The Effects Of Brain-derived Neurotrophic Factor On Continence Mechanisms After Simulated Birth Injury In A Rat Model

BackgroundStress urinary incontinence (SUI) is one of the most common urological conditions,negatively affecting women's quality of life worldwide. It was defined as involuntary urine leakage during increasing of abdominal pressure. As evidenced by several studies, vaginal delivery is one of the most important mechanisms, due to damage to the pelvic muscles,nerves and connective tissues during the process.Long term follow-up study demonstrated that among women with SUI symptoms 5-7 years postpartum, pudendal nerve terminal motor latency was significantly increased,suggesting an incomplete innervation of external urethral sphincter (EUS)_ Our previous study also indicated that SUI rat model with abnormal pudendal nerve neuromuscular junction even when the continence function has returned to normal. Together these studies highlighted the importance of treating the pudendal nerve as a novel therapeutic target of clinical SUI.Brain-derived neurotrophic factor (BDNF) was known as an important neurotrophins in the body to promote nerve survival, growth and regeneration process after injury.Moreover, it is one of the major neuromodulators participated in the regulation of lower urinary tract function as well as pathophysiology of abnormal conditions, including overactive bladder, SUI, interstitial cystitis/bladder pain syndrome. Our previous animal model study demonstrated that BDNF is needed following pudendal nerve trauma.Therefore, we tend to evaluate the effect of BDNF on continence mechanisms in a SUI rat model.ObjectivesThe goal of present study was to determine the role of BDNF on continence maintaining using a dual injury SUI rat model. Our results may strengthen the existing evidence that neuromuscular abnormality plays an essential role in the development of clinical SUI. It could also provide a novel modality to treat and to prevent SUI. The study will be carried out as the following three parts:Part one: To determine the effects of exogenous BDNF local treatment on the continence mechanisms in an SUI rat model.Part two: To study the effects of short-term electrical stimulation of pudendal nerve motor branch on BDNF expression and lower urinary tract function.Part three: To discuss the impact of periodic pudendal nerve stimulation on BDNF expression and continence mechanisms recovery.Study designPart one: Ninety-three female age-matched SD rats were randomized into 3 groups:SUI+BDNF, SUI + saline and sham injury + saline. The development of SUI rat model consists of both pudendal nerve crush (PNC) and vaginal distension (VD). BDNF and saline were delivered by mini-osmotic pumps which were implanted bilaterally in each rats.Sham injured rats received the same procedures without PNC or VD. A set of these rats were used for LPP and EUS EMG recordings as well as the assessment of the neuromuscular junction immunostaining. The rest were sacrificed at 4, 8 and 12 days after injury followed by BDNF and ??-tubulin expression assessment via quantitative PCR.Two-way ANOVA with a Holm-Sidak post hoc test was used for statistical analysis with P<0.05 indicating significant differences.Part two: Forty-six female age-matched rats were randomly assigned into SUI model and sham injury group followed by 1 hour unilateral electrical stimulation to the left pudendal nerve motor branch (no stimulation was given to the right pudendal nerve).Bladder and external anal sphincter functional recordings were performed in one set of rats,while the rest of them were used for BDNF and ??-tubulin expression 2 days and 1 week after stimulation. Statistical assessment of the parameters before, during and after stimulation were carried out with Two way ANOVA followed by a Student-Newman-Keuls post hoc test. BDNF and ??-tubulin expression comparisons were performed with a simple t test. P<0.05 were used to indicate statistical significant difference in all tests.Part three: Sixty age-matched female SD rats were randomized and received either simulated birth injury (SUI model) or sham injury followed by immediate wire electrode implantation bilaterally. A set of these rats were further divided into 3 groups: SUI +stimulation, SUI + sham stimulation and sham injury + sham stimulation. Two weeks later,the bladder and continence function were assessed. The other part of these animal received unilateral stimulation to the left pudendal nerve and sham stimulation to the right pudendal nerve. Quantitative assessment of BDNF and ??-tubulin expression in the Onuf's nucleus were performed using RT-PCR. Two way ANOVA followed by a Student-Newman-Keuls post hoc test was adopted to compare parameters among groups. BDNF and ??-tubulin expression between left and right pudendal nerve nucleus were compared with a simple t test. P<0.05 were used to show statistical significant difference in all tests above.ResultsPart one: Local BDNF treatment to the pudendal nerve promote early recovery of continence mechanisms and restored neuromuscular morphology. Besides, two weeks of BDNF treatment significantly increased BDNF and ??-tubulin expression in the Onuf's nucleus.Part two: One-hour pudendal nerve electrical stimulation dramatically enhanced BDNF and ??-tubulin expression in the Onuf's nucleus. It also significantly improved bladder and external anal sphincter function.Part three: Periodic bilateral pudendal nerve stimulation dramatically enhanced BDNF and ??-tubulin mRNA expression in the Onuf's nucleus. Moreover, it could significantly promote continence recovery as well as restoring bladder and urethral function.ConclusionsIn this study, we applied exogenous local BDNF treatment, short-term and long-term electrical stimulation,respectively,to SUI rat model and demonstrated BDNF is important to the maintaining of continence mechanisms possibly through a neuroregenerative effects to the pudendal nerve. Therefore,regulation of BDNF expression could serve as a novel treatment and preventive approach to clinical SUI.