Striatal dopamine uptake and swim performance of the aged rat

The striatum and olfactory tubercle of 30-month-old F344 rats contain significantly (21-24%) less dopamine compared with young adult (8-month) animals. However, rats of the two age groups show identical Km and Vmax values for the kinetics of [3H]dopamine uptake into striatal homogenates; uptake into the olfactory tubercle also appeared unaffected in old age. The preservation of dopamine uptake despite reductions in content of the transmitter suggests that the forebrain dopaminergic nerve terminals are intact, but that reduced dopamine synthesis and/or enhanced degradation may occur in the existing terminals. Administration to senescent animals of the dopamine uptake blockers nomifensine or bupropion (but not the norepinephrine uptake blocker desmethylimipramine) improved their swim performance to levels comparable with young adult animals. The findings suggest that amine reuptake may limit the synaptic effectiveness of dopamine released in the aged striatum.