Projections to gyrus sigmoideus from the substantia nigra in the cat, as revealed by the horseradish peroxidase retrograde transport technique

After injections of horseradish peroxidase in the gyrus sigmoideus of the cat frontal cortex, labelled neurones were found in the substantia nigra and the ventral tegmental area of Tsai. Neurones distributed bilaterally clearly predominated in the side of the injection in the rostral sections, but differences in number were less at caudal levels. The present findings confirm the existence of a direct mesencephalocortical projection from this ventral tegmental region, and provide a morphological substrate for a better understanding of the role of the dopaminergic systems in the motor cortical regulation.