Behavioral effects after ibotenic acid, 6-OHDA and electrolytic lesions in the central amygdala nucleus of the rat.

Selective lesions of central amygdaloid neurons with ibotenic acid and electrolytic destruction of the nucleus both led to marked increases in open field activity and activity during passive avoidance conditioning. However, electrolytic lesions of both neurons and fibers resulted in the most pronounced passive avoidance impairments and it is suggested that this lesion effect should be attributed to a combined destruction of intrinsic neurons and neurons located outside the central amygdala nucleus. The 6-OHDA lesions resulted in no significant changes in the behavioral parameters under investigation or in plasma corticosterone levels. The lack of reduced corticosterone levels in any of the lesioned groups do not indicate that general fear arousal is critically dependent on intact central amygdala neurons in the rat. The behavioral data are, however, still compatible with a hypothesis of a temporary reduction in fear arousal during the initial phase of the passive avoidance conditioning.