CYCLIC-AMP MEDIATES MU AND DELTA, BUT NOT KAPPA-OPIOID ANALGESIA IN THE SPINAL-CORD OF THE RAT

Intrathecal (i.t.) injection of the membrane-permeable cyclic AMP (cAM P) analogue dibutyryl-cyclic AMP(Bt2CAMP) in 3 successive doses of 12. 5, 12.5 and 25 ug in rats was very effective in reversing the antinoci ceptive effects produced by mu agonist morphine or delta agonist DPDPE , but not that by kappa agonist dynorphin A-(1-13). cAMP content of th e spinal cord was significantly decreased by morphine, but not by dyno rphin A-(1-13). The results imply that a decrease in spinal cAMP conte nt may be important for the antinociceptive effect elicited by mu and delta, but not kappa opioid receptor agonists.