Social decision making network involved in intrasexual aggression in zebrafish

Abstract

The neural substrate of social behavior has been described as a “social behavior network” (SBN), and each brain area is involved in multiple forms of social behavior which are reciprocally connected, including aggression. Moreover, the mesolimbic reward system and the SBN are better understood as an integrated social decision-making (SDM) network regulating responses to salient stimuli. Aggression and the neural mechanisms involved in fighting behaviors are usually studied in males but not in females, despite the fact that in different species both sexes show aggressive behavior. The aim of this study is to compare male and female intrasexual aggression in agonistic encounters, and to compare patterns of brain activation in the SDM network in winners and losers from both sexes. We exposed adult zebrafish to social interaction with an opponent of the same sex (n = 20 contests per sex). We recorded the encounter and, after distinguishing a winner and a loser, samples were collected to determine brain activation by immunohistochemistry of the phosphorylated ribosomal protein pS6. The latency did not vary between sexes, while the time of resolution is shorter in females. Our results suggest that in both sexes, animals exposed to social interaction had higher overall brain activation than non-interacting controls. Moreover, females show more overall brain activation than males. In order to study how brain activation is interconnected among different areas in each social group, we performed network analysis. Our analysis suggests that female winners have a brain network with majority of positive correlations, while brain network in female losers is more similar to males, with mainly negative correlations. These results suggest that, even though intrasexual aggression follows similar structure and behavioural displays in both sexes, females solve conflict faster than males and this could be related to differential pattern of brain activation.