Brain mediation of Anolis social dominance displays II. Differential forebrain serotonin turnover, and effects of specific 5-HT receptor agonists

Serotonin (5-HT) functions are associated with social dominance status in d iverse species, but to date the brain regions wherein 5-HT exerts such effe cts are uncertain. Here, we indexed 5-HT turnover in male Anolis carolinens is as the ratio of 5-HT to its metabolite, 5-hydroxy-indol-acetic acid, and also as the accumulation of the in vivo tracer C-14-alpha-methyl-tryptopha n (C-14-AMT). After patching one eye, displaying dominant animals increased both measures of 5-HT turnover in the forebrain hemisphere receiving displ ay-evocative visual stimuli, compared to control, contralateral brain, wher eas both 5-HT turnover indices were decreased when animals displayed submis sively. In contrast, various non-displaying controls showed forebrain symme try on both measures. Drugs that stimulate 5-HT2C receptors in mammals, and have 5-HT2C-like binding in A. carolinensis, evoked some elements of domin ant display behaviors in non-dominant anole males and also activated dorsol ateral basal ganglia as seen in non-medicated dominants when they display [ Baxter et al., 2001]. Thus, acute changes in forebrain 5-HT output from bas eline equilibrium, acting at 5-HT2C-like receptors, might effect some eleme nts of the dominant vs. submissive male anoles' territorial displays. A mec hanistic model of how this might occur is offered. Given similarities in 5- HT systems, forebrain functions, and territorial display routines, similar mechanisms might have similar functions in other amniotes, including primat es. Copyright (C) 2001 S. Karger AG, Basel.