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

The mammalian superior colliculus (SC) may be divided into distinct layers on the basis of cytoarchitectonic criteria. These layers have different functions and patterns of connectivity. The superficial layers (stratum zonale, stratum griseum superficiale (SGS) and stratum opticum) are intimately associated with the processing of visual information. In the present study, we have investigated the morphology of the SC neurons that project ipsilaterally to the dorsal lateral geniculate nucleus (dLGN). Rhodamine latex microspheres were injected into the dLGN of nine adult rabbits. Retrogradely labeled cells were then intracellularly injected with Lucifer Yellow. The somata of the cells from which the projection originated were primarily located in a band occupying the medial third of the SGS and were found to reside at an average depth of 373 microns. Morphological analysis of these neurons revealed that 37% had a stellate shape, 27% were vertical fusiform, 18% were globular/pyriform, 14% were oriented horizontally and 4% were pyramidal in their morphology. Within each morphological class, we have examined the different subtypes with respect to incidence, localisation and characteristics of the dendritic arborizations.