Physiological control of nutrient self-selection in Heliothis zea larvae: The role of serotonin

Abstract

Larvae of Heliothis zea (Boddie), offered two portions of defined diet that are nutritionally complete except that one lacks protein and the other is missing a digestible carbohydrate, select a mixture of the two that is optimal for growth and development. Eating a diet high in sucrose but lacking protein, larvae have larger amounts of brain serotonin than when on a protein-containing diet. If an inhibitor of serotonin production ( p-chlorophenylalanine) is incorporated in the food of larvae which have the opportunity to self-select, brain serotonin levels remain low and sucrose consumption increases by 85%. Adding a serotonin precursor, tryptophan, to the diet results in neither a significant increase in brain serotonin nor a decrease in sucrose intake, but does effect a significant increase in protein consumption. The data suggest that serotonin is involved in a physiological feedback loop that monitors and apportions the intake of different nutrients.