TONIC IMMOBILITY AND SKIN COLOR IN ANOLES - EFFECTS OF SEROTONIN PRECURSORS AND METABOLITES

Previous studies have implicated a serotonergic neurochemical system in the control of tonic immobility. The present study examined the effects on immobility of peripheral injections of chemicals found in the various stages of serotonin synthesis and metabolism. Anoles (Anolis carolinensis) were selected to study because certain of these substances produce skin color changes in the anole, affording a check on the efficacy of the chemicals administered. Although tryptophan produced no significant changes, 5-hydroxytryptophan darkened the anole's skin and decreased the number of inductions required to produce tonic immobility. Serotonin also darkened the anole's skin, but produced little change in immobility. 5-Hydroxyindole acetic acid, N-acetylserotonin, and melatonin all significantly lengthened durations of tonic immobility and lightened skin color, and melatonin had the most profound effects on both. These findings suggest that the metabolic byproducts of serotonin, melatonin and 5-hydroxyindole acetic acid, may play a crucial role in the neurochemical control of tonic immobility. © 1979.