Stimulation of 5-HT receptors in anterodorsal BNST guides fear to predictable and unpredictable threat.

Through pharmacological manipulation of the serotonergic (5-Hydroxytryptamin, 5-HT) system, combined with behavioral analysis, we tested the hypothesis that fear responses to predictable and unpredictable threat are regulated through stimulation of 5-HT receptors (5-HT-R) in the anterodorsal section of the bed nucleus of the stria terminalis (adBNST). Local adBNST application of 5-HT1A-R antagonist WAY100635 and 5-HT1B-R antagonist NAS-181 before fear retrieval enhanced freezing, 24 h after predictable fear conditioning. In contrast, increased fear responses to unpredictable threat were blocked by 5-HT1A-R agonist Buspirone (given before conditioning or retrieval) and 5-HT1B-R agonist CP-94253 (applied before training). Prolonged fear responses were also blocked by local application of the 5-HT2A-R antagonist R-96544 before fear retrieval, and conversely, local application of the 5-HT2A-R agonist NBOH-2C-CN hydrochloride before fear retrieval enhanced freezing 24 h after predictable conditioning, indicating augmented fear responses. Activation of inhibitory 5-HT1A- or 5-HT1B-Rs and the blockade of the excitatory 5-HT2A-R before unpredictable fear conditioning significantly reduced freezing during retrieval. The results from this study suggest that modulation of inhibitory 5-HT1A/1B-R and/or excitatory 5-HT2A-R activity in the adBNST may represent potential targets for the development of new treatment strategies in anxiety disorders. In addition, this study supports the validity and reliability of the mouse model of modulated fear to predictable and unpredictable threats to study mechanisms of fear and anxiety in combination with pharmacological manipulations. [ABSTRACT FROM AUTHOR]