Dissociating the anti-fear effects of septal and amygdaloid lesions using two pharmacologically validated models of rat anxiety.

Effects of septal and amygdaloid lesions were compared in 2 models of rat "anxiety." Septal lesions decreased burying behavior in the "shock-probe burying test" and increased open-arm exploration in the "elevated plus-maze test," whereas amygdaloid lesions produced neither of these anxiolytic effects. However, amygdaloid lesions increased rats' contacts of the electrified probe, an anxiolytic effect not produced by septal lesions. Each of these distinct, anxiolytic effects of septal or amygdaloid lesions were displayed together in animals with lesions of both structures. Furthermore, the magnitude of these anxiolytic effects after combined lesions was comparable to their magnitude after individual lesions. Taken together, these results suggest the amygdala and the septum independently control the expression of different fear-related behaviors.