Noradrenaline transmission within the ventral bed nucleus of the stria terminalis is critical for fear behavior induced by trimethylthiazoline, a component of fox odor.

The bed nucleus of the stria terminalis (BNST) is involved in the mediation of fear behavior in rats. A previous study of our laboratory demonstrated that temporary inactivation of the BNST blocks fear behavior induced by exposure to trimethylthiazoline (TMT), a component of fox odor. The present study investigates whether noradrenaline release within the BNST is critical for TMT-induced fear behavior. First, we confirmed previous studies showing that the ventral BNST is the part of the BNST that receives the densest noradrenaline innervation. Second, using in vivo microdialysis, we showed that noradrenaline release within the BNST is strongly increased during TMT exposure, and that this increase can be blocked by local infusions of the alpha2-receptor blocker clonidine. Third, using intracerebral injections, we showed that clonidine injections into the ventral BNST, but not into neighboring brain sites, completely blocked TMT-induced potentiation of freezing behavior. The present data clearly show that the noradrenergic innervation of the ventral BNST is important for the full expression of behavioral signs of fear to the predator odor TMT.