DIFFERENTIAL INTERACTIONS OF CHOLECYSTOKININ AND FLFQPQRF-NH2 WITH MU-OPIOID AND DELTA-OPIOID ANTINOCICEPTION IN THE RAT SPINAL-CORD

An in vivo preparation of the rat spinal cord was used to investigate the electrophysiological actions of two non-opioid peptides, cholecystokinin (CCK8) and FLFQPQRF-NH2 (FMRFamide-like peptide) applied intrathecally. These compounds were examined alone and as a pretreatment before DAGO, a μ opioid agonists, and DSTBULET, a δ opioid agonist, both which selectively reduce C-fibre evoked dorsal horn neurone activity elicited by transcutaneous electrical stimulation. Given alone, CCK8 (1 μg) elicited a modest enhancement of C-fibre induced activity which returned to control levels after 20 min, while FLFQPQRF-NH2 (10 μg) had no significant effect on C-fibre evoked firing. As a pretreatment, however, both peptides selectively prevented the inhibition of C-fibre evoked activity normally resulting from intrathecal DAGO, while having no effect on that resulting from DSTBULET. Further, CCK8 enhanced the facilitation of C-fibre evoked firing normally observed with low doses of DAGO. These data indicate that the anti-opioid roles suggested for CCK8 and FLFQPQRF-NH2 may be specific for neural elements utilizing the μ opioid receptor. © 1990.