Characteristics of the “Receptor” for Narcotic Analgesics in Synaptic Plasma Membrane Fraction from Rat Brain

Abstract

Abstract: The characteristics of the interaction between dihydromorphine (DHM) and a synaptic plasma membrane (SPM) fraction from rat brain cerebral cortex have been studied. DHM at 10 +9 M concentration is bound in a reversible process which is partly specific. The specific binding is inhibited by the sulphydryl reagents, N‐ethylmaleimide and p ‐chloromercuribenzoic acid. The binding is strongly inhibited by 10 −8 M levorphanol but significantly less inhibited by its optical antipode, dextrorphan, which is much less analgetic. At 10 −8 M concentration, nalorphine and naloxone were strongly inhibitory while heroin at 10 −8 M and codeine at 10 −7 M were nearly inactive. A mixture of 10 −5 M acetylcholine and 2.5 × 10 −5 M eserine caused a moderate inhibition while dopamine, noradrenaline, serotonin, histamine and propranolol were classified as inactive (i. e. caused less than 25 % inhibition at 10 −5 M). The observed binding characteristics of the SPM fraction are compatible with those which might be expected for the actual narcotic receptor. Analogous SPM preparations from subcortical parts of the cerebrum and from the brain stem also showed stereospecific binding of narcotics.