Open field activity and passive avoidance responses in rats after lesion of the central amygdaloid nucleus by electrocoagulation and ibotenic acid.

The effect of two types of bilateral lesion of the central amygdaloid nucleus on open field activity and on the acquisition of a passive avoidance conditioning in a run way was studied in male Wistar rats. The animals were divided into three groups: sham-operated, a group with lesions caused by electrocoagulation, and a third group lesioned by local application of ibotenic acid. Ibotenic acid is a neurotoxin which damages the neurons but spares the passing fibres. The results indicate that lesion by electrocoagulation leads to a significant increase in the number of rearing responses in the open field. Moreover, lesion by electrocoagulation, but not by ibotenic acid, leads to a deficit in the acquisition of passive avoidance conditioning. This latter result suggests that the deficit is caused by lesion of the fibres crossing the central amygdaloid nucleus and not by the intrinsic elements of the nucleus.