Telencephalic enkephalinergic systems in the rat brain

Abstract

The comparative distribution of Leu-enkephalin and an enkephalin precursor fragment, BAM-22P, was studied in the rat telencephalon using immunocytochemical procedures. Although the enkephalins have previously been localized to telencephalic neurons, the use of high doses of colchicine in the present study has permitted the visualization of widespread enkephalin-containing systems in cortical-limbic regions. Rats were treated intraventricularly with colchicine (300 to 400 micrograms) to enhance the visualization of neuronal perikarya. Leu-enkephalin immunoreactivity was noted in perikarya as well as processes of neurons in many telencephalic regions including the olfactory bulb, parolfactory areas, olfactory tubercle, basal ganglia, nucleus accumbens, septal nuclei, amygdala, hippocampal formation, and several paleocortical regions such as the piriform, entorhinal, and cingulate cortex, as well as regions of the frontal, parietal, and occipital neocortex. In the majority of regions investigated, analysis of sections adjacent to those processed for Leu-enkephalin histochemistry showed BAM-22P immunoreactivity to be localized to perikarya and processes in the same region. These results suggest that brain enkephalin-positive neurons may possess mechanisms for enkephalin biosynthesis similar to those found in adrenal medullary enkephalin cells.