A quantitative study of the effects of monocular enucleation and deprivation on cell growth in the dorsal lateral geniculate nucleus of the cat

Systematic, quantitative studies are presented concerning the effects of visual deprivation and deafferentation on the growth of developing neurons in the dorsal lateral geniculate nucleus of the cat. Three sets of experiments are described. In the first set, kittens were enucleated monocularly at one week postnatal, and sacrificed at intervals that ranged from one day to 40 weeks. The second set was similar in design, but enucleation was done at four weeks postnatal. The third series of experiments did not involve enucleation. Instead, kittens were deprived by suturing the lids of one eye closed at the time of normal eye opening. They were then allowed to survive for periods of time that varied from two to 32 weeks. In addition, two cats were studied that had been deprived for 16 weeks by sewing the nictitating membrane across the cornea of one eye. Cell counts in the binocular segment of lamina A indicate that enucleation at one week postnatal leads to rapid cell death in the lateral geniculate nucleus. Approximately 27% of deafferented cells die during the first week after enucleation. Comparable cell loss also occurs in kittens enucleated at four weeks, but its onset is delayed until the second week following eye removal. There is no loss of neurons in the lateral geniculate in cats raised with monocular eyelid suture. Measurements of cell sizes show that the primary effect of visual deprivation or deafferentation is to alter the growth of lateral geniculate neurons. In deprived kittens or those enucleated at one week, affected cells continue to grow, albeit slower than normal, for 3–4 weeks postoperatively, at which time all further cell growth stops. Subsequently, there is no marked cellular atrophy, and deprived or deafferented neurons remain at approximately two-thirds normal size. Enucleation at four weeks produces more severe effects. Eye removal arrests cell growth immediately, and approximately one month later deafferented neurons undergo significant atrophy. In these cats as well as in visually deprived animals, lateral geniculate cells receiving uncrossed input from the retina undergo greater changes in perikaryal size than neurons innervated contralaterally. In each set of experiments, rates of cell growth were compared in the binocular and monocular segments of lamina A ipsilateral and contralateral to the operated eye. No major differences were found between cells in the binocular segment and those in the dorsal portion of the monocular segment (that part of the monocular segment that lies adjacent to the lateral border of lamina A1). Furthermore, in enucleated cats, cell size changes throughout the deafferented monocular segment are equivalent, in general, to those in the binocular segment. By contrast, in visually deprived cats, neurons in the dorsal and ventral parts of the monocular segment respond differently. The present results suggest that a gradient of susceptibility to deprivation exists in the monocular segment since neurons located in the dorsal portion of the monocular segment are affected similarly to binocular segment cells, whereas cells in the ventral part ofthe monocular segment are resistant to deprivation. Neurons in the normally innervated binocular segment of lamina A in deprived or deafferented cats tend to grow somewhat faster than cells in normal animals, but do not attain larger than normal sizes. These experiments therefore do not provide evidence that normally innervated lateral geniculate neurons hypertrophy following monocular deprivation or enucleation.