Evidence for Direct Stimulation of the Mammalian Nervous System with Ionizing Radiation

Abstract

In a behavioral study designed to detect the most immediate reaction of the intact nervous system to ionizing radiation, rats were exposed while asleep to X rays (250 kvp), and measurements of behavioral arousal and heart rate were made to indicate activation of the central nervous system. A transitory behavioral arousal was exhibited within 12 seconds at an exposure rate of 0.25 r/second.At a higher dose rate of 1.9 r/second this initial reaction increased in scope and by 30 seconds included sub-cortical activation as well, as indicated by a heart rate response.These reactions depended upon the rate of exposure and not upon the total dose. In blinded animals, exposure at the high intensity evoked both the behavioral arousal and the heart rate response. This indicates that CNS activation cannot be attributed to the direct effect of radiation on the visual receptor system. Although radiation may act as a stimulus to the CNS through other sensory systems it was also suggested that the nervous system itself is directly sensitive to ionizing radiation.

Behavioral Arousal and Neural Activation as Radiosensitive Reactions

“…A preliminary report of some results obtained during the first minute of exposure in Series I and II has been made (46). mhih report extends these findings to effects observed during and immediately following exposure.…”

Lick rates in rats exposed to gamma-irradiation

“…The systemic physiological concomitants produced by irradiation which are responsible for eliciting this aversion are not presently understood, but previous studies have shown that the onset of irradiation is accompanied by (1) increased heart rate (Hunt & Kimeldorf. 1962).…”

THRESHOLD FOR CONDITIONED SUPPRESSION USING X‐RAYS AS THE PRE‐AVERSIVE STIMULUS1

“…Hug (1960) identified reflex-like reactions in insects and marine invertebrates. Smith, Kimeldorf, and Hunt (1963) used dose-rates as low as 0.01 R/sec to demonstrate that a brief burst of X-rays elicited wing beat activity in the moth less than 1 sec after the onset of exposure.Hunt and Kimeldorf (1962) immediately aroused sleeping rats with an X-ray dose-rate as low as 0.25 R/sec.Using instrumental conditioning apparatus, Garcia, Buchwald, Feder, and Koelling (1962) demonstrated an immediate detection of X-rays in rats. They placed animals in a standard apparatus with the lever removed and gave 40 conditioning trials consisting of a 10-sec X-ray exposure (SI) with intermittent electric shock (S2) during the last 8 sec.…”

“…Hunt and Kimeldorf (1962) immediately aroused sleeping rats with an X-ray dose-rate as low as 0.25 R/sec.…”

“…Smith, Kimeldorf, and Hunt (1963) used dose-rates as low as 0.01 R/sec to demonstrate that a brief burst of X-rays elicited wing beat activity in the moth less than 1 sec after the onset of exposure. Hunt and Kimeldorf (1962) immediately aroused sleeping rats with an X-ray dose-rate as low as 0.25 R/sec.…”