Establishment of new transurethral catheterization methods for male mice

Abstract

Transurethral catheterization in mice is multifaceted, serving essential functions such as perfusion and drug delivery, and is critical in the development of various urological animal disease models. The complex anatomy of the male mouse urethra presents significant challenges in transurethral catheterization, leading to a predominance of research focused on female specimens. This bias limits the utilization of male mice in lower urinary tract disease studies. Our research aims to develop new reliable methods for transurethral catheterization in adult male mice, thereby expanding their use in relevant disease research. Experiments were conducted on adult male C57BL/6J mice. Utilizing a PE10 catheter measuring 4.5-5 cm in length, the catheter was inserted into the bladder via the mouse's urethra under anesthesia. The intubation technique entailed regulating the insertion force, ensuring the catheter's lubrication, using a trocar catheter, modifying the catheter's trajectory, and accommodating the curvature of the bladder neck. Post-catheter insertion, ultrasound imaging was employed to confirm the catheter's accurate positioning within the bladder. Subsequent to catheterization, the bladder was perfused using trypan blue. This method was further validated through its successful application in establishing an acute urinary retention (AUR) model, where the mouse bladder was infused with saline to a pressure of 50 or 80 cm H₂O, maintained steadily for 30 min. A thorough morphological assessment of the mouse bladder was conducted after the infusion. Our study successfully pioneered methods for transurethral catheterization in male mice. This technique not only facilitates precise transurethral catheterization but also proves applicable to male mouse models for lower urinary tract diseases, such as AUR.

Keywords: bladder; bladder perfusion; lower urinary tract; male mouse; transurethral catheterization.

Figure 1.

Anatomical structure of the male mouse urethra. (A) Bladder of the male mouse and the pubic bone, showing the urethra passing beneath. (B) Anatomical structure of the lower urinary tract in male mice. (C) Lateral schematic representation of the lower urinary tract structure. (D) Urethral length in male mice.

Figure 2.

Noninvasive transurethral catheterization in male mice. (A) PE10 catheter, the black mark indicates the insertion end. (B) Elevate the mouse’s lower abdomen by 1 cm and secure the tail using adhesive tape, forming an arched posture. (C) Expose the mouse's penis. (D) The external urethral opening is located beneath the baculum (black arrow). (E) For intubation, adjust the catheter to obtain an insertion angle nearly parallel to the mouse's body. (F) Ultrasound examination showcasing the catheter, as indicated by white arrows and white dashed lines. (G) Comparison between the PE10 catheter and a needle, with the needle tip positioned 2 mm from the catheter end. Black triangles mark the insertion end of the catheter, and a black star shows where the needle is inserted into the catheter. (H) Schematic representation showing the catheter navigating the curvature of the urethra. (I) Diagram illustrating the needle insertion into the catheter. (J) Depiction of the needle insertion into the catheter, followed by bladder entry through the urethral opening. (K) Extract the needle from the catheter. (L) Ultrasound examination with the catheter highlighted by white arrows and white dashed lines.

Figure 3.

Bladder perfusion via noninvasive transurethral catheterization. (A) Transurethral intubation of the bladder in male mice. (B) Gentle abdominal compression to facilitate urination post-catheter insertion. (C) Administration of trypan blue into the bladder. (D) Incision made in the abdomen to visualize the bladder, now filled with trypan blue.

Figure 4.

Minimally invasive transurethral catheterization in male mice. (A) Area designated for the minimally invasive surgical procedure, where the circle represents the bladder and the box highlights the intended surgical incision site. (B) Dimensions of the surgical incision approximating 0.5 cm. (C) Transurethral catheter insertion navigating past the pubic bone. (D) Needle insertion into the catheter up to the marked point, followed by its progression through the urethral opening into the bladder. (E) Modification of the bladder neck’s curvature. The dashed line delineates the bladder and the urethra’s path. (F) Ultrasound examination executed, with white arrows and white dashed lines signifying the catheter’s location.

Figure 5.

Bladder perfusion via minimally invasive transurethral. (A) Transurethral catheter insertion in male mice. (B) Applying pressure to the abdomen after removing the needle from the catheter to promote urination. (C) Introducing trypan blue into the bladder. (D) Inspection of the bladder infused with trypan blue.

Figure 6.

Pressurizing the bladder causes significant injury and edema in bladder tissue. (A–C) Control mouse bladder, showcasing normal structure. (D) Thickening of the bladder wall in mice after 50 and 80 cm water pressure perfusion. (E–G) Mouse bladder post-50 cm water pressure perfusion, illustrating changes due to pressure application. (H) Reduction of the urothelium layer thickness in mice after 50 and 80 cm water pressure perfusion. (I–K) Mouse bladder following 80 cm water pressure perfusion, depicting more pronounced alterations. (L) Thickening of the lamina propria layer thickness in mice after 50 and 80 cm water pressure perfusion. (M) Reduction of the muscle layer thickness in mice after 50 and 80 cm water pressure perfusion. In each set of images, the urothelium (U), lamina propria (LP), and bladder smooth muscle (BSM) are identified. The dotted line demarcates the boundaries between U, LP, and BSM. Black stars highlight edema and the widened gap between the lamina propria and the smooth muscle layer. Black triangles within the lamina propria signify hyperemia, indicative of reperfusion injury. Black arrows in the muscle layer point to increased interfascicular spaces, suggesting underlying muscle damage and interstitial edema.