Age-related decline in rat striatal dopamine metabolism is regionally homogeneous

Previous research has established that the age-related decrease in rat striatal D2 sites occurs predominantly in the posterior ventral caudate-putamen, and the present work was undertaken to determine whether a corresponding preferential reduction in dopamine, its metabolites, or its synthesis rate occurs in this region. Male F344 rats 4-8 or 25-27 months old were used for regional HPLC electrochemical determinations of 1) dopamine, homovanillic acid (HVA), or dihydroxyphenylacetic acid (DOPAC) obtained from striatal micropunch samples, or 2) 3,4-dihydroxyphenylalanine (DOPA) concentrations in these same micropunch regions 30 minutes after treatment with the aromatic amino decarboxylase inhibitor, NSD-1015 (100 mg/kg, IP). Aged rats had significantly less dopamine, HVA, and DOPAC in their striatal samples than did young adult controls, as well as having less DOPA accumulation after NSD-1015. However, for none of these measures was the age x region interaction significant, suggesting that the decline in these markers of presynaptic dopaminergic function occurs uniformly throughout the striatum. The results provide evidence that the effects of aging on striatal dopamine receptors are dissociable from the influences on the dopaminergic innervation of this structure, suggesting independent control of pre- and postsynaptic elements of these synapses during the lifespan.