The lateral nucleus of the amygdala (LA) is believed to be the site through which an auditory conditioned stimulus (CS) is relayed in classical fear conditioning. However, how a visual CS is connected to the amygdala in rats is less well understood. The present study attempted to determine whether the basolateral nucleus of the amygdala (BLA) was specifically involved in fear conditioning using a visual CS. Seven rats with lesions in the BLA (AMY-B group), 8 rats with lesions in both the LA and the BLA (AMY-L-I-B group), and 16 control rats were trained with a visual CS (25 W light, 3.7 sec) paired with footshock (1.0 mA, 0.5 sec). The behavioral index of fear conditioning was the potentiation of the startle reflex in the presence of the CS. As a result, although BLA-lesioned rats showed the potentiation whether the lesions of the LA were made or not, the extent of the potentiation in BLA-lesioned rats was less visible than that of control rats. These results suggest that the BLA may be a site where visual CS information enters the amygdala.

Key words: fear conditioning, the basolateral nucleus of the amygdala, visual CS