The Central Amygdala (CeA) is a component of a limbic fear-anxiety circuit, and has also been implicated in modulating the hypothalamic-pituitary-adrenal (HPA) stress axis. CeA receives dense noradrenergic innervation, and norepinephrine (NE) release in CeA is elevated by immobilization stress (IMM) (Khoshbouei, SFN 2000). We hypothesized that NE release in CeA may modulate stress-induced anxiety-like behavioral responses and HPA activation. To examine the role of NE in the CeA on stress-induced behavioral responses, male Sprague-Dawley rats were tested on the Social Interaction (SI) and Elevated Plus-Maze (EPM) tests after bilateral microinjection of adrenergic antagonists into CeA (0.25 μl) immediately prior to 5 min IMM. In the SI test, the α1-antagonist benoxathian (2 nmole) blocked the anxiogenic effect of acute stress (p<0.05), while β-receptor blockade (betaxolol + ICI181555, 1 nmole each) had no effect. By contrast, neither α1 nor β antagonists blocked the anxiogenic effect of IMM on the EPM, sugge...