Fear generalization is a conserved survival mechanism that can become maladaptive in the face of traumatic situations, a feature central to certain anxiety disorders including posttraumatic stress disorder (PTSD). However, the neural circuitry and molecular mechanisms underlying fear generalization remain unclear. Recent studies have shown that prophylactic treatment with (R,S)-ketamine confers protective effects in stress-induced depressive behaviors and enhances contextual fear discrimination, but the extent to which these effects extend to fear generalization after auditory fear conditioning remains unclear. Here, we build on this work by using a behavioral model of fear generalization in mice involving foot shocks with differential intensity levels during auditory fear conditioning. We find that prophylactic (R,S)-ketamine treatment exerts protective effects that results in enhanced fear discrimination in wild type mice. As the growth factor, brain-derived neurotrophic factor (BDNF), has been shown to mediate the rapid antidepressant actions of (R,S)-ketamine, we used a loss-of-function BDNF mouse line (BDNF Val66Met) to determine whether BDNF is involved in (R,S)-ketamine’s prophylactic effects on fear generalization. We found that BDNF Val66Met mice were resistant to the protective effects of prophylactic (R,S)-ketamine administration on fear generalization and extinction. We then used fiber photometry to parse out underlying neural activity and found that in the ventral hippocampus there were significant fear generalization-dependent patterns of activity for wild type and BDNF Val66Met mice that were altered by prophylactic (R,S)-ketamine treatment. Overall, these findings indicate a role for the ventral hippocampus and BDNF signaling in modulating the mitigating effects of prophylactic (R,S)-ketamine treatment on generalized fear.

Anxiety disorders are more prevalent in females than in males, yet a majority of basic neuroscience studies are performed in males. Furthermore, anxiety disorders peak in prevalence during adolescence, yet little is known about neurodevelopmental trajectories of fear expression, particularly in females. To examine these factors, we fear conditioned juvenile, adolescent, and adult female mice and exposed them to fear extinction and a long‐term recall test. For this, we used knock‐in mice containing a common human mutation in the gene for fatty acid amide hydrolase (FAAH), the primary catabolic enzyme for the endocannabinoid anandamide (FAAH‐IN). This mutation has been shown to impart a low‐anxiety phenotype in humans, and in rodents relative to their wild‐type littermates. We find an impact of the FAAH polymorphism on developmental changes in fear behavior. Specifically, the FAAH polymorphism appears to induce a state of hypervigilance (increased fear) during adolescence. We also used markerless pose estimation software to classify alternative behaviors outside of freezing. These analyses revealed age differences in vigilance to indicators of threat and in the propensity of mice to explore an aversive environment, though genotypic differences were minimal. These findings address a gap in the literature regarding developmental patterns of fear learning and memory as well as the mechanistic contributions of the endocannabinoid system in females.