Androgen receptor alpha regulates aromatase expression in the ventromedial hypothalamus of male cichlids

Social behaviors are regulated by sex steroid hormones such as androgens and estrogens. However, the specific molecular and neural processes modulated by steroid hormones to generate social behaviors remain to be elucidated. We investigated whether some actions of androgen signaling in the control of social behavior may occur through the regulation of estradiol synthesis in the highly social cichlid fish Astatotilapia burtoni. Specifically, we examined the expression of cyp19a1, a brain-specific aromatase, in the brains of male A. burtoni lacking a functional AR gene, which was recently found to be necessary for aggression in this species. We found that cyp19a1 expression is higher in wild-type males compared to AR mutant males in the homolog of the mammalian ventromedial hypothalamus (VMH), a brain region that governs aggression across taxa. Using in situ hybridization chain reaction (HCR), we determined that AR+ and cyp19a1+ cells are commonly nearby, but very infrequently was co-expression observed, including in the fish VMH. We speculate that AR may modulate cyp19a1 expression in the fish VMH to govern aggression through an indirect, potentially transsynaptic, mechanism. These studies provide novel insights into the hormonal mechanisms of social behavior and lay a foundation for future functional studies.