Prefrontal lesion effects on suppression of open-field activity in young and adult rats

Abstract

A total of 108 rats, 18-20, 30-32, or 100-130 days of age, received dorsomedial, orbital prefrontal, or sham lesions. After recovery, the subjects were assigned to one of three Pavlovian training conditions. Thirty-six subjects of each age level and surgical treatment received 2 days of 20 presentations of a 3D-sec, 3,OOO-Hz tone, during which inescapable shock of .5 sec duration was administered. The same number of subjects received the same treatment but without the shock, while the remaining subjects were simply placed in the apparatus with no stimuli presented. Four hours after Pavlovian treatment on both days, the subjects were placed in the open field for baseline measurement of ambulations and rearings. On 3 successive days after Pavlovian training and baseline activity measurement, the subjects were tested for suppression of activity by alternating intervals of tone/no tone in the open field. The results of baseline activity measures showed decreasing activity with increasing age, and both surgical groups were more active than the shams, with lateral subjects most active. During suppression testing, activity in the laterals given tones and shocks was most disrupted by tone presentations; shams showed least suppression. The lateral suppression tended to be greatest in the youngest subjects. The data were considered in terms of Pavlovian extinction processes and the maturation of inhibitory centers.333

Mesial cortical lesions and fear behavior in the wild rat

“…Anteromedial lesions of approximately the same size as those of the present study have been shown to impair a number of behaviors, such as spatial reversals (Divac, 1971), delayed alternation (Eichenbaum, Clegg, & Feeley, 1983), open-field activity (Brennan, 1979), and responding to reinforcement omission (McDonough & Manning, 1979). Thus, our negative results cannot be attributed simply to the small size of the lesions.…”