DISSIMILAR EFFICACY OF OPIOIDS TO PRODUCE MU-MEDIATED ANALGESIA - ROLE OF G(X Z) AND G(I2) TRANSDUCER PROTEINS/

Intracerebroventricular (i.c.v.) administration to mice of IgGs raised against alpha subunits of G(i2) or G(x/z) transducer proteins lessene d the activation of low Km GTPase induced by morphine, DAMGO and DADLE in P-2 membranes from mouse periaqueductal grey matter (PAG). In mice injected with anti G(i2)alpha, DADLE, DPDPE and [D-Ala(2)] Deltorphin II, but not beta-endorphin-(1-31), antagonized the analgesic activity of morphine. Conversely, following anti G(x/z)alpha, morphine antagon ized the antinociceptive potency of DADLE. It is concluded that opioid s display diverse efficacy at mu-G(i2) and mu-G(x/z) complexes to prod uce supraspinal analgesia in mice.