Locomotor activity and exploratory behavior after medial entorhinal cortex lesions in the albino rat

Abstract

Male Wistar albino rats were subjected to bilateral electrolytic lesions of the dorsomedial entorhinal cortex and their open-field activity (four daily sessions of 15 min each) was tested 8–12 days postoperatively. Exploratory behavior directed at a novel object was assessed on the fourth day of testing. In Experiment I (“forced exploration”), activity was studied in an ordinary open field. Compared with a sham-operated control group ( n = 8), rats with lesions of the entorhinal cortex ( n = 7) crossed more squares on all 4 days and made more rearings on all but the first day. The rats with lesions made more contacts with the novel object, while the time spent in contact with the object did not differ between the groups. In Experiment 2 (“free exploration”), the open field was modified such that the animals could freely initiate their activity from a small box attached to the side of the field. With regard to both locomotion and rearing, the entorhinal cortexlesioned rats ( n = 8) were more active in the field on all days, but when first exposed to the situation, they did not enter the field any sooner than the control group ( n = 14). It was concluded that the increased locomotor activity observed in the rats with entorhinal cortex lesions was not primarily due to reduced fear but rather could have resulted from enhanced exploration.