WERF Endometriosis Phenome and Biobanking Harmonisation Project for Experimental Models in Endometriosis Research (EPHect-EM-Pain): methods to assess pain behaviour in rodent models of endometriosis

Pain is a debilitating symptom of endometriosis, and its mechanisms are often explored using rodent models. However, a lack of harmonization amongst models and behavioural measures, in addition to inconsistent reporting, might limit the overall clinical relevance and hinder translation of findings. An additional challenge is accurately linking rodent behaviour to human experiences of endometriosis. This study aimed to: (i) review current measures of pain-associated behaviours used in endometriosis studies; (ii) recommend best practices for each method and their suitability to study endometriosis-associated pain; and (iii) develop internationally agreed-upon standard operating procedures ('EPHect-EM-Pain SOPs'). The World Endometriosis Research Foundation (WERF) assembled an international working group, from which a 'pain behaviour working group' consisting of experts in the field was established. The group used additional consultation from experimental pain model scientists in the broader field. Stimulus-evoked (reflexive) and stimulus-independent (spontaneous) measures are currently used to assess pain-associated behaviours in rodents with experimental endometriosis. All existing methods offer advantages and limitations regarding ethological relevance, output quality, and equipment/training requisites. Internationally standardized pain SOPs as well as summary documentation outlining the minimum and standard requirements for several behavioural measures were developed, as well as consensus recommendations on experimental designs and documentation. To more closely reflect the lived experiences of those with endometriosis, the consortium recommends that, following validation, multiple types of pain-related and/or parallel rodent behaviours (e.g. anxiety) should be quantified as surrogate outcome measures for endometriosis-associated pain. These harmonized methods and documentation for endometriosis research will facilitate essential comparisons among studies, improve translational applicability, and provide a superior holistic view of animal (and thus human) wellbeing.