Corticotrophin releasing factor mRNA expression in the sheep brain during pregnancy, parturition and lactation and following exogenous progesterone and oestrogen treatment.

In the multiparous ewe, intracerebroventricular (i.c.v.) infusions of corticotrophin releasing factor (CRF) act centrally to facilitate the induction of maternal behaviour if administered with vaginocervical stimulation. Changes in CRF mRNA expression in the brains of multiparous ewes were therefore examined as a function of late pregnancy, parturition and lactation using in situ hybridisation histochemistry. As the induction of maternal behaviour in sheep is steroid dependent, a comparable analysis was undertaken in ovariectomised ewes treated with the sex steroids oestrogen and progesterone. Changes in CRF mRNA were quantified in the paraventricular nucleus (PVN) and in the bed nucleus of the stria terminalis (BNST). Expression levels in both the PVN and BNST were unaltered during pregnancy and lactation, but were significantly increased immediately post partum. CRF expression in the BNST, but not in the PVN, was significantly increased in response to treatments with progesterone and oestrogen alone or in combination, although there were no significant differences between treatments. These results indicate that CRF mRNA expression is increased in neuroanatomical locations relevant to the control of maternal behaviour when this behaviour is induced or, in the case of steroid influences on the BNST, is inducible by vaginocervical stimulation. They also indicate, that CRF mRNA expression in the BNST and PVN is differentially influenced by sex steroids.