Social signals regulate gonadotropin-releasing hormone neurons in the green treefrog

Animals coordinate their physiological state with external cues to appropriately time reproduction. These external cues exert effects through influences on the gonadotropin-releasing hormone neurons (GnRH), at the apex of the hypothalamus-pituitary-gonad (HPG) axis. In green treefrogs, mating calls are important regulators of reproductive behavior and physiology. Reception of mating calls causes an increase in androgen levels, and androgens promote the production of mating calls, demonstrating a mutual influence between the communication and endocrine systems. In order to investigate the central nervous system correlates of social regulation of the HPG axis in green treefrogs, we exposed males to a mating chorus or a control stimulus (tones), counted the resulting number of septo-preoptic GnRH-immunoreactive cells (GnRH-ir), and measured changes in plasma androgens. We found that reception of the mating chorus caused an increase in the number of GnRH-ir cells. As previously shown, we also found that the reception of the mating chorus resulted in higher androgen levels, suggesting that the higher GnRH-ir cell number represents increased GnRH production and release. We suggest that mating calls are an important supplementary cue that promotes GnRH production and release within the context of GnRH regulation by seasonal cues. Previous studies have proposed a neuroanatomical link between the anuran auditory system and GnRH neurons. Our results demonstrate a functional role for this proposed sensory-endocrine circuit, and show for the first time an influence of acoustic signals on GnRH neurons.