Hippocampal lesions induced by ionizing radiation: a parametric study.

The selective lesion of granule cell populations in the dentate gyrus induced by ionizing radiation has been proposed as a useful method for evaluating the effects of hippocampal lesions on behavioral tasks. In the first part of the present study we confirmed the induction of the selective lesion of hippocampal dentate gyrus by ionizing radiation in infant Wistar rats, reported previously, but to a smaller extent with less cell loss. A parametric study was thus performed to assess the effect of modification of the parameters previously tested, comprising three further steps: an increase in the total dose of X-rays and modification of the fractionating schedule; use of three radiation types, X-ray, gamma-ray, and electrons (at two energy levels, 3 and 7 mev); use of three X-ray energy levels, 180, 200 and 250 kVp; and assessment of the effect of five total X-ray doses, at 200 kVp, 10, 14, 16, 18 and 20 gy (grays). The data suggests that X-ray radiation, in a total dose of 14 gy, at the 200 kVp energy level, fractionated into seven consecutive exposures of 2 gy each and produces a lesion of about 85% of the dentate gyrus granule cells.