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 conscious rat during the normal process of aging is reviewed. Using a novel approach, that of blocking the reuptake of glutamate, the effects of increasing concentrations of endogenous glutamate on the extracellular concentrations of dopamine in striatum and nucleus accumbens in the young rat were investigated. It was found that increasing concentrations of glutamate correlated significantly with increasing concentrations of dopamine in striatum and nucleus accumbens. Moreover the increase of dopamine in both structures was significantly reduced after blockade of NMDA and AMPA/kainate glutamate receptors, suggesting that the increase of dopamine was mediated by glutamate. The interaction glutamate/dopamine expressed by its ratio showed a significant age-related decrease in nucleus accumbens but not in striatum, so that 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 balance is disrupted. In addition, we also speculate on the significance of this glutamate-dopamine disruption in relation to the changes in motor behavior found with age.