Cytoplasmic laminated bodies in the lateral geniculate nucleus of normal and dark reared cats

The postnatal development of cytoplasmic laminated bodies in lamina A cells of the lateral geniculate nucleus in normal and dark reared cats has been studied quantitatively with light microscopy. In the normal cat laminated bodies develop between the sixth and eighth postnatal week and increase steadily in number thereafter. These inclusion bodies are found chiefly in medium size cells and are distributed more densely in the medial part of lamina A than laterally. Laminated bodies appear not to be a general feature of the visual pathways since they are not found in cells of the visual cortex, superior colliculus, or ventral lateral geniculate. In the dark reared cat laminated bodies develop at about the same time as in the normal animal, but approximately twice as many of them are seen at all ages investigated. Our experiments indicate that dark rearing does not cause a proliferation of multiple laminated bodies within single neurons, but rather induces the formation of a laminated body in cells that normally would not acquire one. This effect appears to be permanent since it is not reversed by long term dark rearing nor by periods of normal visual experience following deprivation. Physiological experiments (Sherman et al., '72) have shown that fewer Y‐cells are recorded in binocularly deprived cats than in normally reared animals. On the basis of the present results, it is suggested that dark rearing influences the functional specificity of developing lateral geniculate neurons. In this view, deprivation prevents normal numbers of Y‐cells from developing. Neurons which would have become Y‐cells develop instead as X‐cells; a change in functional organization which is associated structurally with an increase in the number of cells that contain cytoplasmic laminated bodies.