Abstract
Purpose: :
A brief period of monocular deprivation in early postnatal life can alter the structure of neurons within deprived layers of lateral geniculate nucleus (LGN). The modification of structure is accompanied by a marked reduction in labeling for neurofilament, a protein that composes the stable cytoskeleton and supports neuron structure. This study examined the possibility for recovery of neurofilament labeling in cats that were monocularly deprived and then had their deprived eye opened (BR - binocular recovery), or had the deprivation reversed to the fellow eye (RO - reverse occlusion). We also examined the extent to which recovery was dependent on visually-driven activity by placing monocularly deprived animals in complete darkness (dark rearing).
Methods: :
Kittens were monocularly deprived for 7 days starting at postnatal day 34, and recovery of neurofilament protein was examined in layers of the LGN after a duration of binocular vision or reverse occlusion that lasted 1 (N=4), 4 (N=4), or 8 days (N=4). The extent to which recovery was dependent upon visually-driven activity was examined in monocularly deprived cats that were placed in complete darkness for 1 (N=2), 4 (N=4), or 8 days (N=8). Cell counts of neurons immunoreactive for neurofilament were made with a computerized stereology system. Cell structure was assessed by measurement of the cross-sectional area of Nissl-stained neurons.
Results: :
The reduction in neurofilament labeling following monocular deprivation recovered to normal levels when the deprived eye was opened to provide simultaneous vision to both eyes (BR), or when the deprived eye was opened and the fellow eye was closed (RO). The degree and speed of recovery was comparable between recovery conditions, and it occurred in synchrony with the recovery of neuron structure. Results from monocularly deprived animals placed in complete darkness revealed an overall reduction in neurofilament labeling, which indicated that recovery in BR and RO was dependent upon visually-driven experience.
Conclusions: :
The loss of neurofilament produced by monocular deprivation was ameliorated equally by BR and RO when the competitive disadvantage of the deprived eye was removed, and results from dark rearing demonstrated that recovery additionally required visually-driven activity, as its removal blocked recovery. The role of neurofilament in providing stable neural structure raises the intriguing possibility that dark rearing, which reduced overall neurofilament levels, could be used to reset the deprived visual system so as to make it more ameliorable with treatment by experimental manipulations.
Keywords: amblyopia • cytoskeleton • thalamus/lateral geniculate nucleus