Microstructural analysis of the anorectic action of peripherally administered 5-HT.

The anorectic action of systemically administered 5-HT (1, 2 and 4 mg/kg SC) was investigated in food deprived rats using the technique of microstructural analysis; small food pellets were delivered to a food hopper, and the time and occurrence of each pellet removal was recorded. Log-survivor analysis of inter-pellet intervals was used to define feeding bouts, and this was then used to compute measures of bout frequency, bout size, bout duration and eating rate. The 5-HT reduced food intake by selectively decreasing bout size and bout duration. No effects of 5-HT were observed on any of the other parameters measured. These effects of 5-HT are robust over a range of bout criteria, and replicable. Methysergide (3 mg/kg IP) attenuated the anorectic action of 5-HT by a significant increase in bout frequency and an attenuation of the effects of 5-HT on bout size, and bout duration. The results are discussed in terms of a possible role for peripheral 5-HT in the control of satiety, and implications for the mode of action of serotonergic anorectic agents such as fenfluramine.