| Abstrakt: |
The distributions of μ, δ, and χ opiate receptors within visual regions in the cat cortex, thalamus and midbrain were determined by in vitro autoradiography. The overall distribution of receptors was examined using [H]-etorphine, a ligand that nonselectively labels all types of opiate receptors. [H]-[D-Ala, N-Me-Phe, Gly(ol)]-enkephalin (DAGO) was used to selectively label μ receptors, [H]-[D-Pen]-enkephalin (DPDPE) for δ receptors, and [H]-bremazocine for χ receptors. Each of the areas examined showed clear opiate receptor binding with [H]-etorphine and a differential distribution of μ, δ, and χ receptors. Compared to other cortical regions, opiate binding in layers 3 and 4 of areas 17 and 18 was sparse. In the adjacent areas a more uniform distribution across layers was observed. The density of χ opiate receptors was greater in cortex than in subcortical structures, whereas the reverse was the case for μ receptors. Nevertheless, all three types of opiate receptors were found in the ventral and dorsal subdivisions of the lateral geniculate (LGN), the pulvinar complex, and the suprageniculate nucleus. In the midbrain, the superficial layers of the superior colliculus were heavily labelled with the μ, receptor ligand, and modestly with the χ ligand. Compared with other midbrain and diencephalic areas, δ binding was low in the superior colliculus. These results suggest that the diverse effects of opiates on visual perception are mediated by the unique distributions of opiate receptor types throughout the visual areas in the brain. [ABSTRACT FROM AUTHOR] |
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