Influence of Malnutrition in Early Life on Exploratory Behavior of Rats

Abstract

Development of exploratory behavior during the preweaning period and the intensity of exploratory activity in adults were studied in rats subjected to nutritional deprivation in early life. In the preweaning period, the dams of experimental animals were fed a low protein diet (12% casein) to suppress milk production. Control rats were provided a well-balanced basal (25% casein) diet. At 3 weeks of age the pups were weaned and divided into 3 treatment groups. One group was fed an extremely low protein diet (5% casein), a second group was fed the basal diet in restricted amount to prevent any growth, and the third group was provided basal diet ad libitum. After 4 weeks, protein- or calorie-restricted animals were rehabilitated by feeding the basal diet. Control rats were fed the basal diet throughout the entire experimental period. Protein restriction of lactating rats soon affected growth and behavior in their offspring. Lower body weight and slower development of exploratory behavior were found in experimental animals from day 10 of life. After weaning, severe protein or calorie restriction caused an elevation of spontaneous activity in male rats and calorie-restricted females. Animals fed the low protein diet during only the preweaning period did not show increased intensity of exploratory activity in the postweaning period. After nutritional rehabilitation, exploratory activity declined rapidly in all treatment groups. At day 75 and day 85 of life, all previously malnourished rats showed a very low exploratory drive. A consistent tendency to reduce spontaneous activity was found both in the group that was malnourished only in the preweaning period and in rats that also had been restricted for 4 weeks after weaning. At day 85 of life, all experimental groups differed significantly from normally fed rats. Similar trends in behavioral changes were observed in males and in females.