Is bladder outlet obstruction rat model to induce overactive bladder (OAB) has similarity to human OAB? Research on the events in smooth muscle, collagen, interstitial cell and telocyte distribution

**Background:** Overactive bladder (OAB) is a common condition characterized by poor bladder compliance and detrusor overactivity, leading to lower urinary tract symptoms. The pathophysiology and morphological changes of OAB are incompletely understood, partly due to limitations in studying human bladder tissue. Bladder outlet obstruction (BOO) animal models have been used to induce OAB, but their similarity to human OAB has not been confirmed. Interstitial cells of Cajal (ICCs) and telocytes (TCs) are important for smooth muscle conductivity, yet they have not been well investigated in previous BOO models. This study aimed to investigate the morphological pattern of cellular, cytoskeletal, and telocyte distribution in a BOO rat model at two time points (6 and 8 weeks) and compare findings to human OAB.

**Methods:** Thirty female Sprague-Dawley rats were randomly divided into three groups: sham (n=10), BOO for 6 weeks (BOO 6W, n=10), and BOO for 8 weeks (BOO 8W, n=10). BOO was induced using a minimally invasive technique: under ketamine anesthesia, a sterile floppy guidewire (0.038 inches diameter) was placed in the urethra, and a 4-0 silk suture was tied around the paraurethral tissues over the guidewire, which was then removed. Sham animals underwent the same procedure without tying the suture. After 6 or 8 weeks, the urinary bladder was retrieved under anesthesia, and rats were euthanized via isoflurane inhalation. Bladders were processed for histopathology (H&E and Masson's trichrome staining), immunohistochemistry (IHC) for c-Kit (CD117) to label ICCs, and transmission electron microscopy (EM) to identify TCs and telopodes (Tps). Statistical analysis used one-way ANOVA with Tukey post-hoc test; p<0.05 was considered significant.

**Key Results:** Bladder weight in the sham group was 110±7 mg, in BOO 6W was 130±15 mg (note: unit discrepancy in text—likely mg), and in BOO 8W was not separately reported but body weight did not differ between groups. Gross inspection showed bladder wall thickening in both BOO groups compared to sham. Histopathology revealed thinner urothelium and condensation of collagen between muscle bundles in BOO groups, with a collagen-to-smooth muscle ratio of 2, while sham had normal urothelium and well-arranged muscle bundles with minimal collagen. IHC showed high expression of c-Kit-positive ICCs densely distributed along muscle bundles in BOO 6W and BOO 8W, whereas sham had few or no detectable ICCs. EM demonstrated frequent TCs with characteristic nuclei and long, cylindrical, varicose-like telopodes containing vesicles, situated between collagen fibers in BOO groups. The mean number of TCs per TEM field was 2.27±0.7 in BOO 6W, 2.47±0.7 in BOO 8W, and 0.62±0.4 in sham (p<0.001). Findings at 6 and 8 weeks were comparable, indicating stabilization of changes.

**Clinical Implications:** This study demonstrates that a minimally invasive BOO procedure in rats produces morphological changes—increased collagen/smooth muscle ratio, high ICC density, and presence of TCs—that closely resemble those observed in human OAB. The stability of changes at 6 and 8 weeks mirrors the clinical course of OAB in humans, where bladder changes are often stable and rarely decompensate or become fibrotic. The identification of TCs in the BOO rat model is described for the first time, suggesting that TCs and ICCs may contribute to the pathophysiology of OAB by facilitating communication between smooth muscle cells and possibly playing a role in regenerative processes. These findings support the validity of this animal model for future research on OAB mechanisms and potential therapies, including personalized medicine approaches targeting TCs.