MORPHINE-INDUCED STRAUB TAIL RESPONSE - MEDIATED BY CENTRAL MU(2)-OPIOID RECEPTOR

The opioid receptor mechanism involved in the morphine induced straub tail response was investigated in mice. Morphine (2.5, 5, 10 and 20 mg /kg s.c.) produced a dose dependent straub tail response and analgesia (hot plate test). Naloxone (5 mg/kg s.c.) and the mu-opioid receptor antagonist beta-funaltrexamine (10 mu g i.c.v.) blocked both the strau b tail response and analgesia while the mu(1)-opioid receptor selectiv e antagonist naloxonazine (35 mg/kg s.c.) blocked only analgesia and d id not affect the straub tail response. Morphine (20 mu g) administere d by the i.c.v. route also produced the straub tail response as well a s analgesia. Pretreatment with naloxonazine (35 mg/kg s.c.) antagonise d i.c.v. administered morphine induced analgesia while the straub tail response was not affected. The results indicate that the morphine ind uced straub tail response is mediated by central mu(2)-opioid receptor s.