Influence of aversive cue detection sensitivity on extinction in adult male rats

Threat detection prompts reactions classified either as fear (obvious, predictable, immediate threat) or anxiety (ambiguous, sustained, distant threat). Hypervigilance is a state of sensitivity to threatening stimuli and an attentional bias symptomatic of anxiety disorders. In rodents, threat detection can be measured by freezing behaviour and production of ultrasonic vocalisation (USV) alarm calls. The amygdala is classically associated with fear-like responses, whereas the bed nucleus of the stria terminalis (BNST) has been proposed to be preferentially recruited by anxiogenic stimuli. The conditioned responses triggered by aversive cues can be extinguished through repeated exposure of a subject to the threat stimulus but without any aversive reinforcement. The extent of extinction acquisition and consolidation are notedly variable across individuals. It has been reported that NMDA-type glutamate receptor co-agonists, like D-cycloserine, can enhance extinction consolidation. In the experiments herein, the salience of a threat cue was modified to compare the relative activation of the brain vigilance networks to an obvious cue, and to test whether sensitivity to the aversive cue at such a ‘vigilance screen’ might predict subsequent ability to extinguish conditioned responses. We demonstrated activation of the BNST by a low salience aversive cue. Rats that had the propensity to make alarm ultrasonic vocalisation calls reacted more strongly to aversive cues and had deficits in conditioned freezing extinction. Finally, we demonstrated the potential to enhance extinction consolidation by targeting glycine transmission. Taken together these results demonstrate how threat detection and responses are sensitive to cue salience and can be manipulated by combined pharmacological and behavioural interventions.