Stimulation of postsynaptic 5-HT1A receptors is responsible for the anticonflict effect of ipsapirone in rats

Serotonin-related, anxiety/aggression-driven, stressor-precipitated depression. A psycho-biological hypothesis

The concept of a 5-HT related, anxiety and/or aggression-driven, stressor-precipitated depression is formulated and discussed. It comprises the following elements. The 5-HT ergic disturbances found in some depressed individuals - and of them particularly lowered CSF 5-HIAA - are linked to the anxiety- and the aggression-components of the depressive sydrome. In this type of depression - called 5-HT related depression - dysregulation of anxiety and/or aggression are primordial and mood lowering is a derivative phenomenon. In other words this is a group of anxiety/aggression-driven depressions. The 5-HT ergic impairment in certain types of depression is a trait-phenomenon, ie, persists during remission. This disturbance makes the individual susceptable for perturbation of anxiety- and aggression-regulation. Anxiety and (overt or suppressed) anger, are core constituents of the stress-syndrome. Thus, the 5-HT ergic disturbance will induce a heightened sensitivity for stressful events, ie, the latter will induce more readily than normal, stress phenomena , among which anxiety and anger. The latter psychological features induce lowering of mood and thus “drive” the patient into a fullblown depression. Furthermore it is predicted that anxiolytics and serenics (ie, anti-aggressive drugs) that act via normalisation of 5-HT ergic circuits, will exert a antidepressant effect in 5-HT related depression, in addition to their therapeutic actions in anxiety disorders and states of increased aggressiveness, respectively. The exact nature of the 5-HT ergic impairment in 5-HT related depression has yet to be elucidated.

5-HT1A receptor-dependent modulation of emotional and neurogenic deficits elicited by prolonged consumption of alcohol

Repeated episodes of binge-like alcohol consumption produce anxiety, depression and various deleterious effects including alterations in neurogenesis. While the involvement of the serotonin receptor 1 A (5-HT1A) in the regulation of anxiety-like behavior and neurogenesis is well documented, its contribution to alcohol withdrawal-induced anxiety and alcohol-induced deficits in neurogenesis is less documented. Using the Drinking-In-the-Dark (DID) paradigm to model chronic long-term (12 weeks) binge-like voluntary alcohol consumption in mice, we show that the selective partial activation of 5-HT1A receptors by tandospirone (3 mg/kg) prevents alcohol withdrawal-induced anxiety in a battery of behavioral tests (marble burying, elevated-plus-maze, open-field), which is accompanied by a robust decrease in binge-like ethanol intake (1 and 3 mg/kg). Furthermore, using triple immunolabelling of proliferation and neuronal differentiation markers, we show that long-term DID elicits profound deficits in neurogenesis and neuronal fate specification in the dorsal hippocampus that are entirely reversed by a 2-week chronic treatment with the 5-HT1A partial agonist tandospirone (3 mg/kg/day). Together, our results confirm previous observations that 5-HT1A receptors play a pivotal role in alcohol drinking behavior and the associated emotional and neurogenic impairments, and suggest that 5-HT1A partial agonists represent a promising treatment strategy for alcohol abuse.

Therapeutic role of 5-HT1A receptors in the treatment of schizophrenia and Parkinson's disease

5-HT(1A) receptors have long been implicated in the pathogenesis and treatment of anxiety and depressive disorders. Recently, several lines of studies have revealed new insights into the therapeutic role of 5-HT(1A) receptors in treating schizophrenia and Parkinson's disease. Specifically, 5-HT(1A) receptors seem to be a promising target for alleviating antipsychotic-induced extrapyramidal side effects (EPS) and cognitive/affective disorders in schizophrenia. In the treatment of patients with Parkinson's disease, 5-HT(1A) agonists are expected to improve not only affective symptoms (e.g., anxiety and depression), but also the core parkinsonian symptoms as well as antiparkinsonian agents-induced side effects (e.g., L-DOPA-induced dyskinesia). Here, the therapeutic mechanisms mediated by 5-HT(1A) receptors in schizophrenia and Parkinson's disease are reviewed. This evidence should encourage discovery of new 5-HT(1A) ligands, which can resolve the unmet clinical needs in the current therapy.

Involvement of presynaptic 5-HT(1A) and benzodiazepine receptors in the anticonflict activity of 5-HT(1A) receptor antagonists

In the present paper, we examined the effect of lesions of 5-hydroxytryptamine (5-HT) neurons, produced by p-chloroamphetamine (p-CA; 2 x 10 mg/kg), and the influence of flumazenil (Ro 15-1788, 10 mg/kg), a benzodiazepine receptor antagonist, on the anticonflict activity of N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide (WAY 100635) and trans-1-(2-methoxy-phenyl)-4-[4-succinimidocyclohexyl]piperazine (MP 349), pre- and postsynaptic 5-HT(1A) receptor antagonists, and 1-(2-methoxyphenyl)-4-(4-succinimidobutyl)piperazine (MM 77), a postsynaptic 5-HT(1A) receptor antagonist, in the Vogel conflict drinking test in rats. Diazepam was used as a reference compound. WAY 100635 (0.5-1 mg/kg), MP 349 (0.25-0.5 mg/kg), MM 77 (0.03-0.25 mg/kg) and diazepam (2.5-5 mg/kg) significantly increased the number of shocks accepted during experimental sessions in the conflict drinking test. In p-chloroamphetamine-pretreated rats, neither WAY 100635 (1 mg/kg) nor MP 349 (0.25 mg/kg) induced an anticonflict effect, whereas MM 77 (0.06 mg/kg) did produce it. Flumazenil fully blocked the anticonflict effects of WAY 100635 (1 mg/kg) and diazepam (5 mg/kg), and it partly but significantly reduced the anticonflict effects of MP 349 (0.25 mg/kg) and MM 77 (0.06 mg/kg). p-Chloroamphetamine and flumazenil alone were inactive in the conflict drinking test. The present results suggest that, first, the anticonflict effect of the 5-HT(1A) receptor antagonists, WAY 100635 and MP 349, but not MM 77, is linked to the presynaptically located 5-HT(1A) receptors, and second, benzodiazepine receptors are indirectly involved in such effects of WAY 100635, MP 349 and MM 77, due maybe to a possible interaction between the 5-HT and the gamma-aminobutyric acid (GABA)/benzodiazepine systems.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

The Vogel conflict test: procedural aspects, gamma-aminobutyric acid, glutamate and monoamines

A multitude of mechanisms are involved in the control of emotion and in the response to stress. These incorporate mediators/targets as diverse as gamma-aminobutyric acid (GABA), excitatory amino acids, monoamines, hormones, neurotrophins and various neuropeptides. Behavioural models are indispensable for characterization of the neuronal substrates underlying their implication in the etiology of anxiety, and of their potential therapeutic pertinence to its management. Of considerable significance in this regard are conflict paradigms in which the influence of drugs upon conditioned (trained) behaviours is examined. For example, the Vogel conflict test, which was introduced some 30 years ago, measures the ability of drugs to release the drinking behaviour of water-deprived rats exposed to a mild aversive stimulus ("punishment"). This model, of which numerous procedural variants are discussed herein, has been widely used in the evaluation of potential anxiolytic agents. In particular, it has been exploited in the characterization of drugs interacting with GABAergic, glutamatergic and monoaminergic networks, the actions of which in the Vogel conflict test are summarized in this article. More recently, the effects of drugs acting at neuropeptide receptors have been examined with this model. It is concluded that the Vogel conflict test is of considerable utility for rapid exploration of the actions of anxiolytic (and anxiogenic) drugs. Indeed, in view of its clinical relevance, broader exploitation of the Vogel conflict test in the identification of novel classes of anxiolytic agents, and in the determination of their mechanisms of action, would prove instructive.

Effects of 8-OHDPAT administration into the dorsal raphe nucleus and dorsal hippocampus on fear behavior and regional brain monoamines distribution in rats

The effects of R(+)-8-hydroxy-dipropylaminotetralin (8-OHDPAT) administration into the dorsal raphe nucleus (DRN) or bilaterally into the dorsal hippocampus (HIP) on fear behavior in a modified version of the light-dark transitions test and regional brain monoamines (NA, DA, 5-HT) and their metabolites (MHPG, DOPAC, 5-HIAA) in the hypothalamus, midbrain central gray matter, amygdala, hippocampus and pons were examined. The experiments were performed on 36 male, 3-month old Wistar rats. Administration of 8-OHDPAT (200 ng) into the DRN reduced time out from the illuminated part of the chamber and time of motionless behavior in the illuminated part, increased the number of returns from the dark to illuminated part and number of head dipping from the dark to illuminated part without effect on time of motionless behavior in the dark part and on time of locomotor activity in the illuminated as well as in dark part of the chamber. HPLC analysis showed reduction of 5-HT content in the midbrain and amygdala, reduction of 5-HIAA content in pons, increased 5-HIAA/5-HT ratio in the hippocampus and increased DOPAC/DA ratio in the hypothalamus, midbrain, hippocampus and pons without affecting the MHPG/NA ratio and NA content. The administration of 8-OHDPAT (100 ng per site) into the HIP reduced time out from the illuminated part of chamber, time of locomotor activity in the illuminated part and head dipping from the dark to illuminated part without effect on the number of returns from the dark to illuminated part, time of locomotor activity in the dark part and time of motionless in the illuminated as well as in the dark part of chamber. HPLC analysis showed reduction of NA content in the hypothalamus, amygdala and pons, increased the MHPG content in all the investigated structures, increased MHPG/NA ratio in all the investigated structures except the hypothalamus. Dopamine content decreased in the hypothalamus and amygdala, and DOPAC/DA ratio increased in the amygdala and hippocampus. Concentrations of 5-HT, 5-HIAA and 5-HIAA/5-HT ratio were unchanged. The results obtained indicate that 8-OHDPAT acting on the pre-synaptic 5-HT1A receptors decreases fear behavior and acting on 5-HT1A post-synaptic receptors increases fear behavior in the light-dark transitions test. The neurochemical base of anxiolytic and anxiogenic effects evoked by 8-OHDPAT is being discussed.

Influence of 5-HT1A receptor antagonism on plus-maze behaviour in mice. II. WAY 100635, SDZ 216-525 and NAN-190

To understand further the role of 5-hydroxytryptamine receptor subtype 1A (5-HT1A) mechanisms in anxiety, the behavioural effects of 5-HT1A receptor antagonists with different selectivity and intrinsic activity were examined using an ethological version of the murine elevated plus-maze test. WAY 100635 (0.03-9.0 mg/kg) produced a behavioural profile indicative of an anxiolyticlike effect, with an apparent bell-shaped dose-response relationship and increases in nonexploratory behaviours at the largest dose tested. SDZ 216-525 exerted a dose-dependent antianxiety action at doses of 0.05-0.8 mg/kg, with some loss of activity at 3.2 mg/kg. In contrast, smaller doses of NAN-190 had a significant effect, whereas higher doses (2.5-10.0 mg/kg) decreased locomotor activity and other active behaviours, a profile similar to that produced by the alpha1-adrenoceptor antagonist prazosin (2.5 mg/kg), which also inhibited open arm activity. Findings are discussed in relation to 5-HT1A receptor and alpha1-adrenoceptor antagonism and corresponding neurochemical changes. The results of the present series support the view that 5-HT1A receptor antagonists have therapeutic potential in the management of anxiety.

Faulty cortisol/serotonin interplay. Psychopathological and biological characterisation of a new, hypothetical depression subtype (SeCA depression)

The hypothesis is proposed of a new subtype of depression named: stressor-precipitated, cortisol-induced, serotonin-related, anxiety/aggression-driven depression (SeCA depression). Biologically, these patients are characterized by impaired 5-HT synthesis and reduced 5-HT1A receptor sensitivity. Under normal conditions these functions proceed marginally; in times of stress they easily fail, due to sustained overproduction of cortisol. Psychopathologically this depression type shows the following characteristics: anxiety and aggression, not mood lowering, heralding a depressive episode; the personality structure shows 'character neurotic' impairments and tolerance for (certain) traumatic life events is low. As specific therapeutic agents selective 5-HT1A agonists and cortisol or CRH antagonists are proposed. Prophylactically, maintenance treatment with 5-HT1A agonists seems indicated as well as psychological interventions to increase the stressor threshold.

Sleep and EEG power spectrum effects of the 5-HT1A antagonist NAN-190 alone and in combination with citalopram

The sleep and waking and EEG power spectrum effects of the putative 5-HT1A antagonist NAN-190 (0.5 mg/kg, i.p.) were studied alone and in co-administration with the selective serotonin re-uptake inhibitor citalopram (5.0 mg/kg, i.p.) in the rat. Citalopram, as in a prior dose-response study, reduced REM sleep. In addition, a slight increase in NREM sleep was observed. Citalopram reduced NREM fronto-parietal (FP) EEG power density in the 5-20 Hz range. When administered alone, NAN-190 suppressed REM sleep in the first 2 h, and reduced SWS-2 in the first 4 after administration. NAN-190 also suppressed selectively NREM sleep slow-wave activity in both fronto-frontal (FF) and FP EEG power spectrum. When administered in combination with citalopram, an attenuation of the power density reduction in the 7-15 Hz range in the FF EEG of citalopram alone, was observed. However, the EEG power spectral density and REM sleep suppressive effects of NAN-190 were both augmented. The results are compatible with the notion that serotonin is involved in the modulation of the slow wave activity in the EEG during NREM sleep. The results are cordant with other data suggesting that postsynaptic 5-HT1A stimulation might increase slow wave activity in the NREM EEG, and that serotonergic stimulation of other receptor subtypes (possibly 5-HT2) may decrease slow wave activity in the NREM EEG.

Sleep/waking effects following intrathecal administration of the 5-HT(1A) Agonist 8-OH-DPAT alone and in combination with the putative 5-HT(1A) antagonist NAN-190 in rats

Sleep, waking, and EEG power spectra were investigated in rats after intrathecal (IT) administration of a 5-HT(1A) agonist and a 5-HT(1A) antagonist. Total slow wave sleep (TSWS) was increased and waking was decreased over the 8-h recording period after the 5-HT(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (38 nmol). Within TSWS, SWS1 was unchanged while SWS-2 tended to be increased. The 5-HT(1A) antagonist 1-[2-Methoxyphenyl)-4-(4-(2-phthalimido)-butyl]piperazine hydrobromide (NAN-190) did not change any sleep/waking stages. Combined treatment with 8-OH-DPAT and NAN-190 increased variance. Following the combination, sleep and waking were not significantly different from control. SWS-2 tended to be reduced compared to the effect of 8-OH-DPAT alone. There were no systematic changes in neither waking nor TSWS fronto-frontal or fronto-parietal EEG power spectrum after any of the treatments, indicating that sleep quality was not changed. The results confirm earlier data suggesting that in the spinal cord, stimulation of 5-HT(1A) receptors have a dampening effect on transmission of sensory information, leading to deactivation and thereby increased sleep tendency. The reason why the 8-OH-DPAT effect was not clearly antagonized by the putative 5-HT1A antagonist NAN-190, may be due to the generally weak antagonistic and also partial agonistic effect of NAN-190 as reported in the literature.

5-HT1A receptor full and partial agonists and 5-HT2C (but not 5-HT3) receptor antagonists increase rates of punished responding in rats

Drugs with different intrinsic activity at 5-HT1A receptors and antagonists at 5-HT2A/2C and 5-HT3 receptors were studied for their ability to increase the rates of punished operant responding in rats. Like chlordiazepoxide (5 and 10 mg/kg) and diazepam (1.25 and 2.5 mg/kg), 0.125 mg/kg 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a 5-HT1A receptor agonist, and 5 and 10 mg/kg ipsapirone, a partial agonist at these receptors, increased the rates of punished responding, whereas (S)-WAY 100135, a 5-HT1A receptor antagonist, had no effect at doses from 1 to 10 mg/kg. 8-OH-DPAT and ipsapirone, like benzodiazepines, significantly reduced unpunished responding. The 5-HT2A/2C receptor antagonists ritanserin (2 mg/kg), mianserin (8 mg/kg), and mesulergine (0.1 mg/kg) significantly increased the rates of punished responding, whereas 0.5-2 mg/kg ketanserin, that has higher affinity for 5-HT2A than 5-HT2C receptors, had no effect. Antagonists, at 5-HT3 receptors such as ondansetron (0.001-0.1 mg/kg) and tropisetron (0.001-0.1 mg/kg), had no effect on punished or unpunished responding. The results show that agents acting as full or partial agonists at 5-HT1A receptors and blockers of postsynaptic 5-HT2C receptors have anxiolytic-like effects in a model of punished operant responding, whereas antagonists at 5-HT1A and 5-HT3 receptors have no such effect.

Presynaptic 5-HT1A receptors mediate the effect of ipsapirone on punished responding in rats

The effect of ipsapirone, a partial agonist at 5-HT1A receptors, and of diazepam on punished operant responding was studied in rats injected intracerebroventricularly with 150 microg 5,7-dihydroxytryptamine to deplete brain serotonin or pretreated with (S)-WAY 100135 (N-tert-butyl) 3-4-(2-methoxyphenyl)piperazin-1-yl-2-phenylpropanamide dihydrochloride), an antagonist at 5-HT1A receptors. 5,7-Dihydroxytryptamine markedly depleted brain serotonin and caused a sustained increase in punished responding with no effect on rates of unpunished responding in sham-operated rats but had no effect in animals which had received 5,7-dihydroxytryptamine. At 5 and 10 mg/kg ipsapirone reduced unpunished responding similarly in sham-operated and 5,7-dihydroxytryptamine-treated rats. Diazepam 2.5 mg/kg i.p.significantly increased punished responding and reduced rates of unpunished responding similarly in sham-operated and in 5,7-dihydroxytryptamine-treated animals. At 3 and 10 mg/kg (S)-WAY 100135 did not modify punished or unpunished responding but at 10 mg/kg it completely antagonized the effect of 5 mg/kg/s.c. ipsapirone on unpunished and punished responding. The results suggest that ipsapirone releases behaviour that is suppressed by punishment by stimulating presynaptic 5-HT1A receptors.

The role of hippocampal 5-hydroxytryptamine 1A (5-HT1A) receptors in the anticonflict activity of beta-adrenoceptor antagonists

The nonselective beta-adrenoceptor antagonists pindolol and cyanopindolol, which bind to 5-HT1A and 5-HT1A receptors showed an anticonflict effect by increasing the number of punished licks in the Vogel conflict test in rats, when administered directly into the CA, region of the dorsal hippocampus (i.hp.). The maximum effect was observed after intrusion of 1 microgram of pindolol and 3 microgram of cyanopindolol. However, the selective beta 1-and beta2-adrenoceptor antagonists betaxolol and ICI 118,551, respectively, which have a negligible affinity for 5-HT receptors, did not affect the punished responding, when administered i.hp. in doses up to 10 micrograms. The anticonflict effect of pindolol (1 microgram) was significantly reduced by (S)-WAY 100135, a selective 5-HT1A-receptor antagonist, administered i.hp (0.1 microgram) or s.c. (10 mg/kg). Furthermore, (S)-WAY 100135 injected i.hp (0.3 micrograms) significantly antagonized the anticonflict effect of pindolol injected i.p. (8 mg/kg). (S)-WAY 100135 given alone i.hp. (0.03-3 micrograms) or s.c. (5-10 mg/kg) did not affect the punished responding in rats. These results indicate that the anticonflict effect of the beta-blockers which were tested, or at least pindolol, depends on their agonist action on postsynaptic 5-HT1A receptors located in the hippocampus.

Aggression, anxiety and vocalizations in animals: GABAA and 5-HT anxiolytics

A continuing challenge for preclinical research on anxiolytic drugs is to capture the affective dimension that characterizes anxiety and aggression, either in their adaptive forms or when they become of clinical concern. Experimental protocols for the preclinical study of anxiolytic drugs typically involve the suppression of conditioned or unconditioned social and exploratory behavior (e.g., punished drinking or social interactions) and demonstrate the reversal of this behavioral suppression by drugs acting on the benzodiazepine-GABAA complex. Less frequently, aversive events engender increases in conditioned or unconditioned behavior that are reversed by anxiolytic drugs (e.g., fear-potentiated startle). More recently, putative anxiolytics which target 5-HT receptor subtypes produced effects in these traditional protocols that often are not systematic and robust. We propose ethological studies of vocal expressions in rodents and primates during social confrontations, separation from social companions, or exposure to aversive environmental events as promising sources of information on the affective features of behavior. This approach focuses on vocal and other display behavior with clear functional validity and homology. Drugs with anxiolytic effects that act on the benzodiazepine-GABAA receptor complex and on 5-HT1A receptors systematically and potently alter specific vocalizations in rodents and primates in a pharmacologically reversible manner; the specificity of these effects on vocalizations is evident due to the effectiveness of low doses that do not compromise other physiological and behavioral processes. Antagonists at the benzodiazepine receptor reverse the effects of full agonists on vocalizations, particularly when these occur in threatening, startling and distressing contexts. With the development of antagonists at 5-HT receptor subtypes, it can be anticipated that similar receptor-specificity can be established for the effects of 5-HT anxiolytics.

5-Hydroxytryptamine pathways in anxiety and its treatment

The effects of manipulating 5-hydroxytryptamine (5HT) neuronal function in humans and in animals are reviewed. 5HT pathways do not have a unitary function in modulating anxiety. It is proposed that, rather than acting as input or output channels for brain aversive systems, these pathways provide information concerning waking/motor status, which is crucial to the organisation of appropriate responses to threat. Each terminal region can make use of this information in different ways. Globally, the influence of 5HT neurones on higher centres appears predominantly to facilitate information processing relevant to threat, while their major influence on brainstem centres may be a restraining one.

5-Hydroxytryptamine-interacting drugs in animal models of anxiety disorders: more than 30 years of research

An overview of the behavioral data arising from the vast literature concerning the involvement of 5-hydroxytryptamine (5-HT) neurotransmission in the regulation of anxiety is presented. More than 1300 experiments were carried out in this area and they provide evidence that: (1) results obtained in ethologically based animal models of anxiety with drugs stimulating 5-HT transmission are most consistent with the classic 5-HT hypothesis of anxiety in that they show an increase in animals' emotional reactivity; (2) no category of anti-anxiety models are selectively sensitive to the anxiolytic-like effects of drugs targetting 5-HT1A, 5-HT2A or 5-HT2C receptor subtypes; (3) anxiolytic-like effects of 5-HT3 receptor antagonists, in the great part, are revealed by models based on spontaneous behaviors. Taken together, these observations lead to the conclusion that different 5-HT mechanisms, mediated by different receptor subtypes, are involved in the genesis of anxiety.

Anxiolytic effect of the 5-HT1A compounds 8-hydroxy-2-(di-n-propylamino) tetralin and ipsapirone in the social interaction paradigm: evidence of a presynaptic action

This study analyses at which site, pre- or postsynaptic, the 5-HT1A ligands--8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and ipsapirone--induce their anxiolytic action. The experimental anxiety was assessed in the social interaction test. An anxiolytic action was observed after the systemic administration of 8-OH-DPAT (0.25 and 0.5 mg/kg) and ipsapirone (5 but not 10 mg/kg). In 5,7-dihydroxytryptamine (5,7-DHT, 150 micrograms/10 microliters) lesioned rats the anxiolytic effect of 8-OH-DPAT and ipsapirone was not observed, suggesting a presynaptic action of these drugs. When directly injected into the dorsal raphe nucleus 8-OH-DPAT (0.1 microgram/microliter) and ipsapirone (0.2 microgram/microliter), both compounds produce anxiolytic effects. At same doses, these drugs lacked an effect after their intrahippocampal infusion. All data strongly suggest that both drugs act presynaptically to reduce the anxiety levels in the social interaction paradigm.

The role of postsynaptic 5-HT1A receptors in the anticonflict effect of ipsapirone

In the present paper we have studied the anticonflict effect (in the Vogel test) of ipsapirone, a partial agonist of 5-hydroxytryptamine1A (5-HT1A) receptors, administered to the hippocampus of rats. In addition, a comparison of the effect of ipsapirone with the effect of other 5-HT1A receptor ligands (busipone, gepirone and 8-OH-DPAT) has been carried out. Finally, the interaction between ipsapirone and NAN-190 (an antagonist of 5-HT1A receptors and alpha 1-adrenoceptors) has also been examined. It has been found that ipsapirone injected intrahippocampally (i.hp.) in doses of 0.3, 1 and 3 micrograms (bilaterally) shows an anticonflict effect by increasing the number of punished licks by about 36, 151 and 109%, respectively. A similar effect has also been found after i.hp. injections of buspirone (0.3-3 micrograms), gepirone (3-30 micrograms) and 8-OH-DPAT (0.3-3 micrograms). We have also demonstrated that the anticonflict effect of ipsapirone injected i.hp. is antagonized by NAN-190 administered i.hp. (0.3 or 1 microgram) or intraperitoneally (i.p., 1 mg/kg). Furthermore, NAN-190 injected i.hp. (0.3 microgram) antagonizes the anticonflict effect of ipsapirone administered i.p. (5 mg/kg). At the same time, the anticonflict effects of ipsapirone are not affected by prazosin (0.3-1 microgram i.hp. or 0.5-1 mg/kg i.p.), a selective antagonist of alpha 1-adrenoceptors. Our results seem to indicate that the anticonflict effect of ipsapirone stems from stimulation of postsynaptic 5-HT1A receptors in the hippocampus.

Effects of 5-HT1A receptor ligands on a safety signal withdrawal procedure of conflict in the rat

The present study evaluated in the rat the ability of various 5-HT1A receptor agonists to exert an "anxiolytic-like" release of the suppression of lever pressing for food induced by the withdrawal of a conditioned signal for safety without presentation of a conditioned signal for punishment. During the period associated with the safety signal withdrawal (Saf.CS-/Pun.CS-), control rats exhibited a typical pattern of responding with an initial strong blockade of responding that lessened over the period as presses were rewarded and shocks omitted. The 5-HT1A receptor partial agonists buspirone (0.125-0.5 mg/kg) and 8-(2-[2,3-dihydro-1,4-benzodioxin-2-yl- methylamino]ethyl)-8-azaspiro[4,5]decane-7,9-dione methyl sulfonate (MDL 73005EF; 0.5-2 mg/kg) and the full agonist (+)-4-[N-(5-methoxy-chroman-3-yl)-N-propylamino]-butyl-8- azaspiro[4,5]decane-7,9-dione (S 20499; 0.125-1 mg/kg) produced a robust and dose-related release of pressing during the Saf.CS-/Pun.CS- period. This effect was less marked with ipsapirone (0.125-1 mg/kg). Conversely, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.06-0.25 mg/kg), a full agonist, was completely inactive and did not prevent MDL 73005EF (1-2 mg/kg) or diazepam (0.125 mg/kg) from releasing the suppressed behavior. The specific 5-HT1A antagonist (+)-N-tert-butyl-3-4-(2-methoxyphenyl)piperazin-1-yl-2-phenylpr opa namide [(+)-WAY 100135; 0.25-8 mg/kg] and the beta-adrenoceptor/5-HT1A antagonist (-)-tertatolol (2-8 mg/kg) did not modify the behavioral blockade, nor did (+)-WAY 100135 (2-4 mg/kg) reduce the ability of buspirone (0.25 mg/kg) to enhance responding during the Saf.CS-/Pun.CS- period.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of 5-hydroxytryptamine1A (5-HT1A) receptors in the anticonflict activity of beta-adrenoceptor antagonists

Using the conflict drinking test as a model, we studied in rats the effect of the nonselective beta-adrenoceptor blockers pindolol and cyanopindolol which bind to 5-HT1A and 5-HT1B receptors, and of the selective beta 1- and beta 2-adrenoceptor antagonists betaxolol and ICI 118,551, respectively, which have a negligible affinity for 5-HT receptors. Both pindolol (2.0-8.0 mg/kg) and cyanopindolol (0.5-2.0 mg/kg) showed an anticonflict effect, having dose dependently increased the number of punished licks. On the other hand, neither betaxolol nor ICI 118,551--administered separately or in combination--affected the punished responding. The anticonflict effects of pindolol and cyanopindolol were completely abolished by the 5-HT1A receptor and alpha 1-adrenoceptor antagonist 1-(2-methoxyphenyl)-4-[4-(2-phtalimmido)butyl]piperazine (NAN-190), but were not modified by the selective alpha 1(-)-adrenoceptor antagonist prazosin. The effects of pindolol and cyanopindolol were also not modified in animals with lesions of 5-HT neurons, produced by p-chloroamphetamine (PCA). Moreover, it was also found that the anticonflict effects of pindolol and cyanopindolol in PCA-pretreated rats were antagonized by NAN-190 but not prazosin. Our results indicate that the anticonflict effects of pindolol and cyanopindolol depend on their agonist action on postsynaptic 5-HT1A receptors.

Serotonergic innervation of the hippocampus and nucleus accumbens septi and the anxiolytic-like action of midazolam and 5-HT1A receptor agonists

An involvement of serotonergic innervation of the hippocampus (HP) and the nucleus accumbens septi (NAS) in anxiolytic activity of benzodiazepine midazolam and 5-HT1A receptor agonists was studied in two different animal models of anxiety. Injection of midazolam (10.0 and 20.0 micrograms) or 8-OH-DPAT (0.5 and 1.0 micrograms) into the hippocampus increased punished consumption of water in the Vogel conflict test. Buspirone given at 0.1, 0.5 and 1.0 microgram was ineffective in the Vogel test, while at 5.0 micrograms it enhanced shock-induced suppression of drinking. In the open-field test midazolam (0.01 and 0.1 microgram), 8-OH-DPAT (0.1, 0.5 and 1.0 microgram) and buspirone (2.5 and 5.0 micrograms) increased the number of entries into the central part of the open-field and the time spent in the central sector. Depletion of 5-HT had no influence on the anxiolytic-like effect in the open-field test of intrahippocampally-administered 8-OH-DPAT (0.5 microgram), but the drug tended to increase motor activity in lesioned animals. Midazolam and buspirone injected into the NAS did not have an anxiolytic effect in the Vogel test. A small increase in punished drinking was observed after 8-OH-DPAT (1.0 and 2.5 micrograms). Following intra-NAS injection, midazolam, 8-OH-DPAT and buspirone all failed to produce any marked anxiolytic-like effect in the open-field test. It appears that the hippocampus, rather than the NAS, is involved in mediating anxiolytic-like effects of 5-HT1A receptor agonists. Hippocampal postsynaptic 5-HT1A receptors may account for the anti-emotional influence of this group of drugs. The results indicate some similarities in the psychotropic profile of 5-HT1A receptor agonists and midazolam.