Pathophysiological roles of galanin-like peptide in the hypothalamus and posterior pituitary gland

The hypothalamo–neurohypophyseal system is known to be involved in the regulation of body fluid balance, reproduction and stress response. Galanin-like peptide (GALP) is a 60-amino acid peptide, which has been isolated and cloned from porcine hypothalamus. GALP is abundantly expressed in the arcuate nucleus (Arc) neurons of the hypothalamus and the pituicytes of the posterior pituitary gland (PP). Intracerebroventricular administration of GALP causes significant increases of neurohypophyseal hormones (arginine vasopressin and oxytocin) and ACTH in rat plasma. GALP-containing neurons in the Arc are activated by foot shock stress. The expression of the GALP gene in the Arc is up-regulated by acute inflammatory stress but not chronic stress. On the other hand, the expression of the GALP gene in the pituicytes of the PP is up-regulated by both acute and chronic stress such as nociception, inflammation and osmotic challenge. These results suggest that GALP in the hypothalamus and PP has different pathophysiological roles in the regulation of stress responses involving the hypothalamo–neurohypophyseal system.