pS6 immunohistochemistry as a tool to study brain activity in cichlid fish

Individuals in social hierarchies engage in agonistic encounters through aggressive behaviour, driving experience-dependent shifts in social status. Although aggression has historically been studied mainly in males, it is also an important component of female social interactions. The brain network known as the Social Decision-Making Network (SDMN) regulates various social behaviours and provides a suitable framework for studying the neural mechanisms underlying aggression. The cichlid fish Cichlasoma dimerus, presents high levels of aggression in both sexes. In females the aggressive behavior is linked to high circulating estradiol concentrations. To investigate the neural mechanisms underlying female aggression, we aimed to establish a pS6 immunohistochemistry protocol as a proxy for neuronal activity in brain regions of the SDMN. Female brains were sampled to assess pS6 immunoreactivity in different telencephalic areas (dorsal and ventral) and the preoptic area. We successfully established a pS6 immunohistochemistry protocol that allowed the detection and quantification of neuronal activity in these brain regions. Results show a clear cytoplasmic immunostaining in neurons. This methodological approach provides a valuable tool for investigating the neural mechanisms underlying female aggression and, in future experiments, for assessing the role of estradiol by manipulating aromatase activity with fadrozole.