AGE-RELATED DECREASE IN THE N-METHYL-D-ASPARTATE(R)-MEDIATED EXCITATORY POSTSYNAPTIC POTENTIAL IN HIPPOCAMPAL REGION CA1

Glutamatergic fast synaptic transmission is known to be altered with a ge in a region-specific manner in hippocampus of memory-impaired old r ats. In the present experiment, presynaptic fiber potentials and non-N -methyl-D-aspartate (NMDA(R)) and NMDA(R)-mediated synaptic responses in CA1 were compared in three ages of behaviorally characterized male F-344 rats. In the CA1 region, old rats showed approximately equivalen t reductions in non-NMDA(R)- and NMDA(R)-excitatory postsynaptic poten tial amplitudes for a given size of presynaptic fiber potential. There was no change in magnitude of the presynaptic response itself at any stimulus level. These results are consistent with the hypothesis that there is a reduction in the number of Schaffer collateral synapses per presynaptic axon. This pattern of results in CA1 is very different fr om what is known to occur at the perforant path-granule cell synapse. In fascia dentata the non-NMDA(R)-mediated excitatory postsynaptic pot ential is increased in amplitude, although the NMDA(R)-mediated excita tory postsynaptic potential is reduced for a given presynaptic input. These data suggest that age-related functional alterations in neurotra nsmitter receptor subtypes occur differentially between closely-relate d anatomical subregions. (C) 1997 Elsevier Science Inc.