Whole-cell patch-clamp recordings in combination with axonal tracing techniques were used to investigate the effects of chronic spinal cord injury on the electrical properties of dorsal root ganglion neurones innervating the urinary bladder or colon of the adult rat. 2. In spinal intact animals, the majority (73-74%) of bladder and colon neurones which were small in size exhibited high-threshold humped spikes mediated by tetrodotoxin (TTX)-resistant Na+ channels, whereas large neurones had low-threshold narrow spikes mediated by TTX-sensitive Na+ channels. 3. In chronic spinal transected animals, 60% of bladder afferent neurones exhibited TTX-sensitive low-threshold spikes. The average diameter and input capacitance of the cells were significantly larger than those of cells obtained from spinal intact animals. 4. In bladder afferent neurones from chronic spinal transected rats, the density of TTX-resistant Na+ currents significantly decreased from 60.5 to 17.9 pA pF-1, whereas that of TTX-sensitive currents increased from 32.1 to 80.6 pA pF-1. 5. These changes in action potential and Na+ current characteristics were not detected in colon afferent neurones following spinal cord injury. 6. The results indicate that spinal cord injury increases bladder afferent neurone excitability by shifting the expression of Na+ channels from a high-threshold TTX-resistant type to a low-threshold TTX-sensitive type. This change in properties may occur in response to alterations in neurotrophic signals originating in the hypertrophied bladder.
摘要
采用全细胞膜片钳记录技术结合轴突追踪技术，研究慢性脊髓损伤对成年大鼠支配膀胱或结肠的背根神经节神经元电生理特性的影响。2. 在脊髓完整的动物中，大多数（73 - 74%）体积较小的膀胱和结肠神经元表现出由河豚毒素（TTX）抗性Na⁺通道介导的高阈值驼峰状动作电位，而大神经元具有由TTX敏感Na⁺通道介导的低阈值窄动作电位。3. 在慢性脊髓横断的动物中，60%的膀胱传入神经元表现出TTX敏感的低阈值动作电位。这些细胞的平均直径和输入电容显著大于脊髓完整动物的细胞。4. 在慢性脊髓横断大鼠的膀胱传入神经元中，TTX抗性Na⁺电流密度从60.5 pA pF⁻¹显著降低至17.9 pA pF⁻¹，而TTX敏感电流密度从32.1 pA pF⁻¹增加至80.6 pA pF⁻¹。5. 脊髓损伤后，结肠传入神经元未检测到动作电位和Na⁺电流特性的这些变化。6. 结果表明，脊髓损伤通过将Na⁺通道的表达从高阈值TTX抗性类型转变为低阈值TTX敏感类型，增加了膀胱传入神经元的兴奋性。这种特性的变化可能是对肥大膀胱中神经营养信号改变的反应。
