Evidence for the existence of a projection from the dorsal column nuclei to the substantia nigra in the cat.

Discrete injections of horseradish peroxidase in the substantia nigra of cats resulted in moderate to scant retrograde neuronal labeling of the contralateral dorsal column nuclei (nucleus gracilis and nucleus cuneatus). A moderate number of degenerating synaptic boutons emanating from the axons of stereotaxically lesioned dorsal column nuclei were identified by electron microscopy in the neuropil of the contralateral substantia nigra zona compacta and its dorsal division-nucleus parabrachialis pigmentosus. The present findings furnish evidence for a moderate, entirely crossed afferent projection of the dopaminergic neurons of the mesencephalic tegmentum, arising in the dorsal column nuclei.