The primary optic projections in pigmented and albino guinea pigs: an experimental degeneration study

Abstract

Summary An eye was enucleated in each of 6 pigmented and 6 albino guinea pigs. Six to 8 days later the animals were killed and their brains were prepared by the Nauta and Nissl methods in order to study the course and terminal distribution of the degenerating optic fibers. Several major differences were demonstrated between the pigmented and albino guinea pigs in the terminal distribution of the crossed and uncrossed optic fibers. First, it was shown that in the pigmented animals the ventral and dorsal lateral geniculate nuclei, the nucleus tractus opticus, the nuclei praetectalis anterior and posterior, and the superior colliculus all receive inputs from both retinae; whereas in the albino animals these same nuclei could be found to receive organized inputs only from the contralateral retina. Second, it was found that the pattern of the contralateral retinal input to the ventral and dorsal lateral geniculate nuclei, but not to the pretectal nuclei, the superior colliculus and the terminal accessory optic nuclei, differs between the two strains of animals. In both the pigmented and albino guinea pigs it was shown that the accessory optic system is composed entirely of crossed optic fibers and consists of two fiber groups (inferior and superior fasciculi) and 3 terminal nuclei (dorsal, lateral and medial terminal nuclei). It was also shown that in both strains of animals the degenerating optic fibers that lie in and adjacent to the ventral and dorsal lateral geniculate nuclei and the pretectal nuclei course within two distinct fiber systems oriented perpendicularly to each other.