The central and basolateral amygdala differentially mediate the anxiolytic effects of benzodiazepines

Microinfusions of the benzodiazepine anxiolytic midazolam into the central or basolateral amygdaloid nuclei produced different anxiolytic effects in two tests of rat 'anxiety'. Infusions into the basolateral nucleus impaired open-arm avoidance in the elevated plus-maze test, but did not impair shock-probe avoidance in the shock-probe burying test. In contrast, infusions into the central nucleus impaired shock-probe avoidance, but did not impair open-arm avoidance. Both of these site-specific, midazolam-induced anxiolytic effects were blocked by a pre-infusion of the benzodiazepine receptor antagonist Ro 15-1788 (flumazenil). None of the treatments affected defensive burying. These results suggest that benzodiazepine receptors in the central and basolateral amygdaloid nuclei differentially mediate the anti-anxiety effects of benzodiazepine anxiolytics.