stress-induced adrenal hormone increase may upregulate gnih release, as some gnih neurons have adrenal glucocorticoid receptors. gnih may therefore mediate interactions between the hpg and hpa (hypothalamic-pituitary-adrenal) axes and play a role in stress-related infertility. gnih neurons of the paraventricular nucleus in the hypothalamus also express melatonin receptors. because melatonin secretion is modulated by environmental light patterns, melatonin influence on gnih production may enable photoperiodic regulation of reproduction in seasonally breeding birds, rodents, and sheep.