Postcritical‐period reversal of effects of monocular deprivation on dorsal lateral geniculate cell size in the cat

If cats are raised with monocular lid suture, cells in dorsal lateral geniculate (DLG) laminae which receive inputs from the deprived eye are smaller than normal when the animals reach maturity. Previous studies have shown that after a critical period of development, these morphological changes cannot be reversed by closing the initially experienced eye and opening the initially deprived eye (reverse suture). The present experiment investigated whether removal of the experienced eye, a procedure which rapidly reverses some of the physiological effects of monocular deprivation on striate cortex neurons (Kratz et al., '76), also would produce a reversal of the effects of monocular deprivation on DLG cell size. In addition, if a morphological reversal in DLG cell size could be observed, we were interested in knowing its time course relative to the physiological reversal in striate cortex. Nine control kittens were raised with monocular lid suture until they were four to eight months old (group MD). Comparison with a group of six normally reared kittens (group N) showed the usual effects of monocular deprivation on DLG cell size (cross-sectional area) which have been reported previously; i.e., a marked reduction in cell size in the deprived binocular segments of laminae A and A1, and a smaller reduction in cell size in the deprived monocular segment of lamina A. Ten additional kittens were raised with monocular lid suture until they were four to five months old, at which time the experienced eye was enucleated. Five of these kittens (group MD-DE-Immed) were allowed to survive 30 hours after the enucleation. There was no significant difference in DLG cell size between these animals and the MD control animals. The remaining five kittens (group MD-DE-3 mo) were allowed to survive three months after enucleation of the experienced eye, and the deprived eye remained closed during this time. In these kittens, cells in the deprived DLG laminae were significantly larger than cells in the deprived laminae of kittens in both the MD-DE-Immed and the MD control groups. In addition, they were not significantly different from normal. The increased cell size in the MD-DE-3 mo cats was present in the deprived binocular segments of both laminae A and A1, and to a lesser extent in the deprived monocular segment of lamina A. Cell sizes also were measured in the deafferented (initially experienced) laminae of cats in the MD-DE-Immed and MD-DE-3 mo groups. They showed a slight decrease in size relative to DLG cells in the experienced laminae of MD control cats. These results indicate that deprived DLG cells can resume their growth after the previously defined critical period. Comparisons with previous studies indicate that it is necessary to completely remove the inputs from the experienced eye for the new growth to occur. However, it is not necessary to provide the deprived eye with visual experience. In addition, the increase in deprived DLG cell size occurs sometime after the increase in ability of the deprived eye to drive striate cortex cells (Kratz et al., '76). Thus, the functional recovery of cortical cells precedes the morphological recovery of DLG cells.