Hormonal responses to a potential mate in male birds

Social interactions rapidly modulate circulating hormone levels and behavioral patterns in most male animals. In male birds, sexual interaction or visual exposure to a conspecific female usually causes an increase in the levels of peripheral reproductive hormones, such as gonadotropins and androgens. Although the perception of a female presence is processed in the brain and peripheral hormonal levels are regulated by the hypothalamus–pituitary–gonadal (HPG) axis, the specific neural circuitry and neurochemical systems that translate social signals into reproductive physiology in male birds were not well understood until 2008. Today, there is growing evidence that two neuropeptides localized in the hypothalamus, gonadotropin-releasing hormone and gonadotropin-inhibitory hormone, are responsive to social information. These two neuropeptides have thus begun to be regarded as modulators translating social stimuli into changes in the levels of peripheral reproductive hormones. Here, we review previous studies that investigated the male responses of the HPG axis to the mere presence of a female or to sexual interaction, and describe the neurochemical pathways linking visual perception of a potential mate to rapid peripheral hormonal changes via the brain–pituitary endocrine system in sexually mature male Japanese quail.