Vulnerability of the hippocampus to kainate excitotoxicity in the aged, mature and young adult rat.

Sensitivity to excitotoxic damage was assessed in young adult, mature and aged male Sprague-Dawley rats. Kainic acid was injected into the hippocampus and the size of the hippocampal lesion rated. Intrahippocampal injection of kainic acid produced lesions in aged animals that were significantly smaller than lesions in the young rats (P < 0.05), while lesion size in mature rats was intermediate. Excitotoxic damage was localized primarily to the CA3 region of the hippocampus in the aged rats. Young adult rats had more damage to the hippocampus with involvement of CA1 pyramidal and dentate granule cells. These results suggest that increased age may reduce susceptibility to excitotoxic damage.