The internal organization of the mouse caudate nucleus: evidence for cell clustering and regional variation.

From paraffin-embedded brains of adult mice, ten-micron sections were taken through the entire-extent of the caudate nucleus. Coronal, horizontal or sagittal sections stained with cresyl violet were used to examine two aspects of the internal organization of the nucleus: regional variation and cell clustering. A core of large cells located centrally in the head of the nucleus and ventrally in the body was described. This core is bounded by zones containing medium cells. Slightly larger medium cells occur laterally in the head of the nucleus than elsewhere. Based on these results, three zones have been described in the head of the nucleus: a lateral periphery, a central core area and a medial periphery. The dorsal area of the body of the nucleus probably corresponds most nearly to the lateral periphery, and the ventral area to the central core. Cell clustering is dominant pattern of organization within each zone. Only one large cell was seen per clumped cell grouping, and this cell could occupy either a peripheral or central position in the cluster. Medium cells participated in the clumped arrangement of cells, and also formed rings around fibers of the internal capsule.