Development and segmental organization of rostrocaudal dendrites of rat sympathetic preganglionic neurons

The longitudinal organization of preganglionic sympathetic neurons in the adult mammalian spinal cord takes the general form of a ladder. In the rat, the preganglionic neurons of the intermediolateral cell column (IML) have extensive dendritic arborizations in both rostrocaudal and mediolateral directions. We have studied the development of the rostrocaudal dendritic projection by retrogradely labeling single sympathetic preganglionic spinal segments with the membrane label DiI. The rostrocaudal dendrites of sympathetic preganglionic neurons in the IML begin to develop prenatally on embryonic day 19-20 (E19/20), several days after these neurons develop mediolaterally oriented dendrites. Between E19 and postnatal day 1 (P1), the rostrocaudal dendrites attain a length of approx. 200 microns. As the rostrocaudal dendrites elongate, the preganglionic neurons form distinct clusters between which dendritic bundles are seen. Following a growth spurt from E19 to P1, the average rostrocaudal dendritic length approximates twice the distance between clusters from P1 to P9.