Glutamate Receptor-Mediated Restoration of Experience-Dependent Place Field Expansion Plasticity in Aged Rats

Place fields of hippocampal pyramidal cells expand asymmetrically when adult rats repeatedly follow the same route. This behaviorally induced expression of neuronal plasticity uses an NMDA_R-dependent, LTP-like mechanism and could be used by hippocampal networks to store information. Aged spatial memory-impaired rats exhibit defective experience-dependent place field expansion plasticity. One possible explanation for this aged-associated deficit is alterations in glutamatergic function. In fact, both NMDA_R- and AMPA_R-mediated field excitatory postsynaptic potentials in CA1 decrease with aging. The current study investigated whether modulation of either AMPA or NDMA receptor activity could restore this experience-dependent plasticity by prolonging AMPA_R activity with the ampakine CX516 and modulating the NMDA_R with the noncompetitive antagonist memantine. The spatial firing characteristics of multiple CA1 pyramidal cells were monitored under both treatment conditions as aged rats repeatedly traversed a circular track. Compared to the saline baseline condition, acute administration of memantine, but not CX516, reinstated experience-dependent place field expansion. Taken together, these data suggest that pharmacological manipulation of the NMDA_R can improve the function of hippocampal networks critical to optimal cognition in aging.