Pizotifen (BC-105) attenuates orienting and Pavlovian heart rate conditioning in rabbits

Acquisition session length modulates consolidation effects produced by 5-HT2C ligands in a mouse autoshaping-operant procedure

Although the neurotransmitter, 5-hydroxytryptamine (serotonin, 5-HT), has been implicated as a mediator of learning and memory, the specific role of 5-HT receptors in rodents requires further delineation. In this study, 5-HT2C receptor ligands of varying relative intrinsic efficacies were tested in a mouse learning and memory model called autoshaping-operant. On day 1, mice were placed in experimental chambers and presented with a tone on a variable interval schedule. The tone remained on for 6 s or until a nose-poke response occurred to produce a dipper with Ensure solution. Mice were then injected with saline, MK212 (full agonist), m-chlorophenylpiperazine (partial agonist), mianserin, and SB206 553 (inverse agonists), and methysergide and (+)-2-bromo lysergic acid diethylamide (+)-hydrogen tartrate (neutral antagonists). Each compound was injected after either 1 or 2-h acquisition sessions on day 1 to investigate the role of acquisition session length on consolidation. Day 1 injection of the 5-HT2C inverse agonist mianserin produced greater retrieval impairments of the autoshaped operant response on day 2 than any other agent tested. Furthermore, decreasing the length of the acquisition session to 1h significantly increased the difficulty of the autoshaping task further modulating the consolidation effects produced by the 5-HT2C ligands tested.

Failure of serotonin antagonist pizotifen to stimulate feeding or weight gain in free-feeding rats

The serotonin antagonist pizotifen (BC-105) is prescribed as an appetite and weight enhancer (Mosegor--Wander, also commercialized under brand names Sanmigran or Sandomigran--Sandoz, Switzerland) for anorectic and convalescent humans. There has been, however, difficulty in demonstrating any orexigenic effect of pizotifen in laboratory animals. In the present report, the influence of chronic administration of pizotifen (0.1-30.0 mg/kg b.wt. per day, SC) on food intake and body weight gains was studied in rats given a standard diet (SD-energy content 14.5 kJ/g, 9% fibre), and in rats either habituated to a low energy content, carbohydrate-free diet (DD-7.3 kJ/g, 45% fibre), or given the DD after habituation to the SD. Pizotifen failed to increase food intake or weight gain. Nor did it shorten a period of initial depression of intake of the unfamiliar DD. On the contrary, pizotifen seemed to diminish food intake and weight gain in rats fed the low energy content diet. Since it has been reported that other 5-HT antagonists, e.g., cyproheptadine, methysergide, and ritanserin can enhance feeding, it is of some interest that pizotifen failed to affect food intake or weight gain in rats. The results suggest that the effects of pizotifen (and, possibly, of serotonin) in rats may differ from those in man. The possibility that feeding in the rat is mediated by 5-HT1 rather than 5-HT2 receptors is discussed.