Cytoarchitectonic coincidence with the discontinuous connectional pattern in the deep layers of the superior colliculus in the rat

The aims of the present study are to demonstrate cytoarchitectonically columnar structures in the deep layers of the rat's superior colliculus, and to show experimentally the existence of a clear correlation between the cytoarchitectonically defined columnar structures and the discontinuous patterns of the tectal connections in the deep layers. Injections of horseradish peroxidase conjugated to wheat germ agglutinin (HRP-WGA) into the prefrontal cortex produced orthograde labeling in the columnar structures in the deep layers of the superior colliculus, while HRP-WGA injections into the somatic sensory cortex resulted in orthograde labeling in the areas outside the columnar structures, so that the distribution patterns of terminals from these two different cortical areas are complementary in the deep layers. Cells of origin of the tectal efferents are also differentiated in terms of the columnar structures; HRP-WGA injections into the dorsal medial nucleus of the thalamus yielded retrograde labeling of spindle-cells within the columns, whereas the injections into the trigeminal sensory nuclei produced retrograde labeling of polygonal cells in the areas outside of the columns. These results suggest that as in the dorsoventral laminar coincidence with the tectal connections, there is a well organized mediolateral registration of the tectal connections with the cytoarchitectonically defined cell arrangement in the deep layers of the superior colliculus.