Circadian changes in PACAP type 1 (PAC(1)) receptor mRNA in the rat suprachiasmatic and supraoptic nuclei

A receptor for pituitary adenylate cyclase activating polypeptide (PACAP), denoted as PAC(1), is expressed in the suprachiasmatic nuclei (SCN). Since the circadian clock demonstrates phase-dependent sensitivity to PACAP, we h ave used in situ hybridization histochemistry to examine whether PAC(1) mRN A is differentially expressed in the rat SCN across the 24-h cycle. There w as a significant variation in PAC(1) mRNA within the SCN and supraoptic nuc lei during the light-dark cycle and in constant darkness, with peaks at the middle of both the real and subjective day and night; no significant varia tion was observed in the cingulate cortex. The results suggest that the pha se-dependent actions of PACAP on the clock may involve phase-specific chang es in the availability of PAC(1) receptors within the SCN. (C) 1998 Publish ed by Elsevier Science B.V. All rights reserved.