The bed nucleus of the stria terminalis is required for the expression of contextual but not auditory freezing in rats with basolateral amygdala lesions

Previous data suggest that overtraining can overcome fear conditioning deficits in rats with lesions of the basolateral complex of the amygdala (BLA). We have previously shown that the central nucleus of the amygdala (CEA) is essential for the acquisition and expression of conditional fear to both contextual and auditory conditioned stimuli (CSs) after overtraining. This provides strong evidence that the CEA can compensate for the loss of the BLA. Another brain area that may compensate for the loss of the BLA is the bed nucleus of the stria terminalis (BNST). We explored this possibility by examining the consequences of lesions or reversible inactivation of the BNST on the expression of overtrained fear in rats with BLA lesions. We demonstrate that lesions or inactivation of the BNST block the expression of freezing to the conditioning context, but not to an auditory conditional stimulus. These results reveal that the BNST has a critical role in the expression of contextual fear, but not fear to an auditory CS, and is therefore not the essential locus of compensation for fear learning in the absence of the BLA.

Research highlights
► Rats with basolateral amygdala lesions acquire Pavlovian fear conditioning after overtraining.
► Excitotoxic lesions of the bed nucleus of the stria terminalis impair the expression of conditional freezing to the training context, but not an auditory conditional stimulus, after overtraining.
► Reversible inactivation of the bed nucleus of the stria terminalis with the glutamate antagonist, NBQX, impairs the expression of conditional freezing to the training context, but not an auditory conditional stimulus, after overtraining.
► The bed nucleus of the stria terminalis has a selective role in the expression of contextual fear, but not a general role in the associative processes that maintain memories of Pavlovian fear conditioning.