptive effects of MGM-9 were mediated by both mu- and kappa-opioid receptors. Subcutaneous administration of MGM-9 twice daily for 5 days led to antinociceptive tolerance. In the gastrointestinal transit study, MGM-9 inhibited gastrointestinal transit, but its effect was weaker than that of morphine at equi-antinociceptive doses. Furthermore, MGM-9 induced less hyperlocomotion and fewer rewarding effects than morphine. The rewarding effect of MGM-9 was blocked by a mu antagonist and enhanced by a kappa antagonist. Taken together, the results suggest that MGM-9 is a promising novel analgesic that has a stronger antinociceptive effect and weaker adverse effects than morphine.
 
Article
We found that both MPTP and its metabolite MPP+ decrease dopamine and increase acetylcholine content of mouse neostriatum when administered intracerebroventricularly (ICV). These observations support the notion that MPP+ may be the active neurotoxin formed in brain after MPTP administration. They also suggest that cholinergic mechanisms may be a target of the neurotoxin.
 
Article
Lithium has been reported to exert neuroprotective activity in several neuronal cell cultures and in vivo models against glutamate toxicity. Since this action was reported to be associated with alterations in the antiapoptotic Bcl-2 family proteins, the effect of chronic lithium diet on the ability of the parkinsonism neurotoxin, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to deplete striatal dopamine in mice was determined. Mice were fed for with a diet containing 1.1, 2.2, 3.3, and 4.4 g/kg lithium chloride (LiCl) for 4 weeks, during which time serum levels of lithium were monitored. The 3.3 g/kg lithium diet gave serum level value very similar to what is observed in lithium therapy in man and the 4.4 g/kg well above this. At the end of this period the mice received 24 mg/kg MPTP i.p. once daily for 3 days. A direct relation was established with the increase in serum lithium and its ability to prevent MPTP induced depletion of striatal dopamine (DA) and its metabolites DPOAC and HVA. With the diet containing the highest lithium concentration there was an almost complete prevention of striatal dopamine depletion and the reduction in tyrosine hydroxylase activity and protein and it prevented the increase in dopamine turnover (DOPAC + HVA/DA) normally observed in MPTP treatment. Lithium did not interfere with the metabolism of MPTP, or with its brain uptake, since, the level of its monoamine oxidase (MAO) B derived metabolite, MPP+, in the striata of lithium and non-lithium treated mice were almost identical. Striatal Bcl-2 was significantly decreased, while Bax was increased in MPTP treated mice. Lithium treatment not only increased striatal Bcl-2 in control mice, but also prevented its reduction as induced by MPTP, and an opposing effect was seen with Bax. The neuroprotective action of lithium in this model of Parkinson's disease has been attributed to its antiapoptotic activity which among other factors includes induction of Bcl-2 and reduction of Bax.
 
Article
Albino mice and pigmented mice were treated for 6 days with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at the maximum tolerated doses (2 days at 30 mg/kg i.p., 2 days at 40 mg/kg i.p. and 2 days at 50 mg/kg i.p. in white mice, 6 days at 30 mg/kg i.p. in pigmented mice) and the effects of simultaneous treatment with the monoamine oxidase inhibitors, deprenyl (1 mg/kg, i.p.), MDL 72145 (0.5 mg/kg, i.p.) and clorgyline (5 mg/kg, i.p.), determined behaviourally (daily for 6 days and for 4 days after withdrawal) and biochemically (92 hr after withdrawal of drug). In albino mice MPTP caused depletions of dopamine (90%), dihydroxyphenylacetic acid (DOPAC; 82%) and homovanillic acid (HVA; 65%) in the striatum and in dopamine (54%), DOPAC (51%) and HVA (53%) in the nigra. However, MPTP was not selective in its action since the levels of dopamine and its metabolites were also reduced in limbic tissue. Further, MPTP affected the function of noradrenaline, with reduced levels in tissues of the striatum (74%) and nigra (46%). Pigmented mice were as susceptible as albino mice to the actions of MPTP to reduce the levels of dopamine and metabolites in the striatum. However, the limbic areas and substantia nigra of the pigmented mouse were more resistant to the actions of MPTP. Treatment with deprenyl and MDL 72145 (but not clorgyline) could be shown to reduce the biochemical and behavioural consequences of the action of MPTP (although behavioural changes, development of severe motor incapacitation and prostrate appearance, appeared to be non-specific).(ABSTRACT TRUNCATED AT 250 WORDS)
 
Article
Male albino mice were injected subcutaneously with 50 mg/kg of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Seven days after administration, the striatal levels of dopamine(DA) and its metabolites were markedly reduced, as was the cortical level of noradrenaline (NA). Pretreatment with the selective inhibitor of DA uptake, GBR 13098, selectively and totally prevented the reduction of DA and its metabolites, whereas the selective inhibitor of NA uptake, maprotiline, selectively protected against NA depletion. The unselective inhibitors of DA and NA uptake, mazindol and nomifensine, prevented the MPTP-induced depletion of both DA and NA.
 
Article
Amphetamine has been shown to either potentiate or protect against MPTP neurotoxicity. The time course of changes in dopamine and its metabolites was examined after MPTP, amphetamine, or MPTP plus amphetamine administration. Results suggest that under conditions of granular depletion and release of dopamine by 10 mg/kg amphetamine, increased MPTP neurotoxicity occurs. Amphetamine injections at 2-5 mg/kg prevents the decline in dopamine possibly by blockade of the uptake of MPP+, rather than by an inhibition of monoamine oxidase.
 
Article
The effect of GM1 ganglioside on the recovery of concentrations of dopamine (DA) in the striatum, following administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was studied in mice of various ages. At the start of the study, the mice were 8 weeks, 6, 12 and 20 months old. Mice from each age group received MPTP for 5 days, followed by either GM1 ganglioside or saline for 4 or 8 weeks. Animals older than 8 weeks, that did not receive GM1 showed no spontaneous recovery of striatal levels of DA in the striatum, over either 4 or 8 weeks. Animals that received GM1 showed varied amounts of recovery of levels of DA in the striatum. The young animals (8 wk old) had the most pronounced effect from GM1. With increasing age, the magnitude of the effect of GM1 became attenuated and recovery had a longer latency. The results suggest that GM1 can be effective in at least partially restoring MPTP-depleted levels of DA in the striatum, even in aged mice.
 
Article
Based on behavioral observation alone, poorly characterized paroxysmal motor abnormalities have been reported in mice after acute MPTP administration. This study investigated electroencephalographic (EEG) and behavioral effects of acute MPTP in young and older mice. Single MPTP injections (30 mg/kg i.p.) produced limbic and/or generalized seizures in older (6 mo) and frank epileptiform interictal hippocampal spikes in younger (6-8 wks) mice. These latter showed behavioral seizures only after the 3rd drug administration. Studies of the acute effects of MPTP must take in consideration that seizures "per se" modify brain biochemical and metabolic activity and alter the permeability of the blood brain barrier, adding several confounding variables.
 
Article
Treatment of mice with the proximate neurotoxin MPTP depletes striatal dopamine levels. Depletion of striatal dopamine and metabolites in MPTP-treated mice is accompanied by depletion of glutathione (GSH) in the substantia nigra (SN). Striatal GSH and nigral amino acid levels were not significantly affected by MPTP. Results suggest that GSH depletion in SN may represent an index of regional vulnerability to metabolic oxidative stress and also of selective susceptibility to the toxic effects of MPTP.
 
Article
Several epidemiological studies have indicated that there may be an inverse relationship between smoking and Parkinson's disease. The purpose of this study was to determine whether chronic exposure to cigarette smoke alters the parkinsonian-like neurochemical changes caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice. Following 4 weeks of brief, intermittent exposure to smoke, mice were treated with MPTP, 10 mg/kg. Smoke exposure was found to reduce the decrease in striatal dopamine and metabolite levels caused by MPTP. Although smoke exposure inhibited cerebral MAO-B activity, tissues from smoke-treated mice were able to metabolize MPTP in a normal fashion. This suggests that inhibition of cerebral MAO may not be a major mechanism for the apparent protective effect of cigarette smoke.
 
Article
Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 2 X 8 mg/kg retro-orbital) to BALB/cBy mice reduced [3H]mazindol binding to striatal membranes by 50%. Reactive oxygen derivatives have been suggested to be involved in MPTP neurotoxicity; therefore we examined the effects of ascorbic acid (an antioxidant). Ascorbic acid (100 mg/kg) given 20 min prior to MPTP administration appreciably prevented the reduction of [3H]mazindol binding. The involvement of oxidative processes in the mechanism of MPTP neurotoxicity may suggest a relationship to the etiology of Parkinson's disease, and the possible benefit of treatment with ascorbic acid.
 
Article
The present results show the potentiating effect of amphetamine on the ability of MPTP to destroy dopaminergic neurons in striatum of the mouse. A single injection of MPTP (8 mg/kg, retro-orbital) reduced the binding of [3H]mazindol, a marker for dopamine terminals, by 24%. When D-amphetamine (10 mg/kg, s.c.) was given 20 min prior to MPTP, the binding of [3H]mazindol, measured 3-5 days later, was reduced by 58%. It is proposed that the mechanism of this potentiation primarily involves an increased release of dopamine by D-amphetamine, and free radical-mediated processes. Although nicotine also releases dopamine from the striatum, no effect was observed when it was administered prior to MPTP. The lack of effect is probably related to short duration of action of nicotine and the modest effect on release of dopamine as compared to that of amphetamine.
 
Article
The results reported here indicate that treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) caused significant changes in the dopamine-synthesizing enzyme, tyrosine hydroxylase. The authors examined the effects of two doses of MPTP on the activities of tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH) in the striatum, and also the time-course of these effects. Rats received an intraperitoneal loading dose, followed by a 24-hr infusion of MPTP (total doses of 21 or 42 mg) from subcutaneously-implanted osmotic pumps. Seven days after treatment, the activity of tyrosine hydroxylase was decreased by MPTP (42 mg); however, the activity of tryptophan hydroxylase was not affected. In time-course experiments, the activity of tyrosine hydroxylase was maximally reduced at 3 and 7 days after treatment with MPTP (42 mg). The activity of tryptophan hydroxylase did not significantly change at any time-point. Concurrent administration of haloperidol (HALO; 2 mg/kg, 4 doses) with MPTP significantly enhanced the depression of the activity of tyrosine hydroxylase in the striatum caused by MPTP, while treatment with haloperidol alone had no such effect. Concentrations of dopamine in the striatum were maximally decreased to approx. 50% of control in animals treated with haloperidol and MPTP (42 mg), whereas treatment with MPTP alone decreased concentrations of dopamine to approx. 70% of control.
 
Article
T-817MA (1-{3-[2-(1-benzothiophen-5-yl)ethoxy]propyl} azetidin-3-ol maleate) is a candidate therapeutic agent for Alzheimer's disease that inhibits oxidative stress and nitric oxide-induced neurotoxicity and acts as a neurotrophic factor. The present study examines the effect of T-817MA on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity in C57BL/6J mice. MPTP treatment (10mg/kg, s.c.x4 at 2-h intervals) impaired rotarod performance, and T-817MA improved this deficit. MPTP treatment also decreased dopamine levels and tyrosine hydroxylase immunostaining in the substantia nigra (SNc) and striatum. Pretreatment with T-817MA (10 and 30mg/kg as T-817, p.o.) attenuated these decreases in dopamine levels and tyrosine hydroxylase immunoreactivity, but did not affect brain levels of 1-methyl-4-phenylpyridinium ion, an active metabolite of MPTP. The protective effect was almost complete in the SNc, but only partial in the striatum. MPTP increased levels of the lipid peroxidation product, thiobarbituric acid reactive substance, only in the midbrain, which could be blocked by T-817MA. MPTP caused microglial activation both in the SNc and striatum, but T-817MA did not affect the activation of microglia. These results suggest that T-817MA protects against MPTP-induced neurotoxicity by blocking lipid peroxidation in the SNc, and imply that this compound may be useful for treating neurodegenerative disorders related to oxidative stress, such as Parkinson's disease.
 
Article
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes the damage of dopaminergic neurons as seen in Parkinson's disease. Oxidative stress has been as one of several pathogenic hypotheses for Parkinson's disease. Here we investigated whether arundic acid, an astrocyte-modulating agent, can protect against alterations of nitric oxide synthase (NOS) and superoxide dismutase (SOD) expression on MPTP neurotoxicity in mice, utilizing an immunohistochemistry. For this purpose, anti-tyrosine hydroxylase (TH) antibody, anti-dopamine transporter (DAT) antibody, anti-Cu/Zn-SOD antibody, anti-Mn-SOD antibody, anti-nNOS antibody, anti-eNOS antibody and anti-iNOS antibody were used. The present study showed that the arundic acid had a protective effect against MPTP-induced neuronal damage in the striatum and substantia nigra of mice. The protective effect may be, at least in part, caused by the reductions of the levels of reactive nitrogen (RNS) and oxygen species (ROS) against MPTP neurotoxicity. These results suggest that the pharmacological modulation of astrocyte may offer a novel therapeutic strategy for the treatment of Parkinson's disease. Furthermore, our results provide further evidence that a combination of nNOS inhibitors, iNOS inhibitors and free radical scavengers may be effective in the treatment of neurodegenerative diseases. Thus our present results provide valuable information for the pathogenesis of degeneration of the nigrostriatal dopaminergic neuronal pathway.
 
Article
To examine how mGlu2/3 metabotropic glutamate receptors affect nigro-striatal degeneration, we used the agonist, LY379268, and the antagonist, LY341495, in mice challenged with the nigro-striatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In control mice, high doses of MPTP (20 mg/kg, i.p., injected four times with 2 h of interval) induced a nearly total degeneration of the nigro-striatal pathway, as shown by measurements of striatal dopamine (DA) levels and by immunohistochemical analysis of tyrosine hydroxylase, high affinity dopamine transporter, and glial fibrillary acidic protein in the corpus striatum and substantia nigra. Lower cumulative doses of MPTP (30 mg/kg, i.p., injected only once) produced a partial lesion of the nigro-striatal pathway (about 50% reduction of striatal DA content). Systemic injection of LY379268 (1 mg/kg, i.p., 30 min prior to each injection of MPTP) partially reduced the extent of nigro-striatal degeneration induced by high doses of MPTP. Similar results were obtained by continuously delivering LY379268 (1 mg/kg/d for 7 d) by means of a subcutaneous osmotic minipump. The protective effect of LY379268 was antagonized by LY341495 (also delivered by the osmotic minipump). In mice challenged with the lower cumulative dose of MPTP, injection of LY379268 did not produce a significant neuroprotective effect. In contrast, the lesion was amplified by the antagonist, LY341495. Neither LY379268 nor LY341495 influenced the central bioavailability and the local half-life of MPTP, as shown by measurements of the toxin and its active metabolite, MPP(+), in the striatum. We conclude that mGlu2/3 receptors play a protective role against MPTP toxicity, and that the efficacy of the agonist, LY379268, critically depends on the extent of the nigro-striatal lesion.
 
Article
The effect of nicotine on MPTP-induced changes in striatal dopamine receptors binding activity was investigated. Dopamine D1 and D2 receptors were labeled with [3H]SCH-23390 and [3H]spiperone respectively in BALB/cBy mice. With administration of only MPTP, which caused more than an 80% decrease in striatal dopamine level, binding of 0.15 nM [3H]spiperone was increased by 37%; whereas 0.3 nM [3H]SCH-23390 binding was unchanged. With chronic nicotine treatment (0.4 mg/kg twice daily for 7-9 days), [3H]SCH-23390 binding activity was increased by 27% and [3H]spiperone binding activity was unchanged. When nicotine was administered after MPTP, their separate effects could be seen in that both the D1 and D2 dopamine receptor ligand binding activities were increased and that nicotine elevated the ratio of D1/D2 receptor binding activities in MPTP-treated mice.
 
Article
The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the synthesis and release of dopamine (DA) was investigated in the retina of the rabbit in vitro. The results indicated that MPTP did not affect the synthesis of DA, but increased its release. Blockade of the activity of monoamine oxidase (MAO) with pargyline (100 microM) did not abolish the capacity of MPTP to release DA. Similarly, these pharmacological effects of MPTP were not dependent on the presence or absence of melanin.
 
Article
A pharmacological study using monkeys, in which parkinsonism was induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was undertaken to elucidate the mechanism underlying urinary bladder dysfunctions in Parkinson's disease. Under ketamine anesthesia, cystometrograms showed that, in MPTP-treated monkeys, a contraction of the urinary bladder was induced with smaller bladder volume than that in normal monkeys. In MPTP-treated monkeys, subcutaneously injected SKF 38393, a dopamine D1 receptor agonist, significantly increased the bladder volume and pressure thresholds for inducing the micturition reflex without affecting those in normal monkeys. In contrast, subcutaneous injections of quinpirole, a dopamine D2 receptor agonist, and apomorphine, a dopamine D1 and D2 receptor agonist, slightly, but significantly reduced the volume threshold of the bladder for the micturition reflex in both normal and MPTP-treated groups. These results indicate that, in parkinsonism, the degeneration of dopaminergic neurons in the substantia nigra leads to the detrusor hyperreflexia, probably due to a failure of activation of dopamine D1 receptors.
 
Article
The present study evaluates the pharmacological profile of the new neutral cannabinoid CB1 receptor antagonist 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-3-hexyl-1H-1,2,4-triazole -LH-21- on feeding behavior and alcohol self-administration in rats, two behaviors inhibited by cannabinoid CB1 receptor antagonists. Administration of LH-21 (0.03, 0.3 and 3 mg/kg) to food-deprived rats resulted in a dose-dependent inhibition of feeding. Subchronic administration of LH-21 reduced food intake and body weight gain in obese Zucker rats. Acute effects on feeding were not associated with anxiety-like behaviors, or induction of complex motor behaviors such as grooming or scratching sequences, usually observed after central administration of cannabinoid receptor blockers with inverse agonist properties. LH-21 did not markedly reduce alcohol self-administration (30% reduction observed only at a high dose of 10 mg/kg). This pharmacological pattern partially overlaps that of the reference cannabinoid CB1 receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide, SR141716A, (0.3, 1 and 3 mg/kg) that reduced feeding and alcohol self-administration with similar efficacy. In vitro analysis of blood-brain barrier permeability using a parallel artificial membrane permeation assay demonstrated that LH-21 has lower permeation through membranes than SR141716A. That was confirmed in vivo by studies showing lower potency of peripherally injected LH-21 when compared to SR141716A to antagonize motor depression induced by intracerebroventricular administration of the CB1 agonist CP55,940. The neutral antagonist profile and the lower penetration into the brain of LH-21 favour this class of antagonists with respect to reference inverse agonists for the treatment of obesity because they potentially will display reduced side effects.
 
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Previous reports suggest that γ-aminobutyric acid type A (GABAA) receptors containing α1 subunits may play a pivotal role in mediating the discriminative stimulus effects of benzodiazepines (BZs). L-838,417 (7-tert-Butyl-3-(2,5-difluoro-phenyl)-6-(2-methyl-2H-[1,2,4]triazol-3-yl methoxy)-[1,2,4]triazolo[4,3-b]pyridazine) is a GABAA receptor modulator with intrinsic efficacy in vitro at α2, α3, and α5 subunit-containing GABAA receptors, and little demonstrable intrinsic efficacy in vitro at α1 subunit-containing GABAA receptors. The present study evaluated the discriminative stimulus effects of L-838,417 in order to determine the extent to which the α2, α3, and α5 subunit-containing GABAA receptors contribute to the interoceptive effects of BZ-type drugs. Squirrel monkeys (Saimiri sciureus) were trained to discriminate L-838,417 (0.3 mg/kg, i.v.) from vehicle under a 5-response fixed-ratio schedule of food reinforcement. Under test conditions, L-838,417 administration resulted in dose-dependent increases in drug-lever responding that were antagonized by the BZ-site antagonist, flumazenil. Administration of non-selective BZs, compounds with 10-fold greater affinity for α1 subunit-containing GABAA receptors compared to α2, α3, and α5 subunit-containing GABAA receptors, barbiturates and ethanol (which modulate the GABAA receptor via a non-BZ site), all resulted in a majority of responses on the L-838,417-paired lever (65-100% drug-lever responding). βCCT, an antagonist that binds with 20-fold greater affinity for α1 subunit-containing GABAA receptors relative to α2, α3, and α5-containing GABAA receptors, had no significant effect on the discriminative stimulus effects of L-838,417 or the L-838,417-like effects of diazepam or zolpidem. These data suggest that efficacy at α2, α3, and/or α5 subunit-containing GABAA receptors likely are sufficient for engendering BZ-like discriminative stimulus effects.
 
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The effects of acute and chronic administration desipramine (DMI) and the potential antidepressant, MDL 26,479 (2,4-dimethyl-5-(3-fluorophenyl)-3H-1,2,4-triazole-3-thione) were compared on the sensitivity of Purkinje neurons in the cerebellum of the rat to iontophoretically applied norepinephrine (NE) and gamma-aminobutyric acid (GABA). Neither compound, administered acutely at 10 mg/kg (i.p.), altered the spontaneous firing rate of Purkinje neurons or the depression of the rate caused by iontophoresed NE. However, MDL 26,479 did significantly reduce the enhancement of inhibitory responses to GABA, produced by NE. Administered chronically (10 mg/kg x 21 days, i.p.), neither compound altered the slowing of Purkinje neurons evoked by NE. Chronic treatment with MDL 26,479, but not with DMI, produced a small but significant decrease in average spontaneous firing rate of Purkinje neurons. Both compounds substantially attenuated the enhancement of the inhibitory responses to GABA produced by NE, with MDL 26,479 having a more marked effect than DMI. These effects of MDL 26,479 on the activity of Purkinje neurons are consistent with the compound having antidepressant potential and further suggest, since similar effects were seen after a single dose, that the compound may have a rapid onset of antidepressant action.
 
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The effects of the catalase inhibitor, 3-amino-1,2,4-triazole (AT), on maintenance of voluntary consumption of ethanol was tested in male Long-Evans rats. AT produced a dose-dependent reduction in ethanol intake but did not affect total fluid consumption. AT also produced a dose-dependent inhibition of brain catalase lasting throughout the drinking period. These results suggest a role for brain catalase in determining the level of ethanol intake in rats.
 
Top-cited authors
Nicholas M. Barnes
  • University of Birmingham
Trevor Sharp
  • University of Oxford
A. Richard Green
  • University of Nottingham
Darrryle D Schoepp
Wojciech Danysz