Abstract
Systemic administration of the noradrenergic neurotoxin DSP-4 results in a complete loss of staining of noradrenergic (NA) axons in the dorsal horn and intermediate zone of the rat spinal cord. NA axon staining in the ventral horn and in the intermediolateral cell column is only slightly decreased by the drug treatment. We have taken advantage of this differential effect of DSP-4 on NA axons to determine the location and number of cells that give rise to NA axons in the ventral horn and the intermediolateral cell column. Retrograde transport of the fluorescent tracer True blue was combined with dopamine-beta-hydroxylase immunohistochemistry 2 weeks after treatment of rats with 50 mg/kg of DSP-4. Compared with controls, the drug treatment resulted in a more than 90% decrease in the number of retrogradely labeled NA neurons in the locus coeruleus and an only 30– 50% reduction in the number of retrogradely labeled NA cells in the A5 and A7 groups. The results reveal different sites of termination in the spinal cord of NA axons originating in the LC and in NA cells of the A5 and A7 groups: the LC distributes fibers mainly to the dorsal horn and the intermediate zone, while NA cells of the A5 and A7 groups project to motoneurons of the ventral horn and the intermediolateral cell column.