The effects of nerve transection on the endoneurial collagen fibril sheaths

Summary The connective tissue changes during Wallerian degeneration and subsequent regeneration were studied in the distal stump of transected sciatic nerves of Wistar rats. In half of the animals regeneration was prevented by suturing the distal stump to muscle and in the rest spontaneous regeneration was allowed. Intact contralateral nerves served as controls. By 4 weeks after transection the Schwann cell columns became surrounded by a layer of thin collagen fibrils that were, on average, 25–30 nm in diameter. This was only half of the fibril diameter observed elsewhere in the endoneurium or in control nerves. The layer of thin fibrils diminished in thickness when axonal regeneration reached the distal stump, especially as the axons became myelinated. At all stages of the experiment the fibril diameter distribution in the surrounding normal endoneurial stroma was comparable with that observed in control nerves. Segments of Schwann cell basement membrane were observed to be closely associated with collagen fibrils both in freely regenerating, as well as in non-regenerating, nerves. The diameter of these fibrils corresponded to that observed in the zone of thin fibrils surrounding the Schwann cell columns. Such areas were not found in control nerves. The data obtained show that deposition of thin collagen fibrils occurs around the Schwann cell columns as a reaction to transection. Our observations on the regenerating nerves indicate that this connective tissue reaction does not prevent regeneration in the early phases following injury and that its progression is limited concomitantly with axonal regeneration.Supported by a grant (to V. S.) from the Emil Aaltonen Foundation and by institutional grants from the Turku University Foundation and the Sigrid Jusélius Foundation     

Endoneurial fibrosis following nerve transection

Summary Indirect immunofluorescent techniques with antibodies to type I, III, and V collagens and fibronectin were used to study rat sciatic nerve tributaries after transection with intact contralateral nerves as controls.Codistribution of type I and III collagens characterized the epineurium of normal nerve. In the perineurium, however, type I collagen was absent, but type III and V collagens and fibronectin were detected. Type I and III collagens were codistributed in the endoneurial stroma where a homogeneous staining by antibodies to fibronectin was also observed.During the 4-week observation period after transection the perineurium reacted by slight thickening which was most clearly demonstrated by staining with antibodies to fibronectin and to type V collagen. A widening of the type I-negative cleft also occurred. Endoneurial, type V collagen-positive cuffs around the nerve fibers became disorganized, and a concomitant increase of the stroma containing type I and III collagens and fibronectin was observed.The codistribution of the fibrous collagen types appeared similar in normal epineurium and endoneurium. Type V collagen was locatd in the perineurium and in endoneurial cuffs surrounding the nerve fibers. The present data indicate that collagen accumulation takes place in the perineurium and endoneurium of transected nerve. The cell type responsible for the synthesis of the connective tissue material is discussed.Financially supported by a grant (to V. S.) from the Research and Science Foundation of Lääke Oy and by institutional grants from the Turku University Foundation and the Sigrid Jusélius Foundation     

The dynamics of macrophage recruitment after nerve transection

In the present study rat sciatic nerves (n = 60) were transected; in half of the animals the nerve was allowed to regenerate freely, in the other half the regeneration was prevented by suturing beside the point of transection. Macrophages were stained with ED-1 antibody and counted (number/mm²) in both the epi- and endoneurium 3, 7, 14, 48 and 56 days post transection. Macrophages were observed first in the epineurium; the local density of macrophages was considerably higher in the epineurium than in the endoneurium during the first few days. The number of macrophages in the epineurium was maximal at 3 days (1000–2000/mm²), and thereafter it declined sharply. In the endoneurium macrophages were most abundant after 2 weeks (1000/mm²), after which their number declined steadily. A migration of epineurial macrophages appeared to take place through the perineurium from epineurial areas containing a high concentration of macrophages. Initially an endoneurial accumulation of macrophages was noted in the subperineurial area. These findings suggest an alternative route for macrophages into the endoneurial space. No statistical difference was observed between the regenerating and non-regenerating experimental groups. The present study indicates that regenerating axons do not have an effect on the number of macrophages in either the epineurium or the endoneurium. Received: 21 March 1996 / Revised, accepted: 25 September 1996     

Reversible endoneurial changes after nerve injury

Summary Endoneurial changes in the rat sciatic nerve were studied during Wallerian degeneration and subsequent regeneration. After total axotomy two different experimental models were used. In the first the cut ends of the sciatic nerves were left free to allow reinnervation. In the second model the distal end of the transected nerve was sutured to the adjoining muscle to prevent regeneration. Within 2 weeks after the axomoty, a Wallerian type of degeneration was seen with axonal destruction and phagocytosis of myelin sheaths. After 4 weeks endoneurial fibroblastic cells formed circular structures around the Schwann cell columns, i.e., the bands of Buengner in both groups. These fascicle-like structures became more pronounced in the non-regenerating nerves up to 8 weeks, while during reinnervation the cellular reaction in the endoneurium nearly disappeared within this time. Ultrastructurally, the endoneurial fibroblast-like cells showed marked phagocytotic activity and also fragments of basement membrane on their surface. The appearance of thin (25–30 nm in diameter) collagen fibrils closely related to the basement membrane was noted around the bands of Buengner, as well as the appearance of an amorphous extracellular gap between the newly synthetized thin collagen fibrils and normal endoneurial collagen (50–60 nm). The reversible endoneurial compartmentation seems to be important for maintaining the nerve structure, serving as a support for axonal regeneration in addition to the bands of Buengner.Supported in part by grants from the Emil Aaltonen Foundation and from the Research and Science Foundation of Farmos (to V. S.) and institutional grants (to Dept. Med. Chem.) from the Sigrid Jusélius Foundation and the Turku University Foundation     

Differences between the peripheral and the central nervous system in permeability to sodium fluorescein

Sodium fluorescein (SF) was used as a very small tracer (mol wt 376; 5 A° diameter) to examine diffusion barriers in peripheral nerves and to compare them to those in other regions of the nervous system. The technique involved immobilization of the tracer by rapid freezing, followed by freezedrying and vacuum embedding in paraffin. The localization of the SF was then determined in tissue sections using fluorescence microscopy. Even at the highest doses of intravenously (IV) injected tracer, no extravasation could be detected in the cerebral cortex. On the other hand, SF penetrated very rapidly into peripheral ganglia and into the epineurium and perineurium of large peripheral nerves. The penetration of SF into the endoneurium of large nerves was, however, much more restricted with tracer detectable within the endoneurium only at high doses and long survival times. Even in such cases, the level of SF fluorescence was much lower within nerve fascicles than in the epineurium and the perineurium, and a sharp gradient in fluorescence intensity persisted at the inner border of the perineurium. The extent of extravasation into the endoneurium varied markedly between different fascicles of the same nerve and between different nerves in the same animal. Experiments involving injection of high doses of SF adjacent to the nerve indicated relatively little movement of SF across the perineurium, which indicates that the observed accumulation of tracer within the endoneurium was the result of direct extravasation of SF from the endoneural blood vessels. Small nerve branches (< 100 μ in diameter) showed an earlier and more extensive penetration of SF into the endoneurium than large nerves like the sciatic, hypoglossal, or ventral tail nerve. This may be due to a diffusion of SF along the extracellular space of the endoneurium from nerve terminals where the perineurial barrier is open-ended. In experiments involving IV injection of a solution containing both green fluorescent SF and red fluorescent Evans Blue (Evans Blue-serum albumin complex, EBA = mol wt 69,000), the distribution of SF could be directly compared at various sites and sacrifice times to that of EBA, a much larger tracer. SF appeared more rapidly and extensively than EBA in the various compartments in ganglia and peripheral nerve. The distribution of EBA was the same as is typically seen when this tracer is injected alone, indicating that there was no change in vascular permeability associated with IV injection of SF. Since SF is of very small size, freely diffusible, nontoxic, and detectable at very low concentrations, it should be a useful complement to existing tracers. When tissues are processed according to the indicated procedure, one can obtain a very sensitive and reliable localization of this tracer which should be of value for studies in the nervous system concerning various pathological conditions associated with permeability alterations.     

Spontaneous mineralization of the sciatic nerve of senescent rats

Summary A spontaneous mineralization of the sciatic nerve of senescent specific pathogen-free-bred rats (aged 42 months) is reported. Deposits were found in the endoneurium of different branches of the nerve at mid-thigh level. They appeared as small discrete deposits or as large tubular-shaped concretions, probably formed by the growth and merger of the smaller deposits. Some of the concretions were found in close proximity to blood vessels. Deposits consisted of dense aggregations of randomly entangled spicules spreading within bundles of collagen fibrils. Calcium was detected by histochemistry and X-ray dispersion microanalysis. Phosphorus was also found, possibly associated with calcium to form hydroxyapatite.Supported by grants from the FRFC and carried out within the framework of the Commission of the European Communities Concerted Action on Ageing and Diseases (EURAGE). E.T. was supported by a grant from the IRSIA.     

The analysis of collagen in glutaraldehyde-fixed,osmicated peripheral nerve

Summary Glutaraldehyde fixation and osmication of rat sciatic nerve and human sural nerve did not appreciably alter the apparent weight of collagen in nerve fasciculi as determined by hydroxyproline analysis of hydrolysed samples. The collagen content of autopsied peripheral nerve is unaltered at least up to 24 h after death. The mean endoneurial weight of collagen per fascicle in rat sciatic nerve was 123 g (all results expressed for 1 cm length). In human sural nerve the mean weight was 57 g and the mean fascicular volume 1.74 mm³. Human endoneurial collagen fibrils gave a unimodal distribution of diameters with a peak at 40 nm.     

Thrombospondin expression in nerve regeneration I. comparison of sciatic nerve crush, transection, and long-term denervation

Patterns of expression of the extracellular matrix molecule thrombospondin (TSP) were examined during peripheral nerve regeneration following sciatic nerve crush or transection. In noninjured nerve, was present in the axoplasm, Schwann cells, endoneurium, and perineurium of the adult mouse sciatic nerve. Following nerve crush or nerve transection, levels of TSP rapidly increased distal to the trauma site. Elevated levels of TSP were present distal to regenerating axons, while expression gradually returned to normal proximal to the regenerating axons. When reinnervation was blocked, TSP levels remained high in the endoneurium in excess of 30 days, but TSP was absent by 60 days. Following reanastomosis of the proximal and distal segments after 60 days of denervation, TSP was re-expressed in the distal nerve stump. These results indicate that TSP, which is involved in neuronal migrations in the embryo and neurite outgrowth in vitro, appears to play a role in axonal regeneration in the adult peripheral nervous system.     

Transplanted neuronal progenitor cells in a peripheral nerve gap promote nerve repair

A basic experiment of peripheral nerve regeneration using neuronal progenitor cells embedded in collagen gel was performed in a rat sciatic nerve defect. First, when neuronal progenitor cells derived from the fetal rat hippocampus were cultured in atelocollagen-containing medium, neurospheres positive for anti-nestin antibody were confirmed after 8 days. These cells differentiated into astrocytes positive for anti-glial fibrillary acidic protein (GFAP) antibody, oligodendrocytes positive for anti-galactocerebroside (GalC) antibody and neurons positive for anti-neurofilament 200 (NF200) antibody, and they were capable of extending axons. They also differentiated into Schwann-like supportive cells positive for anti-s100 and anti-p75 antibody. Next, a 15-mm defect was prepared in the sciatic nerve of mature rats, and the nerve was bridged with a silicone tube filled with neuronal progenitor cells (1 x 10(5)) embedded in collagen gel. The transplanted neuronal progenitor cells were labeled in advance with 5-bromo-2-deoxyuridine (BrdU). When the regenerated tissue was examined 6 weeks and 10 weeks after grafting, the number and diameter of myelinated fibers were significantly increased compared with a control tube without neuronal progenitor cells. Action potentials were detected in the regenerated nerve. Also, cells positive for both anti-BrdU antibody and anti-S100 or anti-p75 antibody were observed in the regenerated tissue, and part of the grafted neural stem cells were considered to have differentiated into Schwann cell-like supportive cells. From these results neuronal progenitor cells derived from the fetal rat hippocampus are considered to retain their proliferative and differentiating abilities in collagen gel, and when transplanted to a site of peripheral nerve defect, part of them differentiate into supportive cells and they contributed to promotion of axonal regeneration.     

Collagen-GAG Substrate Enhances the Quality of Nerve Regeneration through Collagen Tubes up to Level of Autograft

Peripheral nerve regeneration was studied across a tubulated 10-mm gap in the rat sciatic nerve using histomorphometry and electrophysiological measurements of A-fiber, B-fiber, and C-fiber peaks of the evoked action potentials. Tubes fabricated from large-pore collagen (max. pore diameter, 22 nm), small-pore collagen (max. pore diameter, 4 nm), and silicone were implanted either saline-filled or filled with a highly porous, collagen-glycosaminoglycan (CG) matrix. The CG matrix was deliberately synthesized, based on a previous optimization study, to degrade with a half-life of about 6 weeks and to have a very high specific surface through a combination of high pore volume fraction (0.95) and relatively small average pore diameter (35 μm). Nerves regenerated through tubes fabricated from large-pore collagen and filled with the CG matrix had significantly more large-diameter axons, more total axons, and significantly higher A-fiber conduction velocities than any other tubulated group; and, although lower than normal, their histomorphometric and electrophysiological properties were statistically indistinguishable from those of the autograft control. Although the total number of myelinated axons in nerves regenerated by tubulation had reached a plateau by 30 weeks, the number of axons with diameter larger than 6μm, which have been uniquely associated with the A-fiber peak of the action potential, continued to increase at substantial rates through the completion of the study (60 weeks). The kinetic data strongly suggest that a nerve trunk maturation process, not previously reported in studies of the tubulated 10-mm gap in the rat sciatic nerve, and consisting in increase of axonal tissue area with decrease in total tissue area, continues beyond 60 weeks after injury, resulting in a nerve trunk which increasingly approaches the structure of the normal control.     

Subperineurial space of the sural nerve in various peripheral nerve diseases

Summary The size of the subperineurial space of the sural nerve has been evaluated quantitatively in 69 cases of various peripheral nerve diseases and in controls. A significant increase was found in beriberi neuropathy (6 cases) and idiopathic polyradiculoneuropathy (9 cases) as compared with the control (8 cases). On electron microscopy a few macrophages, fibroblast processes, collagen fibrils with a diameter of 50 nm, microfibrils with a diameter of 8 nm, and amorphous material were observed in both the enlarged subperineurial space and the endoneurial intercellular space. They were less frequently observed in controls. No significant correlation was found between the size of subperineurial space and the density of myelinated fibers.     

Distribution of tetanus toxin in rat peripheral nerve trunks during the development of local tetanus

Summary Mouse bioassay studies were made on the tetanus toxin content of three different segments of both sciatic nerve trunks after unilateral gastrocnemius muscle injections. Multiple toxin dosages, sampling times, nerve transections, and nerve dissections to produce three samples per segment (undissected nerve, epineurium, and perineurium plus endoneurium) were used.The results showed that after i.m. injections a dosage dependent bilateral toxin distribution could be detected in the undissected nerve or its epineurium. The characteristics of this epineurial toxin distribution are discussed.A unilateral toxin distribution was detected only in the stripped (perineurium plus endoneurium) nerve segment from the injected extremity. This unilateral toxin distribution had the characteristics of centripetal toxin transport along the tissue spaces or axons to the spinal cord. This unilateral centripetal toxin gradient was temporally related to the onset of local tetanus. Both the toxin gradient pattern and local tetanus due to i.m. injected toxin could be prevented by nerve transection.These data suggest that peripheral nerves do transport tetanus toxin to the spinal cord and that this transport in an important factor in the pathogenesis of local tetanus.     

Mouse sciatic nerve regeneration through semipermeable tubes: A quantitative model

The regeneration of transected mouse sciatic nerves using semipermeable acrylic copolymer tubes to enclose both stumps has been qualitatively assessed from 1 to 30 weeks post-operative. Quantitative morphometric analysis of electron micrograph montages of complete transverse sections of the segment regenerated between stumps has permitted determinations of the percents of total area occupied by the various tissue constituents—blood vessels, epineurium, perineurium, endoneurium, myelinate d axon/Schwann cell units, and unmyelinated axon/Schwann cell units. Significant differences were found in the total cross-sectional area of segments regenerated through tubes of 1.0 mm versus 0.5 mm internal diameters. Segments regenerated with the distal stump inserted in the tube contained significantly greater percentages of neural units and were significantly larger at 8 weeks post-operative compared to segments regenerated for 9-10 weeks with the distal stump avulsed. The morphometric method permits rapid quantitation of sizeable electron micrograph montages which at 1300 × permit all types of tissue components, including the unmyelinated axons, to be visualized.     

Nerve growth activities in rat peripheral nerve

Nerve growth activities in rat sciatic nerves were assayed by recording the neuritic outgrowth from chick embryonic ganglia cultured in collagen gels beside nerve fragments for two days. Living nerve explants released activity that resembled nerve growth factor (NGF) in its effect on sympathetic ganglia and that was almost totally blocked by an antiserum to 2.5 S mouse NGF. Frozen and thawed specimens from normal nerves elicited responses from sympathetic ganglia that were only partially suppressed by anti-NGF and also induced neuritic outgrowth from ciliary ganglia. Thus, from observations on normal nerves, at least two agents promoting axonal extension in vitro were deduced to exist; one substance similar to NGF plus another, non-NGF factor. The level of NGF-like activity was low in killed segments of normal nerves but higher in autologous nerve grafts and degenerating nerves two days after grafting or cutting. However, one or two weeks after nerve transection, distal nerve segments contained little nerve growth activity of either kind. Furthermore, when endoneurial fragments from chronically denervated stumps were cultured, they appeared to have lost some of their capacity to produce NGF-like activity in vitro although the production of activity had, if anything, increased in the perineurial region. In summary, rat peripheral nervous tissue releases two or more soluble substances that stimulate neuritic outgrowth. The level of one or both activities in the endoneurium can be altered by manipulation of nerves in vivo.     

Peripheral nerve pathological findings in familial amyloid polyneuropathy: a correlative study of proximal sciatic nerve and sural nerve lesions

To analyze the peripheral nerve pathological abnormalities in familial amyloid polyneuropathy, a correlative pathological study was carried out on the spinal nerve roots, proximal sciatic nerves, sural nerves, and brachial plexuses from 3 patients with the disease in Japan. The spinal nerve roots appeared to be unaffected except for amyloid deposition on the epineurium. In sciatic nerves and brachial plexuses the nerve lesions had a multifocal distribution, showing prominent interstitial edema in the endoneurium frequently adjacent to deposits of amyloid; in these regions the nerve fibers were severely depleted. A teased-fiber study revealed that segmental demyelination was the predominant type of nerve fiber abnormality. However, these findings were not seen in the sural nerves; instead a diffuse fiber loss with axonal degeneration was observed. It is suggested that multifocal lesions in the proximal portions of the long extremity nerves could summate distally to produce a symmetrical polyneuropathy in the disease. In addition to a space-occupying effect of amyloid deposits in the endoneurium, severe endoneurial edema associated with amyloid deposition in blood vessels and the endoneurial interstitium may induce ischemia in nerve fibers, thus causing the progressive polyneuropathy in this disorder.     

Drainage of molecules from subarachnoid space to spinal nerve roots and peripheral nerve of the rat

The purpose of the present investigation was to find out if a compound injected into the spinal subarachnoid space, after having entered ventral and dorsal nerve roots, can be traced to the epineurial-perineurial sheaths and the endoneurium of peripheral nerves. This would indicate a centrifugal movement of substances from the cerebrospinal fluid along nerves; one route of drainage of cerebrospinal fluid which in the past has been widely discussed. In vivo studies were made using Evans blue-albumin and lanthanum chloride as tracers. Evans blue-albumin is macromolecular in size and emits a red fluorescence after exposure to ultraviolet light. Lanthanum ions are small and easily visible in the electron microscope. The tracers were injected into the cervical subarachnoid space and 15 min to 24 h later sampled from roots, dorsal root ganglia, proximal part of spinal nerves and the median nerves were taken and further processed for detection of tracers. Fluorescence microscopy from samples removed 15 min and 24 h after the injection of Evans blue-albumin showed a red fluorescence of low intensity in the endoneurium of nerve roots, ganglia and proximal spinal nerve. After 24 h also the median nerve elicited some fluorescence. The sheaths around these structures were also fluorescent. Lanthanum was detected between cell layers of the nerve root sheath as well as inside the nerve root parenchyma. In about 50% of the samples from dorsal root ganglia extracellular lanthanum was found in the capsule. The tracer was also found in the epineurium of 50% of the spinal nerves and occasionally in the perineurium. At 15 min, 6 h and 15 h lanthanum was often present in the endoneurium of the spinal nerve sample but always absent in the median nerve. At 24 h electron-dense particles identical to, and suspected to be, lanthanum was rarely seen also in the median nerve. The results show that substances in the cerebrospinal fluid can be transferred to other parts of the peripheral nervous system indicating a centrifugal spread, which may take place in [1] extracellular spaces of the sheaths covering roots, ganglia and nerve, and [2] endoneurial spaces in roots, ganglia and nerve after passage across the sheath surrounding spinal nerve roots. If absorption of tracer into the blood occurs following injection into the subarachnoid space, leaky blood vessels in ganglia and epineurium may add tracer molecules to the extra-cellular environment of the peripheral nervous system.Supported by grants from the Swedish Medical Research Council, project 12X-03020, Trygg Hansa, Svenska Sällskapet för Medicinsk Forskning, Söderbergs stiftelser, Thurings stiftelse, P. and A. Hedlunds stiftelse, Riksföreningen för Trafik och Polioskadade, Henning Larssons fond, Thyr och Thure Stenemarks och Ruth Trossbecks minnesfond and the Multipel Sclerosis Society of Sweden     

Collagen and protein content of autopsied peripheral nerve

Summary Rat sciatic nerve was assayed for total collagen and total protein both immediately postmortem and at weekly intervals after death. No significant difference was found in collagen and protein content between corresponding nerve segments assayed fresh and up to 4 weeks post mortem. However, variation was found in peripheral nerve collagen content between adjacent lengths of sciatic nerve. These results suggest that peripheral nerve collagen and protein remain stable under cool-room conditions for several weeks after death.     

Contribution of wild-type transthyretin to hereditary peripheral nerve amyloid

To elucidate the contribution of wild-type transthyretin (TTR) to amyloid polyneuropathy in TTR amyloidosis, we biochemically investigated amyloid fibrils isolated from sciatic nerve of an autopsied patient with TTR Ala25Ser variant and compared the amount of wild-type and variant TTR in the nerve to that in the heart. Amyloid subunit protein from isolated fibrils was solubilized in 6M guanidine HCl and purified by gel filtration chromatography. The relative amounts of variant and wild-type TTR in the purified protein were estimated from the recovered amounts of tryptic peptides with Ser25 or Ala25. Approximately 60% variant and 40% wild-type TTR were found in both the nerve and heart amyloid deposits. Our results indicate that wild-type TTR co-deposits in the peripheral nerves with variant TTR as amyloid fibril, and therefore that progression of amyloid deposition in the peripheral nerves from wild-type TTR may occur after liver transplantation, as has been seen in the heart.     

The endoneurial response to microsurgically removed epi- and perineurium

The purpose of the study was to examine the response of the endoneurium of the rat sciatic nerve after removal of the epi- and perineurium. For this purpose, segments (4-5 mm long) of the whole epi- and perineurium around the rat sciatic nerve were microsurgically removed (the peel-off area) and the endoneurium was left intact. The post-operative changes were followed up to 5 weeks post-operatively (PO) by histo- and immunohistochemical studies. Additionally, neuromorphometric analyses considering the number of Schwann cells, axons, macrophages and endothelial cells were examined in the peel-off area. The results showed that at the operative area the central part of the endoneurium (65% of the total area of the endoneurium) remained morphologically intact, but the outer part of the endoneurium (35% of the total area) reacted strongly and showed Wallerian type of degeneration. The number of axons and Schwann cells decreased 3 days PO. However, after 2 weeks the number of Schwann cells increased markedly and the highest number was noted 5 weeks PO. A great number of capillaries were observed in the outer part 1 week PO. A rapid invasion of macrophages was noted at the outer part of the endoneurium immediately after the operation. During the regeneration the endoneurial fibroblasts in the peripheral zone started to form minifascicle-like formations, which resulted in a distinct dense outer part of the endoneurium. This dense outer zone was preserved up to 5 weeks PO and participated in the formation of a new perineurium-like structure, but no distinct new perineurium was formed. At the border zone, areas beside the normal epi- and perineurium proliferation of preserved perineurial cells were noted, which fused to the outer part of the dense endoneurium. On focal areas, an attachment of the operated area to the adjoining muscle was observed. This study shows for the first time that despite the microsurgical removal of epi- and perineurium, the inner part of the endoneurium stays intact, but in the outer part of the endoneurium marked reactive changes ensue, probably to protect the injured peripheral nerve.     

Tacrolimus reduces scar formation and promotes sciatic nerve regeneration

A sciatic nerve transection and repair model was established in Sprague-Dawley rats by transecting the tendon of obturator internus muscle in the greater sciatic foramen and suturing with nylon sutures. The models were treated with tacrolimus gavage (4 mg/kg per day) for 0, 2, 4 and 6 weeks. Specimens were harvested at 6 weeks of intragastric administration. Masson staining revealed that the collagen fiber content and scar area in the nerve anastomosis of the sciatic nerve injury rats were significantly reduced after tacrolimus administration. Hematoxylin-eosin staining showed that tacrolimus significantly increased myelinated nerve fiber density, average axon diameter and myelin sheath thickness. Intragastric administration of tacrolimus also led to a significant increase in the recovery rate of gastrocnemius muscle wet weight and the sciatic functional index after sciatic nerve injury. The above indices were most significantly improved at 6 weeks after of tacrolimus gavage. The myelinated nerve fiber density in the nerve anastomosis and the sciatic nerve functions had a significant negative correlation with the scar area, as detected by Spearman’s rank correlation analysis. These findings indicate that tacrolimus can promote peripheral nerve regeneration and accelerate the recovery of neurological function through the reduction of scar formation.