CAPSAICIN-EVOKED RELEASE OF PITUITARY ADENYLATE-CYCLASE ACTIVATING PEPTIDE (PACAP) AND CALCITONIN-GENE-RELATED PEPTIDE (CGRP) FROM RAT SPINAL-CORD IN-VIVO

Capsaicin-evoked release of pituitary adenylate cyclase activating pep tide (PACAP)-like immunoreactivity (LI) from rat spinal cord was exami ned in vivo. In anaesthetized rats, a catheter was inserted through th e atlanto-occipital membrane into the subarachnoid space at the level of the sacral spinal cord for infusion of artificial cerebrospinal flu id. Another catheter was placed in the cisternal opening for outflow. Blood pressure was monitored and kept stable during the experiment. Pe rfusion samples were analyzed for PACAP and calcitonin gene-related pe ptide (CGRP) by radioimmunoassay. The addition of capsaicin (10 mu M) to the perfusate elevated the concentrations of PACAP-27-LI in the art ificial cerebrospinal fluid by 177%, PACAP-38-LI by 93% and CGRP-LI by 692%. In view of the presence of PACAP-immunoreactive nerve fibres in the superficial layers of the dorsal horn and the expression of PACAP in the small sized neurons in the dorsal root ganglia, the findings s uggest that PACAP is released into the artificial cerebrospinal fluid from C-fibres in the spinal card. PACAP conceivably plays a modulating role in nociception. (C) 1997 Elsevier Science B.V.