A quantitative study of the effects of prenatal X-irradiation on the development of cerebral cortex in rats

Abstract

Pregnant rats were exposed to a single whole body X-irradiation on day 15 of gestation at a dose of 1.0 Gy. The offspring showed microcephaly at 7 weeks of age. Their body weight, brain weight, cortical thickness and the numerical density of neurons and synapses in the somatosensory and visual cortex were examined. Significant decreases in cortical thickness in both somatosensory (25%) and visual (16%) cortex were observed. However, there were no significant changes in the numerical density of neurons and synapses, nor in synapse-to-neuron ratios in both cortical regions between control and X-irradiated groups. These results suggest that prenatal X-irradiation can decrease the number of neurons, and the neurons which survive X-irradiation proliferate and elaborate connections in a normal fashion. This is in contrast to the animals exposed to ochratoxin A, in which numerical density of neurons in the somatosensory cortex is increased, with normal numerical density of synapses, resulting in low synapse-to-neuron ratios. The discrepancy in the synapse-to-neuron ratios between the X-irradiation and ochratoxin A-treatment might derive from a different effect on the developing neurons.