DIFFERENTIAL MODULATION OF MU-OPIOID AND DELTA-OPIOID ANTINOCICEPTIONBY NEUROPEPTIDE FF RECEPTORS IN YOUNG MICE

The ability of neuropeptide FF (NPFF) to modulate mu- and delta-opioid -induced analgesia by intracerebroventricular administration was compa red in adults and 14-day-old mice. In adults, opioid-induced analgesia was predominantly mediated by mu-receptors whereas mu- and delta-rece ptors were equally involved in pups. An NPFF analog, 1DMe, reduced the analgesic effect of DAGO and [D.Ala(2)]deltorphin-I, mu and delta sel ective agonists respectively. However, a high dose of 1DMe (22 nmol) i ncreased both morphine and [D.Ala(2)]deltorphin-I-induced analgesia. D ose-response curves for 1DMe in the presence of naltrindole or naltrex one, delta- and mu-opioid selective antagonists respectively, indicate that 1DMe preferentially reversed mu-receptor-mediated but increased delta-receptor-mediated analgesia. These findings demonstrate differen ces in control of mu- and delta-induced analgesia by NPFF receptors.