Effects of 5-hydroxytryptamine and d-fenfluramine on sham feeding and sham drinking in the gastric-fistulated rat.

Previous experiments indicated that drug treatments which increase serotonergic activity produce dose-related reductions in sucrose sham feeding. In the present studies, 5-hydroxytryptamine (5-HT, 2 mg/kg, IP) significantly reduced sham feeding; its effect was reversed by the peripheral 5-HT receptor antagonist, xylamidine (3 mg/kg, IP). At the same dose, 5-HT did not affect water sham drinking. These are the first data to implicate serotonergic activity at peripherally located 5-HT receptors in the modulation of sucrose sham feeding. d-Fenfluramine (3 mg/kg, IP) also reduced sham feeding, an effect that was weakly attenuated by xylamidine, suggesting substantial mediation of its effect by centrally located 5-HT receptors. Sham drinking was reduced by d-fenfluramine (3 mg/kg), although to a lesser degree. In comparison with the previous studies, the present data suggest that in smaller doses d-fenfluramine is relatively selective in its effect on sham feeding, but that, in larger doses, the selectivity may be lost.