Endocrine Abstracts

The brain controls reproduction through the secretion of GnRH, but a series of higher brain centres control the secretion of GnRH into the hypophysial portal system. Whereas GnRH might be considered the ‘speaker’ for the brain in the reproductive axis, there is significant ‘cross-talk and chatter’ relating to the higher brain centres of control. Most prominently, kisspeptin mediates the feedback effect of sex steroids on GnRH cells, which may be effected at the level of the GnRH cell bodies or the secretory terminals in the median eminence. Gonadotropin inhibitory hormone (GnIH) has also emerged as a major negative regulator of GnRH secretion and action, acting on the GnRH neurons but also being secreted into the hypophysial portal system to act on the pituitary gonadotropes. This provides ‘cross-talk’ and data will be reviewed for GnIH function in mammals. The ‘chatter’ within this system involves input from centres within the brain that respond to altered nutritional status/metabolic condition, season and stress. Alterations in energy balance change the activity of appetite regulating peptide neurons in the hypothalamus. These neurons interact with kisspeptin cells, leading to changes in GnRH secretion. Season also involves changes in kisspeptin function as well as GnIH secretion. Stress has a negative impact on the reproductive neuroendocrine system and very recent data show that this involves upregulation of GnIH gene expression. In essence, GnRH neurons are controlled by serial and converging neuronal inputs from various brain centres. The same appears to be true for GnIH neurons, so the combined output of GnRH and GnIH dictates reproductive function.