PARALLEL STIMULATIONS OF IN-VITRO AND IN-SITU [S-35] GTP-GAMMA-S BINDING BY ENDOMORPHIN-1 AND DAMGO IN MOUSE BRAINS

Metabotropic activities of endomorphin 1, a candidate for endogenous m u-opioid receptor ligands, were examined in comparison with the action s of [D-Ala(2), N-Me-Phe(4), Gly(5)ol]- enkephalin/DAMGO, a well-known synthetic mu-opioid agonist. Endolnorphin 1 stimulated [S-35]GTP gamm a S binding to synaptic membranes from the mouse amygdala in a naloxon e-reversible manner. DAMGO had the same effect in such preparations. I n in situ [S-35]GTP gamma S binding experiments using brain sections, both endomorphin 1 and DAMGO similarly stimulated this binding in spec ific cellular locations throughout the brain regions. These findings s trongly support the view that endomorphin 1 selectively acts on a mu-o pioid receptor. (C) 1998 Elsevier Science.