Sprouting of optic tract projections in the brain stem of the rat

Abstract

Abstract The present experiments examine axonal sprouting of optic tract projections as a consequence of occipital cortex removal. Eyes were removed bilaterally in experimental rats 16 months following unilateral occipital cortex ablation. Seven animals survived this procedure. Controls included rats sacrificed 16 months after unilateral occipital cortex ablation, one week after unilateral occipital cortex destruction, and one week after bilateral or unilateral eye removal. Brains were serial‐sectioned and stained by the Nauta‐Gygax method for degenerating axons. Sprouting occurred only at two loci, the caudal half of the ventral lateral geniculate nucleus, pars lateralis, and the caudal portion of lateral nucleus of the optic tract and subjacent medial quarter of pretectal nucleus. These loci have in common that they are regions of convergence in a major fashion of the two fiber systems, the occipitofugal and retinofugal projections on which experiments were done. However, sprouting did not occur in other similarly deafferented regions. Explanations for this specificity of sprouting are discussed. Optic tract sprouting was observed only at paraterminal portions of the axon and not as collateral sprouts along its course. A suggested relationship between axonal sprouting and functional plasticity is discussed.