Parallel stimulations of in vitro and in situ [35S]GTPγS binding by endomorphin 1 and DAMGO in mouse brains

Metabotropic activities of endomorphin 1, a candidate for endogenous mu-opioid receptor ligands, were examined in comparison with the actions 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 gamma S binding to synaptic membranes from the mouse amygdala in a naloxone-reversible manner. DAMGO had the same effect in such preparations. In in situ [S-35]GTP gamma S binding experiments using brain sections, both endomorphin 1 and DAMGO similarly stimulated this binding in specific cellular locations throughout the brain regions. These findings strongly support the view that endomorphin 1 selectively acts on a mu-opioid receptor. (C) 1998 Elsevier Science.