ENTORHINAL CORTEX LESIONS AS A MODEL OF AGE-RELATED-CHANGES IN HIPPOCAMPAL FUNCTION

This study investigated unilateral entorhinal cortex lesions as a mode l of age-related changes in hippocampal function relative to more exte nsive bilateral lesions previously employed. Spatial memory and hippoc ampal physiology were examined in male rats (3 months) following bilat eral or unilateral entorhinal cortex lesions, or in sham controls. All groups exhibited cue discrimination in a water escape task. Only cont rol and unilaterally lesioned rats exhibited acquisition of the spatia l version of the task. A probe trial administered 24 h after spatial t raining demonstrated impaired retention for unilaterally lesioned anim als. Lesions decreased perforant path fiber potentials and synaptic re sponses; however, compensatory modifications of surviving perforant pa th afferents were observed for unilaterally lesioned animals. Behavior al and physiological changes following unilateral lesions were similar to those observed during aging, indicating that partial lesions provi de a better model of aging than do bilateral lesions. In addition, the results emphasize retention as a cognitive constituent of the hippoca mpal-entorhinal system.