Response of hypothalamic oxytocinergic neurons to immobilization stress is not dependent on the presence of corticotrophin releasing hormone (CRH): a CRH knock-out mouse study.

This study explores the quantitative patterns of immunolabeled Fos protein incidence in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON) oxytocinergic (OXY) neurons in response to immobilization (IMO) stress in corticotrophin releasing hormone deficient (CRH-KO) mice. Adult male mice, taken directly from cages or 120 min after a single IMO, were sacrificed by intracardial perfusion with fixative. Coronal brain sections of 30 mum thickness were processed for dual Fos/OXY immunohistochemistry. In control wild type (WT) and CRH-KO mice, scattered Fos immunoreactivity was observed in hypothalamus, including the PVN where scanty Fos signal occurred in both parvocellular and magnocellular PVN subdivisions. Dual Fos/OXY immunostainings revealed higher basal Fos expression in the PVN of control CRH-KO mice. IMO evoked a marked rise in Fos expression in OXY neurons of the PVN and SON in both WT and CRH-KO groups of mice. The present data demonstrate that 1/ CRH deficiency upregulates the basal activity of hypothalamic PVN OXY cells in CRH-KO mice and 2/ IMO stress in both WT and CRH-KO mice affects distinctly the activity of OXY cells in both SON and PVN. Our data indicate that CRH deficiency does not alter the responsiveness of PVN and SON OXY cells to IMO stress.