Behavioural changes on diet selection and serotonin (5-HT) turnover in rats under pizotifen treatment

The effects of pizotifen on protein and carbohydrate self-selection in rats over a seven-day period, and on 5-HT turnover was studied. Four groups of male Wistar rats were individually caged and ad lib fed with a standard (SD) and (50%) carbohydrate-enriched diet (CED), sweet (diet group I) or not (diet group II). Food intake was measured daily 4 hr after IP injection of pizotifen (2.5 mg/kg) or vehicle. 5-HT and 5-HIAA in the hypothalamus (Hy), striatum (St) and hippocampus (Hi) were assayed on the 8th day of the experiment. Pizotifen increased the consumption of SD. The absolute intake of CED remained totally and daily unchanged, while the percentage proportion was reduced. Total food intake was increased by the drug which seemed to affect the proportion rather than the absolute amounts of carbohydrate and protein consumed. This effect was independent of the carbohydrate taste. There was a decrease of 5-HT levels in the Hi, while 5-HIAA/5-HT ratio was increased in the Hy and in the Hi of animals that consumed sweet carbohydrate. The above data suggest a role of pizotifen on 5-HT central metabolism and diet selection and support the view that changes of 5-HT metabolism in the Hy and Hi are responsible for protein selection and the regulation of SD/CED ratio, but they cannot explain drug's effect on total food intake.