Differentiation of delta and mu opiate receptor localizations by light microscopic autoradiography.

Abstract

Discrete populations [2] of opiate receptors that are differently localized in rat brain were observed. Morphine-like (.mu.) receptors, labeled by 125I-labeled [D-Ala-2MePhe4Met(O)5-ol]enkephalin, are concentrated selectively in lamina IV of the cerebral cortex, certain thalamic nuclei and the periaqueductal gray, while .delta. receptors, labeled by 125I-labeled [D-Ala2D-Leu5]enkephalin, are more diffused, having high densities in cerebral cortex, corpus striatum, amygdala and olfactory tubercle. Because of similarities in their localizations, it was proposed that .mu. and .delta. receptors are, respectively, the physiologic receptors for [Met]- and [Leu]enkephalin neurons. These distributions reflect the different physiological functions attributed to .mu. and .delta. receptors and thus represent discrete functions of [Met]- and [Leu]enkephalin neurons.