Effect of Malnutrition in Early Life on Avoidance Conditioning and Behavior of Adult Rats

Abstract

The influence of malnutrition in infancy upon the development of certain behavioral characteristics was investigated by studying conditioned avoidance learning and extinction in adult rats subjected to nutritional deprivation in early life. In the preweaning period, young rats suckled dams fed a low protein diet (12% casein) which suppressed milk production. At 3 weeks of age the pups were weaned and divided into 3 treatment groups. One group was fed a low protein diet (5% casein). The second group was provided a basal diet (25% casein) but in restricted amount to maintain the same body weight as at weaning. The third group was changed to the basal diet ad libitum. After 4 weeks, protein- and calorie-restricted animals were rehabilitated by feeding them the basal diet. Control rats were fed the basal diet throughout the entire experimental period. From 95 days of age, all rats were subjected to avoidance conditioning. They learned to jump on a vertical screen when a conditioned stimulus (sound) was presented. The unconditioned stimuli, shocks from electrified floor grids, occurred after presenting the conditioned stimulus for 10 seconds. Duration of the latent periods and spontaneous activity throughout the periods of observation were recorded. After 6 tests of conditioning, 1 extinction experiment was carried out. There were no significant differences between control and previously malnourished rats in the learning rate expressed in terms of the duration of latent periods, but striking behavioral disturbances developed in groups of rats which had been restricted both before and after weaning. During 12 days of the experiment, increased excitability was recorded in these rats. Behavioral abnormalities were manifested as inadequate stereotyped movements and inability to delay or to extinguish the fixed conditioned reactions. Animals restricted in the preweaning period only did not show signs of disturbances which characterized the behavior of rats restricted both before and after weaning.