Undernutrition and Overnutrition in the Neonatal Rat: Long-Term Effects on Noradrenergic Pathways in Brain Regions

Abstract

To determine whether neonatal nutrition influences development of CNS noradrenergic systems, litter sizes were manipulated at birth to produce undernutrition (16-17 pups/litter) or overnutrition (five to six pups) and compared to rats reared in normal litter sizes (10-11 pups). Studies were conducted throughout the preweaning period in which nutrition was manipulated, as well as during postweaning nutritional rehabilitation. Sparing of brain growth occurred, evidenced by much smaller changes in brain region wt than in body wt. Similarly, neonatal malnutrition produced major deficits in norepinephrine levels in peripheral sympathetic pathways, but levels in the brain remained within normal limits. Development of [3H]norepinephrine synaptosomal uptake, a biochemical index for presynaptic terminals, was unimpaired by malnutrition; indeed, higher uptake values were seen than in the control population. Nevertheless, norepinephrine turnover was severely attenuated during nutritional restriction and the effect persisted into adulthood; the deficit was greater in the cerebral cortex than in the cerebellum, despite the fact that cerebellar growth showed less sparing. Development of binding capabilities of noradrenergic receptors, particularly the alpha 2- and beta-subtypes, were also adversely affected in cerebral cortex, again suggestive of a deleterious effect on synaptic function. Animals exposed to neonatal overnutrition showed only slight effects on brain region wt or norepinephrine levels, but did display some suppression of [3H]norepinephrine synaptosomal uptake and enhancement of norepinephrine turnover; changes in receptor binding capabilities in the overnourished animals were attributable to the small alterations in brain region wt. These data indicate that neonatal nutrition alters presynaptic and postsynaptic markers of noradrenergic function that remain abnormal even when nutritional rehabilitation occurs.