Underlying mechnism of electroacupuncture for treating detrusor hyperreflexia after suprasacral spinal cord injury through the PACAP-cAMP signaling pathway

Objective

To elucidate the underlying mechanism and effect of electroacupuncture (EA) on the neurogenic bladder following suprasacral spinal cord injury (SSCI). A rat model of detrusor hyperreflexia after SSCI was established to examine the urodynamics, detrusor muscle tissue morphology, the protein and mRNA expression levels of pituitary adenylate cyclase activating peptide (PACAP) and its receptor PAC1R, and cyclic adenosine monophosphate (cAMP) content in the detrusor muscle with a focus on the PACAP-cAMP signaling pathway.

Method

A total of 72 female SD rats were randomized into control group and sham operation group (n=12 per group) by using a random number table. The remaining 48 rats were established into the model of detrusor hyperreflexia after SSCI. After successful modeling, these rats were randomly assigned to model, EA, and EA + PACAP6-38 groups (n=12 per group). The unsuccessful modeled rats were used for exploratory observation. For the rats in EA group, “Ciliao (BL32)” “Zhongji (CV3)”, and “Sanyinjiao (SP6)” were needled and stimulated by EA. The PACAP receptor antagonist PACAP6-38 was administered intraperitoneally in the EA + PACAP6-38 group before EA, and EA was applied for seven consecutive days. After treatment, the urodynamics of the rats were analyzed, and hematoxylin and eosin staining was used to examine rat bladder detrusor tissue morphology. The expressions of PACAP-38 and PAC1R were detected by immunohistochemistry and Western blot. The mRNA expression levels of PACAP-38 and PAC1R were examined by RT-qPCR, while cAMP content was detected by ELISA.

Results

(1) Compared with sham operation group, it was exhibited disarray in the transitional epithelium cells of the bladder in the modeled rats. The intercellular space was significantly widened, accompanied by inflammatory cell infiltration and noticeable tissue edema. Both the bladder initial pressure and leak point pressure of the rats were higher (P < 0.01), whereas the maximum cystometric capacity and bladder compliance were lower (P < 0.01). The protein and mRNA expression levels of PACAP-38 and PAC1R in the detrusor muscle, together with the cAMP content, were lower (P < 0.05). (2) Compared with the model rats, the EA group showed reduced inflammatory response in the detrusor muscle tissue, with decreased monocyte infiltration and less severe tissue edema. The bladder smooth muscle cells exhibited increased integrity, and there was decreased cellular tissue edema, inflammatory cell infiltration, and fibroplasia. The bladder initial pressure and leak point pressure were lower (P < 0.05), while the maximum cystometric capacity and bladder compliance were higher (P < 0.01). The protein and mRNA expression levels of PACAP-38 and PAC1R in the detrusor muscle, along with the cAMP content, were higher (P < 0.05). (3) Compared to the EA group, the EA + PACAP6-38 group showed a less organized arrangement of muscle fibers in the detrusor muscle tissue, larger intercellular space, monocyte infiltration, and considerable tissue edema. The changes in bladder initial pressure and leak point pressure were not significant (P > 0.05), while the maximum cystometric capacity and bladder compliance were lower (P < 0.05). The changes in the protein and mRNA expressions of PACAP-38 within the detrusor muscle were not significant (P > 0.05), whereas the protein and mRNA expressions of PAC1R were reduced (P < 0.05), and the cAMP content within the detrusor muscle was lower (P < 0.05).

Conclusion

EA can ameliorate the uninhibited contractile condition of the detrusor muscle in the bladder following SSCI. By mediating the PACAP-cAMP signaling pathway, it reduces the pathological damage to the detrusor muscle, thereby improving bladder function.