Emotionality and exploratory behavior following cortico-basomedial amygdala lesion in rat

Twelve rats with amygdaloid lesion (CBM group) and 20 sham operated (Control group) were tested. Emotional reactivity evaluated by six category scale showed transient decrease in CBM group with respect to Control one. The CBM lesion enhanced the locomotor activity in electromagnetic activity meter in the initial phase of confinement in the apparatus. Open-field ambulation was higher in CBM rats than in controls on the first day of examination, while on the second day both groups showed similar locomotor activity. No between group differences were found in response to introduction of novel object. Both groups preferred to stay in box placed in open-field than move around the field. However, CBM rats were engaged in box exploration, whereas controls spent major proportion of time sitting motionless. These results indicate that CBM lesion increases some components of response to novelty. The pattern of changes and their transitory character suggest that cortico-basomedial region of the amygdala is involved in the control of processes underlying the initial phase of responding to novel environment.