Radiation Conditioning: A Specific Aversion to Feeding after a Single Exposure to 50 r

Abstract

During a series of experiments in which rats were given a barium meal, it became necessary to measure the dose of radiation received by the bariumfilled stomach. We decided to re-feed a litter of four rats which six weeks earlier had been used in one of the barium meal experiments. To our surprise, two rats ate the full quantity of barium meal but the other two, after eating a few mouthfuls, refused to eat any more. On consulting the records it was found that the rats which had refused to eat had been given 100 r of x-rays after their previous barium meal. It appeared that we had accidently observed a radiation-conditioned avoidance, sinlilar to that described by Kimeldorf (1962). To confirm this and to test whether the technique could provide a suitable method for investigations into this form of conditioning, a series of formal experiments were undertaken. 2. METHOD The technique was based on that used for giving rats barium meals before taking serial radiographs (Hulse 1957, 1958). Nine litters of four adult male rats were used, each litter having been caged together since weaning. The rats were trained to eat from a metal spatula by offering them a stiff paste made from ' Horlicks Malted Milk '. The training lasted for about two weeks, at the end of which the rats would usually eat the ' Horlicks ' avidly. The single exception occurred in the ninth Jitter, one rat of which was untrainable. The rats were starved from 4 p.m. on the day before the first feeding with barium so that all the animals would, presumably, be avid for the barium meal. The litter, in its home cage, was kept overnight in a room in the x-ray suite so that the rats would be used to the room in which they were going to be fed. It was necessary that each rat should eat only its own barium meal and should not eat any intended for another ; consequently one person could not easily feed more than two rats at a time. The next morning, therefore, the four rats were put into two separate cages exactly similar to their normal living quarters. After they had explored the fresh cage, each animal was fed from a metal spatula with 5 g of ' Horlicks Shadow Meal' made into a stiff paste with 13 drops of water, the ' Horlicks Shadow Meal ' consisting of one part of Horlicks, two parts of barium sulphate and a sufficiency of gum tragacanth. The feeding was usually completed in 5 min.