Projection from the superficial layers of the tectum to the pretectal complex in the cat.

The projection from the superficial layers of the tectum to the pretectal complex in the cat was examined using the retrograde transport of wheat germ agglutinin-horseradish peroxidase. Restricted injections were made into different parts of the pretectum. Neurons in the superior colliculus were found to be arranged in a mediolateral array that corresponds to the rostromedial to caudolateral array of their axon projections to the nucleus of the optic tract and posterior pretectal nucleus. These results suggest that similar parts of the retinotopic maps present in the pretectum and superior colliculus are connected. The labeled cells in the superior colliculus were located within the deep part of stratum griseum superficiale and the superficial part of stratum opticum, and were composed of multipolar cells, vertical fusiform cells and horizontal cells. We conclude from this study that the cells of origin in the superior colliculus originate in the same region to which the contralateral retinal Y-cells project and that have also the morphological diversity, as do other tecto-thalamic neurons.