Effects of early protein undernutrition and later frontal cortex damage on habit acquisition and reversallearning in the rat

Abstract

Rats from dams that were undernourished (8% casein diets) during pregnancy and lactation or weH fed (25% casein diets) received frontal corticallesions at maturity. The animals were then tested for the ability to master a simple sensory discrimination and to learn reversals of that discrimination. Main effects of undernutrition and the frontal corticallesion were found in originallearning but not on the reversals, and animals that received both early undernutrition and the later focal brain lesion made more errors in originallearning than did rats that sustained only undernutrition or only the lesion. The suggestion that early nutritional history may be one of a number of factors that can help to explain why patients with seemingly similar brain lesions do not always show identical symptoms is discussed.Subjects who receive lesions of the same brain structures do not always exhibit identical degrees of behavioral impairment (Finger & Stein, 1982). Several factors have now been proposed to account for this variability, which has been observed both with clinical populations and laboratory animals. For example, under some conditions it is known that age at the time of insult can affect the degree of functional sparing (Johnson & Almli, 1978), as can the speed of growth or "momentum" of the lesion (Finger, 1978b). In addition, nonspecific environmental "enrichment" has also been shown to enhance behavioral recovery, at least on simple maze-learning tasks following cortical or hippocampal lesions (Finger, 1978a).A variable that has only recently been explored in this context is the early nutritional history of the sub-[ect. Early undernutrition can affect several indices of brain function, including cellular growth and differentiation and synapse formation and myelination, and it has also been established that some behaviors can be affected if undernutrition is experienced during the period of rapid brain growth (Winick, 1976). These observations may be interpreted to suggest that early undernutrition can also affect recovery from later brain damage-a hypothesis that has now been examined in three recent studies from this laboratory, using the pups of rat dams that had experienced 50010 less food than control dams during the lactation period.The results of two of these studies have shown that early undernutrition can affect performance following a brain lesion later in life, even under conditions in which poor early diet has little or no effect on the scores of rats without focal brain lesions. In one case (Mangold, Bell, Gruenthal, & Finger, 1981), in which rats with posterior corticallesions were tested for the ability to make a brightness discrimination, poor early nutrition retarded recovery following the focal lesion. In the other, in which rats with hippocampal lesions were tested on a battery of DRL operant conditioning tasks, undernutrition attenuated the lesion effect (Finger & Green, 1983). The generality of the latter finding was examined in a third study (Laughlin, Finger, & Bell, 1983) in which rats were...

Relation between the severity of early malnutrition and the effects of later frontal cortical lesions in rats

“…The procedures employed in this study were·basically identical to those of Silva et al (1984), except for the conditions of the dietary treatment. The animals studied were 20 male and 17 female albino rat (Charles River, "CD" strain) offspring from 11 litters.…”

“…These rats will henceforth be referred to as the severely malnourished (SM) animals. The normal-birth-weight, 8 %-casein-diet rats studied previously (Silva et al, 1984) will be termed the moderately malnourished (MM) rats, and the 25%-casein-diet rats from the same study will be referred to as well-fed (WF) rats for purposes of comparison.…”

“…Analyses of variance were used to compare the scores of the present severely malnourished (SM) groups with those of the moderately malnourished (MM) and well-fed (WF) groups, since this was the original intent of the study by Silva et al (1984).…”

“…We have now been able to study severely malnourished (low-birth-weight, 6 % casein diet) rats under procedures nearly identical to those of Silva et al (1984). Because these offspring were extremely small and immature at 3 weeks after birth, we delayed weaning them from their dams until 40 days postnatal in an attempt to reduce the high mortality rate of the previous study.…”

“…This procedural change was successful in reducing (but not eliminating) the high mortality rate, and the behavioral and anatomical effects associated with severe malnutrition will be described. Further, these severely malnourished animals will be compared to the moderately malnourished (8 % casein) and well-fed rats tested under identical conditions by Silva et al (1984), in order to achieve a better understanding of the relationship between the severity of early malnutrition and learning, brain growth, and the response to an acute cortical lesion sustained later in life.…”