MORPHOLOGY OF RETINO-GENICULATE AXONS IN THE CAT

When horseradish peroxidase is injected into the optic tract, retino-geniculate axons and their terminals become filled throughout their length and resemble axons impregnated by the Golgi methods. In the optic tract, labeled axons and collateral branches ranging from 0.5 to 5.0 μm in diameter can be traced to the dorsal lateral geniculate nucleus. Larger diameter axons branch frequently and terminate in laminae A, Al, C and in the medial interlaminar nucleus. These axons have terminal swellings that range from small (1-2μm) and spherical to large (7-l0μm) and crenulated. The swellings may be arranged in clusters, in chains connected by fine axons, or singly at the ends of axons. Fine diameter axons project to laminae Cl and C2, and intermingle with larger fibers in C and in the medial interlaminar nucleus. These fine axons branch infrequently and usually give rise to single terminals or chains of swellings, but rarely bear clusters of terminals. The distribution of these groups of axons suggests that they may correspond to classes of retino-geniculate axons that have been characterized elect rophysiologically. The larger diameter axons show the same distribution as X- and Y-cell axons, while the finer axons appear to correspond to W-cell axons. Within each of these structural groups, however, individual axons display remarkable diversity in their overall patterns of branching as well as in the types and arrangements of their terminals. © 1979.