Increased [3H]glutamate receptor binding in aged rats.

Na-independent [3H]glutamate binding to rat hippocampal membranes increases progressively as a function of age. The increased binding represents an increased number of binding sites without changes in their apparent affinity for glutamate. However, [3H]glutamate binding, measured with a saturating concentration of calcium does not change at various ages. This does not reflect a change in the apparent affinity of calcium ions to stimulate [3H]glutamate binding, but a decrease in their maximal stimulatory effect. These results are discussed in relationship to age-related changes in certain physiological and behavioral functions.