Origin and termination of the diencephalo-spinal dopamine system in the rat

Using a combination of neonatal 6-hydroxydopamine and adult 5,7-dihydroxytryptamine treatment we have been able to achieve a 94-99% depletion of noradrenaline in the spinal cord. In such animals the dopamine levels are only marginally affected in the dorsal horn (at all levels) and in the intermediate zone at thoraco-lumbar levels. This combined treatment thus offers new possibilities for selective studies of the spinal dopamine projection. In agreement with the biochemical data the fluorescence histochemistry shows that the spinal dopamine innervation is mainly confined to the dorsal horn, the intermediolateral cell column and associated parts of the intermediate and central gray. Injections of fluorescent retrograde tracer combined with monoamine fluorescence histochemistry reveal that the diencephalic A11 cell group is the principal, and perhaps exclusive, source of this innervation. The area of termination, as well as the organizational similarities with certain diencephalic peptide-containing projections to the spinal cord, suggest that the diencephalo-spinal dopamine system may be importantly involved in autonomic regulatory processes.