Mu opiate isoreceptors: differentiation with kappa agonists.

In vivo pharmacological data support the concept of mu (mu) isoreceptors in the rat CNS. The mu 1 receptor mediates analgesia and regulation of cholinergic neurons. Naloxazone may be a specific antagonist of this receptor type. In contrast, the mu 2 receptor is responsible for respiratory depression and regulation of nigrostriatal dopaminergic neurons. In this case, the kappa agonists EKC and MR-2034 appear to be specific mu 2 antagonists.