Some fiber projections to the superior colliculus in the cat

Our knowledge of fiber projections to the optic tectum or superior colliculus, an important way-station in the visual system of vertebrates including mammals, is still inadequate. Studies of these fiber projections, utilizing different techniques, have been made in various mammals (Tsai, '25; Bodian, '37 in opossum; Johnson, '54, in mole; Cajal, '11, in mouse; Lashley, '34; Tsang, '37; Le Gros Clark, '42; Krieg, '47; Nauta and Bucher, '54, in rat; Castaldi, '23-'26; Hess, '58, in guinea pig; Cajal, '11; Loepp, '12; Minkowski, '20; Brouwer, Zeeman and Houwer, '23; Overbosch, '27, in rabbit; Jefferson, '40, in ferret; Monakow, 1889; Probst, '02; Cajal, '11; Poljak, '26; Barris, Ingram and Ranson, '35; Bucher and Biirgi, '50; Biirgi, '57, in cat; Brouwer and Zeeman, '26; Mettler, '35; Hirasawa, '38; Crosby and Henderson, '48; Whitlock and Nauta, '56; Polyak, '57, in monkey; and Juba, '39, in man). The majority of these investigations has been concerned with retinal projection and with projections from the spinal cord and visual cortex. In the present study, which is a continuation of a previous one (Altman and Carpenter, '61) dealing with the efferent connections of the superior colliculus in the cat, we investigated by means of the Nauta-Gygax ('54) staining technique projections to the superior colliculus in the cat from (a) the retina, (b) the lateral geniculate nucleus, (c) the pulvinar, and (d) the visual cortex. In addition, attention was paid to projection from these structures to other mesencephalic and also to the various diencephalic nuclei. MATERIALS AND METHODS Eleven adult cats were used in this experiment. The animals were anesthetized with Nembutal, and surgery was performed under aseptic conditions. In two animals the right orbit was unroofed and the optic nerve was cut. Stereotaxic lesions were produced in the right lateral geniculate nucleus in five animals, and in the right pulvinar in one animal. In three animals large portions of the right visual cortex (lateral and postlateral gyri) were removed by suction. Most of the animals were permitted to survive for 11 days; two of them were sacrificed after a shorter period. All animals were sacrificed by cardiac perfusion with 10% neutral formalin. The brains were sectioned in 2-3 mm blocks perpendicular to the axis of the brain stem and further fixed in 10% neutral formalin. Four or five selected blocks of the brain were cut serially at 25 LI on a freezing microtome, and the