Recovery of continence function following simulated birth trauma involves repair of muscle and nerves in the urethra in the female mouse

Abstract

Background: The natural history and the mechanisms behind the alteration of vaginal distension (VD) in a mouse model are not clear.

Objective: We examined the temporal sequelae of VD and pudendal nerve transection (PNT) on leak-point pressure (LPP) and the muscular and nerve components of the urethra in mice.

Design, setting, and participants: Seventy-two virgin female C57BL/6 mice were equally distributed into three groups. The VD group underwent VD for 1h. The PNT group received bilateral PNT. A control group underwent sham VD.

Intervention: Each group was divided into four subgroups of six mice for measurement of LPP at 0, 4, 10, and 20 d after VD or PNT.

Measurements: LPP was measured. Morphology and neurofilament-immunoreactive nerve of the urethra were assessed.

Results and limitations: LPP was decreased at 0, 4, and 10 d but not at 20 d after VD. Decreased LPP persisted to 20 d in the PNT group. The external urethral striated muscle appeared disrupted and/or wavy in two mice at 0 d, in three mice at 4 d, in one mouse at 10 d, and in one mouse in 20 d after VD. The density of neurofilament-immunoreactive nerve in the urethra was reduced at 4 and 10 d after VD, but not at 20 d, and at 4, 10, and 20 d after PNT compared with the corresponding values of the sham VD group. The limitation of this animal model is that the pelvic floor structure of the mouse is different from that of female humans. Therefore, results of this study should be carefully applied to human subjects.

Conclusions: VD causes reversible stress urinary incontinence in female mice. Recovery of continence function following VD is associated with repair of the external urethral sphincter and reinnervation of the urethra. This mouse model will be useful for mechanistic investigation and targeting of therapeutic intervention by taking advantage of genetic manipulation.

Fig. 1

Leak-point pressure (LPP) values at 0, 4, 10, and 20 d after vaginal distension (VD), pudendal nerve transection (PNT), and sham VD groups. Results are expressed as the mean plus or minus standard error of the mean of six individual mice. * Significantly different from corresponding value in the sham group (p < 0.01). # Significantly different from corresponding value in the sham and VD groups (p < 0.01).

Fig. 2

Images (Masson's trichrome staining) of transverse sections of the midurethra at (a) 0 d after vaginal distension (VD), (b) 4 d after VD, (c) 10 d after VD, (d) 20 d after VD, (e) 4 d after pudendal nerve transection, and (f) 4 d after sham VD.

Fig. 3

The width of urethral striated muscle from the mean of the four regions of striated muscle, near the two diagonal lines, in midurethra in vaginal distension (VD), pudendal nerve transection (PNT), and sham VD groups. Results are expressed as the mean plus or minus standard error of the mean of four to six individual mice.

Fig. 4

Representative images of neurofilament-immunoreactive positive nerves in transverse sections of the midurethra at (a) 0 d after vaginal distension (VD), (b) 4 d after VD, (c) 10 d after VD, (d) 20 d after VD, (e) 4 d after pudendal nerve transection, and (f) 4 d after sham VD.

Fig. 5

The density of neurofilament-immunoreactive positive nerves in transverse sections of the midurethra in vaginal distension (VD), pudendal nerve transection (PNT), and sham VD groups. Results are expressed as the mean plus or minus standard error of the mean of four to six individual mice. * Significantly different from corresponding value in the sham group (p < 0.01).