Short-term individual housing induced social deficits in female Mongolian gerbils: attenuation by chronic but not acute imipramine.

Mongolian gerbils are highly sensitive to manipulations of their social environments. Housing females individually for short periods (in the order of 7-21 days) has been shown to produce robust and reliable impairments of their subsequent social behaviour. These effects are typified by a marked reduction in the social investigation of an unfamiliar male in a neutral arena and/or a marked increases in levels of freezing whilst and only whilst they are being socially investigated (Immobile in contact). These responses demonstrate housing induced impaired motivation to socially interact. These effects have also been shown to be sensitive to treatment with chronic (but not acute) administration of the selective serotonin reuptake inhibitor (SSRI) fluoxetine. It was therefore of interest to know if similar effects would be produced by treatment with the tricyclic antidepressant Imipramine. This mixed NA/5-HT reuptake inhibitor first developed in the 1950's is a commonly used standard in animal models of depression and remains in clinical use today. Female gerbils were individually housed for 7 days or maintained in single-sex groups of 4 for the same period. All animals were then randomly allocated to be administered with either 0, 10 or 20 mg/kg imipramine. Acute administration did not reverse the social impairments produced by the individual housing but did produce non-specific stimulant effects on locomotion in both housing conditions. These social impairments were however reduced after a further 14 days chronic treatment with 10 or 20 mg/kg imipramine and stimulant effects were no longer seen. Following chronic administration in group-housed animals locomotor stimulation was replaced with sedation, which resulted in a reduction in social behaviour. That is, opposite to the effect seen in Individual housed animals. It is therefore concluded that chronic treatment with imipramine serves to increase social behaviour but only in those animals with a pre-existing social deficit.

Analysis of gene expression in two large schizophrenia cohorts identifies multiple changes associated with nerve terminal function.

Schizophrenia is a severe psychiatric disorder with a world-wide prevalence of 1%. The pathophysiology of the illness is not understood, but is thought to have a strong genetic component with some environmental influences on aetiology. To gain further insight into disease mechanism, we used microarray technology to determine the expression of over 30 000 mRNA transcripts in post-mortem tissue from a brain region associated with the pathophysiology of the disease (Brodmann area 10: anterior prefrontal cortex) in 28 schizophrenic and 23 control patients. We then compared our study (Charing Cross Hospital prospective collection) with that of an independent prefrontal cortex dataset from the Harvard Brain Bank. We report the first direct comparison between two independent studies. A total of 51 gene expression changes have been identified that are common between the schizophrenia cohorts, and 49 show the same direction of disease-associated regulation. In particular, changes were observed in gene sets associated with synaptic vesicle recycling, transmitter release and cytoskeletal dynamics. This strongly suggests multiple, small but synergistic changes in gene expression that affect nerve terminal function.

Characterization of a CNS penetrant, selective M1 muscarinic receptor agonist, 77-LH-28-1.

BACKGROUND AND PURPOSE: M1 muscarinic ACh receptors (mAChRs) represent an attractive drug target for the treatment of cognitive deficits associated with diseases such as Alzheimer's disease and schizophrenia. However, the discovery of subtype-selective mAChR agonists has been hampered by the high degree of conservation of the orthosteric ACh-binding site among mAChR subtypes. The advent of functional screening assays has enabled the identification of agonists such as AC-42 (4-n-butyl-1-[4-(2-methylphenyl)-4-oxo-1-butyl]-piperidine), which bind to an allosteric site and selectively activate the M(1) mAChR subtype. However, studies with this compound have been limited to recombinantly expressed mAChRs. EXPERIMENTAL APPROACH: In this study, we have compared the pharmacological profile of AC-42 and a close structural analogue, 77-LH-28-1 (1-[3-(4-butyl-1-piperidinyl)propyl]-3,4-dihydro-2(1H)-quinolinone) at human recombinant, and rat native, mAChRs by calcium mobilization, inositol phosphate accumulation and both in vitro and in vivo electrophysiology. KEY RESULTS: Calcium mobilization and inositol phosphate accumulation assays revealed that both AC-42 and 77-LH-28-1 display high selectivity to activate the M1 mAChR over other mAChR subtypes. Furthermore, 77-LH-28-1, but not AC-42, acted as an agonist at rat hippocampal M1 receptors, as demonstrated by its ability to increase cell firing and initiate gamma frequency network oscillations. Finally, 77-LH-28-1 stimulated cell firing in the rat hippocampus in vivo following subcutaneous administration. CONCLUSIONS AND IMPLICATIONS: These data suggest that 77-LH-28-1 is a potent, selective, bioavailable and brain-penetrant agonist at the M1 mAChR and therefore that it represents a better tool than AC-42, with which to study the pharmacology of the M1 mAChR.

Dopamine D2 receptor stimulation inhibits cold-initiated thermogenesis in brown adipose tissue in conscious rats.

Dopamine D(2)-like receptor agonists cause hypothermia. We investigated whether inhibiting heat production by interscapular brown adipose tissue (iBAT), a major thermogenic organ in rats, contributes to hypothermia caused by dopamine D(2)-like receptor agonists. Temperature of iBAT and tail artery blood flow were measured in conscious rats. Activity in postganglionic sympathetic nerves supplying iBAT was assessed in anesthetized rats. Conscious rats were housed in a warm cage maintained at 26-28 degrees C and then transferred to a cold cage at 5-10 degrees C to induce iBAT thermogenesis. Cold exposure increased iBAT temperature (+0.7+/-0.1 degrees C, 30 min after transferring to the cold cage, P<0.01, n=54). The mixed dopamine D(2)/D(3) receptor agonist, 7-hydroxy-2-(di-n-propylamino)tetralin (7-OH-DPAT, 0.5 mg/kg s.c.) reversed the cold-induced increase in iBAT temperature (-2.8+/-0.2 degrees C at 30 min after 7-OH-DPAT treatment during cold exposure vs. +0.3+/-0.1 degrees C at 30 min after vehicle treatment during cold exposure, n=8). These temperature changes were blocked by pre-treatment with the D(2) receptor antagonists spiperone (20 microg/kg i.p.) and L-741,626 (2.5 mg/kg i.p.), but not by the selective D(3) receptor antagonist SB-277011A (10 mg/kg i.p.). Another mixed dopamine D(2)/D(3) receptor agonist, quinpirole (0.5 mg/kg s.c.) also reversed cold-induced iBAT thermogenesis, and this effect was also prevented by pre-treatment with spiperone, but not with a peripherally acting dopamine receptor antagonist, domperidone (2 mg/kg s.c.). Neither 7-OH-DPAT nor quinpirole reversed cutaneous vasoconstriction elicited by cold exposure. In anesthetized rats, quinpirole (0.5 mg/kg i.v.) abolished iBAT sympathetic nerve discharge elicited by cooling the trunk, and this change was reversed by spiperone (20 microg/kg i.v.). These results demonstrate that activation of CNS dopamine D(2) receptors inhibits sympathetically-mediated iBAT thermogenesis in response to cold exposure. Furthermore, they suggest that in rats hypothermia induced by dopamine D(2) receptor agonists in cold environments is mainly due to decreased heat production rather than to increased heat loss.

Isolation rearing induces recognition memory deficits accompanied by cytoskeletal alterations in rat hippocampus.

Social isolation from weaning affects hippocampal structure and function in the rat. The intrinsic dynamic instability of the cytoskeletal microtubular system is essential for neuronal development and organization. Accordingly, the present paper investigated the effects of social isolation on hippocampal levels of alpha-tubulin isoforms associated with microtubule dynamics, the dendritic marker MAP-2 and alterations in locomotor activity and recognition memory. Male Lister Hooded rats (postnatal day 25-28) were housed either in groups or singly (isolated animals) for 30 days. Locomotor activity in a novel arena and novel object recognition were monitored in activity boxes. The hippocampus was dissected out 18 h after the novel object recognition task. Levels of alpha-tubulin isoforms and MAP-2 were analysed using Western blots. The experiments were conducted in duplicate, using two batches of rats obtained from different suppliers. Isolated animals were hyperactive and showed recognition memory deficits in the novel object recognition task. These behavioural alterations were accompanied by specific alterations in hippocampal alpha-tubulin isoforms and decreased MAP-2 expression. The results confirm that rearing rats in isolation produces hyperactivity and cognitive deficits. The behavioural alterations were accompanied by hippocampal cytoskeletal changes consistent with microtubule stabilization, and by decreased MAP-2 expression. These findings are indicative of an abnormal development of synaptic connections and/or reductions in neuronal cell number. The developmental structural abnormalities in the hippocampus may contribute to the cognitive impairments which result from isolation rearing in rats.

Neuronal plasticity, stress and depression: involvement of the cytoskeletal microtubular system?

In susceptible individuals, stressors can increase the risk of onset of depression and recent brain imaging studies have shown morphometric alterations in the limbic system of patients affected by depression. The volume loss observed in the hippocampus of depressed individuals suggests a possible involvement of structural neuronal plasticity in the pathogenesis of depression. Stressful conditions in animals can result in impaired structural neuronal plasticity in the hippocampus, characterised by retraction of apical dendrites and decreased neurogenesis. The intrinsic dynamic instability of the cytoskeletal microtubular system is essential for neuronal remodelling and plasticity. We have recently shown that both acute and chronic stress decrease microtubular dynamics in the rat hippocampus. Other authors have demonstrated that proteins functionally involved in the regulation of microtubule dynamics can be altered by stress in the rodent hippocampus. Furthermore, the existence of a link between stress-induced microtubular changes and depression is further strengthened by evidence showing that both acute and chronic treatment with antidepressant drugs can affect the expression of microtubular proteins. The present review will introduce a growing body of evidence suggesting that stress-induced alterations in neuronal plasticity might be considered the final result of activation and/or inhibition of molecular cascades regulating the dynamics of the microtubular system. In addition, the prospect of targeting microtubules as a pharmacotherapeutic approach to treat mood disorders will be discussed.

Effects of fluoxetine on social behaviour and plasma corticosteroid levels in female Mongolian gerbils.

Gerbils are a highly social species and extremely sensitive to social manipulations. In this laboratory, separating male/female pairs has been found to produce significant effects on these animal's subsequent social behaviour. The present studies were conducted in order to examine the effects of a short period of individual housing in females of this species, as this may also be predicted to produce alterations in social responding. It was found that 21 days' individual housing induced a marked reduction in social behaviour directed towards an untreated male placed in the same arena. This was indicated by a highly significant increase in immobile-in-contact, a behaviour that involves females freezing while, and only while, they are being socially investigated. This represents the declining of an invitation to socially interact and so high levels of immobile-in-contact indicate low levels of social motivation. There was also an increase in evading, upon another animal's approach, and a decrease in social investigation of other animals. The effects of 15 days of fluoxetine were found to be highly dependent on housing condition. In individually housed females, 10 mg/kg increased their social investigation of other animals and markedly reduced the duration of immobile-in-contact. Twenty mg/kg also reduced levels of immobile-in-contact and increased the frequency of active approaches towards other animals. Fluoxetine therefore acts to increase social motivation in individually housed animals. By direct contrast, in group-housed female gerbils, fluoxetine had no effects on social behaviour and produced clear indications of sedation. While housing condition had no influence on levels of corticosterone, fluoxetine produced dose-related increases in corticosteroid levels in both group- and individually housed animals. These findings show that: (1) a short period of individual housing induces a significant reduction in these animals' motivation towards social behaviour; (2) the effects of fluoxetine on behaviour are greatly influenced by housing condition--prosocial effects are seen in individually housed animals but only sedative effects are seen in animals maintained in groups; and (3) while housing condition has no effects on levels of corticosterone, fluoxetine dose-dependently stimulates corticosteroid release. It can be concluded that the effects of fluoxetine on gerbil behaviour are independent of its stimulatory influence on HPA axis functioning, and that the prosocial effects of this selective serotonin reuptake inhibitor (SSRI) can only be seen in animals with a pre-existing social deficit.

5-HT6 receptor antagonists enhance retention of a water maze task in the rat.

RATIONALE: 5-HT(6) receptors are predominantly located in the brain and may be involved in cognitive processes. The aim of this study was to assess the effects of two potent and selective 5-HT(6) receptor antagonists, SB-271046-A and SB-357134-A, on learning and memory in the rat. METHODS: Spatial learning and memory was assessed by testing the effects of SB-271046-A and SB-357134-A on acquisition and retention of a water maze task. RESULTS: In the water maze, administration of SB-271046-A or SB-357134-A (3 or 10 mg/kg) had no effect on learning per se. At 10 mg/kg, however, both compounds produced a significant improvement in retention of a previously learned platform position when tested 7 days after training. By contrast, the acetylcholinesterase inhibitor, Aricept (donepezil, 0.1, 0.3 mg/kg PO) had no effect in this task. CONCLUSIONS: This study demonstrates that systemic administration of SB-271046-A and SB-357134-A produces improvements in retention of a water maze task in the rat. These data indicate that 5-HT(6) receptor antagonism may be involved in cognitive function.

Long-term evaluation of isolation-rearing induced prepulse inhibition deficits in rats.

RATIONALE: Rats reared in social isolation from weaning show prepulse inhibition (PPI) deficits which are thought to model the sensorimotor gating deficits seen in schizophrenia and other psychiatric disorders. However, recent studies have questioned the robustness of this paradigm. OBJECTIVE: The existence of a substantial dataset generated over 4 years in our laboratory has allowed the investigation of the robustness and reliability of the procedure under a variety of environmental conditions. The effects of atypical antipsychotics (clozapine, olanzapine and risperidone) under different experimental conditions are also reported. METHOD: At weaning, Hooded Lister pups were singly (isolates) or group (n=5) housed (grouped). Eight weeks later, the startle and PPI response of isolates and grouped rats was investigated using conditions of fixed inter-stimulus interval (ISI) (pulse=110 dB/50 ms; prepulse=80 dB/30 ms; ISI=100 ms) or variable

Increased responsiveness of dopamine to atypical, but not typical antipsychotics in the medial prefrontal cortex of rats reared in isolation.

Dopaminergic hypofunction in the medial prefrontal cortex (mPFC) has been associated with the aetiology of negative symptoms and cognitive dysfunction of schizophrenia, which are both alleviated by clozapine and other atypical antipsychotics such as olanzapine. In rodents, early life exposure to stressful experiences such as social isolation produces a spectrum of symptoms emerging in adult life, which can be restored by antipsychotic drugs. The present series of experiments sought to investigate the effect of clozapine (5-10 mg/kg s.c.), olanzapine (5 mg/kg s.c.), and haloperidol (0.5 mg/kg s.c.) on dopamine (DA) and amino acids in the prelimbic/infralimbic subregion of the mPFC in group- and isolation-reared rats. Rats reared in isolation showed significant and robust deficits in prepulse inhibition of the acoustic startle. In group-reared animals, both clozapine and olanzapine produced a significant increase in DA outflow in the mPFC. Isolation-reared rats showed a significant increase in responsiveness to both atypical antipsychotics compared with group-reared animals. In contrast, the administration of haloperidol failed to modify dialysate DA levels in mPFC in either group- or isolation-reared animals. The results also show a positive relationship between the potency of the tested antipsychotics to increase the release of DA in the mPFC and their respective affinities for 5-HT1A relative to DA D2 or D3 receptors. Finally, isolation-reared rats showed enhanced neurochemical responses to the highest dose of clozapine as indexed by alanine, aspartate, GABA, glutamine, glutamate, histidine, and tyrosine. The increased DA responsiveness to the atypical antipsychotic drugs clozapine and olanzapine may explain, at least in part, clozapine- and olanzapine-induced reversal of some of the major behavioral components of the social isolation syndrome, namely hyperactivity and attention deficit.

Central effects of urotensin-II following ICV administration in rats.

RATIONALE: Urotensin-II (U-II) has recently been identified as an agonist for the G-protein-coupled receptor, GPR14. Detection of both U-II and GPR14 mRNA in the brain and spinal cord is consistent with a role for U-II in the CNS. However, the effects of central administration of U-II in rodents have not been reported previously. OBJECTIVES: To determine the localisation of GPR14 mRNA in rat tissues and to investigate the behavioural and endocrine effects of human U-II (hU-II) following intracerebroventricular (ICV) administration in rats. METHODS: Experiments were carried out in male Sprague-Dawley rats. Expression of GPR14 mRNA in rat brain was determined by semi-quantitative RT-PCR. Effects of hU-II on general behaviours were assessed by an observer and the motor activity response was measured by an automated activity monitor. Plasma hormones and [DOPAC + HVA]/[DA] and [5-HIAA]/[5-HT] ratios in five brain areas were measured 20 min post-hU-II (ICV). RESULTS: GPR14 mRNA expression was found in whole brain tissue and in all CNS regions tested. GPR14 mRNA expression was also detected in the periphery; highest levels were found in the heart. Following ICV administration, hU-II (3-10 micrograms ICV) increased rearing and grooming, and increased motor activity in a familiar environment. Further, hU-II increased plasma prolactin and TSH but did not affect levels of corticosterone. hU-II had no effects on dopamine or 5-HT levels or their metabolites in the frontal cortex, hippocampus, hypothalamus, striatum and nucleus accumbens. CONCLUSIONS: These data provide further insight into the distribution of GPR14 mRNA within the CNS and show for the first time that hU-II causes marked behavioural and endocrine effects.

Clozapine enhances breakpoint in common marmosets responding on a progressive ratio schedule.

RATIONALE: Motivational effects of psychotropic drugs may contribute to their therapeutic profile and progressive ratio (PR) schedules provide a method of measuring these effects in animals. OBJECTIVE: Determine effects of selected antipsychotic, psychotomimetic, anxiolytic and antidepressant drugs on PR performance in common marmosets. METHOD: Marmosets were trained to lever press for banana milkshake reinforcement using a PR schedule, in which the number of lever presses to achieve successive reinforcements increased by one until responding ceased (breakpoint). RESULTS: Clozapine administered intramuscularly (0.01-2 mg/kg IM; 30 min pretreatment time (ptt) or by oral gavage (0.1-4 mg/kg PO; 60 min ptt) significantly increased the breakpoint. Independent tests of fluid consumption failed to show enhanced fluid intake after clozapine pretreatment, suggesting this effect was not due to drug induced polydipsia. Neither haloperidol (0.005-0.1 mg/kg PO; 60 min ptt) nor risperidone (0.0025-0.05 mg/kg PO; 60 min ptt) altered breakpoint. Olanzapine (0.01-1 mg/kg PO; 60 min ptt) significantly enhanced the breakpoint at 0.05 mg/kg PO, but the effect was not robust. Amphetamine (0.2-2 mg/kg SC; 30 min ptt) significantly reduced the breakpoint at 2 mg/kg and fluoxetine (0.1-1 mg/kg PO; 60 min ptt) was without effect. Diazepam significantly increased the breakpoint at 0.5 mg/kg PO. Drug-induced polydipsia might play a role in this response as independent tests showed increased fluid consumption following diazepam. CONCLUSIONS: These results demonstrate that, unlike other antipsychotics, clozapine over a wide dose range increased the motivational state of marmosets to respond for banana milkshake. This motivational aspect of clozapine's actions may contribute to its unique clinical profile and the PR procedure may provide a method for detecting novel antipsychotics with a clozapine-like profile.

The effect of SB-269970, a 5-HT(7) receptor antagonist, on 5-HT release from serotonergic terminals and cell bodies.

1. The presence of 5-HT(7) receptor mRNA and protein in 5-HT neurons suggests that this receptor may act as a 5-HT autoreceptor. In this study, the effect of the 5-HT(7) receptor antagonist, SB-269970 ((R)-1-[3-hydroxy phenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine), was investigated on 5-HT release in the guinea-pig and rat cortex and the rat dorsal raphe nucleus (DRN), using the techniques of in vitro [(3)H]-5-HT release or fast cyclic voltammetry, respectively. 2. Cortical slices were loaded with [(3)H]-5-HT and release was evoked by electrical stimulation. 5-CT inhibited the evoked release of [(3)H]-5-HT in a concentration-dependent manner. SB-269970 had no significant effect on [(3)H]-5-HT release while the 5-HT(1B) receptor antagonist, SB-224289 significantly potentiated [(3)H]-5-HT release. In addition, SB-269970 was unable to attenuate the 5-CT-induced inhibition of release while SB-224289 produced a rightward shift of the 5-CT response, generating estimated pK(B) values of 7.8 and 7.6 at the guinea-pig and rat terminal 5-HT autoreceptors respectively. 3. Rat DRN slices were electrically stimulated and the evoked 5-HT efflux detected by voltammetric analysis. 8-OH-DPAT inhibited evoked 5-HT efflux and was fully reversed by WAY 100635. SB-269970 had no effect on either 5-HT efflux per se or 8-OH-DPAT-induced inhibition of 5-HT efflux. In addition, 5-CT inhibited 5-HT efflux in a concentration-dependent manner. SB-269970 was unable to attenuate the 5-CT-induced inhibition of 5-HT efflux. 4. In conclusion, we were unable to provide evidence to suggest a 5-HT autoreceptor role for 5-HT(7) receptors. However, investigations with more selective 5-HT(7) receptor agonists are needed to confirm the data reported here.

Effects of centrally administered orexin-B and orexin-A: a role for orexin-1 receptors in orexin-B-induced hyperactivity.

RATIONALE: Orexin-A and orexin-B are hypothalamic neuropeptides derived from a 130-amino acid precursor, prepro-orexin, and are potent agonists at both the orexin-1 (OX1) and orexin-2 (OX2) receptors. Orexin-A has been ascribed a number of in vivo functions in the rat after intracerebroventricular (ICV) administration, including hyperphagia, neuroendocrine modulation and a role in the regulation of sleep-wake function. The in vivo role of orexin-B is not as clear. OBJECTIVES: To investigate the behavioural, endocrine and neurochemical effects of orexin-B in in-vivo tests. In a number of experiments, these effects were compared with those of orexin-A. METHODS: Experiments were carried out in male, Sprague-Dawley rats with a guide cannula directed towards the lateral ventricle. The effects of orexin-B (ICV) upon grooming behaviour were compared with those of orexin-A. The effects of orexin-B upon the motor activity response to both novel and familiar environments were assessed in an automated activity monitor. Orexin-B was tested upon startle reactivity and body temperature. Further, plasma hormones and [DOPAC+ HVA]/[DA] and [5-HIAA]/[5-HT] ratios in six brain areas were measured 40 min post-orexin-B or orexin-A. RESULTS: The clearest behavioural response to orexin-B was increased motor activity in both novel and familiar environments. Orexin-B-induced hyperactivity was blocked by an OX1 receptor antagonist, SB-334867-A, implicating OX1 receptors in this behavioural response. In common with orexin-A, orexin-B reduced plasma prolactin and failed to influence startle reactivity. However, in contrast with orexin-A, orexin-B increased head grooming but failed to cause a robust whole body grooming response or increase plasma corticosterone levels. Further, orexin-B, but not orexin-A, increased plasma TSH and increased hypothalamic and striatal [5-HIAA]/[5-HT] ratios. CONCLUSIONS: The present study has demonstrated a number of behavioural, neuroendocrine and neurochemical effects of orexin-B that distinguish it from orexin-A. Further, we have demonstrated a role for OX1 receptors in the actions of orexin-B upon motor activity.

Anxiolytic profile of ropinirole in the rat, mouse and common marmoset.

RATIONALE: Some features of Parkinson's disease are exacerbated by stress and anxiety and it is important to understand the effects of dopamine receptor agonists on measures of anxiety. The aim of this study was to assess the effects of the dopamine D2/D3 receptor agonist ropinirole in models of anxiety and depression in the rat, mouse and marmoset. RESULTS: In the rat elevated plus-maze test, ropinirole (0.01-1 mg/kg, i.p.) produced an inverted-U dose-response curve in the percentage time spent in the open arms. Compared with vehicle, ropinirole (0.1 mg/kg) had a significant anxiolytic-like effect, which was similar to that observed with 1.5 mg/kg diazepam. This effect was found at doses that did not affect motor behaviour or induce stereotypy. In the mouse black and white box test of anxiety, ropinirole (0.1-10 mg/kg, i.p.) increased both the rearing time and number of line crosses in the white section. This effect reached statistical significance for both measures at a dose of 0.1 mg/kg and suggests an anxiolytic-like action of the compound. By contrast, the dopamine agonist bromocriptine (0.1-10 mg/kg, i.p.) did not produce significant changes in these behaviours. In the marmoset human threat test, ropinirole (0.01-10 microg/kg, s.c.) reduced the number of postures at all doses tested and this reached statistical significance at 10 microg/kg. Ropinirole did not compromise the effect of amitriptyline in the Porsolt test of depression and in itself produced antidepressant-like effects. CONCLUSIONS: These data demonstrate that systemic administration of ropinirole produces anxiolytic-like effects in three separate models in the mouse, rat and marmoset. This may predict an action of ropinirole in man that would provide a superior profile of action over other presently available anti-parkinsonian agents.

The effect of SB-236057-A, a selective 5-HT1B receptor inverse agonist, on in vivo extracellular 5-HT levels in the freely-moving guinea-pig.

5-HT1B autoreceptors are involved in the control of extracellular 5-HT levels from both the terminal and cell body regions of serotonergic neurones. In this study we report on the effect of a selective and potent 5-HT1B receptor inverse agonist, SB-236057-A (1'-ethyl-5-(2'-methyl-4'-(5-methyl- 1,3,4-oxadiazolyl-2-yl)biphenyl-4-carbonyl)-2,3,6,7-tetrahydros piro [furo[2,3-f]indole-3,4' -piperidine] hydrochloride), on extracellular 5-HT levels in the cortex and dentate gyrus of the freely-moving guinea-pig, using the technique of in vivo microdialysis. SB-236057-A had ca. 23% bioavailability following oral drug administration. In vivo hypothermia pharmacodynamic assays demonstrated it was brain penetrant with a duration of action in excess of 18 h. SB-236057-A (0.75 mg/kg p.o.) increased extracellular 5-HT levels in the dentate gyrus to a maximum of 167+/-7% of basal but had no effect in the frontal cortex. However, a small increase in cortical 5-HT levels (117+11% of basal) was evident at 2.5 mg/kg p.o. In addition, SB-236057-A (0.75 mg/kg and 2.5 mg/kg p.o.) antagonised the sumatriptan-induced inhibition of extracellular 5-HT levels in the guinea-pig frontal cortex. These differences were attributed to MRN-innervated regions (e.g. dentate gyrus) being more responsive to 5-HT1B receptor-mediated negative feedback than DRN-innervated regions (e.g. frontal cortex). In the dentate gyrus, the increase in 5-HT release induced by SB-236057-A (0.75 mg/kg p.o.) was comparable to that after 14 days of paroxetine (10 mg/kg p.o.) administration, reaching a maximum of 183+/-13% of basal. These data suggest that acute 5-HT1B receptor blockade, by virtue of increased 5-HT release in the dentate gyrus, may provide a rapidly acting antidepressant.

Acute and chronic administration of the selective D(3) receptor antagonist SB-277011-A alters activity of midbrain dopamine neurons in rats: an in vivo electrophysiological study.

This study examined the effect of acute and repeated p.o. administration of the selective D(3) receptor antagonist SmithKline Beecham (SB)-277011-A (1, 3, or 10 mg/kg) on the activity of spontaneously active midbrain dopamine (DA) neurons in anesthetized, male Sprague-Dawley rats. This was accomplished with the technique of in vivo extracellular single-unit recording. A single administration of either 3 or 10 mg/kg SB-277011-A produced a significant increase in the number of spontaneously active substantia nigra pars compacta (or A9) DA neurons compared with vehicle-treated (2% methylcellulose) animals. The 10-mg/kg dose of SB-277011-A produced a significant increase in the number of spontaneously active A10 DA neurons compared with vehicle-treated animals. The acute administration of SB-277011-A produced a significantly greater alteration in the firing pattern of spontaneously active A10 DA neurons, particularly at the 3- and 10-mg/kg doses, compared with vehicle-treated animals. The i.v. administration of SB-277011-A (0.01-1.28 mg/kg) did not significantly alter the firing rate or firing pattern of either A9 or A10 DA neurons. The repeated p.o. administration of 1, 3, or 10 mg/kg SB-277011-A once a day for 21 days produced a significant decrease in the number of spontaneously active A10 DA neurons. The repeated administration of SB-277011-A produced a greater effect on the firing pattern of spontaneously active A10 DA neurons, particularly at the 3-mg/kg dose, compared with A9 DA neurons. Overall, our results indicate that SB-277011-A alters the activity of midbrain DA neurons in rats.

Pharmacological actions of a novel, high-affinity, and selective human dopamine D(3) receptor antagonist, SB-277011-A.

SB-277011-A (trans-N-[4-[2-(6-cyano-1,2,3, 4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolininecarboxamide), is a brain-penetrant, high-affinity, and selective dopamine D(3) receptor antagonist. Radioligand-binding experiments in Chinese hamster ovary (CHO) cells transfected with human dopamine D(3) or D(2 long) (hD(3), hD(2)) receptors showed SB-277011-A to have high affinity for the hD(3) receptor (pK(i) = 7.95) with 100-fold selectivity over the hD(2) receptor and over 66 other receptors, enzymes, and ion channels. Similar radioligand-binding data for SB-277011-A were obtained from CHO cells transfected with rat dopamine D(3) or D(2). In the microphysiometer functional assay, SB-277011-A antagonized quinpirole-induced increases in acidification in CHO cells overexpressing the hD(3) receptor (pK(b) = 8.3) and was 80-fold selective over hD(2) receptors. Central nervous system penetration studies showed that SB-277011-A readily entered the brain. In in vivo microdialysis studies, SB-277011-A (2. 8 mg/kg p.o.) reversed the quinelorane-induced reduction of dopamine efflux in the nucleus accumbens but not striatum, a regional selectivity consistent with the distribution of the dopamine D(3) receptor in rat brain. SB-277011-A (2-42.3 mg/kg p.o.) did not affect spontaneous locomotion, or stimulant-induced hyperlocomotion. SB-277011-A (4.1-42.2 mg/kg p.o.) did not reverse prepulse inhibition deficits in apomorphine- or quinpirole-treated rats, but did significantly reverse the prepulse inhibition deficit in isolation-reared rats at a dose of 3 mg/kg p.o. SB-277011-A (2.5-78. 8 mg/kg p.o.) was noncataleptogenic and did not raise plasma prolactin levels. Thus, dopamine D(3) receptor blockade produces few of the behavioral effects characteristic of nonselective dopamine receptor antagonists. The effect of SB-277011-A on isolation-induced prepulse inhibition deficit suggests that blockade of dopamine D(3) receptors may benefit the treatment of schizophrenia.

Design and synthesis of trans-N-[4-[2-(6-cyano-1,2,3, 4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolinecarboxamide (SB-277011): A potent and selective dopamine D(3) receptor antagonist with high oral bioavailability and CNS penetration in the rat.

A selective dopamine D(3) receptor antagonist offers the potential for an effective antipsychotic therapy, free of the serious side effects of currently available drugs. Using clearance and brain penetration studies as a screen, a series of 1,2,3, 4-tetrahydroisoquinolines, exemplified by 13, was identified with high D(3) affinity and selectivity against the D(2) receptor. Following examination of molecular models, the flexible butyl linker present in 13 was replaced by a more conformationally constrained cyclohexylethyl linker, leading to compounds with improved oral bioavailability and selectivity over other receptors. Subsequent optimization of this new series to improve the cytochrome P450 inhibitory profile and CNS penetration gave trans-N-[4-[2-(6-cyano-1, 2,3, 4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolinecarbo xamide (24, SB-277011). This compound is a potent and selective dopamine D(3) receptor antagonist with high oral bioavailability and brain penetration in the rat and represents an excellent new chemical tool for the investigation of the role of the dopamine D(3) receptor in the CNS.