Natural reversal of mandibular condylar cartilage histological damage caused by chronic unpredictable moderate stress in rats

Abstract

Objective To investigate the histological damage recovery of temporomandibular joint condylar cartilage caused by chronic unpredictable moderate stress, aiming to provide an experimental basis for the prevention and treatment of temporomandibular disorder. Methods This animal experiment was approved by the Laboratory Animal Ethical Inspection, School of Stomatology, The Fourth Military Medical University (No. 2020081). 60 male SD rats were randomly divided into control group, stress group, and 2-, 4- and 8-week post-stress recovery groups. Rats were subjected to chronic unpredictable moderate stress (CUMS) for 8 weeks including damp sawdust for 24 hours, tilted cage for 12 hours, noise for 4 hours, light/dark cycle reversal, water immersion, tail clamp, and restraint stress. The serum assessment, behavioral tests, histological and ultrastructural observation were performed 2-, 4- and 8-weeks after stress factors were removed. Serum levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were determined with ELISA. The sucrose preference test (SPT) and the forced swim test (FST) were used to assess the depressive-like behavior. The expression level of interleukin-1α (IL-1α) and matrix metalloproteinases-3 (MMP-3) were determined by Immunohistochemistry and Western blot. Results At the end of 8 weeks of CUMS, the serum levels of CORT and ACTH were significantly higher in stress group compared with control group (P0.05) and higher expression of MMP-3 comparing with the control group (P0.05). The condylar collagen fibers increased and showed a corrugated pattern, and no serious subchondral bone damage as well as irreversible damage occurred. Both of the expression levels of IL-1α and MMP-3 approached those of the control group after 8 weeks of stress removal (P>0.05). Conclusion The behavioral changes and condylar cartilage damage caused by CUMS could be self-repaired. The decline in IL-1α and MMP-3 expression may be one of the intrinsic mechanisms of this self-repair process.

Keywords

• psychological stress
• chronic unpredictable moderate stress
• temporomandibular disorder
• depressive-like behavior
• condylar cartilage
• interleukin-1α
• matrix metalloproteinase-3
• natural reversal