Experimenter familiarization is a crucial prerequisite for assessing behavioral outcomes and reduces stress in mice not only under chronic pain conditions

ABSTARCTRodent behavior is affected by different environmental conditions. These do not only comprise experimental and housing conditions but also familiarization with the experimenter. However, specific effects on pain-related behavior and chronic pain conditions have not been examined. Therefore, we aimed to investigate the impact of different housing conditions, inverted day-night cycles, and experimenter familiarization on male mice following peripheral neuropathy using the spared nerve injury (SNI) model. Using a multimodal approach, we evaluated evoked pain-related-, anxiety- and depression-like behavior, corticosterone metabolite levels and utilized an integrative approach for relative-severity-assessment. Different environmental conditions are represented by individually ventilated cages and standard open cages combined with a reversed day-night-light cycle and experimenter habituation, inducing differentially modulated multidimensional pain- and emotion-like phenotypes in SNI mice. In addition, familiarization reduced the stress level caused by behavioral tests. Although no environmental condition significantly modulated the severity in SNI mice, it influenced pain-affected phenotypes and is, therefore, crucial for designing and interpreting preclinical pain studies. Moreover, environmental conditions should be considered more in the reporting guidelines, described in more detail, and discussed as a potential influence on pain phenotypes.