The effect of age on the monoamines of the hypothalamus

Measurement of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) homovanillic acid (HVA), 3-methoxytyramine (3-MT), noradrenaline (NA), 3-methoxy-4-hydroxyphenyl glycol (MHPG) and serotonin (5-HT) and its main metabolite, 5-hydroxyindol-3-acetic acid (5-HIAA) was assessed in hypothalamus and median eminence of aged rats. Age-related changes were not observed in the concentration of NA and its metabolites in median eminence. In contrast, there was a significant NA decrease in aged hypothalamus compared with 12 months (no differences were found compared with 3 months). No significant differences were found in DA concentration and its metabolites in hypothalamus but DA decreased significantly in aged median eminence compared with 12 months. The ratio 5-HIAA/5-HT, indicative of 5-HT turnover, appeared to increase in the hypothalamus and median eminence of the aged rat. Morphological dissimilarities between hypothalamus of young and aged rats were demonstrated using serotonin-immunocytochemistry. A degeneration of the serotoninergic system, denoted by the appearance of enlarged or swollen varicosities, was observed in the hypothalamus of the aged rat. These aberrant serotoninergic fibers may reflect the local degeneration of serotoninergic hypothalamic afferents during ageing. Such differential age-dependent alterations of the serotoninergic system might be responsible for at least some of the functional deficits in aged animals.