Endocrinology and genetics of the hypothalamic-pituitary-gonadal axis.

Hypothalamic control of the pituitary-gonadal axis in broad terms operates at two levels. The first level mediates longer-term responses to maturational signalling, to environmental and behavioural factors such as changes in photoperiod and availability of food, and to the expression of incubation behaviour. The second level of control mediates shorter-term reproductive responses. Dopamine is emerging as a potential key regulator at both levels of control, being stimulatory at the GnRH-I cell body and inhibitory at the median eminence. This article discusses the hypothalamic control; role of cGnRH-I in key events in the reproductive cycle; neurotransmitter and neuropeptide control of cGnRH-I; pituitary glands; avian GnRH receptors; avian GnRH receptor structure and function; follicle-stimulating hormone (FSH); luteinizing hormone (LH); gonadotrophe common alpha subunit; gonadotrophin inhibitory hormone (GnIH); other forms of GnRH; ovarian gonadotrophin receptors; and the genetics and hypothalamic-pituitary-gonadal axis in poultry.