Abstract
The effects of 5-hydroxytryptamine (5-HT) and tryptamine injected into the paraventricular nucleus of the hypothalamus (PVN) on food intake, and on noradrenaline- (NA) induced feeding were examined. In nondeprived rats, 12.5–100 nmol 5-HT reduced the intake of palatable wet mash diet over a 30-minute period. Tryptamine (50 and 100 nmol) was without effect in this paradigm. However, when tryptamine was injected into the PVN of rats pretreated with the monoamine oxidase inhibitor, pargyline, a strong anorectic effect was observed. The action of tryptamine in pargyline-treated rats was not affected by depletion of 5-HT levels in the PVN with PCPA. This indicates that the effect of tryptamine is not mediated by a release of endogenous 5-HT. Tryptamine injected into the PVN potentiated the effect of a low dose of 5-HT on food intake. This effect may be due to a prolongation of the activity of 5-HT resulting from tryptamine competing with 5-HT for the same reuptake system. Tryptamine and 5-HT attenuated the feeding response elicited by injection of 25 nmol NA into the PVN. Both tryptamine and 5-HT were more potent at attenuating the effects of NA than in reducing the intake of the palatable wet mash diet. Overall, the results suggest that tryptamine may act via the serotonergic system in the PVN to affect food intake, but it is a weaker compound than 5-HT in this respect.
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