Synaptic transmission in hippocampal field CA1 is largely NMDA_R-dependent during the early post-natal period. It then becomes increasingly mediated by AMPA receptors until an adult ratio of AMPA to NMDA receptors is achieved. It is shown here that increases in the AMPA_R-mediated field potential response continue over the lifespan of the F-344 rat at the perforant path-granule cell synapse in the dentate gyrus. By contrast, the NMDA_R-dependent component of the response decreases with age between 1 and 27 months, leading to an increase of AMPA_R/ NMDA_R ratio with age. One possible explanation of this age difference is that the AMPA_R/ NMDA_R ratio can be modifiable by experience. To test the idea that the changed ratio is due to the old rats' longer lives, an intensive 10 month period of enrichment treatment was given to a group of animals, beginning at 3 months of age. Compared to animals housed in standard cages, the enrichment treatment did not alter the glutamatergic response ratio measured with field potential recording methods. These data provide support for the conclusion that the observed change with age is developmentally-regulated rather than experience-dependent. Given the role of the NMDA_R in synaptic plasticity, these changes suggest a progressive commitment of perforant path synapses to particular weights over the lifespan. One possible implication of this effect includes preservation of selected memories, ultimately at the expense of a reduced capacity to store new information.