Behavioral effects of bilateral entorhinal cortex lesions in the balb/c mouse

Abstract

Balb/c mice with small bilateral electrolytic lesions of the entorhinal cortex were compared with both sham and nonoperated subjects in spontaneous and learned behaviors. The operated mice were hyperactive in an open field 1 week but not 6 weeks after surgery; locomotor activity was slightly increased during the night hours 2–3 weeks after lesion. Learning was tested between 2 and 6 weeks postsurgery. Retention of a CRF appetitive operant conditioning task was improved after the lesion, as well as retention of a one-way active avoidance task. In contrast, operated animals were disturbed in an operant task using a discriminative schedule and in passive avoidance conditioning. The observed increase in activity was not sufficient to explain the findings. Considering the connections of the entorhinal cortex with the hippocampal system, we suggest some kind of inhibitory function for this cortex. Because the entorhinal cortex provides multimodal sensory information to the hippocampus, it could be involved in postlearning modulation of information and thus in memory processes.