Immunocytochemical localization of enkephalin in the cat visual cortex.

The localization of enkephalin-immunoreactivity in the cat visual cortex (area 17) was analyzed by using immunohistochemical methods with a monoclonal antibody directed against enkephalin. The majority of the immunoreactive product was localized in neuronal processes. The density of immunopositive fibers was greatest in layer VI, with moderate staining in layers I, II, III and V, and the least dense staining in layer IV. Layer IVab neurons showed a striking concentration of immunopositive puncta around their cell bodies. Immunopositive neurons were scarcely present in the visual cortex. They were found in all cortical layers, but mostly in layer VI. The immunopositive neurons were non-pyramidal, mostly multipolar in shape and occasionally bipolar. The results provide anatomical evidence that enkephalin may have modulatory effects on visual cortical neurons.