Expression of novel androgen receptors in three GnRH neuron subtypes in the cichlid brain.

Within a social hierarchy, an individuals' social status determines its physiology and behavior. In , subordinate males can rise in rank to become dominant, which is accompanied by the upregulation of the entire HPG axis, including activation of GnRH1 neurons, a rise in circulating androgen levels and the display of specific aggressive and reproductive behaviors. Cichlids possess two other GnRH subtypes, GnRH2 and GnRH3, the latter being implicated in the display of male specific behaviors. Interestingly, some studies showed that these GnRH neurons are responsive to fluctuations in circulating androgen levels, suggesting a link between GnRH neurons and androgen receptors (ARs). Due to a teleost-specific whole genome duplication, possess two AR paralogs (ARα and ARβ) that are encoded by two different genes, and , respectively. Even though social status has been strongly linked to androgens, whether ARα and/or ARβ are present in GnRH neurons remains unclear. Here, we used immunohistochemistry and hybridization chain reaction (HCR) to investigate and expression specifically in GnRH neurons. We find that all GnRH1 neurons intensely express but only a few of them express , suggesting the presence of genetically-distinct GnRH1 subtypes. Very few and transcripts were found in GnRH2 neurons. GnRH3 neurons were found to express both genes. The presence of distinct genes within GnRH neuron subtypes, most clearly observed for GnRH1 neurons, suggests differential control of these neurons by androgenic signaling. These findings provide valuable insight for future studies aimed at disentangling the androgenic control of GnRH neuron plasticity and reproductive plasticity across teleosts.