Impaired contraction and decreased detrusor innervation in a female rat model of pelvic neuropraxia

Abstract

Introduction and hypothesis Bilateral pelvic nerve injury (BPNI) is a model of post-radical hysterectomy neuropraxia, a common sequelae. This study assessed the time course of changes to detrusor autonomic innervation, smooth muscle (SM) content and cholinergic-mediated contraction post-BPNI. Methods Female Sprague-Dawley rats underwent BPNI or sham surgery and were evaluated 3, 7, 14 and 30 days post-BPNI (n=8/group). Electrical field stimulated (EFS) and carbachol-induced contractions were measured. Gene expression was assessed by qPCR for muscarinic receptor types 2 (M2) and 3 (M3), collagen type 1α1 and 3α1 and SM actin. Western blots measured M2 and M3 protein expression. Bladder sections were stained with Masson’s trichrome for SM content and immunofluorescence staining for nerve terminals expressing vesicular acetylcholine transporter (VAChT), tyrosine hydroxylase (TH) and neuronal nitric oxide synthase (nNOS). Results BPNI caused larger bladders with less SM content and increased collagen type 1α1 and 3α1 gene expression. At early time points, cholinergic-mediated contraction increased, while EFS-mediated contraction decreased and returned to baseline by 30 days. Protein and gene expression of M3 was decreased 3 and 7 days post-BPNI while M2 was unchanged. TH nerve terminals surrounding the detrusor decreased in all BPNI groups while VAChT and nNOS terminals decreased 14 and 30 days post-BPNI. Conclusions BPNI increased bladder size, impaired contractility and decreased SM and autonomic innervation. Therapeutic strategies preventing nerve injury-mediated decline in neuronal input and SM content may prevent the development of a neurogenic bladder and improve quality of life after invasive pelvic surgery.

Functional and molecular characterisation of the bilateral pelvic nerve crush injury rat model for neurogenic detrusor underactivity

“…An important degenerative sign was vacuolisation of the sarcoplasma, which was markedly more frequent in BPNI bladders. However, we describe an increased detrusor thickness and increased bladder-to-body weight ratio after injury, suggesting detrusor hypertrophy, similar to previous studies [12,18]. Therefore, we hypothesise that detrusor hypertrophy compensates for the degenerative changes of the muscle we observed after BPNI.…”

“…Although detrusor contractility to direct depolarisation and parasympathetic stimulation was preserved, nerve‐induced contractility was reduced during overflow incontinence with only partial recovery in the DU phase. This is in line with previous reports of preganglionic neural crush injury, where partial functional recovery was observed but morphological recovery could not been objectified . Of interest, Payne et al.…”

“…In contrast, BPNI bladders showed increased sensitivity to carbachol. In the literature, increased cholinergic contractility at 1 week after injury to the pelvic plexus with subsequent recovery is reported after BPNI [12,18]. Following a cut injury of the pelvic nerve, a similar increased sensitivity to carbachol was observed.…”

Characterization of voiding function and structural bladder changes in a rat model of neurogenic underactive bladder disease

“…2,15 The multifactorial etiology complicates the development of animal models to study this bladder disorder, as shown by the diversity of animal models 16 : aging models, 17 diabetic bladder dysfunction, 18 bladder outlet obstruction (BOO), 19 bladder ischaemia, 20 and neurogenic models. 21,22 Many of these neurogenic models, including ours, investigate UAB in FIGURE 4 PCR analysis. A, No difference in aSMA expression was found between sham and PNI bladders.…”

Pathophysiology of the underactive bladder

“…There have been several published studies reported as a UAB model by using pelvic nerve crash- or cryoinjury (unilaterally or bilaterally) [ 92 93 94 95 96 ], in which detrusor contractility was remarkably impaired. In case of bilateral pelvic nerve injury by complete resection, the animals showed severe nervous dysfunctions, which were resemble to the situation with SCI [ 95 ].…”