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Opiate receptor sites in rat brain can be labeled in vivo by 3Hdiprenorphine, a potent opiate antagoinst. Using techniques to minimize diffusion in fresh, frozen, unfixed brain, we have localized 3Hdiprenorphine by autoradiography to visualize the distribution of opiate receptors. Silver grains indicative of the binding of labeled 3Hdiprenorphine are discretely localized in numerous areas of the brain with very high densities in the locus coeruleus, the substantia gelatinosa of the spinal cord, and in clusters within the caudate-putamen, amygdala, and parts of the periventricular gray matter.
Pert et al. (1976) studied this question.