SEROTONERGIC INFLUENCES ON FOOD-INTAKE - EFFECT OF 5-HYDROXYTRYPTOPHAN ON PARAMETERS OF FEEDING-BEHAVIOR IN DEPRIVED AND FREE-FEEDING RATS

Three experiments were carried out to examine the effect of the serotonin precursor, 5-hydroxytryptophan, upon food intake and the micro-structure of eating in deprived rats, and on the pattern of meal taking in free-feeding animals. The study also investigated the capacity of a peripheral decarboxylase inhibitor (MK-486) to antagonise the effects of 5-HTP in order to identify a central or peripheral mode of action. In deprived rats 5-HTP brought about a dose related inhibition of food intake which was mildly antagonised by MK-486. A detailed analysis of the behavioural changes occurring during eating showed that the inhibition of food intake by 5-HTP was reflected in a reduced number of eating bouts and a slower rate of eating. MK-486 did not antagonise the effect of 5-HTP on eating rate. In free-feeding rats whose food consumption was continuously monitored for 24-hr periods, 5-HTP gave rise to a reduction in meal size and a slowing of the intra-meal rate of eating. These findings are in keeping with the effects of other serotonergic manipulations on the patterns of feeding in rats. © 1979.