Cytoarchitectural and dendritic patterns of the dorsal column nuclei of the opossum

Cytoarchitectural and dendritic patterns of dorsal column nuclei of the opossum, Didelphis marsupialis virginiana, were studied with Nissl and Golgi preparations. Two basic cell types, round cells and irregular cells, are found. Round cells have a large, round cell body (20-30 mu) with a distinct nucleolus in the nucleus. The cytoplasm is fine, evenly dispersed Nissl material with occasional tigroid bodies. Irregular cells have triangular, multipolar or fusiform cell bodies (8-10 mu) with indistinct nucleus and nucleolus. Three cellular regions differentiate the rostrocaudal axis of the nucleus cuneatus: (1) rostral region (2) obex region and (3) caudal region. These regions are distinguishable on the basis of round cell arrangements, total cell populations, and round cell to irregular cell ratios. In contrast, two cytoarchitecturally distinct regions occur along the rostrocaudal region of the nucleus gracilis: (1) a rostral region and (2) a caudal region. Round cells have a sparse dendritic arrangement of a multiplanar, radiate type. Round cells forming small clusters are arranged as if on the surface of an imaginary sphere with at least one dendrite from each cell radiating toward the center of this sphere. Only fusiform irregular cells were observed with Golgi stains and their cell bodies exhibited a polar, radiating dendritic pattern. Dense dendritic arborizations are observed in the obex region of both gracile and cuneate nuclei.