Effects of Total-Body X-Irradiation in Utero on Early Postnatal Changes in Neuron Volumetric Relationships and Packing Density in Cerebral Cortex

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Abstract
Exposure to a cumulative dose of 300 r of total-body X-irradiation on gestation days 10 to 14 inclusive resulted in a slight decrease in mean values for neuron nuclear volume, cytoplasmic volume, and soma volume in the first 10 days of postnatal life in the white rat. On the 20th day a slight increase in these values was noted in the irradiated animals as compared with controls. No significant differences in neuron packing density between irradiated and control groups were seen at any stage between the 1st and 20th postnatal days. Values for brain weight and cortical thickness, however, were found to be very significantly lower in irradiated than in control animals, although the growth curves for cortical thickness in the 2 groups tended to be parallel in each of the 5 areas studied. Although the total number of cells in the cortex is greatly reduced by in utero irradiation, at the dose and rate levels employed, the surviving cells tend strongly to follow normal growth patterns and establish their normal spatial integrity. This is not to say that the orientation or pattern of dendritic branching is necessarily the same in irradiated and control groups but only that the space or volume of cortex devoted to each neuron is, on the average, the same for the 2 groups.

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