Morphometric data of canine sacral nerve roots with reference to electrical sacral root stimulation

Experiments to investigate restoration of lower urinary tract control by electrical stimulation of the sacral nerve roots are mostly performed on dogs. Yet little morphometric data such as root diameters and fiber diameter distributions are known of the canine sacral roots. The aim of this study was to acquire morphometric data of the intradural canine sacral dorsal and ventral roots (S1–S3). Cross-sections of sacral roots of two beagle dogs have been analyzed using a light microscope and image processing software. The cross-sectional area of each root was measured. The diameters of the fibers and the axons in the cross-sections of the S2 and S3 roots were measured and used to construct nerve fiber diameter frequency distribution histograms. The results show a unimodal diameter distribution for the dorsal roots and a bimodal distribution for the ventral roots. In addition the average ratio g of the axon diameter to fiber diameter has been calculated for each root. © 1996 Wiley-Liss, Inc.     

Electrodiagnosis of human dorsal sacral nerve roots by recording afferent and efferent extracellular action potentials

Single extracellular nerve action potentials from afferent fibres with various functions were recorded from human sacral nerve roots. It was shown that the potentials from these fibres can have different wave forms (amplitude, duration) and conduction velocities. The smaller potentials with longer durations have lower cut-off frequencies for certain identification than the larger potentials of shorter duration. The conduction velocity diagnosis covers a range of velocities with a factor of about 10. The slowest measured conduction velocities were between 4 and 10 m/sec. The identification of the functions of afferents in nerve roots is possible by calculating conduction velocities and stimulated activity increase measurements. Besides touch and pain fibres from the skin, afferents from mechano-receptors of the urinary bladder and the anal canal could be detected in dorsal sacral roots.There is evidence of motoneurons in the dorsal sacral roots supplying fatigue resistant muscle fibres.Sacral nerve root electrodiagnosis can be used in operations to identify physiologically-stimulated afferents and reflex activated motoneurons and, therefore, possibly will be useful in nerve anastomoses and nerve root stimulations in paraplegia.     

Functional reinnervation of the canine bladder after spinal root transection and immediate somatic nerve transfer

This study was performed to determine whether nerve transfer immediately after spinal root transection would lead to bladder reinnervation in a canine model. In one animal, the left T12 intercostal nerve was mobilized, cut and attached to the severed ends of sacral roots inducing bladder contraction using a graft from the T11 intercostal nerve. On the right side and bilaterally in two other dogs, coccygeal roots innervating tail musculature were cut and attached to the severed bladder sacral roots (coccygeal nerve transfer [CG NT]). In four other dogs, bladder sacral roots were transected in the vertebral column, and the genitofemoral nerve was transferred within the abdomen to the pelvic nerve (genitofemoral nerve transfer [GF NT]). After 14 months for CG NT and 4.5 months for GF NT, electrical stimulation of the pelvic nerve induced bladder pressure and urethral fluid flow on the intercostal nerve transfer side, in each of the five CG NT sites and bilaterally in three of the four GF NT animals. Reinnervation was further shown by retrograde labeling of spinal cord neurons following fluorogold injections into the bladder wall and by histological examination of the root/nerve suture sites. In all CG NT animals, labeled neuronal cell bodies were located in ventral horns in lamina IX of coccygeal cord segments. In the three GF NT animals in which pelvic nerve stimulation induced bladder contraction, abundant labeled cell bodies were observed in lamina IX and lateral zona intermedia of upper lumbar cord. These results clearly demonstrate that bladder reinnervation can be accomplished by immediate nerve transfer of intercostal nerves or coccygeal spinal roots to severed bladder sacral roots, or by transfer of peripheral genitofemoral nerves (L1,2 origin) to pelvic nerves.     

A new resorbable wrap-around implant as an alternative nerve repair technique.

Poly-3-hydroxybutyrate (PHB), a bacterial storage product, is available as bioabsorbable sheets and has been used in this study for primary nerve repair. The aim was to assess axonal regeneration following such repair and determine the inflammatory response to PHB. In 20 adult cats, the transected superficial radial nerve was wrapped in PHB sheets, while primary epineural repair was carried out in the contralateral limb. At 6 and 12 months, the repair sites were assessed immunohistochemically for macrophage infiltration and myelinated axons were counted in the distal nerve. Mean macrophage counts across the whole width of the nerve in both groups at 6 and 12 months showed no statistically significant difference. Nor was there any significant difference between the two groups at both time-points in axon counts, axon diameter, myelin thickness and g-ratio. There was a statistically significant increase in fibre diameters at 12 months, indicating that fibres were undergoing continuous maturation.     

A study of the myelinated fibres in the branches of the pelvic plexus

In a 20-year-old human female specimen the nerves to the pelvic organs were dissected and analysed. The gross anatomy of the branches of the pelvic plexus was described. The composition of these nerves was studied and the sizes and distribution of the diameter of a great part of the myelinated nerve fibres were measured and analysed. It was confirmed that the ventral roots S2 and S3 contain many nonmyelinated nerve fibres. There are direct connections between the sacral sympathetic chain and the pelvic plexus. They contain myelinated fibres with sizes as large as 11 μm. There are two different groups of fibres which supply the bladder, one on the dorsal side, mainly nonmyelinated (postganglic sympathetic?), and another group to the lateral side which contains many thin myelinated fibres (parasympathetic preganglionic?). The pelvic plexus and its branches are fixed to the vagina and the rectum. Surgical interventions in this area and perhaps also childbirth can damage the nerve supply to the bladder and the urethra. The functional disturbances of the bladder after such interventions can depend on what group of nerve fibres is most seriously damaged. The large number of thick myelinated fibres which reach the ventro lateral side of the urethra makes it highly probable that these fibres innervate the intrinsic striated urethral musculature. The large number of nonmyelinated nerve fibres in the nerves to the m. levator ani probably innervate smooth muscle tissue which is found in the fasciae of the pelvic floor.     

End-to-end versus peripheral nerve graft repair of the oculomotor nerve in rats: A comparative histological and morphometric study

A comparative study was undertaken to evaluate end-to-end versus peripheral nerve graft repair in cranial nerve reconstruction. In 14 rats, the oculomotor nerve was sharply transected in the cavernous sinus and repaired either by end-to-end coaptation (n = 7) or by interposition of a peripheral nerve graft (n = 7). The results were evaluated 16 weeks after surgery by light and transmission electron microsurgery and by morphometric analysis. The degree of neuroma formation, fibrosis, and axonal disorganisation at the repair site was the same for both groups. Histologically, both end-to-end and graft repair groups revealed various degrees of axonal regeneration with myelinated nerve fibres in the distal nerve segments. In both groups, the number of nerve fibres distal to the repair site was increased compared to proximal to the repair (P < 0.001) but myelinated axon diameter was significantly less than that of control nerves (P < 0.001). No difference existed between the two repair groups in terms of mean myelinated axonal diameter. However, the number and density of myelinated axons was statistically greater in the graft group (P < 0.05). In conclusion, despite the disadvantage of two repair sites, peripheral nerve grafting results in equal or slightly superior axonal regeneration compared to an end-to-end repair in the rodent model of intracranial oculomotor nerve reconstruction. We speculate that this may be due to the structure of the peripheral nerve graft.     

Location of the first and second sacral nerve roots in relation to pedicle screw placement

Dissection and measurements of the first 2 sacral nerve roots with regard to the commonly used entrance points for S1 and S2 pedicle screw placement were performed to determine the location of the first 2 sacral nerve roots in relation to the pedicle screw entrance points in the upper 2 sacral vertebrae. The sacral nerve roots, dural sac, and pedicles were exposed after laminectomy. The mean distance from the reference point to the adjacent nerve roots superiorly and inferiorly at the S2 pedicle level was smaller than those at the S1 pedicle level. The medial angle of the sacral nerve roots progressively decreased from L5 to S3. The nerve root passing through the next foramen formed an immediate medial relation to the sacral pedicle rather than the dural sac. Pedicle screw placement in the first 2 sacral vertebral pedicles has been recommended for lumbosacral fusion and internal fixation of sacral fractures. No anatomic study is available regarding the location of the sacral nerve roots relative to the entrance points of sacral pedicle screw placement. Violation of the sacral canal and foramina by a sacral pedicle screw may injure the sacral nerve roots, especially at the level of the S2 pedicle.     

Peripheral nerve autografts to the injured spinal cord of the rat: An experimental model for the study of spinal cord regeneration

Summary Regenerated central axons have been shown experimentally to penetrate in peripheral nerve segments transplanted into the spinal cord (SC). However, if the nerves are transplanted between the stumps of the transected SC regeneration is impaired by local cavitation and scarring.Our experiment was designed to study whether nerve grafts bridging a severe transverse SC lesion might provide to central regenerating axons a pathway to by-pass the lesion. To this purpose, 2 segments of autologous peripheral nerves were inserted through small dural openings into dorsal longitudinal myelotomies rostral and caudal to a transverse SC lesion in rats. Eighteen weeks after transplantation a large number of well myelinated fibres filled the grafted nerves. Only a few of these fibres, however, could be followed into the SC; they were located in the outer layers of the dorsal white matter. The problems regarding the origin and destination of these fibres are discussed.     

应用T11～L1神经根修复S2、S3神经根的可行性

目的:研究T11到S3神经根的直径和神经纤维数,探讨胸-骶神经根吻合恢复膀胱功能的可行性。方法:24具成人脊柱标本,暴露T11平面以下脊髓神经根。测量T11到S3各神经前后根直径。取3具新鲜尸体脊神经根标本,切取T11到S3脊神经前后根各一段,进行免疫组化研究,统计比较骶神经根神经纤维数与胸或腰神经根的差别。结果:S3前根比任一神经根都细(P<0.05),S2前根与L2前根相近(P>0.05),比T11、T12、L1粗(P<0.05)。S3前根的神经纤维数比任一神经根都少(P<0.05),S2前根与T12、L1、L2神经根的神经纤维数相近(P>0.05),比T11神经根多(P<0.05)。神经根的神经纤维数与其直径呈正相关(rs=0.797)。结论:功能相对次要的T11、T12、L1神经根的神经纤维从数量上为修复S2、S3神经根提供了可行性。     

Identification of myelinated motor and sensory axons in a regenerating mixed nerve

The common peroneal nerves of Wistar rats were transected and repaired to compare the sequential changes in the numbers of regenerating motor and sensory myelinated axons in a single mixed nerve. At sequential intervals (2, 4, and 12 weeks) after nerve repair, 3 kinds of staining were performed: cholinesterase staining (Karnovsky's staining) for motor axons, carbonic anhydrase staining for sensory axons, and antineurofilament immunohistochemical staining for all axons. At 2 weeks there was a large number of carbonic anhydrase-positive axons (600 +/- 98; mean +/- SD) and cholinesterase-positive axons were occasionally seen. Subsequently, there was a striking increase of cholinesterase-positive myelinated axons, reaching to 302 +/- 50 at 12 weeks. The results suggest that the myelinated sensory axons regenerate faster in the early stage of nerve regeneration and that regeneration of the myelinated motor axons is prominent in the subsequent stage. (J Hand Surg 2000; 25A:104-111.     

Anorectal motility responses to selective stimulation of the ventral sacral nerve roots in an experimental model

BACKGROUND: Control of defaecation and continence may be lost in patients with spinal cord injury. Electrical stimulation of sacral nerve roots to promote defaecation simultaneously activates both the rectum and the external anal sphincter (EAS), and may actually obstruct defaecation. The aim of this study was to investigate whether the EAS could be blocked selectively by selective stimulation of the ventral sacral nerve roots, and whether activation of the rectum without activation of the EAS could be obtained by stimulation of the ventral sacral nerve roots. METHODS: Selective electrical stimulation was performed using anodal blocking, a tripolar cuff electrode and monophasic rectangular current pulses applied to the sacral nerve roots in nine G?ttingen minipigs. RESULTS: Simultaneous responses in the rectum and the anal canal were observed in five animals, whereas only anal responses were noted in four. Variations in cross-sectional area and an increase in rectal pressure seemed to facilitate defaecation. Without blocking, the increase in anal canal pressure was 16-45 cmH(2)O. With blocking, this increase was abolished in seven and reduced to 3-6 cmH(2)O in two animals. CONCLUSION: Selective activation of the rectum is possible using an anodal block of somatic motor fibres. This technique holds promise in further development of electro-defaecation.     

Efficient reinnervation of hindlimb muscles by thoracic motor neurons after nerve cross-anastomosis in rats

OBJECT: Peripheral motor axons can regenerate through motor endoneurial tubes of foreign nerves to reinnervate different target muscles. This regenerative capacity has been brought to clinical applications for restorative surgery after nerve or root injury. In this study the authors explore the extent to which nerve cross-anastomosis between lower intercostal nerves and lumbar ventral roots would be effective in inducing reinnervation of paralyzed hindlimb muscles after spinal cord hemisection at the thoracolumbar boundary in rats. METHODS: The proximal extremities of sectioned intercostal nerves T10-12 were surgically connected to the distal extremities of sectioned ipsilateral lumbar ventral roots L3-5, respectively. Motor activity reappeared 2 months postsurgery; however, locomotion was not restored and inappropriate motor patterns persisted at 9 months postsurgery. At that time, data from electrophysiological and histological studies and horseradish peroxidase retrograde labeling demonstrated efficient regrowth of thoracic motor neuron axons that reached hindlimb muscles. They also revealed a persistent maturation defect of regrown fibers, as shown by size heterogeneity and presumable extensive axonal branching. These features are consistent with reduced neural activity subsequent to continuing inappropriate motor patterns. CONCLUSIONS: These results indicate that cross-anastomosis of intercostal nerves with lumbar ventral roots allows efficient reinnervation of paralyzed hindlimb muscles after spinal cord hemisection in rats. Stimulating the reorganization of the neuronal circuitry in the central nervous system by locomotion training or other methods would presumably result in both functional and anatomical improvements. This experimental setting provides a convenient animal model to investigate these processes.     

Thyroid hormone in biodegradable nerve guides stimulates sciatic nerve regeneration: a potential therapeutic approach for human peripheral nerve injuries

It has been already demonstrated that thyroid hormone (T3) is one of the most important stimulating factors in peripheral nerve regeneration. We have recently shown that local administration of T3 in silicon tubes at the level of the transected rat sciatic nerve enhanced axonal regeneration and improved functional recovery. Silicon, however, cannot be used in humans because it causes a chronic inflammatory reaction. Therefore, in order to provide future clinical applications of thyroid hormone in human peripheral nerve lesions, we carried out comparative studies on the regeneration of transected rat sciatic nerve bridged either by biodegradable P(DLLA-(-CL) or by silicon nerve guides, both guides filled with either T3 or phosphate buffer. Our macroscopic observation revealed that 85% of the biodegradable guides allowed the expected regeneration of the transected sciatic nerve. The morphological, morphometric and electrophysiological analysis showed that T3 in biodegradable guides induces a significant increase in the number of myelinated regenerated axons (6862 +/- 1831 in control vs. 11799 +/- 1163 in T3-treated). Also, T3 skewed the diameter of myelinated axons toward larger values than in controls. Moreover, T3 increases the compound muscle action potential amplitude of the flexor and extensor muscles of the treated rats. This T3 stimulation in biodegradable guides was equally well to that obtained by using silicone guides. In conclusion, the administration of T3 in biodegradable guides significantly improves sciatic nerve regeneration, confirming the feasibility of our technique to provide a serious step towards future clinical application of T3 in human peripheral nerve injuries.     

闭孔神经移位修复腰骶丛神经根撕脱伤的解剖学观察及临床应用

目的 观察闭孔神经移位修复腰骶丛神经根撕脱伤的可行性及临床疗效.方法 取15具成人尸体标本,显露双侧闭孔神经及腰骶丛神经根.测量闭孔神经从主干起始部至闭孔入口处的长度及其在闭孔入口处的横径和纵径,计算横截面积,并在高倍显微镜下计数有髓神经纤维数目.以相同方法测量并计算股神经相应指标.2002年1月至2007年9月,共为5例腰骶丛损伤患者进行闭孔神经移位术.行健侧闭孔神经经椎体前腹膜后通路移位与患侧股神经直接吻合4例,闭孔神经移位与同侧S1神经根直接吻合1例.结果 闭孔神经的平均长度为(10.51±0.9)cm,横径(2.03±0.37)mm,纵径(2.78±0.29)mm,有髓神经纤维数目(5974±1996)根;股神经横径(3.79±0.58)mm,纵径(6.53±0.61)mm,有髓神经纤维数目(15 860±4350)根.术后3～7 d,所有患者供肢内收肌肌力均减弱至2～3级;术后3个月,4级2例,3级2例,2级1例(至术后1年时,内收肌肌力恢复3级).4例修复患侧股神经的患者,术后分别随访8个月～5年,股四头肌肌力4级2例,2级1例,1级1例;1例行闭孔神经移位与同侧S1神经根直接吻合的患者,术后11个月时小腿三头肌及屈趾肌肌力恢复至3级.结论 闭孔神经可作为一个安全有效的动力神经源,用其修复腰骶丛神经根撕脱伤可获得满意疗效.     

Carbonic anhydrase histochemistry. A potential diagnostic method for peripheral nerve repair

Many large-diameter myelinated axons in spinal dorsal roots contain carbonic anhydrase activity, whereas few small-diameter ventral root axons stain for this enzyme. This differential localization of carbonic anhydrase in sensory and motor nerve fibers is indicative of the potential of carbonic anhydrase histochemistry to provide a convenient method for identifying predominantly motor or sensory fascicles in cut ends of peripheral nerves, thereby facilitating coaptation of fascicles in peripheral nerve repair.     

Early structural effects of oestrogen on pudendal nerve regeneration in the rat

OBJECTIVE: To determine the early effects of oestrogen on the ultrastructure of the pudendal nerve and distal nerve fascicles near the external urethra sphincter (EUS) after a pudendal nerve crush injury. The pudendal nerve is one of the pelvic floor tissues injured during vaginal delivery, possibly contributing to the development of stress urinary incontinence (SUI) in women, the symptoms of which often do not appear until menopause, implicating hormonal factors. MATERIALS AND METHODS: Twenty-seven virgin female Sprague-Dawley rats were anaesthetized and underwent ovariectomy. Three days later, they had one of four procedures: bilateral pudendal nerve crush plus implant of a subcutaneous oestrogen-containing capsule (NC+E); nerve crush plus implant of a sham saline-containing capsule (NC+S); no nerve crush with an oestrogen capsule; or no nerve crush with a sham capsule. After 2 weeks the pudendal nerves and urethral tissues were prepared for light and electron microscopy. The number of axons, myelin figures and endoneurial nuclei in the pudendal nerve segment distal to the lesion were counted. Nerve fascicles near the EUS were also counted and categorized as normal or showing signs of degeneration and/or regeneration. The location of each nerve fascicle was specified as either ventral or dorsal. RESULTS: As there were no significant differences between the two control groups they were combined to form a single control group. In the distal pudendal nerve there were significantly fewer myelinated axons and large myelinated axons in the NC+E and NC+S groups than in the control group. There were three times as many large unmyelinated axons in the NC+E group than in either the NC+S or control groups (P < 0.05). There were only half as many nerve fascicles near the ventral side of the EUS in the NC+S group than in both the control and NC+E groups (P < 0.05). CONCLUSION: Oestrogen appears to affect large unmyelinated axons in both the injured pudendal nerve and at the denervated EUS target. After pudendal nerve crush, nerve fascicles with evidence of degeneration or regeneration near the EUS appear to be spared with oestrogen treatment, particularly in the ventral region. These observations may reflect the early stages of a neuroregenerative effect of oestrogen. Additional studies are needed to confirm these results at later periods and with functional methods.     

Intercostal nerve transfer in brachial plexus injuries: An experimental study

Eighteen adult mongrel dogs underwent unilateral surgical disruption of the brachial plexus. Twelve animals (Group I) had as a second-stage procedure transfer of T4 and T5 intercostal nerves and their accompanying vascular bundles to the distal musculocutaneous nerve stump. Six animals (Group II) had restoration of musculocutaneous nerve continuity with conventional interpositional sural nerve cable grafts. Group I animals demonstrated significantly better electromyographic evidence of reinnervation and, comparing appearance and weight of operated and unoperated biceps muscles at the time of animal sacrifice, maintained greater gross weight and more normal overall appearance of muscle. Histologic study of muscle tissue showed no significant difference between the two groups whereas musculocutaneous nerve histology distal to all anastomoses revealed less fibrous tissue and a greater number of healthy-appearing axons in Group I. It is concluded that vascularized intercostal nerve transfer as performed in this study has theoretical advantages over conventional nonvascularized intercostal nerve transfer but additional investigation is required to make this determination. The superiority of vascularized intercostal nerve transfers over conventional interpositional sural nerve cable grafts has been demonstrated.     

Effects of gradual bone lengthening on the rabbit tibial nerve

Little is known about the effect of gradual bone lengthening on peripheral nerves. In the present study, an external fixation device was applied to the rabbit tibia, which was then divided. After seven days, the tibia was subjected to 0.7 mm/day callus distraction for periods of up to one month. The tibial nerve was fixed in glutaraldehyde and plastic sections were cut in longitudinal and transverse planes for light and electron microscopy. Light microscopy showed a 64% increase in the gap length at the node of Ranvier in myelinated axons from the experimental side compared with the control side. The cross-sectional area of the non-myelinated axons was not altered significantly. We conclude that gradual stretching of the nerve elongates the nerve fibres at least at the region of the nodes, perhaps a point of least resistance. Diameters of fibres seem to be held more constant during the lengthening procedure.     

The influence of motor axon misdirection on muscle contraction force in early nerve repair in a rat sciatic nerve model.

We examined the influence of misdirection of regenerating motor axons toward the distal sensory Schwann tubes on the muscle contraction force in early nerve repair using a rat sciatic nerve model. At 0, 1, 2, 4 and 8 weeks after severing the tibial, peroneal and sural nerves, the proximal stump of the tibial nerve was anastomosed with the distal stumps of both the peroneal and sural nerves using tubulisation (n=10 in each of five groups). We intentionally used the distal stump of the sural nerve (a sensory nerve) to induce regeneration in motor axons from the proximal tibial nerve stump toward the distal sensory nerve stump. Twenty-four weeks after nerve repair, isometric contraction force and wet weight of the anterior tibial muscle were measured, and the numbers of regenerated myelinated axons (motor and sensory) in the distal sural and peroneal nerves were counted. The rates of sural nerve regeneration were significantly higher at weeks 0 and 1 than at the later repair times. However, muscle contraction force and muscle wet weight did not differ significantly between groups in which nerves were repaired within four weeks of severance. These results indicate that peripheral nerve repair within four weeks of severance does not influence the muscle contraction force of single muscle despite the misdirection of motor axons toward the distal sensory Schwann tubes.