Microstructural Study On Detrusor Muscle After Repairing The Atonic Bladder Caused By Medullary Cone Injury In Rats

Medullary cone injury caused by thoracolumbar fracture is usual in clinicalcases,resulting in the lost of micturition functions,which is the cause of urinary tractinfection and renal failure. there are many therapeutic methods for atonic bladder,but mostof these therapies were non-operative treatment and had lots of complications. Our researchgroup used the normal nerve root up the level of sinal cord injury as the power nerve toreconstruct the urinary function via nerve transposition.it was proved effective in animal testsand clinical cases with little complications. To study the mechanism of atonic bladder, westudied the detrusor muscle and its neuro-muscular junction(NMJ) after the medullary coneinjury in rats, observing the rule of degeneration and proposing the optimal time of operationfor repairing atonic bladder after medullary cone injury. Then whether the reconstruction ofbladder function can effectively prevent or refine the degeneration of detrusor muscle?Forthis purpose,we will study the microstructural change of detrusor muscle and its NMJ afterrepairing atonic bladder caused by medullary cone injury with a normal nerve root above theinjury as the power nerve. our main purpose is to observe that whether early reconstructionof urinary function can effectively constrain the regression of detrusor muscle.Objective: To study the microstructural change of detrusor muscle after repairing atonicbladder of rats caused by medullary cone injury with the method of reconstruction. To provethat reconstruction of urinary function with the reflex pathway of sensor-sensor andmotor-motor can effectively constrain the regression of detrusor muscle. Methods: In all,104adult female Sprague–Dawley rats were equally randomized into sixteen groups: the normalgroups, the groups of repairing urinary function after medullary cone injury:1m、2m、3m、4m、5m、6m after the surgery, assigned as groups T1-T6；and the groups of medullary coneinjury without functional repairment:1m、2m、3m、4m、5m、6m after surgery，assignedas groups t1-t6. The atonic bladder model was established by sharp transaction of spinal cordat the level of L4/5vertebral body. the urinary function is established by transfer of thebilateral L5ventral root (VR) to the S2VR root together and postganglionic spinal nerve transfer of the L5dorsal root (DR) to the S2DR with a nerve graft.The residual urinevolume,the electrophysiology study,the bladder weight,the cross-sectional area andultrastructure of the detrusor muscle and its neuromuscular junction (NMJ), percentage ofconnective tissue were examined individually.Results:1.In groups of t1-t6,the residual urinevolume increases with the extension of the time and there are significant differences amongthese groups (P<0.05);in the repairing group (T1-T6),a rise was observed in the first threegroups(T1-T3),the decrease happened in the following groups (T4-T6).2. Theelectrophysiological studies，action potential were recorded in groups from T3-T6,but not ingroups from T1、T2and groups t1-t6.3. The bladder weight increased in all surgicalgroups,bu more significant in groups of medullary cone injury than the groups offunctional reconstruction.4. The sectional area of detrusor muscle has statistical differencebetween the repairing groups and the injured groups,in tvhe repairing groups,the areadecreases with the extension of time and a significant difference was observed among thesegroups(P＜0.05),however,in the injured groups,the area declines with the first increase.5.Transmission electronic microscopy showed significant degenerative changes of detrusormuscle in both groups of reconstruction and injury,such as atrophy of musclecells,disorganized fiber,decreased or disappeared connection between cells. Reduction ofsynaptic vesicles were noted in NMJ of groups T1-T3,but more vesicles in T4、T5than inT1-T3,vacuolization with none synaptic vesicle was observed in group t3and in group t6NMJ was rarely seen.6. The Masson trichromatic dyeing indicated a great difference betweengroups of medullary cone injury and groups of reconstruction，a significant increase wasnoted among the groups of injury with the extention of time.However,there is no statisticaldifference among groups T3、T4and T5.Conclusion:The reconstruction of bladder functionwith L5nerve root can effectively inhibit the degeneration of detrusor muscle and refine themicrostructural change in rats with medullary cone injury.