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Peak-dose dyskinesia is associated with the dramatic increase in striatal dopamine levels that follows L-DOPA administration. The 'false neurotransmitter' hypothesis postulates that the latter is likely due to an aberrant processing of L-DOPA by serotonergic neurons. In keeping with this hypothesis, two highly selective 'biased agonists' of 5-HT

Serotonin 5-HT1A receptor agonists reduce L-DOPA-induced dyskinesia (LID) in animal models of Parkinson's disease (PD). Here, we compared the effects of novel 5-HT1A receptor 'biased agonists' on LID in hemiparkinsonian rats. F13714 preferentially activates pre-synaptic 5-HT1A autoreceptors. F15599 preferentially activates cortical postsynaptic 5-HT1A heteroreceptors. The partial agonist, tandospirone, does not differentiate these receptor subpopulations. The drugs were also tested on rotational behavior, rotarod and cylinder test for evaluation of locomotor activity, motor coordination and forelimb akinesia. Finally, the effects of F13714 and F15599 on 5-HT, DA, glutamate, and GABA release were investigated by microdialysis. F13714 abolished L-DOPA-induced AIMs even at very low doses (0.02-0.04 mg/kg). This effect was reversed by the selective 5-HT1A receptor antagonist, WAY100635. F13714 also elicited ipsilateral rotations (which were blocked by WAY100635) and potentiated the rotational activity of a sub-threshold dose of L-DOPA (2 mg/kg). F13714 profoundly inhibited striatal 5-HT release on both sides of the brain, and slightly increased DA release on the intact side. F15599 inhibited the L-DOPA-induced AIMs only at a dose (0.16 mg/kg) that reduced 5-HT release. Tandospirone produced a modest attenuation of peak AIMs severity and did not elicit rotations. F13714, F15599 and tandospirone did not modify the action of L-DOPA in the cylinder test but impaired rotarod performance at the highest doses tested. Targeting 5-HT1A receptors with selective biased agonists exerts distinct effects in the rat model of PD and LID. Preferential activation of 5-HT1A autoreceptors could potentially translate to superior antidyskinetic and L-DOPA dose-sparing effects in PD patients.

Drugs acting at the serotonin-2C (5-HT2C) receptor subtype have shown promise as therapeutics in multiple syndromes including obesity, depression, and Parkinson's disease. While it is established that 5-HT2C receptor stimulation inhibits DA release, the neural circuits and the localization of the relevant 5-HT2C receptors remain unknown. This study used dual-probe in vivo microdialysis to investigate the relative contributions of 5-HT2C receptors localized in the rat substantia nigra (SN) and caudate-putamen (CP) in the control of nigrostriatal DA release. Systemic administration (3.0 mg/kg) of the 5-HT2C receptor selective agonist Ro 60-0175 [(αS)-6-Chloro-5-fluoro-α-methyl-1H-indole-1-ethanamine fumarate] decreased, whereas intrastriatal infusions of the selective 5-HT2C antagonist SB 242084 [6-Chloro-2,3-dihydro-5-methyl-N-[6-[(2-methyl-3-pyridinyl)oxy]-3-pyridinyl]-1H-indole-1-carboxyamide; 1.0 μM] increased, basal DA in the CP. Depending on the site within the SN pars reticulata (SNpr), infusions of SB 242084 had more modest but significant effects. Moreover, infusions of the GABA-A receptor agonist muscimol (10 μM) into the SNpr completely reversed the increases in striatal DA release produced by intrastriatal infusions of SB 242084. These findings suggest a role for 5-HT2C receptors regulating striatal DA release that is highly localized. 5-HT2C receptors localized in the striatum may represent a primary site of action that is mediated by the actions on GABAergic activity in the SN. Dopamine (DA) neurons in the substantia nigra pars compacta (SNpc) project to the caudate-putamen (CP; striatum). This circuitry is implicated in numerous pathologies including Parkinson's disease. Using in vivo microdialysis, we demonstrated that blockade of serotonin (5-HT) 2C receptors in the CP increased nigrostriatal DA release. Infusions of a GABA-A agonist into the substantia nigra pars reticulata (SNpr) blocked this increase. This work indicates that striatal serotonin 2C receptors regulate GABAergic tone in the SNpr, which in turn regulates nigrostriatal DA release.

The addictive potential of nicotine is linked to psychomotor and cognition-enhancing effects. Histamine (H) 3 receptor antagonism has similarly received attention for a role in cognition, however, the role of H 3 receptors are far less studied for affects on nicotine-induced locomotor responses. In the present study we tested whether the H 3 receptor antagonist 4-(2-{2-[(2R)-2methylpyrrolidinyl]ethyl}-benzofuran-5-yl) benzonitrile (ABT-239) influenced the psychomotor responses to acute and repeated nicotine, including sensitization and conditioned locomotion. ABT-239 (0.3–3 mg/kg) did not alter basal, nicotine-evoked (0.4 mg/kg) locomotor responses, the expression of sensitization, or cue-conditioned locomotion. However, in combination studies rats pretreated with a separate dose of ABT-239 (1 mg/kg) prior to nicotine (0.4 mg/kg) for 5 days and then challenged with nicotine (0.4 mg/kg) after a 5-day withdrawal period, showed significantly higher locomotor hyperactivity in comparison with the effect observed in nicotine-pretreated and challenged rats. Our findings implicate a limited role for H 3 receptors in locomotor responses to nicotine.

This in vitro study investigates and compares the effects of NK3 receptor ligands on the firing rate of rat and guinea pig midbrain dopamine neurons. The findings are discussed in the light of choosing suitable animal models for investigating pharmacological properties of NK3 receptor antagonists, which have been proposed to possess therapeutic activity in neuropsychiatric diseases like e.g. schizophrenia. In vitro midbrain slice preparations of both species were used to record (extracellularly) the firing rates of dopamine neurons located in the substantia nigra (SN) and ventral tegmental area (VTA). Furthermore, the effect of the D2 receptor agonist quinpirole on guinea pig SN and VTA dopamine neurons was investigated. The efficacy of quinpirole in inhibiting guinea pig dopamine neuron firing activity was much less as compared to that of rat dopamine neurons, suggesting a lower dopamine D2 autoreceptor density on the guinea pig neurons. The NK3 receptor agonist senktide induced in subpopulations of rat SN (55%) and VTA (79%) and guinea pig SN (50%) and VTA (21%) dopamine neurons an increase in firing rate. In responsive neurons this effect was concentration-dependent with EC₅₀ values of 3-5 nM (for both species). The selective NK3 receptor antagonist osanetant (100 nM) was able to partly block the senktide-induced increase in firing rates of dopamine neurons and shifted the concentration-response relation curves for senktide to the right (pA₂ values were ~7.5). The fractional block of the senktide responses by osanetant appeared to be larger in guinea pig dopamine neurons, indicating that osanetant is a more potent blocker of NK3 receptor-mediated responses with noncompetitive properties in the guinea pig.

Rationale The serotonin 5-HT2A and 5-HT2C receptors regulate the capacity of acute cocaine to augment behavior and monoamine levels within the nucleus accumbens (NAC), a brain region involved in cocaine’s addictive and psychotogenic properties. Objectives In the present study, we tested the hypothesis that NAC 5-HT2A and 5-HT2C receptor activation is involved in the expression of cocaine-induced neuroplasticity following protracted withdrawal from a sensitizing repeated cocaine regimen (days 1 and 7, 15 mg/kg; days 2–6, 30 mg/kg, i.p.). Methods The effects of intra-NAC infusions of the 5-HT2A antagonist R-(+)-α-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidine methanol (MDL 100907; 0, 50, 100, 500 nM) or the 5-HT2C antagonist [6-chloro-5-methyl-1-(6-(2-methylpiridin-3-yloxy)pyridine-3-yl carbamoyl] inodoline dihydrochloride (SB 242084; 0, 50, 100, 500 nM) were first assessed upon the expression of locomotor activity elicited by a 15-mg/kg cocaine challenge injection administered at 3-week withdrawal. A follow-up in vivo microdialysis experiment then compared the effects of the local perfusion of 0, 50, or 100 nM of each antagonist upon cocaine-induced dopamine and glutamate sensitization in the NAC. Results Although neither MDL 100907 nor SB 242084 altered acute cocaine-induced locomotion, SB 242084 reduced acute cocaine-elevated NAC dopamine and glutamate levels. Intra-NAC perfusion with either compound blocked the expression of cocaine-induced locomotor and glutamate sensitization, but only MDL 100907 pretreatment prevented the expression of cocaine-induced dopamine sensitization. Conclusions These data provide the first evidence that NAC 5-HT2A and 5-HT2C receptors are critical for the expression of cocaine-induced neuroplasticity following protracted withdrawal, which has relevance for their therapeutic utility in the treatment of addiction.

The objective of this study was to evaluate the efficacy of varenicline, a novel partial agonist at alpha 4 beta 2 and full agonist at alpha 7 nicotinic acetylcholine receptor (nAChR) subtypes, in blocking the locomotor effects of acute or repeated treatments with nicotine (0.4 mg/kg, s.c.) in rats. Varenicline (0.3-3 mg/kg, s.c.) by itself enhanced the basal locomotor activity in naive rats while it had an inhibitory effect on acute nicotine-induced hyperlocomotion. Varenicline (0.3-3 mg/kg) did not change the nicotine-evoked conditioned locomotion, but when administered to nicotine-sensitized rats (0.1 and 1 mg/kg), reduced the expression of nicotine sensitization. In another set of experiments, varenicline (1 mg/kg) administered during the second withdrawal period (days 11-14) to nicotine-treated rats, attenuated the reestablishment of the expression of nicotine sensitization. Our pharmacological analyses further support the hypothesis that varenicline might be a useful treatment for smoking cessation considering its actions on the locomotor and reinforcing effects of nicotine without inhibition of conditioned locomotion.

The present study tested the hypothesis that serotonergic (5-HT) 5-HT2A or 5-HT2C receptors or their pharmacological stimulation modulated the discriminative stimulus effects of nicotine in male Wistar rats. To this end the selective 5-HT2A receptor antagonist R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl)ethyl]-4-piperidinemethanol (M100,907; 0.5-1 mg/kg, i.p.), the functional 5-HT2A receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI; 0.1-1 mg/kg, s.c.), the selective 5-HT2C receptor antagonist 6-chloro-5-methyl-1-{[2-(2-methylpyrid-3-yloxy)pyrid-5-yl]carbamoyl}indoline (SB 242,084; 0.25-1 mg/kg, i.p.) and the 5-HT2C receptor agonists (S)-2-chloro-5-fluoro-indol-1-yl)-1-methylethylamine fumarate (Ro 60-0175; 0.3-1 mg/kg, s.c.) and (7bR, 10aR)-1,2,3,4,8,9,10,10a-octahydro-7bH-cyclopenta-[b][1,4]diazepino[6,7,1hi]indole (WAY 163,909; 0.75-1.5 mg/kg, i.p.) were used. Additionally, the effects of the selective alpha4beta2 nicotinic acetylcholine receptor subtype agonist 5-iodo-3-(2(S)-azetidinylmethoxy)pyridine (5-IA; 0.01 mg/kg, s.c.) were investigated. In rats trained to discriminate (-)-nicotine (0.4 mg/kg, s.c.) from saline in a two-lever, water-reinforced fixed ratio 10 task, substitutions were not observed with 5-HT2 receptor ligands (32% nicotine-lever responding), conversely 5-IA induced a full substitution (100% nicotine-lever responding). In combination studies, fixed doses of M100,907 (0.5-1 mg/kg) or SB 242,084 (0.25-1 mg/kg) did not alter the dose-response curve of nicotine, while DOI (0.3 mg/kg), Ro 60-0175 (1 mg/kg) and WAY 163,909 (1 and 1.5 mg/kg) attenuated the discriminative stimulus effects of nicotine. The decrease in the expression of the discriminative stimulus effects of nicotine produced by DOI was blocked by M100,907 (1 mg/kg), but not by SB 242,084 (1 mg/kg), while that evoked by Ro 60-0175 or WAY 163,909 was blocked by SB 242,084 (1 mg/kg), but not by M100,907 (1 mg/kg). Further studies showed that DOI (0.3 mg/kg) and Ro 60-0175 (1 mg/kg), but not WAY 163,909 (1.5 mg/kg) blocked full substitution of 5-IA (0.01 mg/kg) for nicotine. Our pharmacological analyses indicate that tonic activation of 5-HT2A or 5-HT2C receptors is not required for subjective effects of nicotine, however these receptors appear to have inhibitory influence on nicotine cue, since pharmacological stimulation of either receptor attenuates the discriminative stimulus effects of nicotine.

We have previously demonstrated that nicotine withdrawal produces depression-like behavior and that serotonin (5-HT)2A/2C receptor ligands modulate that mood-like state. In the present study we aimed to identify the mechanisms (changes in radioligand binding, transcription or RNA-editing) related to such a behavioral outcome. Rats received vehicle or nicotine (0.4 mg/kg, s.c.) for 5 days in home cages. Brain 5-HT2A/2C receptors were analyzed on day 3 of nicotine withdrawal. Nicotine withdrawal increased [(3)H]ketanserin binding to 5-HT2A receptors in the ventral tegmental area and ventral dentate gyrus, yet decreased binding in the nucleus accumbens shell. Reduction in [(3)H]mesulergine binding to 5-HT2C receptors was seen in the ventral dentate gyrus. Profound decrease in the 5-HT2A receptor transcript level was noted in the hippocampus and ventral tegmental area. Out of five 5-HT2C receptor mRNA editing sites, deep sequencing data showed a reduction in editing at the E site and a trend toward reduction at the C site in the hippocampus. In the ventral tegmental area, a reduction for the frequency of CD 5-HT2C receptor transcript was seen. These results show that the reduction in the 5-HT2A receptor transcript level may be an auto-regulatory response to the increased receptor density in the hippocampus and ventral tegmental area during nicotine withdrawal, while decreased 5-HT2C receptor mRNA editing may explain the reduction in receptor labeling in the hippocampus. Serotonin (5-HT)2A/2C receptor ligands alleviate depression-like state in nicotine-withdrawn rats. Here, we show that the reduction in 5-HT2A receptor transcript level may be an auto-regulatory response to the increased receptor number in the hippocampus and ventral tegmental area during nicotine withdrawal, while attenuated 5-HT2C receptor mRNA editing in the hippocampus might explain reduced inverse agonist binding to 5-HT2C receptor and suggest a shift toward a population of more active receptors. 5-HT, serotonin; 5-HT2A R, 5-HT2A receptor; 5-HT2C R, 5-HT2C receptor.

L-DOPA is the gold-standard treatment for Parkinson's disease (PD), but induces troublesome dyskinesia after prolonged treatment. This is associated with the 'false neurotransmitter' conversion of L-DOPA to dopamine by serotonin neurons projecting from the raphe to the dorsal striatum. Reducing their activity by targeting pre-synaptic 5-HT1A receptors should thus be an attractive therapeutic strategy, but previous 5-HT1A agonists have yielded disappointing results. Here, we describe the activity of a novel, highly selective and potent 5-HT1A agonist, NLX-112 (also known as befiradol or F13640) in rat models relevant to PD and its associated affective disorders. NLX-112 (0.16 mg/kg, i.p.) potently and completely reversed haloperidol-induced catalepsy in intact rats and abolished L-DOPA-induced Abnormal Involuntary Movements (AIMs) in hemiparkinsonian rats, an effect that was reversed by the selective 5-HT1A antagonist, WAY100635. In microdialysis experiments, NLX-112 profoundly decreased striatal 5-HT extracellular levels, indicative of inhibition of serotonergic function. NLX-112 also blunted the L-DOPA-induced surge in dopamine levels on the lesioned side of the brain, an action that likely underlies its anti-dyskinetic effects. NLX-112 (0.16 mg/kg, i.p.) robustly induced rotations in hemiparkinsonian rats, suggesting that it has a motor facilitatory effect. Rotations were abolished by WAY100635 and were ipsilateral to the lesioned side, suggesting a predominant stimulation of the dopamine system on the non-lesioned side of the brain. NLX-112 also efficaciously reduced immobility time in the forced swim test (75% reduction at 0.16 mg/kg, i.p.) and eliminated stress-induced ultrasonic vocalization at 0.08 mg/kg, i.p., effects consistent with potential antidepressant- and anxiolytic-like properties. In other tests, NLX-112 (0.01-0.16 mg/kg, i.p.) did not impair the ability of L-DOPA to rescue forepaw akinesia in the cylinder test but decreased rotarod performance, probably due to induction of flat body posture and forepaw treading which are typical of 5-HT1A agonists upon acute administration. However, upon repeated administration of NLX-112 (0.63 mg/kg, i.p., twice a day), flat body posture and forepaw treading subsided within 4 days of treatment. Taken together, these observations suggest that NLX-112 could exhibit a novel therapeutic profile, combining robust anti-dyskinetic properties without impairing the therapeutic properties of L-DOPA, and with additional beneficial effects on non-motor (affective) symptoms.

This study examined the effect of the acute and chronic systemic administration of (±)-8-Hydroxy-2-(Di-n-propylamino)Tetralin(8-OH-DPAT) on the number and firing pattern of spontaneously active dopamine (DA) neurons in the ventral tegmental area (VTA or A10) and substantia nigra pars compacta (SNC or A9) in anesthetized male rats. These parameters were measured using extracellular in vivo electrophysiology. A single s.c. injection of 0.01, 0.1, or 1 mg/kg of 8-OH-DPAT did not significantly alter the number of spontaneously active SNC DA neurons compared to vehicle-treated animals (controls). The acute administration of 0.01 or 0.1 mg/kg of 8-OH-DPAT did not significantly alter, whereas the 1 mg/kg dose significantly decreased the number of spontaneously active VTA DA neurons compared to controls. The acute administration of 8-OH-DPAT significantly increased the percentage of VTA DA neurons firing in a bursting pattern. In contrast, there was a significant decrease in the percentage of SNC DA neurons firing in a bursting pattern following the acute administration of 8-OH-DPAT. The number of spontaneously active SNC DA neurons was not significantly altered by the chronic s.c. administration of 8-OH-DPAT (0.01, 0.1, or 1 mg/kg s.c.) as compared to controls. However, the chronic s.c. administration of all doses of 8-OH-DPAT significantly decreased the number of spontaneously active VTA DA neurons compared to controls. The i.v. administration of (+)-apomorphine (50 μg/kg) did not reverse the 8-OH-DPAT-induced decrease in the number of spontaneously active VTA DA neurons, suggesting that this effect is unlikely due to depolarization blockade. The percentage of VTA DA neurons exhibiting burst firing was significantly increased by 0.01 and 0.1 mg/kg, but significantly decreased by 1 mg/kg of 8-OH-DPAT. Overall, the systemic administration of 8-OH-DPAT preferentially affects the activity of spontaneously active A10 DA neurons in rats. Synapse 59:359–367, 2006. © 2006 Wiley-Liss, Inc.

The role of the 5-HT(2A) receptor in modulating amphetamine-induced inhibition of dopamine neuronal firing in A9 and A10 was investigated in rat midbrain slices. The antipsychotic drugs olanzapine and clozapine more potently reversed the amphetamine-induced inhibition in A10 neurons compared to A9 neurons. Risperidone (0.03 and 0.1 microM) reversed amphetamine-induced inhibition of firing activity similarly in A9 and A10. The dopamine D2 receptor antagonist (-)sulpiride (0.05 and 1 microM) reversed the amphetamine (10 microM)-induced inhibition of firing activity in A9 and A10 neurons. The selective 5-HT(2A) receptor antagonist MDL 100907 (0.05 microM), strongly enhanced the reversal of amphetamine-induced inhibition by (-)sulpiride in A10, but its effectiveness was much smaller in A9 dopamine neurons. We conclude that 5-HT(2A) receptor antagonism enhanced reversal of amphetamine-induced inhibition by dopamine D2 antagonism in A10, suggesting that dopamine D(2) receptor antagonism combined with 5-HT(2A) receptor antagonism may play a role in antipsychotic drug atypicality.

Series of thiazoles, triazoles, and imidazoles were designed as bioisosteres, based on the 1,5-diarylpyrazole motif that is present in the potent CB(1) receptor antagonist rimonabant (SR141716A, 1). A number of target compounds was synthesized and evaluated in cannabinoid (hCB(1) and hCB(2)) receptor assays. The thiazoles, triazoles, and imidazoles elicited in vitro( )()CB(1) antagonistic activities and in general exhibited considerable CB(1) vs CB(2) receptor subtype selectivities, thereby demonstrating to be cannabinoid bioisosteres of the original diarylpyrazole class. Some key representatives in the imidazole series showed potent pharmacological in vivo activities after oral administration in both a CB agonist-induced hypotension model and a CB agonist-induced hypothermia model. Molecular modeling studies showed a close three-dimensional structural overlap between the key compound 62 and rimonabant. A structure-activity relationship (SAR) study revealed a close correlation between the biological results in the imidazole and pyrazole series.

5-HT (20 microM) enhanced dopamine (DA) D2-like receptor mediated reduction of the firing rate of DA neurons in the substantia nigra pars compacta (A9) and ventral tegmental area (A10) in a rat midbrain slice preparation. Quinpirole (30 nM) induced a mean reduction of the firing rate in A9 and A10 DA neurons to 64 +/- 4%, respectively, 71 +/- 5% of the baseline value. Bath application of 5-HT in the presence of quinpirole further reduced the firing rate to 37 +/- 7% in A9 and 33 +/- 13% in A10. The 5-HT2 receptor agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI, 500 nM) enhanced quinpirole-induced reduction of firing rate of A10 DA neurons, but not of A9 DA neurons, suggesting that different 5-HT receptor subtypes are involved in modulation of dopamine D2-like receptor mediated inhibition in the two regions. The selective 5-HT2A receptor antagonist MDL100907 and the selective 5-HT2C receptor antagonist SB242084 (50 and 500 nM) both abolished the enhancement of quinpirole-induced reduction by either 5-HT or DOI, suggesting the involvement of direct and indirect (possibly via interneurons) modulation pathways in A10. The involvement of 5-HT and specific 5-HT2 receptors in augmentation of auto-inhibition in A10 could have important implications for our understanding of the mechanism of atypical antipsychotic drug action.

The antipsychotic drug quetiapine increases the firing rate of dopamine neurons in the substantia nigra and the ventral tegmental area of the rat. In the present study we used an in vitro midbrain slice preparation and found that 3 microM quetiapine increases the firing rate of dopamine neuron in both structures by approximately 30%. The magnitude of the increase was not correlated with the basal firing rate of the dopamine neurons. In addition, quetiapine was not able to antagonize the inhibition of the firing evoked by the dopamine D2 receptor agonist quinpirole. Only with a very high concentration (30 microM), quetiapine was able to counteract the amphetamine-induced inhibition of the firing of the ventral tegmental area neurons; this effect was less pronounced in substantia nigra neurons. These findings indicate that the increase in firing rate induced by quetiapine cannot solely be mediated through an interaction with the dopamine D2-like autoreceptor present on the dopamine neurons.

A series of novel 3,4-diarylpyrazolines was synthesized and evaluated in cannabinoid (hCB(1) and hCB(2)) receptor assays. The 3,4-diarylpyrazolines elicited potent in vitro CB(1) antagonistic activities and in general exhibited high CB(1) vs CB(2) receptor subtype selectivities. Some key representatives showed potent pharmacological in vivo activities after oral dosing in both a CB agonist-induced blood pressure model and a CB agonist-induced hypothermia model. Chiral separation of racemic 67, followed by crystallization and an X-ray diffraction study, elucidated the absolute configuration of the eutomer 80 (SLV319) at its C(4) position as 4S. Bioanalytical studies revealed a high CNS-plasma ratio for the development candidate 80. Molecular modeling studies showed a relatively close three-dimensional structural overlap between 80 and the known CB(1) receptor antagonist rimonabant (SR141716A). Further analysis of the X-ray diffraction data of 80 revealed the presence of an intramolecular hydrogen bond that was confirmed by computational methods. Computational models and X-ray diffraction data indicated a different intramolecular hydrogen bonding pattern in the in vivo inactive compound 6. In addition, X-ray diffraction studies of 6 revealed a tighter intermolecular packing than 80, which also may contribute to its poorer absorption in vivo. Replacement of the amidine -NH(2) moiety with a -NHCH(3) group proved to be the key change for gaining oral biovailability in this series of compounds leading to the identification of 80.

Background We have previously demonstrated that serotonin (5-HT) 2A and 5-HT 2C receptor ligands modulate the sensitizing effects of nicotine. In the present study we used male rats to verify the hypothesis that the binding pattern of 5-HT 2A and 5-HT 2C receptors in the brain is altered by chronic nicotine treatment in different environments. Methods Rats were given repeatedly vehicle or nicotine in different sensitizing regimens (home or experimental cages). On day 10, animals were challenged with nicotine (expression of nicotine sensitization) or vehicle in either home or experimental cages, and were sacrificed immediately after the experiment. Results Repeated treatment with nicotine in home cages evoked significant increases in [ 3 H]ketanserin binding to 5-HT 2A receptors in the prefrontal cortex, striatal subregions and ventral tegmental area as well as reductions in [ 3 H]mesulergine binding to 5-HT 2C receptors in subregions of the prefrontal cortex. In contrast, nicotine paired with environmental context produced robust increases in 5-HT 2A receptor labeling in the infralimbic cortex and decreased [ 3 H]ketanserin binding in striatal subregions and ventral tegmental area; 5-HT 2C receptor labeling in the prefrontal cortex fell. Conclusions The present data indicate that chronic nicotine administration in home cages induces bi-directional neuroplastic changes within 5-HT 2A and 5-HT 2C receptors in the prefrontal cortex. Pairing the nicotine with environmental context potentiates the neuroplastic response in the latter region and evokes opposite changes in 5-HT 2A receptor binding in striatal and tegmental regions compared with nicotine administered in the absence of the context, indicating a modulatory role of environmental context in the expression of nicotine-induced sensitization.

The treatment of dyskinesia in Parkinson׳s disease remains poor but H3 receptor agonists have been suggested as a novel pharmacological approach. We examined the effects of the H3 agonist, immepip, in 6-OHDA-lesioned rats exhibiting AIMs (abnormal involuntary movements), a rat analogue of dyskinesia, in response to l -dopa compared to the known anti-dyskinetic agents amantadine, MK-801 and 8-OHDPAT. We then attempted to extend these studies in to dyskinetic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treated common marmosets. Amantadine, MK-801 and 8-OHDPAT all dose-dependently reduced l -dopa-induced axial, lingual and oral (ALO) AIMs in 6-OHDA-lesioned animals accompanied by a reduction in contralateral rotation with higher doses of amantadine and MK-801. By contrast, immepip had no effect on AIMs expression or contralateral rotation. In the MPTP-treated common marmoset exhibiting dyskinesia to l -dopa, immepip alone induced retching and in combination with l -dopa administered subcutaneously or orally induced the rapid onset of retching and vomiting which was not controlled by pretreatment with domperidone. Administration of the unrelated H3 agonist, imetit had the same effect. Despite causing negative side-effects, it appears that both agonists reduced the antiparkinsonian response to l -dopa resulting in reduced dyskinesia. H3 agonists appear unlikely candidates for the treatment of dyskinesia in PD based on lack of evidence of efficacy and potential adverse effects.

The present study focused on the evaluation of behavioral sensitization and cross-sensitization induced by nicotine and varenicline in rats. Furthermore, it examined the influence of varenicline, a partial alpha4beta2 nicotinic receptor agonist, on nicotine-induced sensitization. To assess the development of behavioral sensitization, rats were chronically treated with vehicle, varenicline (0.03-3.0 mg/kg), nicotine (0.4 mg/kg) or combinations for 5 days and locomotor activity was measured. The expression of sensitization was assessed following a withdrawal period (17-26 days). The present results confirmed previous data showing the development and expression of nicotine-induced sensitization of locomotor activity in the rat. Varenicline did not induce sensitization on its own. When varenicline and nicotine were repeatedly administered sequentially, varenicline blocked the development and expression of nicotine-induced sensitization. Acute varenicline blocked the expression of nicotine-induced sensitization in a dose-dependent manner. Acute varenicline did not significantly increase locomotor activity, nor did it attenuate nicotine-induced sensitization. However, varenicline did cross-sensitize to the effects of nicotine, and vice versa. The present study showed that varenicline produced a dose-dependent bidirectional cross-sensitization with nicotine. Taken together, these findings provide pre-clinical evidence that varenicline is able to attenuate the effects of nicotine, yet simultaneously 'substitutes' for the effects of nicotine in the rat. Longitudinal studies would be needed to see if similar effects are seen in the clinical setting, and whether such effects contribute to the actions of varenicline as a smoking cessation aid.

Serotonin (5-HT) appears to play a modulatory role in the behavioral effects of cocaine, although the impact of 5-HT2C receptors in this control has not been fully established. The aim of the present study was to establish whether acute pretreatment with the selective 5-HT2C/2B antagonist SB 206553 (1, 2, and 4 mg/kg i.p.) altered hyperactivity induced by cocaine (15 mg/kg, i.p.) using an open field activity system which recorded central, peripheral, and rearing activity. Pretreatment with 1 and 2 mg/kg of SB 206553 attenuated cocaine-induced central and peripheral activity, respectively; rearing was also attenuated by the latter dose. However, the 4-mg/kg dose of SB 206553 significantly enhanced the effects of cocaine on peripheral activity. Based upon the present observations and an interpretation of previous research to implicate 5-HT2C receptor control of the dopamine (DA) mesoaccumbens pathways in behavior, a thorough and systematic analysis of the role of 5-HT2C (and 5-HT2B) receptors in psychostimulant-induced behaviors is warranted.

Behavioral sensitization is a phenomenon which can develop following repeated intermittent administration of a wide range of psychostimulants. The mechanism underlying this phenomenon is putatively involved in many neuropsychiatric disorders (incl. drug addiction) and therefore, understanding of its mechanism is of great importance. Although these different drugs have diverse molecular targets located across the brain, they share the ability to increase the release of dopamine. The aim of the present study is to investigate the effect of the dopamine D1 ligands on nicotine induced behavioral sensitization and their molecular consequences in the striatum. Wistar rats were chronically intermittent (5 days) treated with vehicle or nicotine (0.4 mg/kg; s.c.) and locomotor activity was measured. After the establishment of sensitization, rats were withdrawn for a period of 5 days followed by administration of a nicotine challenge, with or without a pre-challenge of SCH-23390 (0.03 mg/kg; i.p., a dopamine D1 antagonist) given 30 min prior to the nicotine. Either 45 min or 24 h post-challenge, the dorsal striatum was isolated and used to assess the effect of forskolin, dopamine, and dopamine D1 ligands on intracellular cAMP accumulation ex vivo. The cAMP levels were measured using LC-MS/MS. Acute nicotine administration significantly increased locomotor activity and subsequent chronic nicotine administration induced the development of locomotor sensitization. Moreover, following the 5 days withdrawal period, a nicotine challenge produced a robust sensitized response (i.e. expression of sensitization) and was antagonized by SCH-23390. Nicotine induced sensitization had no effect on forskolin stimulated cAMP accumulation however, it increased the efficacy of dopamine for the dopamine D1 receptor, and decreased the potency of D1 agonists. These effects were antagonized by in vivo pre-challenge with SCH-23390. Moreover, a time dependent effect was observed between tissue taken at 45 min and 24 h post-challenge. In conclusion, the present findings provide a connection between behavioral sensitization and intracellular cAMP accumulation through the dopamine D1 receptor. Therefore D1 signaling in the dorsal striatum may play an important role in the underlying mechanism of the expression of nicotine induced behavioral sensitization. Abbott Healthcare Products BV

Recent studies suggest a potential role for 5-hydroxytryptamine(6) (5-HT(6)) receptors in the regulation of addictive behavior. In the present study, our aim was to investigate whether the novel highly selective 5-HT(6) receptor antagonist compound (CMP) 42 affected nicotine and ethanol seeking behavior in Wistar rats. We have also studied whether CMP 42 had beneficial effects in a model of impulse control, as measured in the 5-choice serial reaction time task (5-CSRTT). Rats were trained to nose poke to receive intravenous infusions of nicotine or an ethanol drop. CMP 42 (3-30 mg/kg intraperitoneally, i.p.) was administered to investigate the effects on nicotine self-administration. Rats were also tested for cue-induced reinstatement of nicotine and ethanol seeking. In addition, the effects of CMP 42 were studied on the number of anticipatory responses in the 5-CSRTT. CMP 42 was effective in reducing nicotine self-administration and reinstatement of nicotine seeking at a dose of 30 mg/kg (i.p.). CMP 42 was also effective in reducing reinstatement of ethanol seeking (30 mg/kg i.p.). In contrast, CMP 42 did not affect anticipatory responding at doses tested, indicating no effects on impulse control. These results add to a body of evidence implicating the 5-HT(6) receptor as a viable target for the control of drug abuse. Specifically, we demonstrated for the first time effects on nicotine self-administration and on nicotine and ethanol reinstatement. Further, these effects are probably not mediated by effects on impulse control.

The short duration of effect of levodopa is linked to pulsatile stimulation of striatal dopamine receptors and dyskinesia induction. However, the recent introduction of intraduodenal (i.d.) infusions and novel oral controlled release formulations of l-dopa may prevent dyskinesia induction and reduce the severity of established involuntary movements. We have compared the effects of twice-daily intraperitoneal (i.p.) administration and daily i.d. infusion of l-dopa on the induction and expression of abnormal involuntary movements in 6-hydroxydopamine (6-OHDA)-lesioned rats. Animals were treated with either twice-daily i.p. administration of l-dopa/carbidopa (7.85/12.5 mg/kg) or an 8-hour i.d. infusion of l-dopa/carbidopa (20/5 mg/mL; infusion rate: 0.04 mL/h) for 14 days, after which treatments were switched between groups and continued for a further 14 days. Pulsatile i.p. administration of l-dopa induced moderate to severe abnormal involuntary movements, which gradually increased in severity over the 14 days, but i.d. infusion of l-dopa induced abnormal involuntary movements of a similar severity. Switching from continuous i.d. to pulsatile i.p. administration of l-dopa continued to provoke severe abnormal involuntary movements expression. Switching from pulsatile i.p. to continuous i.d. l-dopa administration did not alter the peak abnormal involuntary movement severity but tended to reduce their duration. Treatment with less pulsatile l-dopa administration using i.d. infusion does not reduce the risk of the appearance of dyskinesia. By contrast, the duration of established dyskinesia can be reduced by more continuous l-dopa delivery in agreement with clinical experience.

The nonergot ligand pardoprunox (SLV308) is a dopamine (DA) D₂/D₃ and serotonin (5-HT)(1A) receptor agonist and a new candidate for the treatment of Parkinson's disease. We used in vivo electrophysiological paradigm in the rat to assess the effects of pardoprunox on DA neuronal activity in ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) as well as on 5-HT neuronal activity in dorsal raphe nucleus (DRN). In the VTA, pardoprunox (2-20 μg kg⁻¹, i.v.) decreased partially the firing activity of DA neurons. Interestingly, the bursting activity of VTA DA neurons was completely suppressed. This compound both reversed and prevented the inhibition of firing rate induced by the full D₂-like receptor agonist apomorphine, confirming its partial D₂-like receptor agonistic property. Surprisingly in the SNc, pardoprunox (10 μg kg⁻¹, i.v.) either partially or fully suppressed the firing activity in two separate populations of DA neurons. Finally, in the DRN, pardoprunox (5-40 μg kg⁻¹, i.v.) completely suppressed the firing activity of 5-HT neurons. Moreover, the selective 5-HT(1A) receptor antagonist WAY-100,635 prevented and reversed the effects of pardoprunox. The present study shows that pardoprunox acts in the VTA as a potent partial D₂-like receptor agonist reducing preferentially the burst activity linked to the phasic activity of DA neurons. Unexpectedly in the SNc, pardoprunox behaves either as apartial or a full D₂-like receptor agonist. Finally in the DRN, pardoprunox is a potent full 5-HT(1A) receptor agonist. Hence, this in vivo study suggests that pardoprunox represents a promising approach for the treatment of Parkinson's disease.

The mechanism by which the psychostimulant methamphetamine (METH) increases locomotor activity may be attributable to indirect activation of serotonin (5-HT) and dopamine (DA) receptors. In the present study, the ability of the serotonin reuptake inhibitor fluvoxamine, 5-HT1A, 5-HT1B, 5-HT2A and 5-HT2C receptor antagonists WAY100635, GR127935, M100907 and SB242084, and the 5-HT2C receptor agonists WAY163909 and Ro 60-0175 or the 5-HT synthesis inhibitor para-chlorophenylalanine (pCPA) to alter METH-induced hyperactivity was analysed. Further, for comparative purposes, the involvement of the DA D1 and D2 receptor antagonists SCH23390 and haloperidol, D2 partial agonists terguride, (−)3PPP and aripiprazole and finally clozapine were assessed. Doses of pCPA that attenuated 5-HT levels reduced METH activity. The 5-HT1B antagonist GR127935 had no effect on METH-induced locomotor activity but blocked that induced by MDMA. The 5-HT1A antagonist WAY100635 reduced activity but this did not reach significance. In contrast, M100907 (minimal effective dose; MED = 0.125 mg/kg), WAY163909 (MED = 3 mg/kg), Ro 60-0175 (MED = 3 mg/kg), haloperidol (MED = 0.1 mg/kg), clozapine (MED = 5 mg/kg), aripiprazole (MED = 1 mg/kg), (−)3PPP (MED = 3 mg/kg), terguride (MED = 0.2 mg/kg) and SCH23390 (MED = 0.001325 mg/kg) attenuated METH-induced locomotor activity. Administration of 20 mg/kg fluvoxamine attenuated, while SB242084 (MED = 0.25 mg/kg) potentiated METH-induced activity. These results contribute significantly to the understanding of the mechanism of action of this psychostimulant and suggest for the first time, that METH-induced locomotor stimulation is modulated by 5-HT2A and 5-HT2C receptors, but demonstrate that 5-HT1B receptors are not directly involved. The involvement of the dopaminergic system was also demonstrated.

The endogenous brain serotonin (5-HT) system is believed to have an important modulatory influence in mediating drug reward and seeking mechanisms. Data from preclinical behavioral studies have provided emerging evidence that 5-HT(6) receptors, among other 5-HT receptors, may play a significant role in the mechanisms of action of psychostimulant addicted drugs. The aim of the present study was to investigate whether the selective pharmacological blockade or activation of 5-HT(6) receptors altered the maintenance of cocaine self-administration, reinstatement of cocaine-seeking behavior following an extinction of cocaine self-administration or cocaine-evoked conditioned place preference in rats. We also evaluated the effects of 5-chloro-N-(4-methoxy-3-piperazin-1-ylphenyl)-3-methyl)-2-benzothiophene-sulfonamide (SB 271046, a 5-HT(6) receptor antagonist) or N-1-(6-chloroimidazo-[2,1-b]-[1,3]thiazole-5-sulfonyl)tryptamine (WAY 181187, a potent 5-HT(6) receptor agonist) on locomotor activity in rats. Our results indicate that SB 271046 (1-10 mg/kg) altered cocaine-maintained self-administration as well as cocaine-evoked reinstatement of cocaine seeking and expression of cocaine place preference in rats.We also demonstrate that pharmacological stimulation of 5-HT(6) receptors by WAY 181187 (3-30 mg/kg) attenuated the expression of cocaine conditioned place preference but not cocaine self-administration and reinstatement of cocaine seeking. WAY 181187 at the highest dose used (30 mg/kg) reduced basal locomotor activity. Despite current results, the precise function and therapeutic relevance of 5-HT(6) receptors need further clarification.

We verified the hypothesis that serotonin (5-HT)2 receptors control the locomotor effects of nicotine (0.4 mg kg−1) in rats by using the 5-HT2A receptor antagonist M100907, the preferential 5-HT2A receptor agonist DOI, the 5-HT2C receptor antagonist SB 242084, and the 5-HT2C receptor agonists Ro 60-0175 and WAY 163909. Repeated pairings of a test environment with nicotine for 5 days, on Day 10 significantly augmented the locomotor activity following nicotine administration. Of the investigated 5-HT2 receptor ligands, M100907 (2 mg kg−1) or DOI (1 mg kg−1) administered during the first 5 days in combination with nicotine attenuated or enhanced, respectively, the development of nicotine sensitization. Given acutely on Day 10, M100907 (2 mg kg−1), Ro 60-0175 (1 mg kg−1), and WAY 163909 (1.5 mg kg−1) decreased the expression of nicotine sensitization. In another set of experiments, where the nicotine challenge test was performed on Day 15 in animals treated repeatedly (Days: 1–5, 10) with nicotine, none of 5-HT2 receptor ligands administered during the second withdrawal period (Days: 11–14) to nicotine-treated rats altered the sensitizing effect of nicotine given on Day 15. Our data indicate that 5-HT2A receptors (but not 5-HT2C receptors) play a permissive role in the sensitizing effects of nicotine, while stimulation of 5-HT2A receptors enhances the development of nicotine sensitization and activation of 5-HT2C receptors is essential for the expression of nicotine sensitization. Repeated treatment with the 5-HT2 receptor ligands within the second nicotine withdrawal does not inhibit previously established sensitization. Synapse 64:511–519, 2010. © 2010 Wiley-Liss, Inc.

The preclinical characterization of WS-50030 [7-{4-[3-(1H-inden-3-yl)propyl]piperazin-1-yl}-1,3-benzoxazol-2(3H)-one] is described. In vitro binding and functional studies revealed highest affinity to the D(2) receptor (D(2L) K(i), 4.0 nM) and serotonin transporter (K(i), 7.1 nM), potent D(2) partial agonist activity (EC(50), 0.38 nM; E(max), 30%), and complete block of the serotonin transporter (IC(50), 56.4 nM). Consistent with this in vitro profile, WS-50030 (10 mg/kg/day, 21 days) significantly increased extracellular 5-HT in the rat medial prefrontal cortex, short-term WS-50030 treatment blocked apomorphine-induced climbing (ID(50), 0.51 mg/kg) in a dose range that produced minimal catalepsy in mice and induced low levels of contralateral rotation in rats with unilateral substantia nigra 6-hydroxydopamine lesions (10 mg/kg i.p.), a behavioral profile similar to that of the D(2) partial agonist aripiprazole. In a rat model predictive of antipsychotic-like activity, WS-50030 and aripiprazole reduced conditioned avoidance responding by 42 and 55% at 10 mg/kg, respectively. Despite aripiprazole's reported lack of effect on serotonin transporters, long-term treatment with aripiprazole or WS-50030 reversed olfactory bulbectomy-induced hyperactivity at doses that did not reduce activity in sham-operated rats, indicating antidepressant-like activity for both compounds. Despite possessing serotonin reuptake inhibitory activity in addition to D(2) receptor partial agonism, WS-50030 displays activity in preclinical models predictive of antipsychotic- and antidepressant efficacy similar to aripiprazole, suggesting potential efficacy of WS-50030 versus positive and negative symptoms of schizophrenia, comorbid mood symptoms, bipolar disorder, major depressive disorder, and treatment-resistant depression. Furthermore, WS-50030 provides a tool to further explore how combining these mechanisms might differentiate from other antipsychotics or antidepressants.

A pronounced withdrawal syndrome including depressed mood prevents cigarette smoking cessation. We tested if blockade or activation of serotonin (5-HT)(2) receptors affected the time of immobility (as an indirect measure of depression-like behavior) in naive animals and in those withdrawn from chronic nicotine in the forced swim test (FST). The antidepressant imipramine was used as a control. In the FST, the selective 5-HT(2A) receptor antagonist M100,907 (1-2 mg/kg, but not 0.5 mg/kg), the selective 5-HT(2C) receptor antagonist SB 242,084 (0.3-1 mg/kg, but not 0.1 mg/kg), the 5-HT(2C) receptor agonists Ro 60-0175 (10 mg/kg, but not 3 mg/kg) and WAY 163,909 (1.5-10 mg/kg, but not 0.75 mg/kg) as well as imipramine (30 mg/kg, but not 15 mg/kg) decreased the immobility time while the non-selective 5-HT(2) receptor agonist DOI (0.1-1 mg/kg) was inactive in naive rats. We found an increase in immobility time in rats that were withdrawn from nicotine exposure after 5 days of chronic nicotine treatment. This effect increased from day 1 until day 10 following withdrawal of nicotine, with maximal withdrawal effects on day 3. M100,907 (1 mg/kg), SB 242,084 (0.3 mg/kg), Ro 60-0175 (3 mg/kg), WAY 163,909 (0.75-1.5 mg/kg) and imipramine (15-30 mg/kg) shortened the immobility time in rats that had been removed from nicotine exposure for 3 days. Locomotor activity studies indicated that the effects of SB 242,084 might have been non-specific, as we noticed enhanced basal locomotion in naive rats. This data set demonstrates that 5-HT(2A) receptor antagonist and 5-HT(2C) receptor agonists exhibited effects similar to antidepressant drugs and abolished the depression-like effects in nicotine-withdrawn rats. These drugs should be considered as adjuncts to smoking cessation therapy, to ameliorate abstinence-induced depressive symptoms.

Partial D(2/3) dopamine (DA) receptor agonists provide a novel approach to the treatment of the motor symptoms of Parkinson's disease (PD) that may avoid common dopaminergic side-effects, including dyskinesia and psychosis. The present study focussed on the in vivo pharmacological and therapeutic characterisation of the novel D(2/3) receptor partial agonist and full 5-HT(1A) receptor agonist pardoprunox (SLV308; 7-[4-methyl-1-piperazinyl]-2(3H)-benzoxazolone monochloride). Pardoprunox induced contralateral turning behaviour in rats with unilateral 6-hydroxydopamine-induced lesions of the substantia nigra pars compacta (SNpc) (MED=0.03mg/kg; po). In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets, pardoprunox dose-dependently increased locomotor activity (MED=0.03mg/kg; po) and decreased motor disability (MED=0.03mg/kg; po). The effects of pardoprunox were reversed by the D(2) antagonist sulpiride. In contrast pardoprunox attenuated novelty-induced locomotor activity (MED=0.01mg/kg; po), (+)-amphetamine-induced hyperlocomotion (MED=0.3mg/kg; po) and apomorphine-induced climbing (MED=0.6mg/kg; po) in rodents. Pardoprunox also induced 5-HT(1A) receptor-mediated behaviours, including flat body posture and lower lip retraction (MED=0.3mg/kg; po) and these were reversed by the 5-HT(1A) receptor antagonist WAY100635. Collectively, these findings demonstrate that pardoprunox possesses dopamine D2/3 partial agonist effects, 5-HT1A agonist effects and reduces parkinsonism in animal models. functional DA D(2) receptor partial agonist activity and is effective in experimental models predictive of efficacy in PD. The presence of functional 5-HT(1A) agonist activity might confer anti-dyskinetic activity and have effects that control neuropsychiatric components of PD.

A 5-fluoro-tetrahydrocarbazole serotonin reuptake inhibitor (SRI) building block was combined with a variety of linkers and dopamine D2 receptor ligands in an attempt to identify potent D2 partial agonist/SRI molecules for treatment of schizophrenia. This approach has the potential to treat a broader range of symptoms compared to existing therapies. Selected compounds in this series demonstrate high affinity for both targets and D2 partial agonism in cell-based and in vivo assays.

Background 5HT1A agonists have previously been shown to promote recovery in animal models of stroke using ex vivo outcome measures which have raised the hopes for a potential clinical implementation. The purpose of this study was to evaluate the potential neuroprotective properties of a novel 5HT1A agonist DU123015 in 2 different models of transient focal ischaemic stroke of varying severities using both in vivo neuroimaging and behavioural techniques as primary outcome measures. For these studies, the NMDA receptor antagonist MK-801 was also utilized as a positive control to further assess the effectiveness of the stroke models and techniques used. Results In contrast to MK-801, no significant therapeutic effect of DU123015 on lesion volume in either the distal MCAo or intraluminal thread model of stroke was found. MK-801 significantly reduced lesion volume in both models; the mild distal MCAo condition (60 min ischaemia) and the intraluminal thread model, although it had no significant impact upon the lesion size in the severe distal MCAo condition (120 min ischaemia). These therapeutic effects on lesion size were mirrored on a behavioural test for sensory neglect and neurological deficit score in the intraluminal thread model. Conclusion This study highlights the need for a thorough experimental design to test novel neuroprotective compounds in experimental stroke investigations incorporating: a positive reference compound, different models of focal ischaemia, varying the duration of ischaemia, and objective in vivo assessments within a single study. This procedure will help us to minimise the translation of less efficacious compounds.

Male Wistar rats were used to verify the hypothesis that serotonin (5-HT)2A or 5-HT2C receptors may control the locomotor effects evoked by nicotine (0.4mg/kg). The 5-HT2A receptor antagonist (M100,907), the 5-HT2A receptor agonist (DOI), the 5-HT2C receptor antagonist (SB 242,084), and the 5-HT2C receptor agonists (Ro 60-0175 and WAY 163,909) were used. M100,907 (0.5–2mg/kg) did not alter, while DOI (1 mg/kg) enhanced the nicotine-induced hyperlocomotion. The effect of DOI was antagonized by M100,907 (1 mg/kg). SB 242,084 (0.25–1 mg/kg) augmented, while Ro 60-0175 (1 and 3 mg/kg) and WAY 163,909 (1.5 mg/kg) decreased the overall effect of acute nicotine; effects of Ro 60-0175 and WAY 163,909 were attenuated by SB 242,084 (0.125 mg/kg). In another set of experiments, M100,907 (2 mg/kg) on Day 10 attenuated, while DOI (0.1–1 mg/kg) enhanced the nicotine-evoked conditioned hyperlocomotion in rats repeatedly (Days 1–5) treated with nicotine in experimental chambers. SB 242,084 (0.125 or 1 mg/kg) did not change, while Ro 60-0175 (1 mg/kg) or WAY 163,909 (1.5 mg/kg) decreased the expression of nicotine-induced conditioned hyperactivity. Only DOI (0.3 and 1 mg/kg) and SB 242,084 (1 mg/kg) enhanced the basal locomotion. The present data indicate that 5-HT2A receptors are significant for the expression of nicotine-evoked conditioned hyperactivity. Conversely, 5-HT2C receptors play a pivotal role in the acute effects of nicotine. Pharmacological stimulation of 5-HT2A receptors enhances the conditioned hyperlocomotion, while activation of 5-HT2C receptors decreases both the response to acute nicotine and conditioned hyperactivity. Synapse 63:653–661, 2009. © 2009 Wiley-Liss, Inc.

Present Parkinson's disease treatment strategies are far from ideal for a variety of reasons; it has therefore been suggested that partial dopamine receptor agonism might be a potential therapeutic approach with potentially fewer side effects. In the present study, we describe the in vitro characterization of the nonergot ligand SLV308 (7-[4-methyl-1-piperazinyl]-2(3H)-benzoxazolonemonohydrochloride). SLV308 binds to dopamine D(2), D(3), and D(4) receptors and 5-HT(1) (A) receptors and is a partial agonist at dopamine D(2) and D(3) receptors and a full agonist at serotonin 5-HT(1) (A) receptors. At cloned human dopamine D(2,L) receptors, SLV308 acted as a potent but partial D(2) receptor agonist (pEC(50) = 8.0 and pA(2) = 8.4) with an efficacy of 50% on forskolin stimulated cAMP accumulation. At human recombinant dopamine D(3) receptors, SLV308 acted as a partial agonist in the induction of [(35)S]GTPgammaS binding (intrinsic activity of 67%; pEC(50) = 9.2) and antagonized the dopamine induction of [(35)S]GTPgammaS binding (pA(2) = 9.0). SLV308 acted as a full 5-HT(1) (A) receptor agonist on forskolin induced cAMP accumulation at cloned human 5-HT(1) (A) receptors but with low potency (pEC(50) = 6.3). In rat striatal slices SLV308 concentration-dependently attenuated forskolin stimulated accumulation of cAMP, as expected for a dopamine D(2) and D(3) receptor agonist. SLV308 antagonized the inhibitory effect of quinpirole on K(+)-stimulated [(3)H]-dopamine release from rat striatal slices (pA(2) = 8.5). In the same paradigm, SLV308 had antagonist properties in the presence of quinpirole (pA(2) = 8.5), but the partial D(2) agonist terguride had much stronger antagonistic properties. In conclusion, SLV308 combines high potency partial agonism at dopamine D(2) and D(3) receptors with full efficacy low potency serotonin 5-HT(1) (A) receptor agonism and is worthy of profiling in in vivo models of Parkinson's disease.

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.

Male Wistar rats were trained to discriminate (−)-nicotine (0.4 mg/kg) from saline under a two-lever, fixed-ratio 10 schedule of water reinforcement. During test sessions the following drugs were coadministered with saline (substitution studies) or nicotine (0.025–0.4 mg/kg; combination studies): the α 4 β 2 nicotinic acetylcholine receptor subtype antagonist dihydro-β-erythroidine (DHβE), the non-selective nicotinic acetylcholine receptor subtype antagonist mecamylamine, the α 7 nicotinic acetylcholine receptor subtype antagonist methyllycaconitine (MLA), the α 4 β 2 nicotinic acetylcholine receptor subtype agonist 5-iodo-3-(2( S )-azetidinylmethoxy)pyridine (5-IA), the cannabinoid CB 1 receptor antagonist/partial agonist rimonabant, the cannabinoid CB 2 receptor antagonist N -[(1 S )-endo-1,3,3-trimethylbicyclo-[2.2.1]heptan-2-yl]5-(4-chloro-3-methyl-phenyl)-1-(4-methybenzyl)pyrazole-3-carboxamide (SR 144528), the cannabinoid CB 1/2 receptor agonists (−)- cis -3-[2-hydroxy-4-(1,1-dimethylheptyl)-phenyl]- trans -4-(3-hydroxy-propyl)cyclohexanol (CP 55,940) or R (+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]-pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-(1-naphthalenyl)-methanone mesylate (WIN 55,212-2), the endogenous cannabinoid agonist and non-competitive α 7 nicotinic acetylcholine receptor subtype antagonist anandamide, the anandamide uptake and fatty acid amide hydrolase inhibitor N -(4-hydroxyphenyl)-5 Z ,8 Z ,11 Z ,14 Z -eicosatetraenamide (AM-404), the fatty acid amide hydrolase inhibitor cyclohexylcarbamic acid 3′-carbamoyl-biphenyl-3-yl ester (URB 597), AM-404 + anandamide or URB 597 + anandamide. 5-IA (0.01 mg/kg) fully substituted for nicotine, while other drugs were inactive. In combination studies, DHβE and mecamylamine dose-dependently attenuated the discriminative stimulus effects of nicotine and the full substitution of 5-IA, while MLA, rimonabant, SR 144528, CP 55,940, WIN 55,212-2, and URB 597 did not alter the nicotine cue. Pretreatment with AM-404 + anandamide or URB 597 + anandamide weakly enhanced nicotine-lever responding. Our pharmacological analyses demonstrates that the expression of nicotine discrimination is under the control of nicotinic acetylcholine receptor subtypes composed of α 4 β 2 (but not of α 7 ) subunits. Furthermore, we excluded the involvement of either cannabinoid CB 1 and CB 2 receptors or increases in the endocannabinoid tone in the nicotine discrimination.

A series of novel bicyclic 1-heteroaryl-4-[omega-(1H-indol-3-yl)alkyl]piperazines was synthesized and evaluated on binding to dopamine D(2) receptors and serotonin reuptake sites. This class of compounds proved to be potent in vitro dopamine D(2) receptor antagonists and in addition were highly active as serotonin reuptake inhibitors. Some key representatives showed potent pharmacological in vivo activities after oral dosing in both the antagonism of apomorphine-induced climbing and the potentiation of 5-HTP-induced behavior in mice. On the basis of the preclinical data, 8-{4-[3-(5-fluoro-1H-indol-3-yl)propyl]piperazin-1-yl}-4H-benzo[1,4]oxazin-(R)-2-methyl-3-one (45c, SLV314) was selected for clinical development. In vitro and in vivo studies revealed that 45c has favorable pharmacokinetic properties and a high CNS-plasma ratio. Molecular modeling studies showed that the bifunctional activity of 45c can be explained by its ability to adopt two different conformations fitting either the dopamine D(2) receptor pharmacophore or the serotonin transporter pharmacophore.

Based on its proposed ability to block the effect of selective serotonin reuptake inhibitors (SSRIs) on the firing rate of serotonergic neurons, the 5-HT1A partial agonist/beta-adrenergic antagonist pindolol has been examined in clinical trials for its ability to enhance the efficacy of SSRIs. However, varying results have been obtained in these clinical trials. To explore this issue, we examined the effects of pindolol alone and in combination with fluoxetine on the electrophysiological activity of serotonergic neurons in the dorsal raphe nucleus of anesthetized rats. Administration of pindolol (1, 5, and 20 mg/kg, s.c.) alone decreased the number of spontaneously active serotonergic neurons. Administration of fluoxetine (10 mg/kg, i.p.) alone also decreased the number of spontaneously active serotonergic neurons. However, when administered following fluoxetine, pindolol significantly attenuated, but did not block completely, the inhibitory effects of fluoxetine on the number of spontaneously active serotonergic neurons. These results indicate that pindolol can attenuate the effects of fluoxetine on the firing of serotonergic neurons. These results may help explain the varying efficacy of pindolol in clinical trials with SSRIs.

The role of serotonin 5-HT2 receptors (5-HT2R) in the discriminative stimulus effects of fenfluramine was investigated. Male Sprague-Dawley rats were trained to discriminate (+/-)-fenfluramine (2 mg/kg ip) from saline using a 2-lever, water-reinforced paradigm. Drug-lever responding after fenfluramine was dose-dependent. The 5-HT(2C/1B)R agonist mCPP and the 5-HT(2C)R agonist MK 212 fully substituted, whereas the 5-HT(2A/2C)R agonist DOI partially substituted, for the training drug. The 5-HT(2B)R agonist BW 723C86 engendered saline-lever responding. The 5-HT(2C/2B)R antagonist SB 206553 completely antagonized the fenfluramine discrimination a well as the full substitutions of mCPP and MK 212 and the partial substitution of DOI. The selective 5-HT(2A)R antagonist M100907 partially suppressed the stimulus effects of fenfluramine, mCPP, and MK 212 and almost fully attenuated the partial substitution of DOI. RS 102221, a selective 5-HT(2C)R antagonist that does not cross the blood-brain barrier, did not alter the fenfluramine cue. Results demonstrate that the discriminative stimulus effects of fenfluramine are centrally mediated by 5-HT(2C)R and to some extent by 5-HT(2A)R.

Some studies have suggested that reductions in plasma cholesterol might be associated with suicidal behaviour. Serotonergic systems are thought to be involved in suicidal ideation and behaviour and links with altered 5-HT1A and 5-HT2A receptors have been proposed. We have therefore examined the effects of cholesterol reduction using gemfibrozil, upon 5-HT2A and 5-HT1A receptor-related behaviours in rats. Rats were treated chronically (57 days) with gemfibrozil (50 mg/kg p.o.) or gum acacia vehicle and challenged sequentially with the 5-HT1A agonist 8-hydroxy-d-n-aminopropyl tetralin, to elicit 5-HT1A syndrome behaviours, and the 5-HT2 receptor agonist 1-(2, 5-dimethoxy-4-iodophenyl)2-amino-propane to establish their head-shake frequency. Significant cholesterol reduction, within the clinical range, failed to induce any changes in either 5-HT1A or 5-HT2A mediated behaviours. These data suggest that cholesterol reduction fails to induce changes in 5-HT1A and 5-HT2A receptor tone suggesting that the reduction of plasma cholesterol, within the human clinical range, does not result in neuroplasticity of the 5-HT1A and 5-HT2A receptors in rats.