Molecular characteristics of brain opiate and nicotine receptors.

The present review has dealt with some of the molecular characteristics of the receptors associated with the action of opiates and nicotine. The binding characteristics of the opiate receptor in brain membrane preparations has been compared with those of a Triton X-100-solubilized extract of membranes as well as a preparation purified from rat brain by affinity chromatography. The purified opiate receptor appears to consist of three proteins; and the major component, which has a molecular weight of 35,000, may be the site of attachment of the opiate. Although phosphatidylserine appears to be associated with the opiate receptor within the membrane, its exact role in receptor binding is not known. The brain receptor for nicotine, which has a Kd in the nanomolar range, appears to have binding characteristics which differ from that of the classical nicotinic cholinergic receptor. This conclusion is corroborated by a characteristic behavioral response elicited by nicotine and not by cholinergic agonists. Finally, a discussion is presented on the presence of opiate receptors in human erythrocytes and leukocytes and the changes occurring in opiate addicts.