The Expression Of Vanilloid Receptor 1 In Spinal Cord,Urodynamics And Detrusor Ultrastructure In Rats With Spinal Cord Injury

Background and aim: Spinal cord injury (SCI) may result in neurogenic bladder with the symptoms of overactivitive neurogenic urinary incontinence and low bladder compliance. Capsaicin was used to treat detrusor overactivity for the first time in 1989. Intravesical instillation of capsaicin can increase the capacity of urinary bladder, reduce the maximal detrusor pressure and alleviate the symptoms of urinary incontinence. But the underlying mechanism remained unknown. The rat vanilloid receptor 1 (VR1) which can be specially actived by capsaicin and its analog was cloned from rat dorsal root ganglia in 1997. The DNA sequence of human VR1 was confirmed in 1999 and the expression of VR1 in dorsal root ganglia was confirmed at the same time. Therefore it was supposed that the interaction between capsaicin and VR1 inhibited the detrusor overactivity, namely, VR1 may play certain role in the emergence of bladder hyperreflexia. But the internal relationship remained unclear. In the study the VR1 expression in spinal cord is researched, the relationship is discussed and at the same time the detrusor ultrastructure is observed to realize the histological basis of neurogenic urinary incontinence. Material and methods: Sprague-Dawley female rats (body weight: 250-280g; n=70)were used in this study. They were divided into five groups: sham control group (n=20, among which 10 were used for the study of ultrastructure), 1 week after SCI (n =10), 2 weeks after SCI (n=10), 3 weeks after SCI (n=10), and 4 weeks after SCI (n=20, among which 10 were used for the study of ultrastructure). Spinal cord transection was performed in all rats except for the sham control group. Under general anesthesia a midline incision was made over the T8 and T9 vertebra level. After laminectomy, SCI was performed by a complete transection of the spinal cord. In sham control group the rats underwent laminectomy only and spinal cord remained intact. In the first week postoperatively abdomen pressing was performed in all groups to assist the micturition. The urodynamics, in which the maximal detrusor contraction preesure was observed in the bladder filling stage, was examined at the relative time point in SCI groups and 14 days after the operation in sham control group. Spinal cord segments of L4, L5, L6 and SI sections were obtained after cardiac perfusion with saline and 4% polyformaldehyde. The samples were embedded by paraffin and cutted into sections (4 μ m). VR1 receptors were immunoreacted with rabbit anti-capsaincin receptor polyclonal antibody by the SP immunohistochemical method, and the VR1 immunoreaction was measured with the image analysis system. The rat detrusor ultrastructure of sham control and SCI group was observed in 20 cases 4 weeks after the operation.Results: (1) self-micturation was observed in rats of sham control group, and there was no urinary infection and abdomen apophysis observed. Total 7 rats died from infection and other factors in SCI groups. Paralysis in hind limbs and urinary retention was found in SCI groups, and the rats of SCI groups appeared reflexible micturition 1~2 weeks after SCI, namely, the mechanical stimulation around the urethra triggered the micturition reflex; (2)The maximal detrusor pressure in sham control group, SCI 1-week, SCI 2-week, SCI 3-week and SCI 4-week was 1.27±0.31 cmH2O,3.26±0.37 cmH2O,4.39±0.46 cmH2O, 4.67 ±0.74 cmH2O and 5.42±0.99 cmH2O, respectively. There was a significant difference between sham control group and SCI groups (P=0.000< 0.05), and also a significant difference between SCI 1-week group and any other SCI group. No significantdifference was found among the groups of SCI 2-week, SCI 3-week and SCI 4-week. (3) In the spinal cord, VR1-positive staining was confined to the neurofilaments of superficial dorsal horn (Ⅰ~ Ⅱ lamina). No positive staining was found in other area. There was significant difference in VR1-expression among different spinal cord segments (F=527. 662, P=0. 000), and the staining intensity in L4, L5, S1 and L6 spinal cord segments increaseed in turn. VR1 in the dorsal horn expressed a weak staining in the sham control group. After spinal cord injury, the intensity of VR1-positive staining was significantly increased in the SCI groups. There was significant difference in VR1-positive staining among different groups (F=227. 373,P=0.000), between the sham control group and any SCI group (P=0. 000 <0. 05), between SCI 1-week group and SCI 3-week, SCI 4-week group(P=0.042, P=0.024). no significant difference was found among the groups of SCI 2-week, SCI 3-week and SCI 4-week group. (4) there was an intense positive correlation between the staining intensity and the bladder detrusor contraction extent (r=0.951, P=0.000<0.05).(5) The cell junction of detrusor in sham control group was intermediate junction and desmosome, but it was mainly gap junction in SCI groups. Much collagen existed in the cell interval in SCI group but it was not found in the sham control group.Conclusion: (1) The increased expression of VR1 in the superficial dorsal root of spinal cord after SCI may results in the detrusor hypereflexia. (2) The change of detrusor cell junction after SCI is one reason for bladder overactivity, (3) The increased collagen among the cells is the histological foundation for the reduction of bladder compliance.