Experimenter sex modulates mouse biobehavioural and pharmacological responses

Differential rodent responses to the sex of human experimenters could have far reaching consequences in preclinical studies. Here, we show that the sex of human experimenters affects mouse behaviours and responses to the rapid-acting antidepressant ketamine and its bioactive metabolite ( 2R,6R )-hydroxynorketamine. We found that mice manifest aversion to human male odours, preference to female odours, and increased susceptibility to stress when handled by male experimenters. This male induced aversion and stress susceptibility is mediated by the activation of brain corticotropin-releasing factor (CRF) neurons projecting from the entorhinal cortrex to hippocampal area CA1. We further establish that exposure to male scent prior to ketamine administration activates CRF neurons projecting from the entorhinal cortex to hippocampus, and that CRF is necessary and sufficient for ketamine’s in vivo and in vitro actions. Further understanding of the specific and quantitative contributions of the sex of human experimenters to different experimental outcomes in rodents may lead not only to reduced heterogeneity between studies, but also increased capability to uncover novel biological mechanisms. ### Competing Interest Statement CAZ is a co-inventor on a patent for the use of ketamine in major depression and suicidal ideation. PZ, JNH, RM, CAZ and TDG are co-inventors in patent applications related to the pharmacology and use of (2R,6R)-HNK in the treatment of depression, anxiety, anhedonia, suicidal ideation and post-traumatic stress disorders. RM and CAZ have assigned their patent rights to the U.S. government but will share a percentage of any royalties that may be received by the government. PZ, JNH and TG have assigned their patent rights to the University of Maryland Baltimore but will share a percentage of any royalties that may be received by the University of Maryland Baltimore. TDG has received research funding from Allergan and Roche Pharmaceuticals and has served as a consultant for FSV7 LLC, during the preceding three years. All other authors declare no competing interests.