Substitution of the selective serotonin reuptake inhibitors fluoxetine and paroxetine for the discriminative stimulus effects of ethanol in rats

 Rats trained to discriminate ethanol (EtOH, 1 g/kg IP) from saline in a two-lever procedure completely generalized to the selective serotonin reuptake inhibitors (SSRIs) fluoxetine and paroxetine. Substitution of fluoxetine was completely blocked by the selective 5-HT_2A receptor antagonist MDL 100,907 and not affected by the selective 5-HT_1A receptor antagonist WAY-100635. It is suggested that the previously reported effectiveness of SSRIs in reducing EtOH consumption could be based on similarities in discriminative stimulus effects of SSRIs and EtOH. Stimulation of 5-HT_2A receptors may underlie these stimulus similarities and contribute to the EtOH intake-reducing effects of SSRIs. Received: 22 November 1996 / Final version: 30 January 1997     

Discriminative stimulus properties of the selective norepinephrine reuptake inhibitor, reboxetine, in rats

RATIONALE: Although drug discrimination procedures have proven difficult to apply to antidepressant agents, we recently characterized discriminative stimulus properties of the selective serotonin (5-HT) reuptake inhibitor, citalopram, in rats. However, discriminative stimulus properties of selective norepinephrine (NE) reuptake inhibitors remain to be evaluated. OBJECTIVE: We determined the potential discriminative stimulus properties of the highly selective NE reuptake inhibitor and antidepressant, reboxetine. METHODS: Employing a two-lever discrimination procedure, rats were trained to discriminate reboxetine (2.5 mg/kg, IP) from saline. In parallel, the influence of reboxetine (2.5 mg/kg) upon dialysate levels of monoamines in frontal cortex and dorsal hippocampus of freely moving rats was determined. RESULTS: After 54+/-10 training sessions, reboxetine elicited robust stimulus recognition, fully generalizing to itself with an ED50 of 1.2 mg/kg. Two further NE reuptake inhibitors, desipramine (5.3) and maprotiline (1.8), as well as the 5-HT/NE reuptake inhibitor, venlafaxine (1.0), likewise generalized. In contrast, the 5-HT reuptake inhibitors, paroxetine, citalopram and sertraline, and the DA reuptake inhibitors, GBR12935 and bupropion, did not show significant generalization. Reboxetine markedly increased dialysate levels of NE, but not 5-HT, in frontal cortex and hippocampus. Dopamine (DA) levels were also (though less markedly) enhanced in frontal cortex. CONCLUSION: In parallel with an elevation in extracellular levels of NE, the selective NE reuptake inhibitor, reboxetine, elicits a specific discriminative stimulus in rats.     

Further evidence for the importance of 5-HT1A autoreceptors in the action of selective serotonin reuptake inhibitors

The clinical efficacy of antidepressants that block serotonin (5-hydroxytryptamine, 5-HT) reuptake may be restrained by indirect activation of autoreceptors. In vivo microdialysis in rat hippocampus was used to assess the release-inhibitory properties of the 5-HT reuptake inhibitors citalopram and paroxetine. When reuptake was first blocked by infusing citalopram into the hippocampus, systemic administration of citalopram or paroxetine resulted in a 50–70% decrease in hippocampal 5-HT overflow. This presumably reflected the inhibition of 5-HT release subsequent to reuptake blockade in the raphe nuclei and, in turn, activation of somatodendritic autoreceptors. In support, pretreatment with (±)-pindolol or(+)-WAY100135 ((+)-N-tert-butyl-3-(4- (2-methoxyphenyl)piperazine-1-yl)-2-phenylpropanamide dihydrochloride), to block 5-HT_1A autoreceptors, abolished the decrease in 5-HT produced by systemic injection of the uptake blockers.     

The role of 5-HT receptor subtypes in the anxiolytic effects of selective serotonin reuptake inhibitors in the rat ultrasonic vocalization test

 We evaluated whether the anxiolytic effects of selective serotonin reuptake inhibitors (SSRIs) in the rat ultrasonic vocalization (USV) test are preferentially mediated by (indirect) activation of 5-HT_1A, 5-HT_1B/1D, 5-HT_2A, 5-HT₃ or 5-HT₄ receptors. The SSRIs, paroxetine (ED₅₀ in mg/kg, IP: 6.9), citalopram (6.5), fluvoxamine (11.7) and fluoxetine (>30), dose dependently reduced shock-induced USV. The effects of paroxetine (3.0 mg/kg, IP) were not blocked by the selective 5-HT_1A receptor antagonist, WAY-100635 (3.0 mg/kg, IP), the 5-HT_1B/1D receptor antagonist, GR 127935 (30 mg/kg, IP), the nonselective 5-HT_2A receptor antagonists, ritanserin (3.0 mg/kg, IP) and ketanserin (1.0 mg/kg, IP), the 5-HT₃ receptor antagonist, ondansetron (0.1 mg/kg, IP), or the 5-HT₄ receptor antagonist, GR 125487D (3.0 mg/kg, SC). In contrast, the selective 5-HT_2A receptor antagonist, MDL 100,907 (0.1 mg/kg, IP), completely prevented the paroxetine-induced reduction of USV. Under similar conditions, WAY-100635 blocked the anxiolytic-like effects of the selective 5-HT_1A receptor agonist, 8-OH-DPAT [(±)-8-hydroxy-2-(di-n-propylamino)tetralin, 1.0 mg/kg, IP], and ritanserin, ketanserin, and MDL 100,907 blocked the anxiolytic-like effects of the mixed 5-HT_2A/2C receptor agonist, DOI [1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, 3.0 mg/kg, IP]. WAY-100635 (1.0 mg/kg, IP) in combination with ritanserin (3.0 mg/kg, IP), but not ondansetron (0.1 mg/kg, IP), GR 125487D (3.0 mg/ kg, SC), or GR 127935 (30 mg/kg, IP), attenuated the USV reducing effects of paroxetine. Although the results suggest that selective stimulation of 5-HT_1A and 5-HT_2A receptors produces a decrease of USV, we postulate that only 5-HT_2A receptors play a pivotal role in the effects of SSRIs in this model of anxiety. Received: 19 May 1997 / Final version: 21 July 1997     

The selective serotonin reuptake inhibitor paroxetine is effective in more generalized and in less generalized social anxiety disorder

RATIONALE: The DSM-IV includes the specifier "generalized" to refer to social anxiety disorder (social phobia) patients if the fears include "most social situations". The focus on interventions such as the selective serotonin reuptake inhibitors (SSRIs) for generalized social anxiety disorder arguably runs the risk that inadequate treatment will be provided to patients with the non-generalized or discrete subtypes. There are, however, few data to address whether more generalized and less generalized subgroups of social anxiety disorder differ in response to medication. OBJECTIVE: To compare response of more generalized and less generalized social anxiety disorder to pharmacotherapy. METHODS: Data from three randomized placebo-controlled double-blind multicenter trials of the SSRI paroxetine in social anxiety disorder were pooled. Response on the Clinical Global Impression Global Improvement item was analyzed using logistic regression, and change in total Liebowitz Social Anxiety Score was analyzed using analysis of variance, with both models incorporating treatment (paroxetine vs placebo), subgroup (more generalized vs less generalized), demographic, and clinical variables. RESULTS: The prevalence of more generalized social anxiety disorder was higher in females than in males. However, there was no significant difference in terms of age or clinical characteristics (duration of condition, baseline pulse, mean arterial blood pressure). At treatment endpoint there were significant treatment effects (for paroxetine vs placebo), but no significant subgroup effects (for more generalized vs less generalized). CONCLUSIONS: Although the current database is limited insofar as few patients with discrete social anxiety disorder would have been included, it is helpful in addressing the value of medication for patients lying on the spectrum from generalized to non-generalized and discrete social anxiety disorder. Paroxetine was effective in both more generalized and in less generalized social anxiety disorder.     

Effects of co-administration of a selective serotonin reuptake inhibitor and monoamine oxidase inhibitors on 5-HT-related behavior in rats

5-hydroxytryptamine (5-HT) syndrome is a dangerous condition of 5-HT excess that can occur in the case of co-administration of a monoamine oxidase (MAO) inhibitor and a serotonin reuptake inhibitor (SSRI). The goal of the present study was to investigate the effects of acute administration of MAO inhibitors and subchronic administration of fluvoxamine on 5-HT-related behaviors (head shaking and 5-HT syndrome) in rats treated with 5-hydroxytryptophan (5-HTP). Administration of the non-selective MAO inhibitor, pargyline, and the selective MAO-A inhibitor, clorgyline, resulted in 5-HT syndrome in 5-HTP-treated rats, and subchronic co-administration of fluvoxamine intensified the syndrome. However, administration of the selective MAO-B inhibitor, selegiline, did not induce 5-HT syndrome with or without subchronic fluvoxamine co-administration. These data suggest that non-selective MAO and selective MAO-A inhibitors can induce 5-HT syndrome in humans when co-administered with SSRI. Further, the risk of 5-HT syndrome may be lower with the selective MAO-B inhibitor, selegiline.     

5-HT2C receptors are involved in the discriminative stimulus effects of citalopram in rats

 Rats were trained on a fixed ratio 10, food-reinforced schedule to recognize a discriminative stimulus (DS) elicited by the selective serotonin (5-HT) reuptake inhibitor (SSRI), citalopram (2.5 mg/kg, IP). The preferential, high efficacy agonist at 5-HT_2C receptors, Ro60-0175, dose-dependently generalized to citalopram with an ED₅₀ of 0.3 mg/kg, IP. Further, the selective 5-HT_2C receptor antagonist, SB242,084, dose-dependently (ED₅₀=0.1 mg/kg, IP) blocked the citalopram DS. These data suggest that 5-HT_2C receptors are involved in the DS properties of the SSRI, citalopram, in rats. They do not, however, exclude a potential role of other 5-HT receptor types. Received: 15 October 1998 / Final version: 10 December 1998     

选择性5-羟色胺再摄取抑制剂撤药综合征42例的临床分析

目的:探讨选择性5-羟色胺再摄取抑制剂(SSRI)撤药综合征的临床特点、诱发因素及预防。方法:回顾性调查42例SSRI撤综合征的临床症状,诱发因素及处理。结果:42例撤药综合征以头晕、恶心、呕吐、头痛、感觉异常、心情低落、失眠、焦虑、激越等症状为主。撤药症状发生于停药后的1～5d,持续1～7d。42例中应用帕罗西汀27例,舍曲林6例,西酞普兰6例,氟西汀3例。诱发因素:自行突然停药30例,漏服6例,减药4例,换药2例。结论:骤停SSRI可引起撤药综合征,以帕罗西汀较易发生,应引起临床上重视。缓慢减量或使用半衰期较长的SSRI可预防撤药综合征的发生。     

Dose-dependent influence of buspirone on the activities of selective serotonin reuptake inhibitors in the mouse forced swimming test

Recent clinical data suggest that buspirone may enhance the efficacy and/or reduce the latency to therapeutic effect of selective serotonin reuptake inhibitors (SSRIs) in unipolar major depressive disorder. The present study, using the mouse forced swimming test, was performed to investigate further the mechanisms involved in the potential antidepressant-enhancing effects of buspirone. Prior administration of buspirone (0.06 mg kg⁻¹, IP) significantly enhanced the anti-immobility effects of subactive doses of fluvoxamine (4 mg kg⁻¹, IP; P < 0.01), paroxetine (4 mg kg⁻¹, IP; P < 0.01), citalopram (4 mg kg⁻¹, IP; P < 0.01) and sertraline (2 mg kg⁻¹, IP; P < 0.01) in the forced swimming test. However, pretreatment with buspirone did not induce antidepressant-like effects when tested in combination with fluoxetine (4 mg kg⁻¹, IP). Each antidepressant tested reduced immobility time in the forced swimming test [citalopram (16 mg kg⁻¹, IP; P < 0.01), fluoxetine (32 mg kg⁻¹, IP; P < 0.01), fluvoxamine (32 mg kg⁻¹, IP; P < 0.01), paroxetine (16 mg kg⁻¹, IP; P < 0.01) and sertraline (16 mg kg⁻¹, IP; P < 0.01)]. Pretreatment with buspirone (0.5 mg kg⁻¹, IP), or its major metabolite 1-PP (0.5 mg kg⁻¹, IP), attenuated all SSRI-induced anti-immobility effects (P < 0.01). Concomitant studies of locomotor activity ruled out any stimulant or sedative effects of the interactions. The results of the present study suggested that low dose buspirone enhanced the activity of subactive doses of SSRIs in the mouse forced swimming test, probably via an action at 5-HT_1A receptors. On the other hand, a high dose of buspirone attenuated the antidepressant-like effects of active doses of these drugs, possibly via the generation of an active metabolite (1-PP) acting at alpha₂-adrenoreceptors. Received: 19 October 1997 / Final version: 16 December 1997     

Selective serotonin reuptake inhibitor reduces conditioned fear through its effect in the amygdala

Selective serotonin reuptake inhibitors are first-line treatment for most anxiety disorders, but their mechanism of anxiolytic action has not been clarified. Selective serotonin reuptake inhibitors are anxiolytic in conditioned fear stress (re-exposure to an environment paired previously with inescapable electric footshocks). To clarify the brain regions where selective serotonin reuptake inhibitors act, we examined the effect of microinjection of the selective serotonin reuptake inhibitor, citalopram, into the amygdala, medial prefrontal cortex and mediodorsal nucleus of the thalamus on freezing behavior, an index of fear, induced by conditioned fear stress. Bilateral injection of citalopram into the amygdala before testing reduced freezing significantly, while bilateral injection into the medial prefrontal cortex or mediodorsal nucleus of the thalamus did not. These results suggest that the anxiolytic effect of a selective serotonin reuptake inhibitor in conditioned fear is mediated by its effect in the amygdala, and support the hypothesis of serotonin function in anxiety by which facilitation of serotonin neurotransmission decreases anxiety.     

Diminished conditioned responding to the nicotine stimulus by antidepressant drugs with differing specificity for the serotonin and norepinephrine transporter

People diagnosed with depression also tend to have a co-morbid nicotine addiction. Thus, there is interest in whether medications used to treat depression alter the effects of nicotine. This study assessed whether the antidepressant drugs citalopram, imipramine, and reboxetine, with differing specificity for the serotonin and norepinephrine transporter, altered responding controlled by the conditional stimulus (CS) effects of nicotine. Rats received intermixed 20-min nicotine (0.4 mg base/kg, SC) and saline sessions. On nicotine sessions, rats had intermittent access to sucrose; no sucrose was available on saline sessions. After discrimination performance stabilized and a nicotine generalization curve (0.025-0.4 mg/kg) was established, the antidepressant drugs were assessed. In these tests, rats were pretreated with citalopram (1-17 mg/kg), imipramine (1-17 mg/kg), or reboxetine (1-30 mg/kg) before the training dose of nicotine and placement in a chamber for a 4-min extinction test. At the higher doses, all three antidepressant drugs blocked responding evoked by the nicotine CS and decreased nicotine-induced hyperactivity. When these higher doses of citalopram, imipramine, and reboxetine were tested alone (no nicotine), they decreased chamber activity and/or dipper entries. Nevertheless, all three drugs produced partial or complete blockade of the CS effects of nicotine at doses that produced no effect on dipper entries or chamber entries. This finding suggests that both neurotransmitters play a role in the CS effects of nicotine and that modifications in these systems by antidepressants may be clinically relevant.     

Time‐dependent inhibition of CYP3A4 by sertraline,a selective serotonin reuptake inhibitor

Drug–drug interactions associated with selective serotonin reuptake inhibitors (SSRIs) are widely known. A major interaction by SSRIs is the inhibition of cytochrome P450 (P450)‐mediated hepatic drug metabolism. The SSRI, sertraline, is also reported to increase the blood concentration of co‐administered drugs. The potency of sertraline directly to inhibit hepatic drug metabolism is relatively weak compared with the other SSRIs, implying that additional mechanisms are involved in the interactions. The study examined whether sertraline produces time‐dependent inhibition of CYP3A4 and/or other P450 enzymes. Incubation of human liver microsomes with sertraline in the presence of NADPH resulted in marked decreases in testosterone 6β‐hydroxylation activities, indicating that sertraline metabolism leads to CYP3A4 inactivation. This inactivation required NADPH and was not protected by glutathione. No significant inactivation was observed for other P450 enzymes. Spectroscopic evaluation revealed that microsomes with and without sertraline in the presence of NADPH gave a Soret peak at 455 nm, suggesting the formation of metabolic intermediate (MI) complexes of sertraline metabolite(s) with the reduced form of P450. This is the first report indicating that sertraline produced time‐dependent inhibition of CYP3A4, which may be associated with MI complex formation. Copyright © 2013 John Wiley & Sons, Ltd.     

CP-135,807, a selective 5-HT1D agonist: effects in drug discrimination and punishment procedures in the pigeon

 CP-135,807 [3-(N-methylpyrrolidin-2R-ylmeth- yl)-5-(3-nitropyrid-2-yl)amino-1H-indole] binds with high affinity to central 5-HT_1D receptors, and in functional studies produces dose-dependent decreases in extracellular serotonin. These and other findings have suggested that CP-135,807 may act as a terminal 5-HT autoreceptor agonist. In an attempt to characterize the behavioral activity of selective 5-HT_1D ligands, adult male Carneau pigeons were trained to discriminate IM injections of 0.1 mg/kg CP-135,807 from saline under a two-key, fixed ratio schedule of food-reinforced key pecking. CP-135,807 and the structurally unrelated 5-HT_1D agonist CP-286,601 fully and dose-dependently substituted for the training dose. In contrast, little substitution was observed following administration of 8-OH-DPAT, a potent 5-HT_1A agonist, the 5-HT_1B agonist CP-94,253, or the serotonin reuptake inhibitor sertraline. In addition, the discriminative stimulus produced by CP-135,807 was not blocked by WAY 100,635, a selective 5-HT_1A antagonist, but was completely and dose-dependently antagonized by the selective 5-HT_1D antagonist, GR127935. In subjects trained under a multiple schedule of punished and unpunished responding, 8-OH-DPAT produced large increases in punished responding while having little effect on unpunished responding. In contrast, CP-135,807 and CP-94,253 produced no antipunishment effects, while GR127935 produced modest increases in punished responding. Collectively, these results suggest that CP-135,807 produces centrally mediated psychoactive effects that differ distinctly from those of 5-HT_1A agonists. Received: 23 April 1996 / Final version: 9 July 1996     

Following long-term training with citalopram, both mirtazapine and mianserin block its discriminative stimulus properties in rats

RATIONALE: The discriminative stimulus (DS) properties of the selective serotonin (5-HT) uptake inhibitor (SSRI), citalopram, are mediated by 5-HT2C receptors. Interestingly, the "atypical" antidepressants, mianserin and mirtazapine, behave as antagonists at 5-HT2C receptors. OBJECTIVE: Herein, we evaluated the influence of mianserin and mirtazapine upon the DS effects of citalopram. METHODS: In a two-lever drug discrimination procedure, rats initially trained to discriminate citalopram (2.5 mg/kg, i.p.) from saline were retrained with a lower dose of citalopram (0.63 mg/kg, i.p.). Subsequently, generalization and antagonist studies were conducted with mianserin and mirtazapine. RESULTS: Both dose-dependently blocked, but did not generalize to, the DS properties of citalopram without markedly disrupting response rates. Their effective dose50s were 0.1 and 1.4 mg/kg, s.c., respectively. CONCLUSION: These observations are consistent with a role of 5-HT2C receptors in mediation of the interoceptive properties of SSRIs and suggest that the DS effects of citalopram are not related to its "antidepressant" properties per se. Finally, they underline the distinctive nature of mirtazapine and mianserin as compared to antidepressant agents which interact with 5-HT uptake sites.     

The discriminative stimulus properties of cocaine: effects of microinfusion of cocaine, a 5-HT1A agonist or antagonist, into the ventral tegmental area

 Serotonin (5-HT) afferents may modulate the dopamine mesoaccumbens circuit, which has been shown to be critically involved in the locomotor stimulatory, discriminative stimulus, and rewarding properties of cocaine. In the present study, we investigated the role of 5-HT_1A receptors in the ventral tegmental area (VTA) in mediating the discriminative stimulus effects of cocaine. Male Sprague-Dawley rats were trained to discriminate cocaine (10 mg/kg) from saline in a two-lever, water-reinforced FR 20 task. After acquiring the cocaine-saline discrimination, rats were stereotaxically implanted with bilateral guide cannulae into the VTA or adjacent substantia nigra reticulata (SNR). Intraperitoneal administration of cocaine (0.625–10 mg/kg) produced a dose-related increase in drug-lever responding. Both intra-VTA and intra-SNR infusion of cocaine (12.5–50 μg/0.5 μl/side) engendered primarily saline-like responding. Microinjection of the 5-HT_1A agonist 8-hydroxy-2-(di-N-propylamino) tetralin (DPAT; 0.1–10 μg/0.5 μl/side) or the 5-HT_1A antagonist WAY 100635 (0.01–1.0 μg/0.5 μl/side) into the VTA or SNR did not substitute for the systemic cocaine cue. Further, intra-VTA or intra-SNR DPAT or WAY 100635 in combination with systemic doses of cocaine did not alter (i.e., attenuate or potentiate) the systemic cocaine cue. Overall, these data indicate that 5-HT_1A receptors in the VTA do not mediate or modulate the discriminative stimulus effects of cocaine in the rat. Received: 15 April 1997 / Final version: 21 October 1997     

Safety of selective serotonin reuptake inhibitor treatment in recovering stroke patients

Introduction: Selective serotonin reuptake inhibitors (SSRIs) are widely used for psychiatric complications after stroke. Studies have indicated additional effects, and SSRIs could potentially be used as enhancers of stroke recovery. However, beneficial effects should be weighed against potential adverse effects. In particular, the possible association with cerebrovascular events has raised concern.

Areas covered: We review the literature on cerebrovascular events associated with SSRI treatment after stroke. The possible beneficial effects of SSRI treatment for stroke recovery and survival, and potential safety concerns, are discussed.

Expert opinion: Evidence suggests that SSRIs may enhance stroke recovery. Most studies on cerebrovascular risk are from non-stroke populations and little is known about recurrent events and mortality post-stroke. In non-stroke populations treatment has been associated with increased risk of intracerebral and intracranial hemorrhage; however the absolute risk is low. The association between SSRIs and ischemic stroke is less clear. Randomized stroke trials indicate that treatment is safe and well tolerated, and the most common side effects are often benign and transient. The trials are small however and not powered to detect potential differences in cerebrovascular events. We await several ongoing large randomized trials before SSRIs can be recommended as a routine pharmacotherapy in stroke recovery.     

Role of extracellular serotonin levels in the effect of 5-HT<Subscript>1B</Subscript> receptor blockade

The release of serotonin (5-HT) at serotonergic nerve terminals is regulated by 5-HT_1B autoreceptors. Several studies have reported that the effects of selective 5-HT reuptake inhibitors (SSRIs) on extracellular 5-HT are augmented by 5-HT_1B receptor antagonists, whereas administration of these antagonists alone do not enhance 5-HT levels. It has been suggested that 5-HT_1B receptors have low basal endogenous activity and therefore elevated endogenous 5-HT levels are needed to elicit an effect of 5-HT_1B receptor antagonists. To test this hypothesis, different strategies were used to enhance 5-HT levels in the rat frontal cortex to assess the effects of locally applied NAS-181, a new selective 5-HT_1B receptor antagonist. Blockade of 5-HT_1B receptors with NAS-181 dose dependently augmented 5-HT levels when 5-HT levels were enhanced by a SSRI. No additional effect of NAS-181 on 5-HT output was found when 5-HT levels were enhanced by KCl depolarization-induced release or by preventing degradation of 5-HT with the monoamine oxidase inhibitor pargyline. In the presence of fluvoxamine, the increased 5-HT release evoked by KCl depolarization was augmented by NAS-181, supporting the idea that blockade of 5-HT transporters is necessary to measure an effect of 5-HT_1B receptor blockade. In conclusion, the results provide circumstantial evidence that the effect of a 5-HT_1B receptor antagonist depends on extracellular 5-HT levels, but strongly suggest that additional 5-HT reuptake inhibition is required to detect any effect of 5-HT_1B receptor antagonist on 5-HT levels by in vivo microdialysis. Electronic Publication     

Generalization of a restraint-induced discriminative stimulus to cocaine in rats

 The ability of the interoceptive cues produced following exposure to restraint stress to generalize to the discriminative stimulus effects of cocaine was investigated. Rats were trained to discriminate cocaine (10 mg/kg, IP, n=10; or 20 mg/kg, IP, n=6) from saline using a two-choice, food-reinforced, drug discrimination design. Substitution for the 10 mg/kg training dose of cocaine was observed subsequent to exposure to 15 min of restraint when administered immediately following an injection of saline. Restraint-induced generalization in the 20 mg/kg training group was substantial, but not statistically significant. These data suggest that a component of the subjective effects of cocaine may be associated with ”anxiety”. Received: 19 July 1997 / Final version: 1 October 1997     

Involvement of 5-HT1A and 5-HT1B receptors for citalopram-induced hypothermia in the rat

OBJECTIVES: To examine the role of 5-HT1A and 5-HT1B receptors for citalopram-induced hypothermia in the rat. METHODS: Core temperature measurements were performed in adult male Wistar rats (305-340 g) using a computer-assisted recording instrument. The temperature readings were automated and gave a printout when the core temperature had stabilised at +/- 0.1 degree C for 10 s. RESULTS: Citalopram (6.25-100.0 mumol/kg) produced a dose-dependent hypothermia. The effect was maximal within 60 min after administration, and had waned off at 120 min. The 5-HT1B receptor agonist anpirtoline (0.25-4.0 mumol/kg) produced a dose-dependent decrease in core temperature. The citalopram-induced hypothermia (25 mumol/kg) was antagonised by pretreatment with either of the 5-HT1A and the 5-HT1B receptor antagonists, WAY-100,635 (0.04 mumol/kg) and NAS-181 (1.0 mumol/kg), respectively, or by the two drugs in combination. Subchronic treatment with the SSRI zimeldine (100 mumol/kg once daily for 2 weeks) resulted in tolerance to the hypothermic effect of citalopram (100 mumol/kg). CONCLUSIONS: The hypothermia produced by acute administration of the SSRI citalopram is mediated via activation of 5-HT1A, as well as 5-HT1B receptors, and this effect is subject to the development of tolerance.