Primary optic projections in the rabbit.Study using the horseradish peroxidase anterograde labeling technic

Abstract

The primary visual pathways, in particular those to the lateral geniculate body, of 11 albino and 7 pigmented rabbits, were studied using the method of anterograde labelling with horseradish peroxidase following injection of the tracer into the vitreous body of one eye.A heavy projection to the contralateral dorsal lateral geniculate nucleus was seen in all animals.In both albino and pigmented animals a region devoid of label was present in the medial part of the alpha sector of the nucleus.This region corresponded to a compact, oval or wedge-shaped field of terminal label in the ipsilateral nucleus, which was much heavier in pigmented than in albino rabbits.In the ventral lateral geniculate nucleus, contralateral retinal input was almost entirely confined to the caudal half of the lateral sector of the nucleus, where two laminae of dense terminal label, separated by a less densely labelled area, were oriented parallel to one another and to the optic tract.This bilaminar distribution of retinal afferents to the ventral lateral geniculate nucleus has not been described in previous studies.The ipsilateral projection was to the dorsal part of the lateral sector and was most prominent in pigmented animals.The "intergeniculate leaflet" received a prominent contralateral input in all animals, and a clear ipsilateral input in pigmented animals, which overlapped with the contralateral input.Projections to other primary visual centres (pretectal nuclei, superior colliculus, nuclei of the accessory optic tract) are also described.