Inactivation of the bed nucleus of the stria terminalis suppresses the innate fear responses of rats induced by the odor of cat urine

In this study, we investigated whether two brain regions, the bed nucleus of the stria terminalis (BNST) and the basolateral amygdala (BLA), affected male rats’ (Rattus norvigicus) ability to innately discriminate between a predator odor (cat urine) and female rat urine. Muscimol, a GABAa receptor agonist, was bilaterally microinjected into either the BNST or BLA of rats through implanted stainless-steel guide cannulas to temporarily inactivate these brain nuclei. The behavioral responses of the treated rats to female rat urine and cat urine were then tested in an experimental arena. Compared to a saline infusion control, the injection of muscimol into the BNST strongly reversed the innate aversion of rats to cat urine but the injection of muscimol into the BLA had no effect. Furthermore, intra-BNST infusion of muscimol caused rats to be equally attracted to urine from cats and female rats but intra-BLA infusion did not stop rats manifesting fear on exposure to cat urine and exploratory behavior on exposure to female rat urine. We conclude that the BNST plays a more crucial role in modulating innate fear responses in rats than the BLA.

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► Cat urine odor induces fear behavior in rats.
► Injection muscimol into the BNST blocks the freezing induced by cat urine odor.
► The BNST, not BLA, is essential for innate fear responses in rats.