Behavioural changes following lesions of the orbital prefrontal cortex in male rats

Bilateral lesions were made, confined to the orbitofrontal part of the prefrontal cortex (OF) of male WEZOB rats at 3 different ages (30, 45 and 60 days) and behavioural changes were studied in adulthood. In a test situation for intermale aggression OF-lesioned animals showed a higher level of aggression than their control-operated opponents. Such changes were not witnessed in encounters with male rats of the less aggressive Wistar strain which emphasizes the importance of the choice of the opponents in tests for agonistic behaviour. OF lesioning did not interfere with male sexual behaviour. When tested in an open field, activity scores of OF-lesioned animals exceeded those of the control group. OF lesioning resulted in a slight but significant long-term weight reduction, 2-3 months following surgery, in comparison with the control group. However, a severe reduction in food intake (aphagia), immediately after the operation, was not observed. Increase in both aggression and locomotor activity was seen in all 3 age groups, and data do not support the hypothesis that sparing of function had occurred in the 30-day operates, as compared with the 60-day operates. However, the duration of allogrooming bouts per approach in the social agonistic situation did show a pattern depending on the lesion momentum: prepubertal OF lesions resulting in less frequent approaches and grooming bouts of longer duration. These findings are explained in terms of perseverative tendencies following OF lesions.