Morphology of sympathetic preganglionic neurons in the neonatal rat spinal cord: an intracellular horseradish peroxidase study

Understanding the central neural control of autonomic functions requires a knowledge of the morphology of the preganglionic neurons, for the location of the dendritic arborizations of these neurons will indicate which central pathways may have access to them. In the present study, individual sympathetic preganglionic neurons in the neonatal rat spinal cord have been examined by the intracellular injection of horseradish peroxidase (HRP) in an in vitro preparation. Seventeen HRP-labeled preganglionic neurons in thoracic segments T1-T3 were examined in detail; of these, 12 somata were located in the intermediolateral cell column (IML), one in the lateral funiculus (LF), two in the intercalated nucleus (IC), and two at the border between IML and IC. All of the neurons had extensive dendritic arborizations arising from an average of six primary dendrites; the average total dendritic length for these cells was 2,343 microns. The morphology of preganglionic neurons differed depending on the location of their cell bodies. Preganglionic neurons located in the IML were essentially two-dimensional: the cells had some dendrites that coursed rostrocaudally for 300-500 microns within the IML and others that coursed mediolaterally, extending to the lateral surface of the cord and close to the central canal. Axons of these cells coursed ventrally from the cell body and exited from the spinal cord at the first ventral root caudal to the cell body. No intraspinal axon branches were observed.(ABSTRACT TRUNCATED AT 250 WORDS)