Behavioral Arousal and Neural Activation as Radiosensitive Reactions

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Abstract
Whole-body exposure of adult rats to 250-kvp X-rays at rates of 0.25 or 1.9 r/sec produced an immediate transitory arousal from sleep. At the higher dose rate this reaction was accompanied, after a delay, by an acceleration in heart rate. During exposure to a total dose of 1000 r, the high dose-rate animals also exhibited evidence of continued excitation which was absent in the low dose-rate animals. These results indicated that both the immediate and continued effects were dose-rate dependent. Both groups exhibited a transient excitatory effect with termination of exposure. The excitatory effects of irradiation were not dependent on adrenal function, since adrenalectomzed animals showed a sequence of reactions comparable to that shown by normal animals but with longer latencies. Also, these effects were not due to direct retinal stimulation by X-rays, since bilaterally ophthalmectomized animals exhibited arousal reactions within seconds after the start of exposure. Some possible modes for the action of ionizing radiation as a stimulus to the nervous system were discussed, including its possible action as a "distributed stimulus" directly on nervous tissue.