Corticofugal axons in the lateral geniculate nucleus of the cat.

Injections of horseradish peroxidase (HRP) were made into the optic radiations just above the lateral geniculate nucleus of four cats to trace the anterograde filling of corticofugal axons terminating in the perigeniculate and lateral geniculate nuclei. The different types of axons were classified according to axonal diameter and the morphology of the terminal appendages. Judging from their morphological organization we suggest that the corticofugal axons are, in the main, slowly conducting and that they have a restricted terminal distribution which extends, however, to a multiplicity of levels in both perigeniculate and lateral geniculate nuclei. These morphological characteristics may have physiological implications in determining the role of the corticofugal pathway.