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.

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.

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.

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.

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.

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.

Characterization of SB-269970-A, a selective 5-HT(7) receptor antagonist

The novel 5-HT(7) receptor antagonist, SB-269970-A, potently displaced [(3)H]-5-CT from human 5-HT(7(a)) (pK(i) 8.9+/-0.1) and 5-HT(7) receptors in guinea-pig cortex (pK(i) 8.3+/-0.2). 5-CT stimulated adenylyl cyclase activity in 5-HT(7(a))/HEK293 membranes (pEC(50) 7.5+/-0.1) and SB-269970-A (0.03 - 1 microM) inhibited the 5-CT concentration-response with no significant alteration in the maximal response. The pA(2) (8.5+/-0.2) for SB-269970-A agreed well with the pK(i) determined from [(3)H]-5-CT binding studies. 5-CT-stimulated adenylyl cyclase activity in guinea-pig hippocampal membranes (pEC(50) of 8.4+/-0.2) was inhibited by SB-269970-A (0.3 microM) with a pK(B) (8.3+/-0.1) in good agreement with its antagonist potency at the human cloned 5-HT(7(a)) receptor and its binding affinity at guinea-pig cortical membranes. 5-HT(7) receptor mRNA was highly expressed in human hypothalamus, amygdala, thalamus, hippocampus and testis. SB-269970-A was CNS penetrant (steady-state brain : blood ratio of ca. 0.83 : 1 in rats) but was rapidly cleared from the blood (CLb=ca. 140 ml min(-1) kg(-1)). Following a single dose (3 mg kg(-1)) SB-269970 was detectable in rat brain at 30 (87 nM) and 60 min (58 nM). In guinea-pigs, brain levels averaged 31 and 51 nM respectively at 30 and 60 min after dosing, although the compound was undetectable in one of the three animals tested. 5-CT (0.3 mg kg(-1) i.p.) induced hypothermia in guinea-pigs was blocked by SB-269970-A (ED(50) 2.96 mg kg(-1) i.p.) and the non-selective 5-HT(7) receptor antagonist metergoline (0.3 - 3 mg kg(-1) s.c.), suggesting a role for 5-HT(7) receptor stimulation in 5-CT induced hypothermia in guinea-pigs. SB-269970-A (30 mg kg(-1)) administered at the start of the sleep period, significantly reduced time spent in Paradoxical Sleep (PS) during the first 3 h of EEG recording in conscious rats.

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.

[(3)H]-SB-269970--A selective antagonist radioligand for 5-HT(7) receptors

Binding of the 5-HT(7) receptor antagonist radioligand [(3)H]-SB-269970 to human 5-HT(7(a)) receptors expressed in HEK293 cell membranes (h5-HT(7(a))/293) and to guinea-pig cerebral cortex membranes, was characterized and compared with [(3)H]-5-CT binding. [(3)H]-SB-269970 (1 nM) showed full association with h5-HT(7(a))/293 membranes after 40 min. Specific binding at equilibrium represented >90% of total binding and was fully reversible by methiothepin (10 microM), full dissociation occurring by 100 min. The association (k(+1)) and dissociation (k(-1)) rate constants were 0.05 nM(-1)min(-1) and 0.05 min(-1) respectively, giving a K(D) (k(-1)/k(+1)) of 1.0 nM. [(3)H]-SB-269970 bound saturably and apparently monophasically to both h5-HT(7(a))/293 and guinea-pig cortex membranes, with K(D) values of 1.25+/-0.05 and 1.7+/-0.3 nM respectively. The B(max) for [(3)H]-SB-269970 to both h5-HT(7(a))/293 and guinea-pig cortex membranes (5780+/-380 and 125+/-8.2 fmoles mg protein(-1) respectively) was similar to that for [(3)H]-5-CT (6190+/-940 and 143+/-19 fmoles mg protein(-1) respectively). These data suggest that, in each tissue, both radioligands labelled the same population of receptors, which appear to be present in an agonist high affinity state. The profile of compound inhibition of [(3)H]-SB-269970 binding to h5-HT(7(a))/293 and guineapig cortex membranes correlated well (corr. coeff. 0.98) with those for [(3)H]-5-CT binding and were consistent with the profiles reported previously for the human 5-HT(7(a)) and guinea-pig cortex 5-HT(7) receptors using [(3)H]-5-CT. Hill slopes for inhibition of [(3)H]-SB-269970 and [(3)H]-5-CT binding were close to 1, consistent with binding to a single receptor population in both tissues. [(3)H]-SB-269970 represents the first selective 5-HT(7) antagonist radioligand, which should aid further characterization of 5-HT(7) receptors in recombinant and native tissues and help establish their role in brain function.

Practical and theoretical issues in gene-targeting studies and their application to behaviour

Some of the major practical and theoretical issues that are associated with gene-targeting studies in mice are discussed. The availability of sufficient space to house the extensive breeding colonies associated with studies in gene-manipulated mice is an important logistical consideration that requires consideration at an early stage. A practical example is discussed which illustrates some of these issues. Problems associated with disease control and methods of maintaining the health status of valuable colonies are also outlined. Differences in the behavioural phenotype of inbred mouse strains pose important issues for study design and selection of host mouse lines. The results from studies exploring variations in the behavioural phenotype of six common inbred strains are briefly outlined. The impact of phenotypic variation on behavioural studies is considered and the implications for experimental design are discussed.

Evaluation of the spontaneously hypertensive rat as a model of attention deficit hyperactivity disorder: acquisition and performance of the DRL-60s test

CD. However, the pattern of responding at DRL-60s suggested poor schedule control for the WKY rats. Therefore, the performance of SHR in the DRL test does not appear to represent a valid model of ADHD. Further, our findings with the WKY rat suggest that this strain is a poor behavioural control for the SHR.

Use of SHIRPA and discriminant analysis to characterise marked differences in the behavioural phenotype of six inbred mouse strains

Detailed characterisation of six inbred strains of mice commonly used in transgenic and knockout research was carried out using a battery of behavioural tests (SHIRPA) followed by discriminant analysis of the data. In the primary observation screen, DBA/2 mice were relatively irritable and vocalised during handling. C57BL/6 were hyperactive as measured by transfer arousal, arena activity and touch-escape tests. By contrast, C3H were markedly hypoactive, had significantly enhanced grip strength and were also significantly impaired on the visual placing task. In the elevated plus-maze, BALB/c mice showed the highest level of open arm entries and time spent in the open arms, indicating the lowest level of anxiety. There was a clear dissociation of strains on exploratory activity, as measured in the holeboard test and spontaneous locomotor activity (LMA). DBA/2 mice were hyperactive in LMA but demonstrated relatively low levels of holeboard exploration. None of the six strains learnt the water maze spatial learning task particularly well. C57BL/6 and 129/Sv demonstrated most ability and C3H showed no evidence of having acquired the task. The SHIRPA screening battery and discriminant analysis of the data have enabled us to determine the relevant contribution of a number of behavioural measurements to the marked differences in phenotype of mouse strains. These data confirm the importance of carrying out a comprehensive profile in order to accurately characterise the phenotype of gene-targeted and transgenic mice.

Orexin A activates locus coeruleus cell firing and increases arousal in the rat

The localization of orexin neuropeptides in the lateral hypothalamus has focused interest on their role in ingestion. The orexigenic neurones in the lateral hypothalamus, however, project widely in the brain, and thus the physiological role of orexins is likely to be complex. Here we describe an investigation of the action of orexin A in modulating the arousal state of rats by using a combination of tissue localization and electrophysiological and behavioral techniques. We show that the brain region receiving the densest innervation from orexinergic nerves is the locus coeruleus, a key modulator of attentional state, where application of orexin A increases cell firing of intrinsic noradrenergic neurones. Orexin A increases arousal and locomotor activity and modulates neuroendocrine function. The data suggest that orexin A plays an important role in orchestrating the sleep-wake cycle.

Influence of peptide CRF receptor antagonists upon the behavioural effects of human/rat CRF

The effects of the corticotropin-releasing factor (CRF) receptor antagonists, alpha-helical CRF-(9-41), [D-Phe12,Nle21,38, CalphaMe-Leu37]humanCRF-(12-41) (D-PheCRF-(12-41)) and astressin ([cyclo(30-33)[D-Phe12,Nle21,38,Glu30,Lys33]h umanCRF-(12-41) upon hypophagic and motor activation response to human/ratCRF (h/rCRF) were investigated. All three antagonists (100 microg intracerebroventricular (i.c.v.)) blocked the effects of h/rCRF (1 microg i.c.v.) upon food intake and body weight change in food-deprived rats. In contrast, alpha-helical CRF-(9-41) and astressin (both at 100 microg i.c.v., but not lower doses), but not D-PheCRF-(12-41) (up to 100 microg i.c.v.), blocked h/rCRF (0.3 microg i.c.v.)-induced motor activation in rats in a familiar environment. The ability of D-PheCRF-(12-41) to block CRF-induced hypophagia, but not motor activation, suggests a selective action of this antagonist upon the behavioural effects of centrally administered h/rCRF.

The effects of dopamine D3/D2 receptor agonists on intracranial self stimulation in the rat

The effects of the dopamine D3/D2 receptor agonists quinpirole, quinelorane and (+/-)7-OH-DPAT [(+/-) 7-hydroxy-2(N,N-di-n-propylamino) tetralin] on intracranial self-stimulation (ICSS) were investigated. Rats implanted with bipolar electrodes into the lateral hypothalamus were trained to lever press on a continuous reinforcement schedule for positively reinforcing trains of electrical stimulation. Three measures of responding were calculated; the frequency at which responding was 50% of the maximum (M50), the asymptotic response rate and the total area under the curve (AUC) for each frequency sweep. Quinpirole (2.2-66.0 microg/kg SC) significantly increased M50 and reduced both asymptote and AUC. Quinelorane (0.25-79.0 microg/kg SC) had no significant effect on M50 values but significantly reduced both asymptote and AUC. (+/-)7-OH-DPAT (2.5-74.0 microg/kg) did not significantly affect any of the measures. The data show that low doses of quinpirole and quinelorane, but not (+/-)7-OH-DPAT, inhibit ICSS maintained by electrodes in the lateral hypothalamus. Either dopamine D2 or dopamine D3 receptor stimulation may play a role in mediating ICSS inhibition, but studies with more selective receptor agonists and antagonists are required to define the role of each receptor.

Sabcomeline (SB-202026), a functionally selective M1 receptor partial agonist, reverses delay-induced deficits in the T-maze

Sabcomeline, (SB-202026 [R-(Z)-alpha-(methoxyimino)-1 -azabicyclo [2.2.2] octane-3-acetonitrile]), a functionally selective muscarinic M1 receptor partial agonist, was tested in rats trained to perform a delayed, reinforced alternation task in a T maze, a test of short-term spatial memory. For comparison the cholinesterase inhibitor tacrine (THA-9-amino- 1,2,3,4-tetrahydroaminoacridine) and the non-selective muscarinic receptor agonist RS86 (2-ethyl-8-methyl-2,8 diazospiro [4.5]-decane-1,3-dione hydrobromide) were also tested and all three compounds were also compared using a conditioned taste aversion (CTA) task. Sabcomeline (0.001-1.0 mg/kg i.p.) significantly reversed the T-maze choice accuracy deficit induced by a 20-s delay at 0.03 and 0.1 mg/kg. RS86 (0.1-3.0 mg/kg i.p.) reversed the deficit at 1.0 mg/kg and THA (0.1-3.0 mg/kg i.p.) had no effect at any dose. All three compounds induced conditioned taste aversion with minimum effective doses (MED) of 0.3, 1.0 and 3.0 mg/kg, respectively. The results show that sabcomeline reverses delay induced deficits in T-maze choice accuracy in a rewarded alternation task at doses approximately 10 times lower than those required to induce conditioned taste aversion. RS86 was equipotent in both tests. These data support the findings of clinical studies which have shown that SB-202026 provides significant symptomatic improvement in patients with probable Alzheimer's disease at doses which do not induce cholinergic side effects.

The behavioural effects of corticotropin-releasing factor-related peptides in rats

The present study determined the behavioural effects of the corticotropin releasing factor (CRF)-related peptides, human/rat CRF (h/rCRF), ovine CRF (oCRF), sauvagine (SAUV), urotensin I (UT) and the recently discovered neuropeptide, rat urocortin (rUCN). All of the peptides dose-dependently increased motor activity in a familiar environment and reduced feeding in hungry rats. There was no apparent relationship between potency/affinity at CRF2 receptors and effects in these two tests. In a comparison of h/rCRF and rUCN upon discrete spontaneous behaviours, both peptides (3.0 microg i.c.v.) increased activity and grooming, induced a fore-paw tremor and reduced the incidence of motionlessness. However, h/rCRF reduced motionlessness to a greater extent and was a more potent inducer of defaecation, weight loss, oral movements and fore-paw tremor than rUCN. In the elevated X maze, both h/rCRF and rUCN (1.0 microg i.c.v.) had anxiogenic-like effects upon behaviour. In contrast, h/rCRF (1.0 microg i.c.v.), but not rUCN (1.0-10 microg i.c.v.) increased the startle response to an acoustic stimulus. In summary, all the CRF-related peptides increased motor activity and reduced feeding in rats in a similar manner and both rUCN and h/rCRF induced anxiogenesis. However, there were some behavioural differences between rUCN and h/rCRF which require further study. Further pharmacological investigation of the role of CRF receptor subtypes requires the use of subtype selective antagonists.

A comparison of rectal and subcutaneous body temperature measurement in the common marmoset

Two methods of measuring body temperature were compared in common marmosets. Subcutaneous temperatures were measured remotely via previously implanted subcutaneous microchips (Plexx BV, IPTT-100) prior to measurement of rectal temperature using a conventional rectal probe. Marmosets were treated with saline or the brain penetrant, 5-HT1A/B/D receptor agonist SKF-99101H (3-(2-dimethylaminoethyl)-4-chloro-5-propoxyindole hemifumarate) (0.3-3 mg/kg SC), which has previously been shown to induce hypothermia in guinea pigs. Body temperature was sampled immediately before drug administration and at 30-min intervals thereafter for a period of 2.5 h. SKF-99101H dose-dependently induced hypothermia in the common marmoset and there was close agreement between rectal and subcutaneous body temperatures, with an average difference in absolute body temperature of 0.26+/-0.02 degrees C. The data show that subcutaneously implanted microchips provide a simple, reliable measure of body temperature in common marmosets which is sensitive to pharmacological intervention, minimizes handling induced stress, and is minimally invasive.

The selective 5-HT1B receptor inverse agonist 1'-methyl-5-[[2'-methyl-4'-(5-methyl-1,2, 4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl]-2,3,6,7-tetrahydro- spiro[furo[2,3-f]indole-3,4'-piperidine] (SB-224289) potently blocks terminal 5-HT autoreceptor function both in vitro and in vivo

5-HT1 receptors are members of the G-protein-coupled receptor superfamily and are negatively linked to adenylyl cyclase activity. The human 5-HT1B and 5-HT1D receptors (previously known as 5-HT1Dbeta and 5-HT1Dalpha, respectively), although encoded by two distinct genes, are structurally very similar. Pharmacologically, these two receptors have been differentiated using nonselective chemical tools such as ketanserin and ritanserin, but the absence of truly selective agents has meant that the precise function of the 5-HT1B and 5-HT1D receptors has not been defined. In this paper we describe how, using computational chemistry models as a guide, the nonselective 5-HT1B/5-HT1D receptor antagonist 4 was structurally modified to produce the selective 5-HT1B receptor inverse agonist 5, 1'-methyl-5-[[2'-methyl-4'-(5-methyl-1,2, 4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl]-2,3,6, 7-tetrahydrospiro[furo[2,3-f]indole-3,4'-piperidine] (SB-224289). This compound is a potent antagonist of terminal 5-HT autoreceptor function both in vitro and in vivo.

Chronic mild stress-induced reductions in saccharin intake depend upon feeding status

The consumption of a weak saccharin solution was examined in rats subjected to chronic mild stress (CMS). Intake of saccharin was reduced in stressed animals compared to isolated and group control animals but saccharin preference was not affected. Removal of water deprivation from the CMS schedule did not alter the effects of CMS upon saccharin intake. However, when food deprivation was omitted entirely from the CMS schedule the reduction in saccharin intake was eliminated. Similarly, in animals habituated to the full CMS procedure, reduction in saccharin intake was abolished by omitting food deprivation or by delaying the intake test for 24 h. Both CMS and food deprivation reduced water intake but had no effect on food consumed during the fluid-intake test. The presence of food deprivation during CMS appears to be a key factor affecting saccharin intake. Our data suggest that saccharin intake is not an appropriate measure of stress and anhedonia.

Stimulation of 5-HT1B receptors causes hypothermia in the guinea pig

The selective, brain penetrant, 5-HT(1B/D) (formerly 5-HT(1D beta/alpha)) receptor agonist SKF-99101H (3-(2-dimethylaminoethyl)-4-chloro-5-propoxyindole hemifumarate) (30 mg/kg i.p.) causes a dose related fall in rectal temperature in guinea pigs which previous studies have shown to be blocked by the non-selective 5-HT(1B/D) receptor antagonist GR-127935 (N-[4-methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl) [1,1'biphenyl]-4-carboxamide oxalate). The present study shows that the hypothermic response to SKF-99101H is dose-dependently blocked by SB-224289G (1'-methyl-5-(2'-methyl-4'-[(5-methyl-1,2,4-oxadiazol-3-yl)bipheny l-4-yl]carbonyl)-2,3,6,7-tetrahydrospiro[furo[2,3-f]indole-3,4'-pi peridone] hemioxalate) (0.3-10.0 mg/kg p.o.) (ED50 3.62 mg/kg), which is the first compound to be described which is more than 60 fold selective for the 5-HT1B receptor over the 5-HT1D receptor. SB-216641A (N-[3-(2-dimethylamino) ethoxy-4-methoxy-phenyl] 2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-(1,1'-biphenyl)-4-car boxamide hydrochloride) (0.6-20.0 mg/kg i.p.), which is somewhat less selective (30 fold) for the 5-HT1B receptor over the 5-HT1D receptor had a similar effect (ED50 4.43 mg/kg). The brain penetrant 5-HT1D selective receptor antagonist, BRL-15572 (4-(3-chlorophenyl)-alpha-(diphenylmethyl)-1-piperazineethanol+ ++ dihydrochloride) (0.3-100.0 mg/kg i.p.) was inactive. When administered alone neither BRL-15572 (0.1-10 mg/kg i.p.) nor SB-224289G (2.2-22 mg/kg p.o.) had an effect on body temperature. These data demonstrate that 5-HT1B (formerly 5-HT(1D beta)) and not 5-HT1D (formerly 5-HT(1D alpha)) receptors mediate the hypothermic response to SKF-99101H (30 mg/kg i.p.) in guinea pigs. The compounds described are useful pharmacological tools for distinguishing responses to 5-HT1B and 5-HT1D receptors.

Parkinson's disease: prospects for improved drug therapy

L-Dopa has long been the mainstay of therapy for Parkinson's disease but its long-term shortcomings, principally uncoordinated, spasmodic or irregular movements (dyskinesias) and fluctuating control of motor symptoms (on/off fluctuations), are well documented. The postulated neuroprotective properties of L-deprenyl, often used as an adjunct to L-dopa, are under scrutiny and doubts have also been raised regarding its safety. Alternative therapeutic approaches are clearly needed. In this review, Jim Hagan, Derek Middlemiss, Paul Sharpe and George Poste outline some new approaches to treatment, with an emphasis on novel, selective dopamine receptor agonists. In addition, Parkinson's disease is commonly thought to be caused by the neurotoxic effects of an unidentified agent but recent data indicate a greater genetic component than previously recognized. Developments in the genetics of Parkinson's disease may provide the key to the next generation of therapeutics.

A computer-controlled apparatus for measuring and analysing myoclonic jerk activity in guinea pigs

Guinea pigs respond to 5-hydroxytryptophan (5-HTP) with a complex behavioural syndrome which includes distinctive whole-body jerks (myoclonic jerks). These are species-specific, involve all major muscle groups, are highly rhythmic and can occur with relatively high frequency (1-2/s). Current methods of quantifying the response, which rely on observer ratings are unsatisfactory. We report the development of a fully automated, PC-based system for detecting and analysing myoclonic jerks. Floor-mounted accelerometers generate a movement signal and detection is performed by an algorithm based on a detailed analysis of the topography of myoclonic jerk responses. The system can monitor the output from 10 purpose-built test enclosures and it provides for pseudorandom treatment allocation, flexible control of experimental parameters and automated data output to a spreadsheet which generates appropriate graphs, statistical summaries and data analysis. This robust response provides a useful means of exploring the role of novel 5-HT receptor subtypes in guinea-pig behaviour.

The role of 5-HT1D and 5-HT1A receptors in mediating 5-hydroxytryptophan induced myoclonic jerks in guinea pigs

Systemic administration of 5-hydroxytryptophan (5-HTP) to guinea pigs causes species-specific, rhythmic, whole body jerks (myoclonic jerks), the frequency and amplitude of which were measured in an automated apparatus. The brain penetrant 5-HT1D receptor agonist 3-(2-dimethylaminoethyl)-4-chloro-5-propoxyindole hemifumarate (SKF 99101H) (3-30 mg/kg i.p.) and the selective 5-HT1A receptor agonist (+/-)8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (0.3-3 mg/kg s.c.) dose dependently potentiated the frequency and intensity of myoclonic jerks caused by 5-HTP (100 mg/kg). Cotreatment of guinea pigs with 8-OH-DPAT (3 mg/kg s.c.) and SKF 99101H (30 mg/kg i.p.), which were inactive when given alone, gave a marked myoclonic jerk response. Conversely, the myoclonic jerk response to higher doses of 5-HTP (150 mg/kg i.p.) was dose dependently blocked by the 5-HT1D receptor antagonist GR 127935 (N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1 ,2,4-oxadiazol-3-yl)[1,1'-biphenyl]4-carboxamide oxalate) (ED50 0.32 mg/kg i.p.) and the selective 5-HT1A receptor antagonist WAY 100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride) (ED50 0.33 mg/kg i.p.). The response to 5-HTP (150 mg/kg i.p.) was also blocked by ritanserin (0.01-0.3 mg/kg i.p.). Our data therefore confirm previous reports concerning the effects of 5-HT2A/2C receptor blockade on 5-HTP induced myoclonic jerks and suggest that both 5-HT1D and 5-HT1A receptors play an important role in mediating this behavioural response.

Effects of granisetron, a 5-HT3 receptor antagonist, on morphine-induced potentiation of brain stimulation reward

Using the curve-shift method, we studied the effects of four doses (0.003, 0.03, 0.3 and 3 mg/kg, s.c.) of granisetron (endo-N-(9-methyl-9-azabicyclo[3.3.1]non-3-yl)-1-methyl-1H-indazole-3- carboxamide hydrochloride), a selective 5-hydroxytryptamine3 (5-HT3) receptor antagonist, on the potentiation of brain stimulation reward by microinjection of 2.5 micrograms/0.25 microliters of morphine sulphate (7,8-didehydro-4,5-epoxy-17-methylmorphinan-3,6-diol sulphate) into the ventral tegmental area. As previously reported, morphine produced a significant reduction in reward threshold without altering maximal rates of responding. Granisetron attenuated the potentiating effect of morphine at the highest dose and failed to alter reward threshold or maximal rates of responding when given alone, except at the lowest dose where a small and statistically significant increase in threshold was found. These results provide additional evidence that 5-HT3 receptor antagonists may reduce the rewarding effect of opiates and do not impair the ability to produce operant responses. The weak attenuation observed with granisetron alone suggests that 5-HT3 receptors are unlikely to constitute an important influence on the directly stimulated reward-relevant pathway(s).

The 5 -HT3 receptor antagonists, granisetron and ondansetron, do not affect cocaine-induced shifts in intra-cranial self-stimulation thresholds

The effects of the 5-HT( 3) receptor antagonists, granisetron and ondansetron, were investigated on behaviour maintained by intracranial self-stimulation (ICSS). Rats, implanted with bipolar electrodes in the lateral hypothalamus, were trained to lever press on a continuous reinforcement schedule for positively reinforcing trains of electrical stimulation. The frequency at which responding reached 50% of maximum (M50) and the maximum rate of responding (asymptote) were used to measure drug effects. Granisetron (0.01-0.1 mg/kg i.p ) and ondansetron (0.03-0.3 mg/kg i.p ) had no effect on either parameter. In contrast, cocaine (20 mg/kg i.p ) potentiated rewarded responding, reducing M50 values, but neither granisetron (0.01-3.0 mg/kg i.p ) nor ondansetron (0.03-0.3 mg/kg i.p ) blocked this effect. Neither did granisetron (0.1-10.0 mg/kg i.p ) alter the effect of lower doses of cocaine (10 mg/kg i.p.). These data suggest that 5 -HT( 3) receptors do not play a significant role in mediating responding maintained by ICSS in the rat through hypothalamic electrodes. Neither do they modulate cocaine-induced potentiation of the behaviour.

5-HT 1D receptors mediate SKF 99101H-induced hypothermia in the guinea pig

The selective, brain penetrant, 5-HT(1D) receptor agonist SKF 99101H (10-30 mg/kg i.p.) caused a dose-related fall in rectal temperature in guinea pigs which lasted longer than 2 h. Sumatriptan (1.0-100 mg/kg i.p.), a selective 5-HT(1D) agonist which does not penetrate the brain, did not produce hypothermia, suggesting that peripheral mechanisms are not critically involved in the response. The hypothermia induced by SKF 99101H (30 mg/kg i.p.) was dose-dependently blocked by the 5-HT(1D) receptor antagonists GR 127935 (0.01-1 mg/kg i.p.) and GR 125743 (0.01-3 mg/kg i.p.), confirming the role of 5-HT(1D) receptors. Mianserin (0.3-10.0 mg/kg i.p.) and granisetron (0.1-3.0 mg/kg i.p.) were inactive, suggesting that 5-HT(2A/2B/2C) or 5-HT( 3) receptors play no significant role in the generation of the hypothermic response. Nor was the hypothermia reversed by prazosin (0.03-1.0 mg/kg i.p.), idazoxan (0.03-1.0 mg/kg i.p.) or scopolamine (0.01-0.3 mg/kg i.p.), thereby excluding mediation by α(1)- and α(2)-adrenoceptors and muscarinic receptors. WAY 100635 (0.1-1.0 mg/kg) significantly potentiated the effect of SKF 99101H. The antagonists, when given alone, had no effect on body temperature, with the exception of prazosin (0.1 and 1.0 mg/kg). Three days of treatment with parachloroamphetamine (30 mg/kg i.p.) depleted forebrain 5-HT by ∼ 75% in frontal cortex, hypothalamus, hippocampus and striatum, but failed to alter the hypothermic response to SKF 99101H. The hypothermia is, therefore, unlikely to be mediated by 5-HT(1D) receptors located on 5-HT neurons. SKF 99101H-induced hypothermia in the guinea pig may serve as a useful model for investigation of centrally acting 5-HT( 1D) receptor antagonists.

Behavioural and electrophysiological studies of entorhinal cortex lesions in the rat

Bilateral ibotenic acid injections aimed at the entorhinal cortex (EC) lesioned the EC and subiculum in 30% of animals (group EC/S) and caused additional hippocampal damage in 50% (group RH). Both lesions increased acetylcholinesterase (AChE) staining in the intermediate molecular layer of the dentate gyrus. EC/S lesions increased diurnal deep sleep and the incidence of spindles but decreased REM sleep. RH lesions increased nocturnal deep sleep and decreased nocturnal quiet sleep. Both lesions reduced power over the theta frequency range from 6-10 Hz for epochs of REM sleep and quiet waking but not deep sleep. Peak frequency was unaffected. The RH group and a subset of the EC/S group were nocturnally, but not diurnally, hyperactive. Six weeks after the lesion there was no evidence for hyperactivity in a novel open field. The EC/S lesion impaired exploration as indicated by reduced motility and rearing in an open field and by the failure of EC/S-lesioned rats to increase contact time in response to a novel olfactory cue. Place navigation learning in a Morris maze was not affected by EC/S or RH lesions. However, when the spatial location of the hidden platform was shifted EC/S-lesioned rats were impaired. The sprouting response, reduced theta power and exploration deficits resemble those reported following electrolytic lesions, but the lack of effect on place navigation learning contrasts with reports of impaired spatial learning following electrolytic lesions. The data prompt a reexamination of the role which the EC projection to the hippocampus plays in spatial learning.

Morphological, neurochemical, and behavioral studies on serotonergic denervation and graft-induced reinnervation of the rat hippocampus

A procedure was developed to conduct simultaneously immunocytochemical and neurochemical studies on the serotonergic system in adjacent 300-micron-thick slices of rat hippocampus. This procedure was applied to correlate morphological (innervation pattern and density), neurochemical (5-hydroxytryptamine and 5-hydroxyindolacetic acid levels and [3H]5-hydroxytryptamine uptake and release) and behavioral (spatial learning) effects of neurotoxin-induced denervation and reinnervation by grafting fetal mesencephalic raphe cells. Intracerebroventricular injections of a low dose of 5,7-dihydroxytryptamine caused a discrete serotonergic denervation of the hippocampus. Eleven months after lesioning, 5-hydroxytryptamine and 5-hydroxyindolacetic acid levels and [3H]5-hydroxytryptamine uptake capacity were decreased by 50-60%. By this time, the residual fibers displayed an enhanced vulnerability towards K(+)-induced depolarization. Grafting of a fetal raphe cell suspension resulted in a reinnervation of the host hippocampus. The pattern of reinnervation was comparable to control innervation and the density was supranormal at the level of the graft. As observed semiquantitatively, the innervation density decreased with distance from the core of the graft. Neurochemical studies showed that the fibers were capable of synthesizing, metabolizing and releasing 5-hydroxytryptamine. The turnover of 5-hydroxytryptamine in both the denervated and the reinnervated hippocampus was comparable to that in control tissue. Previous behavioral testing of the denervated and of the denervated and implanted animals did not reveal any effect on spatial learning, either in an individual or in a social test paradigm. The latter data substantiate the notion that interference with the hippocampal serotonergic innervation does not hamper adequate spatial learning.

Reaction of gadolinium chelates with endogenously available ions

The extent of reaction of 153Gd-radiolabeled Gd(L) chelates with 25 mM CO23- (25 mF), PO34-, Zn2+ and Cu2+ at pH 7 was determined for L = EDTA, DTPA, DOTA, HP-DO3A, and DO3A. Gd(EDTA)- and Gd(DTPA)2- reacted (greater than 20% in 10 min) with Cu2+ and Zn2+ in the presence of PO34-. These double replacement reactions yielded precipitated GdPO4 and chelated Cu(L). Gd(HP-DO3A), Gd(DO3A) and Gd(DOTA)- were inert to reaction with all four ions at room temperature (less than or equal to 1% reaction detected). The thermodynamic binding constants of the ligands for Gd3+ and Cu2+ were found to be equal (10(20) M-1) for DO3A, while DOTA and HP-DO3A favored Gd3+ over Cu2+ by greater than or equal to 10(2) M-1. The low order of reactivity of Gd(DOTA)- and Gd(HP-DO3A) was anticipated by the binding constants, but the lack of reactivity of Gd(DO3A) is attributed to kinetic inertia. This latter property, desirable in MRI contrast agents, is promoted by the conformational stability of the tetraazacyclododecane macrocycle, which forms the backbone of the ligand. It is concluded that this class of chelates is exceptionally inert in solutions of endogenously available ions, and that thermodynamics alone is an insufficient predictor of the reactivity of the highly inert Gd complexes based on the tetraazamacrocycle.

The effects of forebrain ischaemia on spatial learning

Rats were subjected to 15 min of forebrain ischaemia using the 4-vessel occlusion method. Following recovery they were trained using place navigation learning in a Morris water maze and forced choice rewarded alternation in a T-maze. Ischaemic rats were impaired in place navigation learning but the deficit was transient and there was no impairment of subsequent transfer test performance. Food-rewarded forced-choice alternation in a T-maze revealed a persistent impairment in ischaemic rats. The behavioural deficits were associated with neuropathological damage in the CA1 cell layer of the dorsal hippocampus with varying degrees of damage in layers CA2, CA3 and CA4. Granule cells in the dentate gyrus were not visibly affected. Variable amounts of lesion damage were found in the dorsolateral striatum. Ischaemic rats are therefore impaired on both place navigation and forced choice rewarded alternation, suggesting that ischaemic brain damage affects reference and working memory processes to different extents. Forced choice alternation may be the more sensitive method of assessing cognitive changes caused by forebrain ischaemia.

Therapeutic effect of THA on hemicholinium-3-induced learning impairment is independent of serotonergic and noradrenergic systems

Tetrahydroaminoacridine (THA: Tacrine) has previously been shown to reverse deficits in spatial discrimination learning induced by hemicholinium-3 (HC-3). In the present experiments the effects of prior depletion of serotonin (5-HT) or noradrenaline (NA) on this reversal were examined. In the first experiment 5-HT lesions were made by injecting 5,7-DHT (2 x 50 micrograms/5 microliters) into the lateral ventricles of rats pretreated with desmethylimipramine (DMI 25 mg/kg IP). A permanently indwelling guide tube was then implanted over the right lateral ventricle. Subsequent testing under drug-free conditions, revealed no effect of the lesion on the number of trials needed to attain criterion (nine consecutive correct choices) in two-platform spatial discrimination learning in a watermaze. Using a latin square design rats were then tested for the effects of HC-3 and THA. HC-3 (5 micrograms/5 microliters ICV) or placebo (CSF) were injected 60 min before the start of a 30-trial training session. THA (4.6, 10 mg/kg SC) or placebo were then injected 15 min before training. Choice accuracy but not choice latency was significantly impaired by HC-3 and the effect was reversed by THA in both sham operated and 5-HT lesioned rats. In the second experiment two injections of DSP-4 (50 mg/kg IP) were given, following cannulation, to deplete forebrain NA. The lesion had no effect on spatial learning under drug-free conditions and failed to block the THA-induced reversal of spatial discrimination learning deficits following HC-3. These results confirm that forebrain Ach depletion by HC-3 impairs spatial discrimination learning and that the deficit is reversed by THA.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemicholinium-3 impairs spatial learning and the deficit is reversed by cholinomimetics

The effects of hemicholinium-3 (HC-3) on spatial discrimination learning were studied. Rats were equipped with indwelling cannulae in the right lateral ventricle and, following recovery, were trained on a two platform spatial discrimination task in a water maze. In this task a visible escape platform remains in a fixed position in the pool during a single training session, whilst the location of an identical "float" (which affords no escape) is randomly varied. For each session the location of the fixed escape platform was changed and the rats were retrained to criterion following pretreatment either with artificial cerebrospinal fluid (CSF) or HC-3 (2.5, 5.0 micrograms/rat/ICV) 1 h before training. Each rat received every treatment according to a latin square design. The results showed that spatial learning was dose dependently impaired by HC-3, choice accuracy being reduced to chance levels by the higher dose. There was no evidence of motoric difficulty, as choice latencies were not significantly increased. Experiments were then conducted to test for reversal of the deficit using a range of psychotropic drugs. Rats were treated with CSF or HC-3 (5 micrograms/rat ICV) 60 min prior to testing and test drugs were injected 15 min before testing. Some doses of physostigmine (46-460 micrograms/kg/SC) and tetrahydroaminoacridine (THA) (2.2-10 mg/kg/SC) reversed the spatial learning deficit. The muscarinic agonists arecoline (0.046-1 mg/kg/SC), aceclidine (1-10 mg/kg/SC), oxotremorine (30-100 micrograms/kg/SC) and RS-86 (0.46, 1.0 microgram/kg/SC) were also effective. Pilocarpine (0.22-2.2 mg/kg/SC) showed marginal activity and isoarecoline (4.6-10 mg/kg/SC) was inactive. Nicotine (0.32, 1, 3.2 mg/kg/SC) and piracetam (10, 30, 100 mg/kg IP) were also inactive. The alpha 2 agonist, clonidine (46, 100 micrograms/kg SC) and the antagonist idazoxan (32, 100 micrograms/kg SC) were also inactive. Learning deficits were not reversed by haloperidol (20, 60 micrograms/kg), amphetamine (0.1, 0.46 mg/kg), the selective 5-HT1A agonist 8-OH-DPAT (30, 100 micrograms/kg) or by the benzodiazapine antagonist ZK-93426 (1, 3.2, 10 mg/kg). The results show that forebrain Ach depletion by HC-3 impairs spatial discrimination learning and these deficits are reversed by cholinesterase inhibitors and some muscarinic receptor agonists. Some degree of pharmacological selectivity is indicated by the failure of a range of other drugs to reverse the impairments.