Effects of monocular deprivation on the distribution of cell types in the LGNd: A sampling study with fine-tipped micropipettes

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Abstract
Six cats were reared with monocular eyelid suture from 1 week of age. Two control animals were reared in the same colony. The sutured eye of the monocularly deprived (MD) cats was opened at 8–9 months of age. The effect of monocular deprivation on the distribution of functional classes of neurons in the dorsal lateral geniculate nucleus (LGNd) was evaluated by extracellularly recording the activity of single neurons in the Alaminae of the LGNd ipsilateral to the deprived eye. A similar sampling procedure was used in the LGNd of the two control animals. Recordings were made with extremely fine-tipped micropipettes (impedances= 50–80 MΩ at 200 Hz when filled with 3M NaCl; tip diameters < 0.3 μm when measured with scanning electron-microscopical methods). Micropipettes with these tip sizes were shown previously (Friedlander et al. 1981) to display no sampling bias on the basis of soma size in the LGNd of normal cats. Only data from complete penetrations through the non-deprived and deprived laminae were used in our analysis. Each animal's non-deprived lamina A also provided control data. In addition, we recorded from geniculocortical axons in the optic radiations above the LGNd (ipsilateral to the deprived eye in five cats and both ipsilateral and contralateral to the deprived eye in one cat). The percentages of X- and Y-cells encountered in the LGNd of our control animals is in agreement with previous estimates based on cell size (2:1 X- to Y-cells — Friedlander et al. 1981). In the present study, fewer normal X- and Y-cells were encountered in laminae innervated by the deprived eye than in laminae innervated by the non-deprived eye in every MD animal. When these values were normalized for the shrinkage of the deprived lamina, only the Y-cell population was significantly reduced. These differences are highly significant both when the data from all of the animals are pooled (χ2= 21.77; P < 0.0001), and when the comparisons are made for individual animals (P < 0.02, Mann-Whitney U-test). While some of the reduction in Y-cells may be due to an increase in the number of cells with abnormal receptive field properties, too few abnormal cells were encountered to totally account for the reduction in the number of Y-cells. When recording in the optic radiations of MD cats, we encountered significantly fewer (χ2 = 35.74, p < 0.0001; p < 0.02, Mann-Whitney U-test) geniculocortical axons driven from the deprived eye. This reduction was seen for both X- and Y-cell axons. The decrease in the number of Y-cells in the deprived LGNd laminae supports recent findings (Friedlander et al. 1982) that monocular deprivation has a severe effect on both the physiology and anatomy of LGNd Y-cells. We conclude that the effect is not a sampling artifact due to the reduced size of cells in the deprived laminae of the LGNd.

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