[Multiple opiate receptor sites in the rabbit thalamus and cerebellum: preliminary characterization (author's...

Inhibition of 3H-etorphine binding by D-Ala2, D-Leu5-enkephalin, a delta agonist and by morphiceptin, a mu agonist, reveals the existence of at least two classes of binding sites for the tritiated oviparine in membranes from the Rabbit thalamus and cerebellum. In the thalamus, approximately 50% of these sites appear to be mu receptor sites whereas the other half is neither of the mu nor of the delta subtype. In the cerebellum, at least 80% of the 3H-etorphine binding sites would belong to the mu subtype. This result may be related to the fact that the rabbit cerebellum contains appreciable quantities of methionine-enkephalin but little if any leucine-enkephalin.