Role of the NPS system in fear extinction: Sex differences in emotional regulation in mice

The inability to extinguish learned fear is a hallmark of trauma and stress-related disorders. The inhibitory learning fear extinction is an effective way to treat these disorders, however, the neurobiology of fear extinction has not been clarified. The Neuropeptide S (NPS) has been shown to promote arousal and anxiolytic-like effects and facilitate fear extinction. In rodents, NPS receptors (NPSR) are prominently expressed in brain structures involved in learning and memory. In humans, a correlation between the NPS system and female patients suffering from panic disorders has been shown. Although the correlations between sex and the NPS system underlying emotional regulation are known in humans and rodents, the underlying circuit regulation is yet unclear. This study aims to unravel the role of the NPS system in top-down control of fear memory retrieval and extinction in male and female mice. We focus on the medial prefrontal cortex, crucial for sex-based differences in fear expression and extinction, and its connections to the basolateral amygdala (BLA), a critical region for fear memory formation and expression and extinction learning.For that, we used C57Bl/6N wild-type mice and a NPSR1-Cre driver mouse line to specifically address components of the NPS system in the medial prefrontal cortex and amygdala, combining electrophysiological, behavioral and pharmacological approaches with post-mortem regional analysis of brain mapping activity to detect sex-specific differences in emotion regulation. Males and females showed differences in the extinction of conditioned fear, additionally, after blocking the NPSR1 in the prelimbic area, those differences intensified.