Hormonal Responses to a Potential Mate in Male Birds

Gonadotropin-inhibitory hormone as a regulator of social interactions in vertebrates

The social environment changes circulating hormone levels and expression of social behavior in animals. Social information is perceived by sensory systems, leading to cellular and molecular changes through neural processes. Peripheral reproductive hormone levels are regulated by activity in the hypothalamic-pituitary-gonadal (HPG) axis. Until the end of the last century, the neurochemical systems that convey social information to the HPG axis were not well understood. Gonadotropin-inhibitory hormone (GnIH) was the first hypothalamic neuropeptide shown to inhibit gonadotropin release, in 2000. GnIH is now regarded as a negative upstream regulator of the HPG axis, and it is becoming increasingly evident that it responds to social cues. In addition to controlling reproductive physiology, GnIH seems to modulate the reproductive behavior of animals. Here, we review studies investigating how GnIH neurons respond to social information and describe the mechanisms through which GnIH regulates social behavior.

Noradrenergic alpha-2A receptor activation suppresses courtship vocalization in male Japanese quail

Male Japanese quail produce high-frequency crow vocalizations to attract females during the breeding season. The nucleus of intercollicularis (ICo) is the midbrain vocal center in birds and electrical stimulation of the ICo produces calls that include crowing. Noradrenaline plays a significant role in sexual behavior but the contribution of noradrenaline in the control of courtship vocalizations in quail has not been well established. Using dose-dependent intracerebroventricular injection of clonidine, an α2-adrenergic receptor-specific agonist, crowing vocalization was immediately suppressed. At the same time as crow suppression by clonidine there was a reduction of immediate early gene, zenk mRNA, in the ICo; no zenk mRNA expression was detected in the dorsomedial division of the nucleus. Using histochemistry, we determined that the ICo receives noradrenergic innervation and expresses α2A-adrenergic receptor mRNA. Taken together, these data suggest that noradrenaline regulates courtship vocalization in quail, possibly via the α2A-adrenergic receptor expressed on ICo neurons.

Effects of Social Information on the Release and Expression of Gonadotropin-Inhibitory Hormone in Birds

The social environment changes circulating hormone levels and associated behavior in animals. Although social information is perceived by sensory systems in the brain, and peripheral reproductive hormonal levels are regulated mainly by the hypothalamus-pituitary-gonadal (HPG) axis, the neurochemical systems that convey social information to the HPG axis were not well-understood until the 2000s. In recent years, a growing body of evidence has demonstrated that a neuropeptide localized in the hypothalamus, gonadotropin-inhibitory hormone (GnIH), is responsive to social information. GnIH was first identified in the quail hypothalamo-hypophyseal system and named for its ability to inhibit gonadotropin secretion. Hypothalamic GnIH neurons have thus begun to be regarded as integrators, translating social information into changes in the levels of circulating gonadal hormones through the HPG axis. Here, we review current research investigating the responses of the GnIH neuronal systems to social status, offspring, and the presence/absence of conspecifics, and describe the neurochemical pathways linking visual perception of a potential mate to a rapid change in blood gonadotropin levels via the hypothalamus-pituitary axis in male birds.