Serotonergic modulation of the BNST-CeA circuit promotes sex differences in fear learning

Post-traumatic stress disorder (PTSD) is characterized by intense fear memory formation and is diagnosed more often in women than men. Here, we show that serotonin differentially affects fear learning and communication in the extended amygdala of male and female mice. Females showed higher sensitivity to the effects of pharmacologically increasing serotonin during auditory fear conditioning, which enhanced fear memory recall in both sexes. Optogenetic stimulation of dorsal raphe terminals in the anterior dorsal bed nucleus of the stria terminalis (adBNST) during fear conditioning increased c-Fos expression in the BNST and central nucleus of the amygdala (CeA), and enhanced fear memory recall via activation of adBNST 5-HT2C receptors in females only. Likewise, in females only, serotonin stimulation during learning enhanced adBNST-CeA high gamma (90-140Hz) synchrony and adBNST-to-CeA communication in high gamma during fear memory recall. We conclude that sex differences in the raphe-BNST-CeA circuit may increase risk of PTSD in women.