Hypothesis / aims of study
Traumatic spinal cord injuries are a catastrophic event for patients, representing expensive lifelong health care costs. The most common urinary dysfunction on SCI patients is detrusor-sphincter dyssynergia (DSD), defined as a detrusor contraction synchronous with an involuntary contraction of the urethral and/or periurethral striated muscles. The long-term urological management of the patient with spinal cord injury include catheterization, antimuscarinic medication, botulinum toxin, alpha-blockers, and neuromodulator invasive procedures. However, the use of drugs with neurotrophic properties is another novel strategy for the management of urologic comorbidities after SCI. Gonadotropin-releasing hormone (GnRH) is a hypothalamic decapeptide regulator of the reproductive system as well as is synthetic analog Leuprolide acetate (LA) have been shown neurotrophic properties and improve voiding patterns in rat models of SCI. The aim of this study was to evaluate the effects of a systemic treatment with LA on detrusor-sphincter dyssynergia in rats with compression SCI at the thoracic level
Study design, materials and methods
Thirty Wistar male rats, weighing 250-300g, were used in this study, animals were randomly divided into three groups 1) SHAM group (N=10); 2) Spinal cord injury group (SCI, N=10); and 3) Spinal cord injury treated with LA (SCI+LA, N=10). Under anesthesia, a laminectomy was performed at the thoracic vertebrae T10. In the SCI and SCI + LA groups, the exposed spinal cord at T10 was clamped with a micro-clamp for one minute. As control , in SHAM only the laminectomy without spinal cord clamping was performed. LA administration: SCI-LA group, were daily injected with LA during four consecutive days, thereafter, only one injection was given every 72 hours until completing thirteen doses. SHAM and SCI groups received the same injection schedule with saline solution. One day after the injections, cystometry and needle electromyography studies were performed in fully awake and freely moving rats. The cystometric evaluation was performed until recording 10 micturition cycles. Statistical analysis was performed using a T test or ANOVA tests between groups followed by a Tukey post-test correction for group comparisons (significance set at p ≤ 0.05) . Data are presented as mean ± SEM. The CMG parameters analyzed were: intercontraction interval (ICI), baseline bladder pressure (BP), Residual volume (RV), filling pressure (FP. Under curve area of filling phase), and frequency of non-voiding contractions. The EMG parameters analyzed were: Basal electrical activity (B) and electrical activity of the external urethral sphincter generated by NVCs (EaNVC). To evaluate DSD, the periods of activation and inactivation of the EUS were calculated during the bursting phase, and the logarithm of the ratio of these parameters was calculated.The number of jumps during 5 voiding cycles extrapolated to 1 hour (Jxh).
Eight weeks after SCI with or without LA treatment, no significant differences in basal pressure, maximum pressure or intercontractile interval were found between groups. However, filling pressure in the SCI group was significantly higher than the one observed in either SHAM or SCI-LA groups without significant difference between these two groups. More importantly, the residual volume after voiding was statistically higher in the SCI rats than in the SHAM or SCI-LA animals, without significant differences between these latest groups. The baseline electromyographic activity of the EUS is increased, when compared with SHAM, in SCI animals but restored by LA treatment in the SCI-LA, with statistical significance after group analysis. Similarly, the high electrical activity in the EUS of SCI rats during the appearance of NVCs was decreased by LA application and statitically corroborated in the SCI and SCI-LA groups. The spinal cord injury significantly reduces the ratio between the active and inactive phase during the phase of expulsion of urine, and it was observed that the rats treated with LA, this value was increased to values similar to those found in the SHAM group. We found that elevations in intravesical pressure due to bladder compression, NVCs and urination, generate a motor response of the hind legs in the SCI animals characterized by abrupt, bilateral and repetitive movements of extension and retraction. The SCI rats treated with LA had a lower number of hind-leg movement events, that were significantly lower than in the SCI animals without treatment.
Interpretation of results
The results indicate that needle electromyography is an adequate methodology to study urinary physiology as well as the deleterious effects of spinal cord injury in awake free-moving rats. Likewise, our results show that decentralization, subsequent to severe SCI, generates urodynamic changes in the urinary bladder and external urethral sphincter resembling DSD. On the other hand, these impairments on lower urinary tract function seem to be significantly overturned by LA treatment. We also found that rats with spinal cord injury showed a pattern of abrupt withdrawal movements of the hind legs activated by the increase in bladder pressure and that LA treatment reduces the frequency of these movements to a semi-normal pattern. The study of the physiological and pathophysiological conditions using in vivo animal models present substantial advantages for understanding of the dysfunctional mechanisms inherent in them. Additionaly, beyond teh mechanistic knowledge, the results obtained with animal models are potentially transferable to conditions of human pathology, diagnosis, and treatment. Urodynamic methodologies in awake rats have recently been described using electrodes placed on the surface of the EUS muscle, those novel methodologies open up new possibilities in the study of nervous control of the lower urinary tract. In the SCI rats, a considerable intensity tonic activity of the EUS was observed during the filling phase, corresponding with NVCs. This response suggests a typical spastic activation of muscle affected by upper motoneuron lesions. Thus, when the NVCs were presented, an exaggerated electrotonic response of the EUS was generated, suggesting that the absence of the supraspinal regulatory signals generated an increase in afferent signals. The decrease in the activity-inactivity ratio in the detrusor has been related to DSD in rats with spinal cord injury, so the return to close values of this parameter in rats treated with LA may explain the improvement. In addition to purely urinary manifestations, the rats subjected to mechanical SCI presented a surprising motor behavior characterized by abrupt and rhythmic movements of the hind legs, which generated “jumping” of the rats. We speculate that abnormal signals generated by the neurogenic urinary bladder are transferred by afferent pathways to lumbar and sacral nuclei, where they manage to activate, in a reflexive way, the CPG involved in generating walk, and in this way promoting the observed motor behavior. The neurotrophic effects of GnRH and its analogs have been described in several models, both in vitro and in vivo. There is also evidence that the systemic application of LA generates morphological and molecular changes in the urothelium. Based on such observations it is possible that modulation of the GnRHR in the bladder as well as in the spinal cord, generates trophic and molecular changes. These changes may be involved in the improvement observed for the urinary pattern, as well as in the decrease of the frequency of spasms in the hind legs of the rats treated with LA. In summary, the present study shows how a simple treatment with LA decreases DSD, and at the same time improves bladder filling pressure and residual volume.