The anorectic action of peripheral 5-HT examined in the runway: evidence for an action on satiation.

The hypothesis that systemically administered 5-hydroxytryptamine (5-HT) reduces feeding by a specific action on satiation and satiety processes was examined using a food-rewarded runway task. Over the course of 15 successive trials, with food available for 2 min on each trial, the development of satiation was monitored following treatment with 5-HT (1 and 2 mg/kg SC) and saline. The 5-HT failed to alter runway performance over the early trials, but then induced marked decrements in running speed and food intake. Analysis of cumulative food intake curves showed that 5-HT significantly reduced food intake beginning at the point where a decline in the rate of feeding was observed under control conditions. These results indicate that 5-HT exerts its anorectic effect only after some food has been ingested, and support the hypothesis that 5-HT accelerates the development of satiation and satiety.