The prefrontal corticotectal projection in the cat

Summary

The cells of origin and terminal distribution of the prefrontal corticotectal projection in the cat has been examined using retrograde cell-labeling with horseradish peroxidase (HRP) and anterograde axon-labeling with HRP or ³H-amino acid autoradiography. All prefrontal neurons labeled from unilateral enzyme deposits in the superior colliculus are pyramidal cells scattered through the thickness of layer V. The ipsilateral prefrontotectal neurons are located most densely in the banks and fundus of the presylvian sulcus and, to a lesser extent, in the anterior and frontal polar part of the gyrus proreus. About 10% as many cells are labeled in the contralateral prefrontal cortex in a similar distribution. Injections of HRP restricted to the superficial layers of the colliculus failed to label cells in the prefrontal cortex. Injections of HRP or ³H-proline-leucine in the region of these prefrontotectal neurons results in axonlabeling mainly, but not exclusively, in the ipsilateral superior colliculus where the labeled fibers are distributed in the layers below the stratum opticum. Labeled axons are especially dense in the intermediate gray layer where, caudally, they are arranged in two horizontally arrayed dorsal and ventral sheets interconnected by periodic columns of dense fiberlabeling interposed between columns of lesser fiberlabeling. Thus, the prefrontotectal projection of the cat here reported is consistent with that described earlier for the rat, but differs markedly from the primate in that prefrontal area 8 in monkeys projects also to the superficial tectal layers.