Hyperphagia caused by muscimol injection in the nucleus raphe dorsalis of rats: its control by 5-hydroxytryptamine in the nucleus accumbens.

Muscimol injection in the nucleus raphe dorsalis caused intense eating by rats with access to food. A dose-related reduction of muscimol's effect was found after bilateral injections of 5-hydroxytryptamine (5-HT) in the nucleus accumbens (dose range 2.2-8.8 micrograms in 2 microliter) but no effect was observed when an even higher dose (17.6 micrograms) of 5-HT was injected in the caudate putamen. Eating by food-deprived rats was not changed by any dose of 5-HT injected either into the nucleus accumbens or the caudate putamen. (+)-Norfenfluramine, 20 micrograms, injected in the nucleus accumbens also reduced muscimol-induced eating but had no effect on the food intake of starved rats. The results suggest an important role of 5-HT in the nucleus accumbens in the control of certain types of hyperphagia in rats.