Deviations in brain development due to caloric undernutrition and scope of their prevention by rehabilitation: alterations in the power spectra of the EEG of areas of the neocortex and limbic system

Abstract

Wistar rats underwent caloric undernutrition so as to produce undernourished pups (F 1, both male and female), which were put on a reduced diet throughout life, causing deficits in body weight of 40–70%, and in brain weight of 14–20% by adulthood. These chronic undernourished rats were mated and their progeny (F 2), which had suffered gestational and postnatal undernutrition, were undernourished, like their parents, throughout life until the moment of use in this study. At this degree of chronic undernutrition, rats do not appear to be sick or morbid, but only small-for-age, they are active and can reproduce. The computer-generated power spectra of the EEG of two neocortical areas (visual and motor) and of 3 regions of the limbic system (cingulate, hippocampus and olfactory bulb) of the chronically undernourished pups were obtained at different ages from birth to adulthood, and compared with the normal ontogenetic patterns of corresponding areas obtained from age-matched controls. In another group of rats, the undernutrition was imposed on normal pups from the day of weaning (21st day), i.e., after the major part of the brain growth spurt is over. Finally, the effect of restituting normal rehabilitatory nutrition from the day of weaning on the chronic group was also studied. The results show that all brain regions studied were affected by the chronic caloric undernutrition. The deviations from the normal consist of: (1) an initial lag or delay in the development of the EEG amplitude and activity by several days, (2) a later development of an abnormally high amplitude or power in the EEG power spectra by about the weaning age, and (3) an imbalance in the occurrence of the characteristics of the EEG of the respective areas of the brain (the low and high frequency spindles of slow sleep, the slow and fast theta activities of paradoxical sleep of the hippocampus, the delta rhythm, etc.). While the chronic undernutrition was continuing there was also a certain degree of spontaneous reduction in the magnitude of abnormality after about 80 days of age, instead of worsening with age, perhaps due to an intrinsic adaptational readjustment to the stress of the nutritional deprivation. The results reveal a variation in the susceptibility of development to these abnormalities. Typical examples of the range of variation of the effects are presented in the results showing that there can be nearly normal EEG patterns in some undernourished subjects (about 14–22%), and also that there can be abnormal EEG power spectra in a proportion of normals (up to about 20%). These results imply that there is a range in the plasticity and adaptive mechanisms underlying the cerebral functional reorganization evoked by chronic food deprivation. Rehabilitated groups have shown only a partial reduction in the EEG power abnormality. It is concluded that the chronic caloric undernutrition at an early age can impart permanent shifts in the organization of cerebral functioning, and that the post-growth spurt rehabilitatory feeding can contribute only little to reverse or reduce the effects of the previous undernutrition.