Effect of long-term caloric restriction on brain monoamines in aging male and female Fischer 344 rats

The present study examines the changes in central monoamines and their metabolites in aged male and female rats after long-term caloric restriction. Fischer 344 rats of both sexes (n = 5-10/group) were maintained on one of two dietary regimens: ad libitum NIH 31 diet or 60% by weight of the ad lib. intake (restricted), supplemented with vitamins and minerals. Animals received these diets from the age of 14 weeks until killed at 22.25 months of age. Caudate nucleus (CN), hypothalamus (HYPO), olfactory bulb (OB) and nucleus accumbens (NA) were assayed for content of norepinephrine (NE), dopamine (DA) and its metabolites (dihydroxyphenylacetic acid, DOPAC, and homovanillic acid, HVA) and serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) using HPLC/EC. Relative to the ad lib. group, restricted rats of both sex showed significant decreases in NE content in CN, HYPO and OB. DA and 5-HT content were decreased significantly in the CN and HYPO. No significant changes were found in the levels of DA metabolites in all brain regions studied. While the 5-HIAA level was significantly reduced in the HYPO and NA of the female restricted rats, it was increased several-fold in the OB of the male restricted animals. These preliminary results suggest that long-term caloric restriction alters brain monoamine concentrations, an effect which may in turn modify the normal rate of aging.