ASSESSMENT OF CANINE BLADDER FUNCTION RESTORATION USING BEHAVIORAL MONITORING AND IN-VIVO ELECTROPHYSIOLOGICAL TECHNIQUES

Abstract

Spinal cord injuries and other neurological disorders can disturb the regulation of normal bladder function including continence and micturition. Developing new neuronal pathways by surgically rerouting nerves is a potential approach for restoring bladder function. Our laboratory successfully rerouted somatic nerves to the anterior vesical branch of the pelvic nerve to reinnervate the bladder muscle in canines. Electrical stimulation of these transferred nerves induced detrusor pressure and bladder emptying and we confirmed regrowth of these rerouted nerves using retrograde neurotracing methods. In these studies, reinnervation was proved at 1st and 3rd months after decentralization. We believe that our aim of developing an approach to surgically reinnervate the bladder after long-term decentralization is critical to the success of the reinnervation surgery due to the possibility that patients would delay having a surgery until they try other non-surgical approaches or therapies. We also demonstrated the reinnervation of urethral and anal sphincters by femoral to pudendal nerve transfer after sacral ventral root transection to restore continence. However, these studies did not demonstrate the reinnervation of bladder, urethra and anal sphincter, all in same animal that would be helpful to human patients with lower motor neuron lesioned bladders to restore both continence and emptying. Therefore, prior to applying these surgical procedures to human patients, further investigation is required to prove the effectiveness of nerve transfer strategies in this canine model using multiple experimental techniques. This dissertation is a part of a larger project in canines examining whether surgical rerouting of obturator to pelvic nerve and sciatic to pudendal nerve allows restoration of bladder, urethral and anal sphincter functions, including continence (storage) and emptying (voiding and defecation) functions, in lower motor neuron lesioned bladders. In this study, it was aimed to explore bladder and urethral reinnervation using behavioral observation and in-vivo electrophysiological techniques. In order to completely prove that the reinnervation surgeries are responsible for restoration of bladder and urethral functions, it was first necessary to demonstrate the absence of these functions in animals with long term decentralized bladders and to determine whether the same animals were able to recover functions after reinnervation. In specific aim 1, we addressed this goal by tracking squat-and-void behaviors at monthly intervals after decentralization and reinnervation, using home cage video recordings and evaluation of bladder sensation and emptying after bladder filling. Immediately prior to euthanasia, reinnervation was also explored by electrical stimulation of transferred nerves to evaluate motor function. Retrograde neuronal tracing was also performed to explore sensory reinnervation. Results showed evidence of functional restoration of bladder and urethral function in reinnervated animals based on behavior observation and electrical stimulation of transferred nerves. Also, regrowth of neuronal cells in the new neuronal pathways was observed that were developed by the nerve transfer surgeries. This study also aimed to establish an electroneurogram recording method (part of in-vivo electrophysiological experiments) to explore afferent (sensory) neuronal activity in transferred nerves induced by bladder filling. However, the extraction of neuronal activity from the peripheral nerves is a challenging task. Several factors including noise, interference from surrounding muscle activities and the electronic components can affect these microvolts level recordings. Choice of recording electrode in configuration with the whole recording setup also plays a significant role while performing these low amplitude signal recordings. In specific aim 2, we addressed this issue by refining electroneurogram recording techniques to obtain high strength signal during multifiber recording. We first developed custom electrodes, suitable for varying nerve diameters and available implantation sites, were tested for functionality. Then, we performed multiple testing using these electrodes with different amplifiers to calibrate noise in saline. Testing results helped to establish the recording setup suitable for in-vivo experimental environment. Later, these refined techniques were applied to record afferent (sensory) activity of sciatic nerves and afferent (sensory) and efferent (motor) activity of hypogastric nerves in rats. Based on the recording results, it was aimed to employ similar techniques in order to record nerve activity in the canine model. Prior to applying these refined techniques to explore sensory reinnervation from new neuronal pathways after nerve transfer surgeries, in specific aim 3, we aimed to assess the hypogastric nerve activity in normal intact and acutely lumbosacral decentralized bladders using these refined techniques. The effects of electrical stimulation of hypogastric nerves or lumbar roots on detrusor pressure were determined, as were effects of isoflurane versus propofol anesthetics on hypogastric nerve stimulation evoked pressure. Hypogastric nerve activity was recorded using custom-made bipolar cuff electrodes during bladder filling. To confirm or refute that any increase in electroneurogram during bladder filling is due to afferent activity from the end organ, the hypogastric nerve was transected between the recording electrode and the spinal cord and the effects of bladder filling on afferent but not efferent activity were recorded. Results showed that electrical stimulation of hypogastric nerves evoked low amplitude detrusor pressures that did not differ between the two anesthetics. Upper lumbar (L2) ventral root stimulation evoked detrusor pressures were suppressed, yet not eliminated after transection of hypogastric nerves and all spinal roots below L5. Afferent and efferent hypogastric nerve activity did not change with bladder filling in neuronally intact bladders but decreased in decentralized bladders. No change in afferent activity were observed during bladder filling in normal intact and decentralized bladders. Overall findings in this research indicate that the new neuronal pathways created by nerve transfer can restore bladder sensation and emptying function in lower motor neuron-lesioned canines. A more complete decentralized bladder model needs to include transection of both the lumbosacral spinal roots innervating the bladder and the hypogastric nerves prior to performing nerve transfer surgeries. The refined electroneurogram recording methods may be suitable for evaluating the effectiveness of nerve transfer surgeries by monitoring the sensory activities of the transferred nerve.