Measures of serotonin (5-HT) turnover in A. carolinensis forebrain increase acutely when males exhibit dominant social/territorial display routines, but decrease during submissive displays [Baxter et al., 2001a, b]. The present investigation sought to determine whether a difference in presynaptic regulatory receptors - one that might affect 5-HT flux - distinguish dominant vs. submissive anoles. Both 5-HT(1B) and 5-HT(1D) receptors are presynaptic regulators of output; this role is prominent at 5-HT terminals, where stimulation inhibits 5-HT release. Here, 3H-sumatriptan binding at sites similar to mammalian 5-HT(1B/D) receptors was significantly higher in forebrain regions of submissive anoles than in dominant cagemates; this receptor site seemed pharmacologically more like a 5-HT(1B) than a 5-HT(1D) receptor. Higher densities of presynaptic 5-HT(1B) receptors in subordinates than in dominants might account for differences in 5-HT flux (lower in subordinates than in dominants) observed in displaying anoles of different status. Knockout mice missing the 5-HT(1B) receptor show heightened male territorial aggressiveness, thus similar 5-HT regulatory mechanisms might influence the likelihood of dominance in both mammals and reptiles.
Copyright 2001 S. Karger AG, Basel