Behavioral attenuation of marble burying and digging mirrors evoked and non-evoked phenotypes in the endometriosis mouse model.

Abstract

Endometriosis (ENDO) is an estrogen-dependent chronic gynaecological manifestation of uterine fragments attached outside of the uterus, accompanied by debilitating chronic pelvic pain. The evoked assays often employed fail to capture the subtle behavioral nuances in the mouse model. Thus, this study proposes integrating a range of non-evoked assays alongside the ever-so-often used evoked test to better understand ethological disparities in the endometriosis mouse model. In this current study, we developed a syngeneic mouse model using C57BL/6J mice and injected donor uterine fragments into estrogen-primed recipient mice. The endometriotic (ENDO) mice were subjected to behavioral assays like marble burying (MB) and digging. In addition, findings of MB and digging were validated by standard non-evoked and evoked tests to capture the differential and subtle nuances in behavior post-endometriosis induction. The successful ENDO lesion development was confirmed via hematoxylin and eosin staining of lesions, higher M2 macrophage levels from the peritoneal fluid, and higher estrogen levels obtained from ENDO mice. Compared with control mice, ENDO mice exhibited diminished MB (****p value&#x2009;<&#x2009;0.0001) and digging capacity (****p value&#x2009;<&#x2009;0.0001). The reduced MB and digging positively correlate with diminished active burrowing, grooming, and exploratory behavior during the open-field test, but with increased anxiety as assessed by the elevated plus maze. The highest positive correlation for MB is with increased anxiety (r&#x2009;=&#x2009;0.65), and that for digging is with the overnight burrow score (r&#x2009;=&#x2009;0.62). On the contrary, diminished MB and digging negatively correlate with increased abdominal bouts [(r&#x2009;=&#x2009;-0.44) and (r&#x2009;=&#x2009;-0.46), respectively]. The ENDO mice also showed signs of mechanical and thermal hyperalgesia compared with control mice, as measured by evoked tests. The evaluation of the correlation between MB and evoked tests showed the highest positive correlation with tail flick (r&#x2009;=&#x2009;0.66) and digging with Von Frey (r&#x2009;=&#x2009;0.80). The non-evoked tests, such as MB, digging, and grooming patterns, are novel assays to evaluate in the mouse model of ENDO. When incorporated with other non-evoked and evoked tests, it provides a more detailed understanding of ethological behaviors in the ENDO mouse model.