Undernutrition, brain composition and behavior in rats

Typescript.Bibliography: leaves [89]-97.vii, 106 l illus., tablesThe purpose of the present study was two-fold. The first was to assess the effect of varying periods of undernutrition from birth through nine weeks of age, followed by nutritional rehabilitation with an adequate diet, on growth, brain size and composition and learning capacity in mature male rats; the second was to determine if there is a critical period in the development of the brain after which it is refractory to nutritional rehabilitation. Undernutrition was achieved by feeding litters of 16 pups on a dam fed an 8 per cent casein diet and feeding a diet of 3 per cent casein at weaning. Control rats were fed in litters of eight by a dam on the same 18 per cent casein diet to which the pups were weaned at 21 days. Undernourished pups were changed to an adequate diet at three, five, seven or nine weeks of age. Rats were maintained in an environment controlled for temperature, light and stimulation. Beginning at 16 weeks the mature rats were given a series of behavioral tests--exploratory activity in a novel situation, emotionality, activity level, neuromuscular coordination and learning in an avoidance learning situation. At 19 weeks the animals were killed by ether anesthesia. The weighed brains were analyzed for DNA, RNA, cholesterol and phospholipid phosphorus content. No differences were found in learning capacity as assessed by avoidance conditioning, or in neuromuscular coordination or emotionality. The undernourished animals were significantly (p < .01) more active than the adequately nourished controls whereas the larger, well nourished animals reared on their hind legs more frequently in an exploratory situation. Data on brain composition showed that the animals undernourished during suckling had smaller brains, with fewer cells as measured by DNA content (p < .01) than those adequately nourished from birth. An adequate diet introduced at weaning did not stimulate cell proliferation. Those animals deprived five or more weeks had significantly less total brain cholesterol than those rehabilitated after deprivation during sucking only (p < .01). This confirms other findings and shows that the critical period for cholesterol deposition indicative of myelin formation is in the first five weeks of life. There were no differences in the phospholipid phosphorus content of brains of deprived and adequately nourished rats. RNA values did not differ significantly among groups but were correlated r = 0.90 with DNA values. RNA: DNA ratios were approximately 1.0 for all groups. On the basis of weight there were no differences in the chemical composition of the brains of deprived and well nourished control rats. The animals with smaller brains learned to avoid shock in a shuttle box equally as well as well-nourished controls with larger brains of similar chemical composition and were significantly (p < .01) more active