The Role of Monoaminergic Nuclei during Aggression and Sympathetic Social Signaling

Abstract

A social sign stimulus that is sympathetically induced affects aggressive approaches and influences serotonergic, dopaminergic and noradrenergic activity in the brainstem nuclei of Anolis carolinensis. Darkening of postorbital skin via sympathetic activation of adrenal catecholamines and β₂-adrenergic receptors provides a visual signal that forms more rapidly in dominant than subordinate males during social interactions. This signal limits aggressive interactions. Males were painted postorbitally with green or black paint and then exposed to a mirror. Aggressive approaches to the mirror were inhibited in males viewing a reflection with darkened eyespots, and increased in males viewing a reflection without eyespots (hidden). Noradrenergic turnover in the raphe and locus ceruleus were greatest in test subjects that viewed a reflection with eyespots hidden by green paint. Perception of darkened eyespots stimulated greater serotonergic turnover in raphe, locus ceruleus and substantia nigra/ventral tegmental area (SN/VTA). Dopaminergic turnover was higher in the raphe and SN/VTA of Anolis that viewed a reflection with darkened eyespots. However, these animals had lower dopamine turnover in the locus ceruleus than isolated and hidden eyespot groups. Of the possible roles of perikarya on central function and behavior, our results suggest feedback, cross-nuclear regulation, and some independence of function between nuclei and the forebrain terminal fields. Decreased serotonergic activity corresponds with increased aggression only in the raphe, suggesting that the raphe nuclei might be important for this behavioral trait. Increased serotonergic, noradrenergic and dopaminergic activities in SN/VTA in Anolis that view a reflected opponent with dark eyespots suggests that the SN/VTA might be directly involved in recognition of this social sign stimulus and the resulting inhibition of aggression.