Age-related alterations in receptor density and metabolic activity in the brain

The present experiments were designed to investigate whether or not age-related changes in brain function became detectable by comparing the responsiveness to stimulants or blocking agents between young and relatively aged rats. Oxygen consumption by hippocampal slices under the resting condition (3.5 mM KCl) was not significantly altered by aging (between 26 and 78 wk of age). When KCl concentration was increased to 50 mM, oxygen consumption by the slices from both young and aged groups significantly increased, but the increase was significantly greater in slices from young rats. Enzyme activities of the glycolytic pathway as well as a non-energy metabolizing enzyme, choline acetyltransferase, were not different between 6 and 26 wk of age. [3H]Prazosin binding in the cerebral cortex tended to be lower in the aged (78 wk old) rats but not significantly different from that in the young (13 wk old) ones. On the other hand, the recovery from the reduced prazosin binding following administration of phenoxybenzamine was significantly delayed in the aged rats. These results indicate that the age-related changes in brain function become evident by comparing the responsiveness to stimulants or blocking agents between young and aged rats.