周围神经损伤后脊神经节感觉神经元胞体形态学的变化

目的 研究周围神经损伤后脊神经节感觉神经元胞体形态学的变化以探讨其主要死广性质。方法 切断并原位吻合大鼠右侧坐骨神经，左侧不作任何处理，作为对照；于术后不同时间取L4-L6脊神经节作光镜和电镜观察，观察脊神经节感觉神经元胞体形态的变化。结果 光镜下，损伤的脊神经节感觉神经元胞体染色质浓染；电镜下，细胞膜内陷，分割细胞内容物成凋亡小体；而对侧脊神经节感觉神经元胞体均一、无变化。结论 大鼠坐骨神经损伤后，脊神经节感觉神经元有死亡，其胞体的形态学变化符合细胞凋亡特征。     

Evidence for invasion of regenerated ventral root afferents into the spinal cord of the rat subjected to sciatic neurectomy during the neonatal period

Sectioning the sciatic nerve of experimental animals at the neonatal stage triggers growth of afferent fibers in the ventral root. The present study examined the possibility that the regenerating fiber terminals grow into the spinal cord. The sciatic nerve on one side was cut in neonatal rats. After the rats were fully grown, either an electrophysiological or a histochemical study was performed. The results of electrophysiological experiments showed that stimulation of certain loci in the L5 spinal cord evoked antidromic potentials in the L5 ventral root with a long latency. Various evidence suggests that the long latency potentials are due to activation of C fibers. These C-fiber potentials were on average bigger and were elicited from more numerous loci on the side ipsilateral to the sciatic nerve lesion than on the contralateral side. Furthermore, stimulation of the spinal cord of unoperated normal rats rarely evoked such potentials. For the histochemical study, horseradish peroxidase (HRP) was injected into the L5 spinal cord after cutting the L4-L6 dorsal roots. A lot more cells in the L5 dorsal root ganglion (DRG) on the side ipsilateral to the sciatic nerve lesion were labeled with HRP transported retrogradely through the L5 ventral root than on the contralateral side. Control experiments showed that few DRG cells are labeled with HRP in normal unoperated rats. The combined results of the electrophysiological and histochemical studies suggest invasion of ventral root afferents into the spinal cord, given enough postoperative time. It is not known whether or not these terminals make functional synaptic contacts in the spinal cord.     

Volumetric magnetic resonance imaging of dorsal root ganglia for the objective quantitative assessment of neuron death after peripheral nerve injury

Prevention of neuron death after peripheral nerve injury is vital to regaining adequate cutaneous innervation density and quality of sensation, and while experimentally proven neuroprotective therapies exist, there lacks suitable clinical outcome measures for translational research. Axotomized dorsal root ganglia (DRG) histologically exhibit volume reduction in proportion to the amount of neuronal death within them. Hence, this study evaluated the validity of using magnetic resonance imaging (MRI) to quantify DRG volume as a proxy measure of cell death. A high-resolution 3D MRI sequence was developed for volumetric quantification of the L4 DRG in the rat sciatic nerve model. An unoperated "control" group (n=4), and a "nerve transection" group (n=6), 4 weeks after axotomy, were scanned. Accuracy and validity of the technique were evaluated by comparison with morphological quantification of DRG volume and stereological counts of surviving neurons (optical fractionator). The technique was precise (coefficient of variation=4.3%), highly repeatable (9% variability), and sensitive (mean 15.0% volume reduction in axotomized ganglia detected with statistical significance: p<0.01). MRI showed strong and highly significant correlation with morphological measures of DRG volume loss (r=0.90, p<0.001), which in turn correlated well with neuron loss (r=0.75, p<0.05). MRI similarly exhibited direct correlation with neuron loss (r=0.67, p<0.05) with consistent agreement. MRI volumetric quantification of DRG is therefore a valid in vivo measure of neuron loss. As a non-invasive, objective measure of neuronal death after nerve trauma this technique has potential as a diagnostic modality and a quantitative tool for clinical studies of neuroprotective agents.     

Ion channels associated with the ectopic discharges generated after segmental spinal nerve injury in the rat

In an attempt to identify important ion channels contributing to the generation of ectopic discharges, the present study examined the effects of ion channel blockers on ectopic discharges of injured sensory neurons after spinal nerve ligation. The main focus of the study was to examine the effect of the sodium channel blocker, tetrodotoxin (TTX), in order to identify important subtype(s) (i.e. TTX-sensitive and TTX-resistant) of sodium channels that are involved in ectopic discharge generation. In addition, the effects of potassium and calcium channel blockers were also tested for comparison with the results of previous studies. The dorsal root ganglion (DRG) of the injured segment was removed along with the dorsal root (DR) and the spinal nerve 7-14 days after spinal nerve ligation in the rat. The tissue was placed in an in-vitro recording chamber consisting of multiple compartments that were independently perfused with 35 degrees C artificial cerebrospinal fluid (ACSF). Single unit recordings were made from teased DR fibers. Once a spontaneously active unit was found and characterized, ACSF containing a channel blocker was perfused to the DRG, the site where almost all ectopic discharges originate after spinal nerve ligation. All the recorded spontaneously active units were found to be Abeta and Adelta fibers (no C fibers were detected). Perfusion of the DRG with a sodium channel blocker (lidocaine) at a dose much less than that required to block conduction of action potentials, significantly inhibited ectopic discharges in all recorded fibers. In addition, ectopic discharges were inhibited by TTX perfused to the DRG at a dose much lower (average of 22.1 nM) than that required to block TTX-resistant subtypes of sodium channels. The data suggest that TTX-sensitive sodium channels are likely to be involved in the generation of ectopic discharges. The present study also confirmed the results of previous studies on the additional potential roles of potassium and calcium channels, thus suggesting that multiple ion channels are likely to be involved in the generation of ectopic discharges.