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

Abstract

Four male, 12-week-old Sprague-Dawley rats were used to determine the threshold for behavioral response to X-irradiation using the conditioned suppression technique. They were maintained at 80 per cent body weight and initially trained to stable performance on a VI 1 min schedule with 16 per cent sucrose solution as reinforcement. After a stable baseline was obtained, animals were placed in the instrumental conditioning box beneath the X-ray machine for a half-hour session each day. While subjects were actively pressing the lever for reinforcement, 15-sec X-ray exposures of 0.5 R/sec were administered, followed immediately by electric shock. After all animals had exhibited conditioned suppression, the dose-rate was decreased in subsequent sessions in an effort to establish threshold. The results indicate that X-rays at a dose-rate as low as 0.004 R/sec can be an effective pre-aversive stimulus for the rat.Low intensity exposures of ionizing radiation have been used to demonstrate an immediate behavioral response. 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. The animals were tested while actively pressing the lever for food on an FR 12 schedule by giving the X-ray exposure without the subsequent shock. In many cases, X-ray exposure stopped lever pressing immediately. Animals which did not suppress in the first tests were later shocked if they pressed the lever during X-ray exposure. Over a period of 20 trials, errors (lever pressing during X-ray exposure) decreased by approximately 65 per cent. Their data indicate that dose-rates as low as 0.05 R/sec are effective in obtaining this effect. An unpublished study by the author used the conditioned suppression technique reported by Estes and Skinner (1941) to demonstrate that a brief burst of X-rays could serve as a pre-aversive stimulus for rats. The methodology differed from that of Garcia et al. (1962) in that the pre-aversive stimulus (S1) was followed by an unavoidable electric shock (S2) while the animal was working in the instrumental conditioning box for reinforcement. There was no prior pairing of SI and S2* Animals were trained on an FR 50 schedule for water reinforcement until a stable baseline was obtained. Eight-second X-ray exposures at a dose-rate of 1 R/sec followed by a 300 ms electric shock at 73 v ac were then programmed on 50 per cent of the FR ratios during each session ...

Aversion to sucrose produced by contingent x-irradiation: Temporal and dosage parameters.

“…Since the 0.8-r/min dose was measured by a Victoreen phantom, it remains possible that when S was irradiated the dosage in the head was higher due to scatter through the body. Furthermore, while 0.8 r/min is not enough to elicit an investigatory response (Garcia, Buchwald, Hull, & Koelling, 1964), extensive training by means of a conditioned suppression technique indicates some detection of X-irradiation at even lower dose rates (Morris, 1966). Finally, while it is certain that irradiation of the head is more likely to produce an investigatory reaction than irradiation of the body only, Cooper and Kimeldorf (1964) report that irradiation directed at the body only may produce an investigatory reaction.…”

CONDITIONED SUPPRESSION TO ODOROUS STIMULI IN PIGEONS1,2

“…These odorants embrace a 10-fold range in vapor pressure, and have been employed in electrophysiological (Tucker, 1963) and human threshold (Mullins, 1955) studies. The conditioned suppression procedure has been employed as a technique for threshold determinations in vision (Hendricks, 1966;Powell, 1966), audition (Dalton, 1966), olfaction (Henton et al, 1966) and Xray detection (Morris, 1966). All of these investigations have used a descending series of stimulus intensities and a modified method of limits.…”

STUDIES ON THE MECHANISM OF THE EFFECT OF IONIZING RADIATIONS ON THE OLFACTORY SYSTEM. Progress Report, January 1--September 1, 1967.

“…found by Morris (1966) in behavioral experiments. The minimum threshold dose found in the present experiment was approximately 5 milliroentgens, a value determined during the study.…”