Role of β1-adrenoceptor in the basolateral amygdala of rats with anxiety-like behavior

There are evidence suggesting that the function of adrenergic receptor is affected in the amygdala of animals with anxiety-like behavior. However, beta-adrenoceptor (beta-AR) subtypes, consisting of three subtypes, exert different effects on anxiety regulation. In order to determine the function of the beta(1)-AR subtype in anxiety-like behavior, we investigated the change of beta(1)-AR expression by immunostaining in the basolateral amygdala (BLA) of rats treated by conditional fear training. The results indicated that the level of beta(1)-AR was significantly increased in the BLA of fear-conditioned animals as compared that of controls. In animal behavioral tests, animals treated with selective beta(1)-AR antagonist metoprolol before conditional fear training exhibited a significant attenuation of anxiety-like behavior characterized by increased percentage of time spent and percentage of entries in the open arms, and increased number of head-dips in the elevated plus-maze (EPM) test compared with the animals treated with only saline. Furthermore, the rats pretreated with metoprolol in the conditional fear training significantly decreased the freezing behavior in the test compared with the controls. The results suggested that the beta(1)-AR played an important role in anxiety-like behavior, and inhibition of the beta(1)-AR in the BLA could produce anxiolytic effect. (C) 2008 Elsevier B.V. All rights reserved.