The crossed projection from the temporal retina to the dorsal lateral geniculate nucleus in the rat.

The crossed projection from the temporal crescent in the rat's retina was studied by producing a discrete retinal lesion in one eye and examining the dorsal lateral geniculate nucleus and superior colliculus contralateral to the lesion for anterograde degeneration products. The position of this crossed degeneration was described in relation to the uncrossed retinal termination in the same structures by injecting the opposite eye with [3H]proline and processing the tissue for autoradiography. The location of the retinal lesion in relation to the temporal crescent was identified by injecting the dorsal lateral geniculate nucleus ipsilateral to the lesioned eye with a fluorescent tracer, to retrogradely label the ipsilaterally projecting retinal ganglion cells in the lesioned eye. Retinal lesions that were histologically verified to be restricted to the temporal crescent produced crossed degeneration in the superior colliculus at its rostral border, in accord with this projection's published visual topography. These same lesions consistently yielded a very circumscribed and sparse amount of degeneration in the contralateral dorsal lateral geniculate nucleus at its dorsomedial border, abutting the optic tract dorsally and the lateroposterior nucleus medially. The degeneration bore no consistent relationship to the position of the uncrossed retinal terminal field, which is situated further ventrally in the dorsal lateral geniculate nucleus; rather, this crossed temporal projection terminated in the outer shell of the nucleus along its medial border. This crossed temporal retinogeniculate projection, together with the crossed projection from nasal retina, forms a continuous map of the complete contralateral retina in the outer shell of the dorsal lateral geniculate nucleus, likely to arise from a population of retinal ganglion cells possessing small soma sizes.(ABSTRACT TRUNCATED AT 250 WORDS)