Substantia nigra projections to the reticular formation, superior colliculus and central gray in the rat, cat and monkey.

After horseradish peroxidase injections in different parts of the lower brain stem retrogradely labeled neurons were observed in the substantia nigra, mainly ipsilateral pars reticulata. These findings demonstrate that the substantia nigra projects not only to the striatum and thalamus but also to brain stem areas which give rise to descending spinal projections. These nigral projections to brain stem structures may play an important role in a variety of behaviors and may be involved in clinical syndromes associated with nigral lesions.