The effect of pituitary adenylate cyclase activating peptide (PACAP) on the nociceptive formalin test.

Recent studies have suggested that pituitary adenylate cyclase activating peptide (PACAP) may be involved in nociceptive transmission. The present study examined the effect of low-dose PACAP-27 on nociceptive behavior using the formalin test. PACAP-27 was administered intrathecally. Twenty minutes later, formalin (50 microliters, 5%) was injected subcutaneously into the dorsal surface of the right hind paw. Intrathecal PACAP-27 at 0.6 pmol suppressed the second phase response to formalin, while 5 pmol depressed both phases. PACAP-27 at 5 pmol did not impair motor function. Hence, the data suggest that the effect of PACAP-27 on formalin-induced pain-related behavior is specific. The findings may lead to a better understanding of the role of PACAP in nociceptive transmission.