THORACOLUMBAR SYMPATHETIC PREGANGLIONIC NEURONS IN THE DORSAL COMMISSURAL NUCLEUS OF THE MALE-RAT - AN IMMUNOHISTOCHEMICAL STUDY USING RETROGRADE LABELING OF CHOLERA-TOXIN SUBUNIT-B

The cell morphology of sympathetic preganglionic neurons (SPNs) in the dorsal commissural nucleus was studied by the retrograde labeling tec hnique using cholera toxin subunit B (CTb) as a tracer. A small amount of an aqueous solution of CTb was injected unilaterally into the majo r pelvic ganglion of the male rat. Labeled SPNs were detected immunohi stochemically using anti-CTb antiserum. Most of the labeled SPNs were observed in L1 to L3, and a very small number in T13. They were observ ed bilaterally in the sympathetic nuclei, such as the intermediolatera l cell column, intercalated nucleus and the dorsal commissural nucleus . A loose network of longitudinally or transversely oriented SPN dendr ites was located within the dorsal commissural nucleus itself. The lat eral margin of the dorsal commissural nucleus was roughly demarcated b y longitudinally oriented dendrites. Together with the dendrites of th e SPNs of the intercalated and intermediolateral cell column, laterall y oriented dendrites of the dorsal commissural nucleus converged and f ormed the transverse dendritic bundles in the intermediate zone that c onnect the dorsal commissural nucleus and the intermediolateral cell c olumn. The transverse dendritic bundles were arranged periodically. Th e axons of the SPNs in the dorsal commissural nucleus traveled lateral ly into the transverse dendritic bundles, then turned ventrally near t he intermediolateral cell column, and finally entered the ventral funi culus. After rhizotomy of the ventral roots of the upper lumbar cord, labeled SPNs were found only on the side contralateral to the rhizotom y. The dorsal commissural nucleus appears as a compact single cell col umn, but our results clearly show that this nucleus actually consists of two adjacent parallel columns of cells.