Entorhinal cortex lesions as a model of age-related changes in hippocampal function

This study investigated unilateral entorhinal cortex lesions as a model of age-related changes in hippocampal function relative to more extensive bilateral lesions previously employed. Spatial memory and hippocampal physiology were examined in male rats (3 months) following bilateral or unilateral entorhinal cortex lesions, or in sham controls. All groups exhibited cue discrimination in a water escape task. Only control and unilaterally lesioned rats exhibited acquisition of the spatial version of the task. A probe trial administered 24 h after spatial training demonstrated impaired retention for unilaterally lesioned animals. Lesions decreased perforant path fiber potentials and synaptic responses; however, compensatory modifications of surviving perforant path afferents were observed for unilaterally lesioned animals. Behavioral and physiological changes following unilateral lesions were similar to those observed during aging, indicating that partial lesions provide a better model of aging than do bilateral lesions. In addition, the results emphasize retention as a cognitive constituent of the hippocampal-entorhinal system.