Water deprivation increases the expression of pituitary adenylate cyclase-activating polypeptide gene in the rat subfornical organ

The effect of water deprivation on the expression of pituitary adenylate cyclase-activating polypeptide (PACAP) was examined in the rat subfornical organ (SFO), using a combination of immunohistochemistry and in situ hybridization histochemistry. In the euhydrated condition, PACAP-immunoreactivity (PACAP-IR) and the expression of PACAP gene was observed in the SFO. Water deprivation for 24 h and 48 h caused a significant increase in PACAP gene transcripts in the SFO, compared with euhydrated animals. Additionally, water deprivation for 48 h caused an increase in PACAP-IR. This increase of PACAP-IR was demonstrated in both nerve fibers and cell bodies. High correlation was found between the localization of PACAP-IR cell bodies and PACAP messenger RNA synthesizing cell bodies in the peripheral part of the SFO. These results suggest that PACAP in the SFO may play a role in the humoral and neural changes associated with the regulation of body fluid balance after water deprivation.