Chronic fluoxetine-induced desensitization of 5-HT1A and 5-HT1B autoreceptors: regional differences and effects of WAY-100635

Desensitization of 5-HT(1A) and 5-HT(1B) autoreceptors is thought to be the mechanism underlying the therapeutic effects of fluoxetine and other selective serotonin reuptake inhibitors when these are administered chronically. The blockade of 5-HT(1A) autoreceptors occurring on administration of a selective serotonin reuptake inhibitor together with a 5-HT(1A) autoreceptor antagonist is responsible for the acute increase in 5-hydroxytryptamine (serotonin, 5-HT) levels observed under these circumstances. The effects of repeated administration of selective serotonin reuptake inhibitors together with 5-HT(1A) receptor antagonists have not been widely studied. In this work, we found that the effects of fluoxetine (5 mg/kg, i.p., daily for 12 days) to desensitize 5-HT(1B) autoreceptors in the frontal cortex, as measured by the effect of the locally administered 5-HT(1B) receptor agonist, 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one (CP 93129), and to desensitize 5-HT(1A) autoreceptors as measured by the action of the 5-HT(1A) receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT; 50 microg/kg, s.c.) to reduce 5-HT levels in cortex, were prevented by concomitant administration of the 5-HT(1A) receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide (WAY-100635; 0.3 mg/kg, s.c.). 5-HT(1B) receptor activity in the hypothalamus, as measured by the effects of locally administered CP 93129, and 5-HT(1A) autoreceptor activity, as determined by the effects of subcutaneous 8-OH-DPAT to reduce 5-HT levels in hypothalamus, were not altered either by fluoxetine alone or by fluoxetine in the presence of WAY-100635. The data suggest that the regulation of extracellular levels of 5-HT in the cortex and hypothalamus is subject to different autoregulatory mechanisms.     

Fluoxetine attenuates thermal hyperalgesia through 5-HT1/2 receptors in streptozotocin-induced diabetic mice

Diabetic neuropathic pain, an important microvascular complication in diabetes mellitus, is recognised as one of the most difficult types of pain to treat. A lack of understanding of its aetiology, inadequate relief, development of tolerance and potential toxicity of classical antinociceptives warrant the investigation of newer agents to relieve this pain. The aim of the present study was to explore the antinociceptive effect and possible mechanism of action of a serotonin reuptake inhibitor, fluoxetine, in streptozotocin-induced diabetic mice. Four weeks after a single intraperitoneal injection of streptozotocin (200 mg/kg), mice were tested in the tail-immersion and hot-plate assays. Diabetic mice exhibited significant hyperalgesia compared with control mice. Fluoxetine (10 and 20, but not 5 mg/kg, i.p.) injected into diabetic mice produced an antinociceptive effect in both the tail-immersion and hot-plate assays. The percentage maximum possible effect (% MPE) produced by fluoxetine (20 mg/kg, i.p.) was significantly lower in diabetic mice than in control mice. The antinociceptive effect of fluoxetine (20 mg/kg) in diabetic mice was dose-dependently potentiated by pindolol (5 and 10 mg/kg, i.p., a selective 5-HT(1A/1B) receptor antagonist), attenuated by ritanserin (1 and 2 mg/kg, i.p., a selective 5-HT(2A/2C) receptor antagonist) and remained unaffected by ondansetron (1 and 2 mg/kg, i.p., a selective 5-HT(3) receptor antagonist) in both test systems. These results suggest that fluoxetine-induced antinociception primarily involves serotonin pathway modulation through 5-HT(1) and 5-HT(2) receptors, but not through 5-HT(3) receptors, in the chronic pain associated with streptozotocin-induced diabetic neuropathy. Further, the potentiation of the antinociceptive effect of fluoxetine by pindolol indicates the usefulness of a combination of an antidepressant and a 5-HT(1A/1B) receptor antagonist in the treatment of diabetic neuropathic pain in humans.     

Effects of fluoxetine on ethanol withdrawal syndrome in rats

The present study was designed to investigate the effects of fluoxetine, a selective serotonin reuptake inhibitor, on ethanol withdrawal syndrome in rats. Adult male Wistar rats (218-255 g) were subjects. Ethanol (7.2%, v/v) was given to rats by a liquid diet for 21 days. Control rats were pair fed an isocaloric liquid diet containing sucrose as a caloric substitute to ethanol. Fluoxetine (2.5, 5 and 10 mg/kg) and saline were injected to rats intraperitoneally just before ethanol withdrawal. After 2nd, 4th and 6th hour of ethanol withdrawal, rats were observed for 5 min, and withdrawal signs that included locomotor hyperactivity, agitation, stereotyped behavior, wet dog shakes and tremor were recorded or rated. A second series of injections was given at 6 h after the first one, and subjects were then tested for audiogenic seizures. Fluoxetine produced some dose-dependent and significant inhibitory effects on all the signs of ethanol withdrawal during ethanol withdrawal period. Our results suggest that acute fluoxetine treatment has some beneficial effects on ethanol withdrawal in rats. Thus, this drug may be useful for treatment of ethanol withdrawal syndrome.     

The serotonergic system may be involved in the sleep-inducing action of oleamide in rats

The mechanism underlying the sleep-inducing effect of oleamide, an endogenous fatty acid amide, was studied in rats. Animals implanted with cerebrocortical and dorsal neck muscle electrodes were monitored continuously by electroencephalograph (EEG) and electromyograph (EMG) for 4 h after i.p. or s.c. injection of drugs. Oleamide induced a dose-dependent increase in slow-wave sleep (SWS), a decrease in wakefulness (W) and sleep latency, but had no effect on rapid-eye-movement sleep (REMS). The oleamide-induced increase in SWS was prevented by 5-HT reuptake inhibitors such as fluoxetine or fenfluramine and by agonists at 5-HT_1A receptors such as buspirone or 8-hydroxy-2-(di-N-propylamino) tetralin (8-OH-DPAT). Moreover, the selective 5-HT_1A receptor antagonist WAY100635 markedly antagonized the suppression of the oleamide-induced increase in SWS by 8-OH-DPAT. These data provide the first behavioural evidence that the serotonergic system may be involved in the sleep-inducing action of oleamide in rats.     

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.     

氟西汀与马来酸曲美布汀联合治疗功能性消化不良的临床观察

目的:探讨氟西汀与马来酸曲美布汀联合治疗功能性消化不良(FD)的疗效。方法:将门诊160例FD患者随机分成甲、乙两组,甲组80例予以马来酸曲美布汀治疗,乙组80例予以马来酸曲美汀与氟西汀联合治疗,治疗时间均为8周,以自制FD症状评定量表评定疗效。结果:甲、乙两组有效率分别为62.5%(50例),91.25%(73例),疗效差异有显著性(P<0.01)。结论:氟西汀与马来酸曲美布汀联合使用可显著提高治疗FD的疗效,值得推广。     

颐脑解郁方改善抑郁症肾虚肝郁型患者中医证候的临床观察

目的观察颐脑解郁方对抑郁症肾虚肝郁型患者中医证候的影响。方法将60例抑郁症肾虚肝郁型患者随机分为颐脑解郁组30例和氟西汀组30例。颐脑解郁组给予颐脑解郁方治疗,氟西汀组给予氟西汀治疗,用药疗程均为6周。在治疗2周、4周、6周时,观察两组患者主要中医证候的改善情况。结果颐脑解郁方对性欲减退、时有太息的疗效在2周、4周、6周时均优于氟西汀(P<0.05或0.01);对腰酸背痛的疗效在2周、4周时优于氟西汀(P<0.01),在6周时组间比较无明显差异(P>0.05);对胁肋胀痛的疗效在2周时优于氟西汀(P<0.01),在4周、6周时组间比较无明显差异(P>0.05);对神思不聚的疗效在2周、4周时组间比较无明显差异(P>0.05),在6周时优于氟西汀(P<0.01);对忧愁善感、兴趣索然、精神委靡的疗效与氟西汀相当(P>0.05)。结论颐脑解郁方能有效改善抑郁症肾虚肝郁型患者的主要中医证候。     

Repeated ECS and fluoxetine administration have equivalent effects on hippocampal synaptic plasticity

Rationale: Recent studies have implicated intracellular transduction pathways and neurotrophic factors in the action of antidepressants. Adaptation in these pathways may ultimately affect electrophysiological and morphological properties of neurones. We have previously shown that repeated electroconvulsive stimulation, a safe and effective antidepressant treatment, has profound effects on hippocampal synaptic connectivity and plasticity in the rat. Here, we investigated whether these electrophysiological properties were shared by the chemical antidepressant, fluoxetine. Objectives: To compare the electrophysiological and cognitive effects of two very different antidepressant treatments: repeated electroconvulsive stimulation (rECS); and chronic administration of the serotonin specific re-uptake inhibitor (SSRI), fluoxetine. Methods: Rats were exposed to either rECS or daily fluoxetine administration for 15 days. The animals were then anaesthetised and dentate field excitatory post-synaptic potential (fEPSP) characteristics were measured before and after the induction of long-term potentiation (LTP) by high frequency perforant path stimulation. In a separate experiment, the effects of rECS and chronic fluoxetine administration on acquisition and retention of a spatial learning task in the Morris watermaze were determined. Results: Chronic fluoxetine administration and rECS produced equivalent increases in dentate fEPSP compared to respective control groups. LTP induction was attenuated in both groups. Spatial learning was, in contrast, unaffected by fluoxetine treatment but significantly impaired following rECS. Conclusions: Given that fluoxetine and rECS share antidepressant properties, but differ in their effects on learning and memory, we propose that the common effects on dentate connectivity and synaptic plasticity described here are more likely to relate to affective rather than cognitive function. This result is consistent with other experiments showing that a reduction in dentate connectivity correlates with stress susceptibility in animals. Received: 17 February 1999 / Final version: 23 August 1999     

Fluoxetine suppresses palatability-induced ingestion

Non-deprived rats were allowed 1-h access to a range of saccarin solutions from 0.001 to 0.1 M Na saccharin. Compared to a group of rats drinking tap water, the rats drinking the saccharin solutions ingested a great deal more fluid, with as much as 24–30 ml consumed of the 0.01 M concentration, compared to 3–5 ml in controls. Fluoxetine (IP) decreased this palatability-induced excessive consumption in a dose-related manner. Effects of 10 mg/kg fluoxetine were apparent for 48 h after injection. This effect on palatability-induced ingestion may relate to previously reported effects of fluoxetine on food consumption.