The primary optic projections in the rabbit. An experimental degeneration study

Abstract

The brains of ten rabbits (4 pigmented and 6 albino) sacrificed 6–21 days after unilateral ocular enucleation were prepared by Nauta and Nissl methods and used to study the projection and terminal destribution of degenerating optic axons. The retina is bilaterally represented in the alpha sectors of both ventral and dorsal lateral geniculate nuclei (LGv and LGd), in n. tractus opticus (NTO), in the dorsolateral portions of nn. praetectalis anterior (NPA) and posterior (NPP), and in the superior colliculus (SC). The retina is unilaterally represented in the contralateral terminal accessory optic nuclei. The mode of termination of crossed and uncrossed retinal projections endows the LGd with a concealed laminar organization. Four laminae are recognized and numbered consecutively from lateral to medial. Lamina one is extensive and formed entirely of crossed retinal input. The remaining three laminae occupy the medial zone of the LGd. Of these, laminae two and four are innervated predommantly by the ipsilateral retina while lamina three is supplied mainly by the contralateral retina. Uncrossed retinal innervations of LGv, NTO, NPA, NPP and SC are scant and overlapped entirely by crossed retinal inputs. Chiasmal decussation of the optic nerve is 90–95% complete with the uncrossed component, and specifically the uncrossed retino‐LGd and ‐SC projections, being larger in pigmented as compared with albino rabbits.