Among the several changes that occur in the aged brain is an increase in the concentration of the proinflammatory cytokine interleukin-1beta that is coupled with a deterioration in cell function. This study investigated the possibility that treatment with the polyunsaturated fatty acid eicosapentaenoic acid might prevent interleukin-1beta-induced deterioration in neuronal function. Assessment of four markers of apoptotic cell death, cytochrome c translocation, caspase-3 activation, poly(ADP-ribose) polymerase cleavage, and terminal dUTP nick-end staining, revealed an age-related increase in each of these measures, and the evidence presented indicates that treatment of aged rats with eicosapentaenoate reversed these changes as well as the accompanying increases in interleukin-1beta concentration and p38 activation. The data are consistent with the idea that activation of p38 plays a significant role in inducing the changes described since interleukin-1beta-induced activation of cytochrome c translocation and caspase-3 activation in cortical tissue in vitro were reversed by the p38 inhibitor SB203580. The age-related increases in interleukin-1beta concentration and p38 activation in cortex were mirrored by similar changes in hippocampus. These changes were coupled with an age-related deficit in long term potentiation in perforant path-granule cell synapses, while eicosapentaenoate treatment was associated with reversal of age-related changes in interleukin-1beta and p38 and with restoration of long term potentiation.