Microdialysis studies of basal levels and stimulus-evoked overflow of dopamine and metabolites in the striatum of young and aged Fischer 344 rats

The technique of intracranial microdialysis was used to investigate the eff ects of aging on the striatal dopaminergic system of the anesthetized Fisch er 344 rat. Microdialysis probes were implanted into the striatum of young (2-8 months) and aged (24-28 months) urethane anesthetized rats. Striatal d ialysate levels were analyzed for dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and serotonin (5-HT) by high performance liquid chromatography with electroche mical detection. As compared to the young animals, basal extracellular leve ls of DA and DOPAC were significantly decreased in two groups of aged anima ls. Stimulation with excess potassium added through the microdialysis probe produced a robust overflow of DA in the young and aged rat striatum, but t he evoked overflow of DA was not diminished in the aged rat striatum as com pared to young animals. In contrast, D-amphetamine-evoked overflow of DA wa s again robust in young and aged animals, but was greatly decreased in the aged rat striatum as compared to the signals recorded in the young rats. Ta ken together with previous reports, these data support the hypothesis that a major change in the regulation of DA release that occurs in aging involve s changes in the function of the neuronal uptake of DA, which may be a comp ensatory property of DA neurons in senescence. (C) 1999 Elsevier Science B. V. All rights reserved.