Long-term effects of moderate X-ray doses on the averaged evoked potentials in the rabbit.

The long-term effects of moderate X-ray doses on the averaged evoked potentials (AEPs) recorded from the visual cortex to photic stimulation were studied in 6 adult male Japanese white rabbits with permanently implanted electrodes. One group of 3 animals received 100 R to the whole brain, and another group of 3 received 300 R to the lateral half of the brain. Two of the 3 animals irradiated with 300 RT were used for the study of the recovery cycle (RC) of the AEPs. The RC of the AEPs was obtained with 4 photic stimulus intervals ranging from 110 to 750 msec. The amplitude of the late two components (IV and V) of the AEPs of the 3 animals irradiated with 100 R changed little during the first several months. It showed a gradual decrease thereafter, with individual variations as to degree. The associated peak latencies were even less affected by the radiation. The amplitude of the late two components recorded from the irradiated and unirradiated cortices of the 3 animals exposed to 300 R gradually decreased in the course of time after irradiation. No differences were observed between the changes in the irradiated and unirradiated cortices. The peak latency of some of the 5 components in 2 of the 3 animals showed a slight change after exposure. The recovery ratio of the amplitude of the late two components at a stimulus separation of 220 msec recorded from the irradiated and unirradiated cortices in one of the 2 animals increased 1 month after exposure. It remained grossly unchanged thereafter. There were no differences between the changes in the irradiated and unirradiated cortices. All 6 animals died between 181 and 584 days after exposure.