Comparison of anorexia and motor disruption by cyclazocine and quipazine

Serotonin2 receptor agonists and serotonergic anorectic drugs affect rats' performance differently in a five-choice serial reaction time task

A five-choice serial reaction time task was used to study the effects of serotonin (5-HT) receptor agonists and antagonists on accuracy of performance and food-motivated behaviour. Lysergic acid diethylamide (LSD), 0.1 mg/kg IP and quipazine, 2.5 mg/kg IP significantly reduced the percentage of correct responses and increased the percentage of omissions with no effect on other measures such as latency to collect the reinforcement or to respond correctly. The effects of LSD and quipazine were reversed by 1-2 mg/kg ritanserin, a potent 5-HT2 and 5-HT1C receptor antagonist. Metachlorophenylpiperazine (mCPP) 2.5 mg/kg IP, an agonist at 5-HT1B and 5-HT1C receptors, and d-fenfluramine (DF) 1.25 mg/kg IP, a releaser of 5-HT from nerve terminals and inhibitor of 5-HT uptake, increased the percentage of omissions and the latency to respond correctly or to collect the reinforcement with no effects on the correct responses. Effects similar to those of mCPP and DF were obtained by 60 min access to food before testing. Haloperidol, 0.1 mg/kg IP, did not affect the percentage of correct responses or the latency to collect the reinforcement, but significantly increased the proportion of errors of omission and the latency to respond correctly. The results show that 5-HT2 receptor agonists cause attentional disturbances at doses that have no marked effect on motivation for food or speed.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for 5-HT2 receptor mediation in quipazine anorexia

Doses of d-amphetamine (3.2 mg/kg), fenfluramine (10 mg/kg) and quipazine (8 mg/kg) cause a significant reduction in food intake during a 30-min daily feeding session in food-deprived rats. Pirenperone and ritanserin, 5-HT2 receptor antagonists, significantly blocked the anorectic effect of quipazine, while d-amphetamine and fenfluramine effects were not modified. Metergoline, a non-specific blocker of 5-HT receptors, significantly blocked the anorectic effects of fenfluramine and quipazine, but not the d-amphetamine effect. Pretreatment with alpha- and beta-adrenergic receptor antagonists (prazosin, propranolol and pindolol), dopamine receptor antagonists (haloperidol and pimozide), the catecholamine synthesis inhibitor alpha-methyl-para-tyrosine, and the opioid receptor antagonist naloxone failed to modify the anorectic effects of all three agents, with the exception that quipazine-induced anorexia was significantly reduced by pimozide. These results suggest that the quipazine anorexia is largely mediating through 5-HT2 receptors, although the effect of pimozide remains to be explained. Consistent with previous studies, the fenfluramine effect appears to be mediated through 5-HT1B receptors. Receptors involved in the anorectic effect of higher doses of d-amphetamine are still unidentified by this analysis. Further investigation is required to define the mechanisms by which quipazine and larger doses of d-amphetamine bring about a reduced appetite for food.

Evidence for serotonergic modulation of sucrose sham-feeding in the gastric-fistulated rat

Both the real and sham intakes of a 5% sucrose solution were reduced by d-fenfluramine, quipazine (a 5-HT receptor agonist), and fluoxetine (a selective 5-HT reuptake inhibitor). These data demonstrate a serotonergic inhibitory component in the control of sham-feeding. In support of this, 8-OH-DPAT (a selective 5-HT1A agonist), which inhibits serotonergic activity at small doses via an autoreceptor mechanism, enhanced sucrose sham-feeding and reversed the suppressant effect of d-fenfluramine. Together, the results indicate a serotonergic influence on ingestional responses which is probably closely related to the oropharyngeal control of consumption.