Collateral projections from the substantia nigra to the cingulate cortex and striatum in the rat.

After injecting a retrograde tracer into the posterior cingulate cortex, labeled neurons were found only in the substantia nigra pars compacta, leaving neurons in the ventral tegmental area totally unlabeled. The existence of collateral nigral projections to the cingulate cortex and striatum was clearly established using the fluorescent retrograde double-labeling technique. This constitutes a neuroanatomical substrate for psychotic symptoms expressed by a subpopulation of parkinsonian patients.