Relaxin-3/INSL7 regulates the stress-response system in the rat hypothalamus.

Relaxin-3 (RLN3) is a neuropeptide belonging to the insulin-relaxin superfamily. RLN3-expressing neurons are predominantly located in the dorsal pons known as the nucleus incertus, and project their axons to the forebrain including the hypothalamus. RLN3 has been suggested to be involved in the stress response. In the present study, we investigated the hypothalamic action of RLN3 in the stress-response system by intracerebroventricular (icv) administration of RLN3. Compared with saline icv injection, 1 nmol icv RLN3 injection induced c-Fos expression in the paraventricular nucleus of the hypothalamus (PVN) at 1 h after administration. Some RLN3-induced c-Fos-positive cells in the PVN were also corticotropin-releasing factor (CRF)-expressing neurons. CRF and c-fos mRNA levels in the PVN were increased at 2 h after RLN3 administration. Plasma adrenocorticotropic hormone (ACTH) levels were also increased after RLN3 administration. These results suggest that RLN3 is able to stimulate the hypothalamopituitary CRF-ACTH system during the acute response.