SPINAL ANTINOCICEPTION BY TYR-D-SER(OTBU)-GLY-PHE-LEU-THR, A SELECTIVE DELTA-OPIOID RECEPTOR AGONIST

The spinal antinociceptive potency of the delta-opioid receptor agonist, Tyr-D-Ser(otbu)-Gly-Phe-Leu-Thr (DSTBULET), was studied in rats. The tail flick test was used as nociceptive stimulus and the rotarod test was used to detect any motor or sedative effects. A dose-response curve was also made for the mu-opioid receptor agonist, morphine. The ED50) for DSTBULET was 0.3-mu-g (0.4 nmol) and a near 100% maximum effect was achieved with 5-mu-g (7.5 nmol). No motor or sedative effects were detected. Antinociception by DSTBULET was antagonized by s.c. naltrindole (I mg/kg), a selective delta-opioid receptor antagonist, and naloxone (1 mg/kg), a non-selective opioid receptor antagonist. The ED50 for morphine was 0.5-mu-g (1.0 nmol) and the antinociceptive effects were not antagonized by naltrindole (1 mg/kg). The results evidence further the important role of the delta-opioid receptor in spinal nociceptive processing.