Endogenous interaction of glutamate and dopamine in the basal ganglia of the awake rat during aging

The interaction of glutamate and dopamine in the basal ganglia of fully con scious rat during the normal process of aging is reviewed. Using a novel ap proach, that of blocking the reuptake of glutamate, the effects of increasi ng concentrations of endogenous glutamate on the extracellular concentratio ns of dopamine in striatum and nucleus accumbens in the young rat were inve stigated. It was found that increasing concentrations of glutamate correlat ed significantly with increasing concentrations of dopamine in striatum and nucleus accumbens. Moreover the increase of dopamine in both structures wa s significantly reduced after blockade of NMDA and AMPA/kainate glutamate r eceptors, suggesting that the increase of dopamine was mediated by glutamat e. The interaction glutamate/dopamine expressed by its ratio showed a signi ficant age-related decrease in nucleus accumbens but not in striatum, so th at to a given amount of glutamate less increase of dopamine is produced. It is suggested that the interaction glutamate-dopamine represents a balanced input to the GABA neuron in the basal ganglia and that during aging this b alance is disrupted. In addition, we also speculate on the significance of this glutamate-dopamine disruption in relation to the changes in motor beha vior found with age.