THE DISTRIBUTION OF CHOLINERGIC PERIKARYA WITH RESPECT TO ENKEPHALIN-RICH PATCHES IN THE CAUDATE-NUCLEUS OF THE ADULT CAT

The distribution of cholinergic interneurons with respect to enkephali n-rich patches in the caudate nucleus of the cat was examined using bo th computer-assisted 3-D reconstruction and immunocytochemical techniq ues. Examination of the 3-D distribution of perikarya staining for cho line acetyltransferase (ChAT) revealed that these cells were not evenl y distributed within the caudate nucleus but exhibited areas of increa sed and decreased density. Comparison of the 3-D distribution of choli nergic perikarya to that of the enkephalin-rich patches indicated that areas of increased ChAT+ cell density often corresponded to the posit ions of enkephalin-rich patches within the dorsal-lateral caudate nucl eus. At more ventral regions, there was no clear correspondence betwee n areas of increased ChAT+ cell density and enkephalin-rich patches. I n agreement with these observations, a quantitative analysis of sectio ns double-labeled for ChAT and enkephalin revealed that the density of cholinergic neurons within enkephalin-rich patches was twice that in the surrounding tissue in the dorsal region of the caudate nucleus. In contrast at more ventral levels, the difference in the density of ChA T+ cells in enkephalin-rich patches did not significantly differ from that in the surrounding striatal tissue. Both the results of the 3-D a nd the double-labeling analysis suggest that cholinergic neurons are n ot evenly distributed within the caudate nucleus of the cat but form l oose clusters which are associated dorsally with the enkephalin-rich p atches. These results also provide further evidence of heterogeneity w ithin the striosomal compartment in the cat.