Morphological characteristics of neurons in the superficial layers of the rabbit's superior colliculus projecting to the contralateral dorsal lateral geniculate nucleus.

The neuronal projection between the superficial layers of the mammalian superior colliculus (SC) and the ipsilateral dorsal lateral geniculate nucleus (dLGN) is well established. However, the participation of the contralateral SC remains controversial. In this study we have presented evidence for the existence of SC neurons which project to the contralateral dLGN and also performed a detailed statistical analysis of such SC cells. The dLGN of nine adult rabbits was injected with Rhodamine latex microspheres and the retrogradely labeled cells of the SC were intracellularly injected with Lucifer yellow. The number of labeled cells is less than that found in the ipsilateral SC, but some are always present. The somata of these cells are located mainly in the lower half of the stratum griseum superficiale at a mean depth of 738 microns. 40% of the cells were horizontal, 34% stellate, 23% globular or pyriform and 3% vertical fusiform in their morphology. On the basis of morphology and localization, this population is clearly distinct from the corresponding ipsilateral cell population.