Successful prediction of immediate effects of undernutrition throughout the brain growth spurt on capillarity and synapse-to-neuron ratio of cerebral cortex in rats.

Based on the hypothesis that undernutrition depresses the growth rate of all processes in brain contemporaneous with it to the same extent (Peeling & Smart, 1994), specific predictions were made regarding the effect of undernutrition on two quite different facets of anatomical development within visual cortex. It was predicted that severe undernutrition during the suckling period would leave capillarity unaffected, but would result in a deficit in synapse-to-neuron ratio of similar magnitude to that in brain weight. At birth rat pups were fostered and either well fed to 30 days or undernourished to the same age by underfeeding their foster mothers. Rats were killed at 30 days by perfusion with glutaraldehyde. Visual cortex was dissected out for quantitative histological study. The number of capillary profiles per unit area of section and the area of each profile were assessed with an image analysis system. Quantitative characteristics of the neuron and synapse populations were estimated by light and electron microscopy respectively. Undernutrition resulted in a 21% deficit in brain weight, and a 22% deficit in the number of synapses per neuron. Capillarity, expressed as the fraction of section area occupied by capillary lumen, appeared completely indifferent to nutrition. However, fewer capillary profiles were found per unit area of section in growth-restricted samples, and the profiles which were present were, on average, larger. Neuron density was elevated by 19% in the undernourished group. These findings are in good agreement with the hypothesis.