Abstract
Relatively discrete unilateral lesions were made in the lateral portion of the substantia nigra of eight cats and in the medial substantia nigra of two. After a 10βday survival period the animals were killed, brains were stored in buffered 10% formalin, and frozen sections were stained for degenerating axons and terminals, or by Weil and cresyl violet methods. Electrodes passed through the medial suprasylvian gyrus, pulvinar and/or posterolateral thalamic nucleus and the medial geniculate body. The stria terminalis and hippocampus were undamaged. Degeneration from the lesion followed two paths. One projected through the reticular nucleus into the internal capsule and then ventrolaterally below the putamen to enter the lateral and central amygdaloid nuclei, with degenerated terminals. The second path ran dorsolaterally in the internal capsule to enter the external capsule where some of the fibers spread into the lateral amygdaloid nucleus. It appears that some of the terminals in the lateral amygdaloid nucleus are from the external capsule. Perhaps these connections link the extrapyramidal system to the amygdaloid body.