Anatomical consequences of long-term monocular eyelid closure on lateral geniculate nucleus and striate cortex in squirrel monkey.

The effects of long-term monocular deprivation on the geniculostriate system in squirrel monkeys were studied with neuroanatomical methods. Four neonates were visually deprived by monocular eyelid suture during their first 10 days of life and survived from 9 to 40 months. In the lateral geniculate nucleus (LGN), deprivation resulted in severe cell size changes. Neurons in the deprived laminae were smaller compared to those in the undeprived laminae. Deprivation left the reciprocal connections between LGN and striate cortex intact: After horseradish peroxidase (HRP) injections into striate cortex, retrogradely transported enzyme labeled a wedge of neurons in deprived and undeprived LGN laminae; anterogradely transported HRP filled preterminal and terminal axons in this wedge. Following 3H-proline injections into the deprived eye for transneuronal transport, autoradiography showed in the ipsilateral striate cortex a silver grain distribution over most of layer IVc similar to that in normal squirrel monkeys, except for a small strip in the anterior calcarine fissure. Here, a few, irregularly spaced "patches" of higher grain density occurred deep in layer IVc. Layer IVc of contralateral area 17 was also uniformly labeled over most of its extent, except for a very few and inconspicuous accumulations of slightly increased silver grains. After visual stimulation of the deprived eye, the 14C-2-deoxyglucose method showed in the contralateral striate cortex some alternating "patches" of higher uptake superimposed on the heavy labeling in layer IVc. Layer IVc in the ipsilateral cortex was more uniformly labeled. Regularly spaced arrays of labeled "puffs" in layers II/III were present in both hemispheres. Cytochrome oxidase staining showed no change in the distribution pattern of the enzyme in the deprived monkeys from the basic pattern of normal adults. No changes in cell sizes were found in layer IVc in cresyl-violet-acetate-stained sections. These results lead to the conclusion that in area 17 of squirrel monkeys there is no distinct segregation of inputs from the two eyes into anatomically discrete ocular dominance columns and they support the view of a predominantly binocular organization of area 17.