Title: Developing Novel Prophylactic Interventions for the Prevention of Stress-Induced Psychiatric Disease
Description: Enhancing stress resilience could prevent a variety of stress-induced disorders and thus reduce the global burden of psychiatric disease. It was previously reported that a single administration of the N-methyl-D-aspartate receptor (NMDAR) antagonist (R,S)-ketamine prior to stress could prevent stress-induced fear and behavioral despair in male mice, suggesting the possibility of developing prophylactic drugs to prevent psychiatric disorders. However, it was still unknown whether prophylactic agents could be effective in female mice, if other drugs could exert prophylactic actions, and how prophylactics could alter mechanisms in the brain to increase stress resilience. We hypothesized that targeting different receptors that could significantly alter neuroplasticity in the hippocampus (HPC) would be protective against stress. We first sought to determine whether stereospecific metabolites of (R,S)-ketamine, (2S,6R)-hydroxnorketamine ((2S,6S)-HNK) and (2R,6R)-hydroxynorketamine ((2R,6R)-HNK), could attenuate stress-induced behaviors in male and female mice.

Next, we aimed to test the prophylactic efficacy of fluoroethylnormemantine (FENM), a novel-composition NMDAR antagonist derived from memantine. Subsequently, we examined the protective effects of 3 different serotonin type IV receptor (5-HT4R) agonists against stress. Finally, we sought to determine whether dual targeting of the NMDAR and 5-HT4R could exert additive effects in enhancing resilience to stress against a wide variety of stress-induced behaviors. Drug efficacy was assayed in male and female mice using a battery of stress models and behavioral tests including: contextual fear conditioning (CFC), cued fear conditioning, contextual fear discrimination (CFD), learned helplessness (LH), chronic immobilization stress (CIS), paired-pulse inhibition (PPI), the forced swim test (FST), sucrose splash test (SST), open field (OF), elevated plus maze (EPM), marble burying (MB), and novelty-suppressed feeding (NSF). Liquid chromatography-mass spectrometry (LC-MS), immunohistochemistry, Western blotting, patch clamp electrophysiology, ovariectomy (OVX), and hormone replacement techniques were used to examine how prophylactic drugs alter brain function and test whether ovarian hormones mediate the protective effects of prophylactic compounds in female mice.

We show that (R,S)-ketamine, (2S,6S)-HNK, (2R,6R)-HNK, FENM, and 3 different 5-HT4R agonists are protective against specific stress-induced behaviors when administered in both male and female mice. We demonstrate that multimodally targeting NMDARs and 5-HT4Rs can broadly enhance resilience to protect against a variety of stressinduced maladaptive behaviors in both sexes. Finally, we determine a common mechanism by which various prophylactic compounds, despite targeting different receptors, attenuate bursts of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated activity to exert their protective effects. Together, these data: 1) uncover a variety of novel drug candidates for further preclinical and clinical development, 2) indicate a potential neural substrate underlying resilience to stress, and 3) reveal neurobiological mechanisms contributing to the psychopathology of psychiatric disease.