Axonal outgrowth by identified neurons in the spinal cord of zebrafish embryos

The spinal cord of early zebrafish embryos contains a small number of neurons per hemisegment. The earliest neurons are identifiable as individual neurons or small groups of homogeneous neurons and project growth cones that follow stereotyped, cell-specific pathways to their targets. These growth cones appear to bypass some axons but follow others during pathfinding, suggesting that they can distinguish among the different axons they normally encounter. Furthermore, identified growth cones exhibit cell-specific behaviors in apparent contact with the floor plate cells, which are found at the ventral midline of the early cord. These observations suggest the testable hypothesis that the floor plate may mediate multiple, cell-specific actions on identified growth cones in the zebrafish cord. One hypothesized action is inhibition of specific growth cones to prevent them from crossing the ventral midline.     

S-100β stimulates neurite outgrowth in the rat sciatic nerve grafted with acellular muscle transplants

S-100β promotes neurite extension in vitro and motoneuron survival in the chicken embryo. We demonstrate here that local administration of S-100β stimulates the sciatic nerve regeneration into acellular muscle grafts. Normally there is a 8–10 day delay in the regeneration of axons into such grafts. Local administration of S-100β (0.5–1.0 μg/h) significantly stimulated regeneration into the grafts. In S-100β treated grafts, the regeneration distance was increased with a factor of about 2.3 times as compared to vehicle treated grafts. The distance of regeneration was monitored with pinch test which detects sensory axons. Regenerating axons were growing outside the necrotic muscle cells as revealed with immunohistochemistry for the neurofilament light weight polypeptide. S-100β was demonstrated immunocytochemically in motor neurons of the rat lumbar spinal cord and in large and medium sized neurons of the dorsal root ganglia. The results suggest that S-100β is a physiological growth factor for peripheral nerve axons. © 1997 Elsevier Science B.V. All rights reserved.     

Hyperbaric oxygen treatment has different effects on nerve regeneration in acellular nerve and muscle grafts

Effects of hyperbaric oxygen treatment (HBO) on nerve regeneration in acellular nerve and muscle grafts were investigated in rats. Nerve and muscle grafts were made acellular by freeze-thawing and the obtained grafts were used to bridge a 10-mm gap in the sciatic nerve on the left and right sides, respectively. Rats were treated with HBO (100% oxygen for 90 minutes at 2.5 atmospheres absolute pressure ATA) twice a day for 7 days. Axonal outgrowth, Schwann cell migration and invasion of macrophages were examined 10 days after the graft procedure by staining neurofilaments, S-100 proteins and the macrophage antibodies ED1 and ED2, respectively. Axonal outgrowth and Schwann cell migration in acellular nerve grafts were superior to that found in the acellular muscle grafts. However, there was no difference between HBO-treated and nontreated rats in acellular nerve grafts. Such a difference was found in acellular muscle grafts concerning both axonal outgrowth and Schwann cell migration from the proximal nerve end. No differences in the content of macrophages or neovascularization (alkaline phosphatase staining) in either of the grafts and treatments were seen. It is concluded that there is a differential effect of HBO-treatment in acellular nerve and muscle grafts and that HBO-treatment has no effect on the regeneration process in acellular nerve grafts, in contrast to fresh cellular nerve grafts where a beneficial effect has previously been reported.     

Schwann cells seeded in acellular nerve grafts improve functional recovery

Introduction: This study evaluated whether Schwann cells (SCs) from different nerve sources transplanted into cold‐preserved acellular nerve grafts (CP‐ANGs) would improve functional regeneration compared with nerve isografts. Methods: SCs isolated and expanded from motor and sensory branches of rat femoral and sciatic nerves were seeded into 14mm CP‐ANGs. Growth factor expression, axonal regeneration, and functional recovery were evaluated in a 14‐mm rat sciatic injury model and compared with isografts. Results: At 14 days, motor or sensory‐derived SCs increased expression of growth factors in CP‐ANGs versus isografts. After 42 days, histomorphometric analysis found CP‐ANGs with SCs and isografts had similar numbers of regenerating nerve fibers. At 84 days, muscle force generation was similar for CP‐ANGs with SCs and isografts. SC source did not affect nerve fiber counts or muscle force generation. Conclusions: SCs transplanted into CP‐ANGs increase functional regeneration to isograft levels; however SC nerve source did not have an effect. Muscle Nerve 49 : 267–276, 2014     

Etifoxine provides benefits in nerve repair with acellular nerve grafts

Introduction: Acellular nerve grafts are good candidates for nerve repair, but the clinical outcome of grafting is not always satisfactory. We investigated whether etifoxine could enhance nerve regeneration. Methods: Seventy‐two Sprague‐Dawley rats were divided into 3 groups: (1) autograft; (2) acellular nerve graft; and (3) acellular nerve graft plus etifoxine. Histological and electrophysiological examinations were performed to evaluate the efficacy of nerve regeneration. Walking‐track analysis was used to examine functional recovery. Quantitative polymerase chain reaction was used to evaluate changes in mRNA level. Results: Etifoxine: (i) increased expression of neurofilaments in regenerated axons; (ii) improved sciatic nerve regeneration measured by histological examination; (iii) increased nerve conduction velocity; (iv) improved walking behavior as measured by footprint analysis; and (v) boosted expression of neurotrophins. Conclusions: These results show that etifoxine can enhance peripheral nerve regeneration across large nerve gaps repaired by acellular nerve grafts by increasing expression of neurotrophins. Muscle Nerve 50:235–243, 2014     

Calcium uptake by sarcoplasmic reticulum of muscle grafts in rats

Cross transplantations were carried out in which the soleus (SOL) and extensor digitorum longus (EDL) muscles were switched to each other's muscle bed. Sixty days later, oxalate-supported calcium uptake was measured in homogenates of these grafts and compared with calcium uptake by homogenates of the contralateral control EDL and SOL muscles. With the incubation conditions used, calcium uptake was essentially limited to sarcoplasmic reticulum (SR) vesicles. The velocities of the initial rapid calcium uptake were compared in the grafts and control muscles. Subsequently calcium uptake slowed and the 30-min accumulation of calcium indicated the loading capacity of the SR. In control muscles, the EDL had a faster velocity (0.234 +/- 0.011 mumol/mg/min) of calcium uptake and higher capacity (0.527 +/- 0.017 mumol/mg) for calcium loading than the SOL (0.089 +/- 0.008 mumol/mg/min and 0.26 +/- 0.014 mumol/mg, respectively). The EDL grafts (originally SOL muscles) had faster calcium uptakes than the control SOL muscles or SOL grafts (0.196 +/- 0.013 versus 0.089 +/- 0.008 or 0.126 +/- 0.024 mumol/mg/min). Also, the calcium uptake capacities were higher in EDL grafts than in control SOL muscles (0.400 +/- 0.017 versus 0.261 +/- 0.014 mumol/mg), but not statistically higher than in SOL grafts (0.360 +/- 0.033 mumol/mg). In contrast, SOL grafts (originally EDL muscles) had slower calcium uptakes (0.126 +/- 0.024 mumol/mg/min) than did the control EDL muscles or EDL grafts and the calcium uptake capacities (0.360 +/- 0.033 mumol/mg) were lower in SOL grafts than in control EDL muscles, but not statistically lower than in EDL grafts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Motoneurone survival and neuritic outgrowth promoted by different cell types in embryonic muscle

Different cell types within developing chick skeletal muscle were assayed for their ability to release factors into culture media which could affect the survival and neuritic development of labelled motoneurones and lateral motor column explants. Enriched cultures of myotubes, myoblasts, fibroblasts and mesenchyme were prepared by selective preplating and trypsinisation techniques. Degrees of enrichment were assessed immunofluorescently and morphologically; fibroblasts were the main contaminating cell type. Medium conditioned over each cell type was then tested in dose-response assay against both explants and dissociated motoneurones. In both cases the myotube conditioned medium (MCM) promoted the greatest levels of both survival and neuritic outgrowth, and had the greatest relative potency of all of the cell types. When MCM was preincubated over polycationic substrata, it lost the ability to promote neuritic growth; this could be restored if fresh conditioned medium (CM) was added to the cultures. Thus it was demonstrated that within the MCM there are physically separable agents responsible for neurone survival and neurite expression. The neurite-promoting factor (NPF) within the MCM was stable to collagenase, deoxyribonuclease, neuraminidase and chondroitinase ABC, but was destroyed by trypsin and heparinase. These results imply that a heparan sulfate proteoglycan is essential for the activity of the factor.     

Repairing whole facial nerve defects with xenogeneic acellular nerve grafts in rhesus monkeys

Acellular nerve allografts conducted via chemical extraction have achieved satisfactory results in bridging whole facial nerve defects clinically,both in terms of branching a single trunk and in connecting multiple branches of an extratemporal segment.However,in the clinical treatment of facial nerve defects,allogeneic donors are limited.In this experiment,we exposed the left trunk and multiple branches of the extratemporal segment in six rhesus monkeys and dissected a gap of 25 mm to construct a monkey model of a whole left nerve defect.Six monkeys were randomly assigned to an autograft group or a xenogeneic acellular nerve graft group.In the autograft group,the 25-mm whole facial nerve defect was immediately bridged using an autogenous ipsilateral great auricular nerve,and in the xenogeneic acellular nerve graft group,this was done using a xenogeneic acellular nerve graft with trunk-branches.Examinations of facial symmetry,nerve-muscle electrophysiology,retrograde transport of labeled neuronal tracers,and morphology of the regenerated nerve and target muscle at 8 months postoperatively showed that the faces of the monkey appeared to be symmetrical in the static state and slightly asymmetrical during facial movement,and that they could actively close their eyelids completely.The degree of recovery from facial paralysis reached House-Brackmann grade II in both groups.Compound muscle action potentials were recorded and orbicularis oris muscles responded to electro-stimuli on the surgical side in each monkey.Fluoro Gold-labeled neurons could be detected in the facial nuclei on the injured side.Immunohistochemical staining showed abundant neurofilament-200-positive axons and soluble protein-100-positive Schwann cells in the regenerated nerves.A large number of mid-graft myelinated axons were observed via methylene blue staining and a transmission electron microscope.Taken together,our data indicate that xenogeneic acellular nerve grafts from minipigs are safe and effective for repairing whole facial nerve defects in rhesus monkeys,with an effect similar to that of autologous nerve transplantation.Thus,a xenogeneic acellular nerve graft may be a suitable choice for bridging a whole facial nerve defect if no other method is available.The study was approved by the Laboratory Animal Management Committee and the Ethics Review Committee of the Affiliated Wuxi No.2 People's Hospital of Nanjing Medical University,China(approval No.2018-D-1)on March 15,2018.     

膀胱无细胞基质移植物重建兔阴茎白膜的动态观察**☆

背景：目前膀胱无细胞基质移植物已成功用于替代动物膀胱、尿道和修复尿道下裂，但膀胱无细胞基质移植物重建阴茎白膜有待观察。 目的: 采用同种异体膀胱无细胞移植物替代兔阴茎白膜，观察重建修复效果。 设计：随机对照观察。 单位：四川大学华西医学实验动物中心、华西组织工程实验室及贵阳医学院组织工程实验室。 材料：选用50只雄性健康封闭新西兰兔，动物级别3级，体质量为2.6~3.0 kg,均无包茎及阴茎发育不良，注射生理盐水后无阴茎弯曲，由四川大学华西实验动物中心提供。 方法：实验于2005-12/2007-06在四川大学华西实验动物中心、四川大学组织工程实验室及贵阳医学院组织工程实验室完成。①取10只实验兔膀胱制备膀胱无细胞基质移植物。随机数字表法将40只新西兰兔分为对照组和膀胱无细胞基质移植物组，分别在阴茎背侧切除白膜10 mm×5 mm造成缺损，分别采用白膜原位缝合及膀胱无细胞基质移植物修复，每组20只。②分别于术后2，6，12及24周对2组动物进行阴茎海绵体内快速注射生理盐水诱导阴茎勃起，观察阴茎弯曲情况；于上述时间点分别处死实验兔，于术区取材进行苏木精-伊红、Masson染色观察修复部位组织结构变化；Stirus 染色检测检测Ⅰ型和Ⅲ型胶原纤维阳性面积，免疫组化染色检测炎性标志因子诱导型一氧化氮合酶和促纤维化因子转化生长因子β1的表达。 主要观察指标：①阴茎弯曲情况。②修复部位组织结构变化。③炎性标志因子诱导型一氧化氮合酶和促纤维化因子转化生长因子β1的表达。④Ⅰ型和Ⅲ型胶原纤维阳性面积。 结果：纳入重建阴茎白膜术实验兔40只，2只死于麻醉药物过量，2只死于急性肠炎，其余36只均进入结果分析。①术后6周时弯曲发生率最高，对照组2例，膀胱无细胞基质移植物组1例；术后12周对照组及膀胱无细胞基质移植物组各1例发生弯曲；术后24周对照组1例发生弯曲，膀胱无细胞基质移植物组无弯曲发生。②修复部位组织结构变化：术后2周两组修复部位结构欠清，炎性细胞浸润明显，膀胱无细胞基质移植物组移植部位可见膀胱无细胞基质移植物内细胞生长，Masson染色显示术区白膜纤维纤细，排列欠规律。术后6周时白膜恢复完整性，膀胱无细胞基质移植物不能辨别，两组间无明显差异。术后24周移植部位白膜完整均匀，纤维恢复内环外纵排列，和正常白膜不能区别。③两组术后诱导型一氧化氮合酶及转化生长因子β1，2周表达最强，术后6周只有少数纤维细胞和血管内皮细胞有表达，术后12，24周仅有极少的血管内皮细胞表达诱导型一氧化氮合酶和转化生长因子β1，同时间点2组诱导型一氧化氮合酶和转化生长因子β1没有差别。④术后2周两组Ⅰ型和Ⅲ型胶原纤维共同存在，比例相当。以后Ⅰ型胶原纤维逐渐增加，而Ⅲ型胶原纤维逐渐减少，术后24周以Ⅰ型胶原纤维为主，Ⅲ型胶原纤维已不明显。 结论：膀胱无细胞基质移植物修复新西兰兔阴茎白膜无明显的炎症反应和纤维化，是较为理想的阴茎白膜修复材料。     

脱细胞异体真皮组织补片在智齿拔除中的应用

背景：使用J-1型脱细胞异体真皮组织补片覆盖拔牙创口的报告较少。 目的：探讨异体脱细胞组织补片置入拔牙窝对预防拔牙后并发症的影响。 方法：将400例阻生智齿拔除患者随机分为2组,实验组智齿拔除后拔牙窝内放置医用组织补片;对照组智齿拔除后不放置医用组织补片。分别观察拔牙后组织补片脱落率、肿胀发生率、拔牙窝内血凝块存留和食物残渣残留情况、牙龈是否红肿、对拔牙后出血的影响以及干槽症的发生率。 结果与结论：拔牙后出血的百分比,血凝块留存率,拔牙窝内食物残渣残留百分比,干槽症发生率实验组均明显低于对照组。放置组织补片对术后肿胀和牙龈红肿无明显影响。所有放置在拔牙窝内的组织补片与拔牙创周围组织附着紧密,未见脱落。     

富血小板血浆诱导骨髓间充质干细胞结合化学萃取去细胞神经修复坐骨神经缺损

背景：周围神经损伤早期许旺细胞尚未大量分裂增殖,此时由于解剖连续性的中断,通过轴浆逆向运输提供的营养因子骤减,缺乏神经营养因子支持的神经元有可能死亡,从而使周围神经不能再生或再生乏力。 目的：观察植入经富血小板血浆诱导的骨髓间充质干细胞结合去细胞神经修复坐骨神经缺损的效果。 方法：取新西兰大耳白兔制备坐骨神经缺损模型,随机抽签法分成4组：去细胞神经组,移植同种异体去细胞神经;骨髓间充质干细胞组,移植同种异体骨髓间充质干细胞结合化学萃取的同种异体去细胞神经：经诱导骨髓间充质干细胞组,移植经富血小板血浆诱导的同种异体骨髓间充质干细胞结合化学萃取的同种异体去细胞神经;自体神经组,移植自体神经。术后进行形态学观察与靶肌肉肌湿质量恢复率、运动神经传导速度、轴突直径和髓鞘厚度的检测。 结果与结论：经富血小板血浆诱导的骨髓间充质干细胞结合化学萃取的去细胞神经移植修复神经的靶肌肉肌湿质量恢复率、运动神经传导速度、轴突直径和髓鞘厚度及形态学观察明显优于移植单纯化学萃取的去细胞神经与骨髓间充质干细胞结合化学萃取的去细胞神经的效果,而与移植自体神经修复结果相似。说明经诱导后的骨髓间充质干细胞在体内具有许旺细胞的部分功能,可作为组织工程化外周神经的种子细胞,用于周围神经缺损的修复。     

Relationship of glia to GnRH axonal outgrowth from third ventricular grafts in hpg hosts.

The homozygous mutant hypogonadal (hpg) mouse lacks a functional gene for the neuropeptide gonadotropin releasing hormone (GnRH). The consequence of this defect is an infantile reproductive tract in adulthood. This condition can be reversed by the implantation of normal fetal preoptic area tissue that contains GnRH neurons. Reversal is always preceded by the outgrowth of GnRH axons into the host target tissue, the median eminence, by a stereotyped pathway. In the current experiments we investigated the cellular nature of the path taken by early emerging GnRH axons focusing on their relationship with astrocytic components and with the specialized ependymal population of this area, the tanycytes. In control tissue glial fibrillary acid protein (GFAP) immunoreactivity was confined to the exterior of cerebral blood vessels and glial limitans. Both GFAP and vimentin, another intermediate filament protein, marked the specialized ependymal cells of this region, the tanycytes. There was a robust reactive astrocytic response to the injury of transplantation in both the donor and host tissue within 5 days of implantation and the reactive astrocytes persisted for 60 days. These cells were GFAP-positive and were present in many areas of the host along the cannula tract and not confined to the area of GnRH axonal outgrowth. Vimentin, another intermediate filament, marked only the specialized ependymal cells of this region, the tanycytes, in both control and grafted tissue. Despite the profound reactive gliosis, GnRH axons were shown to exit the implant as early as 5 days after grafting suggesting that the gliotic process did not constitute a barrier to this phenomenon. At the light microscopic level, double label immunocytochemical studies did not reveal any specific association between GFAP or vimentin-positive cellular processes and these pioneer GnRH fibers. However, since normal GnRH axons had been reported to travel in tanycytic channels through the medial basal hypothalamus we reinvestigated the pattern of early emerging GnRH axons at the ultrastructural level. With this higher resolution, GnRH axons were found adjacent to glial elements along their entire traverse from the graft-host interface, through the host basal hypothalamus to their termination on the hypophysial portal capillaries. At the interface, GnRH-positive axons appeared to exit via glial channels similar to those described in other developing and regenerating systems. In the host, GnRH immunoreactive axonal profiles were surrounded by glial processes though the latter could not be further defined as tanycytic or astroglial. Other, immunonegative, axons were frequently seen in axonal bundles or fascicles and not necessarily in contact with glia.(ABSTRACT TRUNCATED AT 400 WORDS)     

Axonal guidance and the development of muscle fiber-specific innervation in Drosophila embryos

The outgrowth of peripheral nerves and the development of muscle fiber-specific neuromuscular junctions were examined in Drosophila embryos using immunocytochemistry and computer-enhanced digital optical microscopy. We find that the pioneering of the peripheral nerves and the formation of the neuromuscular junctions occur through a precisely orchestrated sequence of stereotyped axonal trajectories, mediated by the selective growth cone choices of pioneer motoneurons. We have also examined the establishment of the embryonic muscle fibers and, using intracellular dye fills, have identified cells that are putative muscle pioneers. The muscle fibers of the bodywall have completed their morphogenesis prior to the initiation of synaptic contacts, and owing to the timing of neurite outgrowth from the CNS, synaptogenesis is synchronous at muscle fibers throughout the bodywall. At each muscle fiber the innervating axons make their initial contacts on a characteristic surface domain of the target cell's membrane. Through stereotyped growth cone-mediated trajectories the motoneurons actively establish the basic anatomical features of the mature neuromuscular junction, including the stereotyped, muscle fiber-specific branch anatomy. These events occur without significant process pruning or apparent synapse elimination. Our results suggest that the basic elements of the mature neuromuscular innervation, including the details of the ending trajectory on the target cell's surface, are formed by the precise navigation and presumed recognition by the motoneuron growth cones of muscle membrane surface features.     

Effects of local release of hepatocyte growth factor on peripheral nerve regeneration in acellular nerve grafts

Options for reconstructing peripheral nerve gaps after trauma are limited. The acellular nerve is a new kind of biomaterial used to reconstruct the peripheral nerve defect, but its use could be improved upon. We aimed to investigate the effect of adenoviral transfection with hepatocyte growth factor (HGF) on the functional recovery of transected sciatic nerves repaired by acellular nerve grafting. 30 Rats were divided into three groups (10/group) for autografting and acellular grafting, as well as acellular grafting with adenovirus transfection of HGF (1 × 10⁸ pfu) injected in muscles around the proximal and distal allograft coapation. Sciatic functional index (SFI) was evaluated every 4 weeks to week 16 by measuring rat footprints on walking-track testing. The three groups presented initial complete functional loss, followed by slow but steady recovery, with final similar SFIs. Weight of the gastrocnemius and soleus muscles, histologic and morphometric study and neovascularization in the nerve grafts were evaluated at week 16. Autografting gave the best functional recovery, but HGF-treated acellular grafting gave better recovery than acellular grafting alone. Neovascularization was greater with HGF-treated acellular grafting than with autografting and acellular grafting alone. Axonal regeneration distance of autografting on the 20th postoperative day was the longest in the three groups,while that of acellular grafting alone was the smallest. Acellular nerve grafting may be useful for functional peripheral nerve regeneration, and with human HGF gene transfection may improve on acellular grafting alone in functional recovery.     

Axonal degeneration and focal muscle fiber necrosis in human thallotoxicosis: Histopathological studies of nerve and muscle

Two cases of proven thallium poisoning were studied with special reference to the neuromuscular changes. These cases showed a consistent pattern of symptomatology of peripheral sensorimotor neuropathy, encephalopathy, and alopecia. Light and electron microscopic studies of the sural nerve biopsies exhibited mainly axonal degeneration without concomitant segmental demyelination. The densities of both large and small myelinated fibers were mildly decreased. Biopsied peroneus brevis muscles showed distinct features of focal muscle fiber necrosis which has not been reported before. Muscle fibers with prominent central nucleation and fiber splitting were frequently seen. These findings are compatible with myopathic changes. In spite of the existence of severe axonal degeneration and muscle atrophy on clinical observation, no neurogenic muscle changes were found.     

Quantification of early damage in latissimus dorsi muscle grafts

Acute damage in the latissimus dorsi muscle may account for variable clinical results following dynamic cardiomyoplasty and an ischemic cause has been suggested. Using established techniques, we set out to demonstrate and to quantify the acute muscle damage in a rodent model. The left latissimus dorsi muscle of 5 Sprague–Dawley rats was mobilized on its thoracodorsal vascular pedicle, thus interrupting the regional blood supply to its distal part. The undisturbed contralateral muscle served as a matched control. After 24 hours, the muscle was excised and divided into proximal, middle, and distal thirds. Damage was graded histologically and quantified by nitroblue tetrazolium macrohistochemistry. Both methods of assessment correlated well (r = −0.936; P < 0.001) and demonstrated significant damage, principally in the middle and the distal regions of the ischemic muscles. Therefore, the rodent model appears to be useful for investigating the pathogenesis and prevention of acute ischemic damage in the latissimus dorsi graft under conditions resembling the clinical scenario. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1451–1456, 1998     

Partial correction of an inherited biochemical defect of skeletal muscle by grafts of normal muscle precursor cells

We have attempted to use allografts of normal muscle precursor cells (mpc) to insert donor nuclei, containing a normal genome, into growing or regenerating skeletal muscle fibres of mice with an inherited deficiency of the enzyme phosphorylase kinase (PhK). Analysis of the glucose-6-phosphate isomerase (GPI) isoenzymes of treated muscles showed that myonuclei of donor origin became incorporated into host muscle fibres in 8 of 9 regenerating autografts, but PhK activity was found only in the 3 grafts into which the largest numbers (1-3 x 10(6)) of mpc had been implanted. Following injection of normal mpc into growing PhK-deficient skeletal muscle, mosaic fibres containing myonuclei of donor origin were detected in only 11 of 192 muscles examined from 64 mice, but, of these 11 muscles, 5 contained PhK activity detectable by two separate assays in a further 4 muscles activity was detected by one or other assay.     

Mdx muscle grafts retain the mdx phenotype in normal hosts

Whole muscle grafts were made between mdx and normal mice to investigate whether the mdx myopathic lesion is intrinsic to mdx muscle or is a property of its environment. Grafts were examined between 20 and 101 days. Unequivocal necrotic muscle fibers and/or newly formed basophilic myotubes were noted in 8 of 16 grafts of mdx muscle made in normal hosts but in none of 16 grafts of normal muscle made in mdx hosts. In older grafts, the proportion of centrally nucleated fibers and variability of fiber diameter were both higher in mdx muscle grafted into normal hosts than in normal muscle grafted into either mdx or normal hosts. Analysis of the glucose-6-phosphate isomerase (GPI) isoenzyme content of the grafts indicated that the muscle formed was predominantly of donor origin. These findings provide evidence that the mdx lesion is a primary myopathy rather than secondary to an extramuscular primary lesion.     

Axon outgrowth from grafts of human embryonic spinal cord in the lesioned adult rat spinal cord.

Adult rats with acute partial lesions of their upper thoracic spinal cords were implanted bilaterally with cell suspensions of 6-7 week-old embryonic human spinal cord tissue one segment above or below the lesions. After 14-19 weeks, the animals were perfusion-fixed and the tissue analysed with a light microscope after immunocytochemical labelling with an antiserum recognizing human, but not rat, intermediary neurofilaments. Using this method, extensive efferent projections were demonstrated extending longitudinally from the grafts into the host spinal cord, both in the caudal and rostral directions. Within the white matter tracts, dense bundles of fibres extended for about 3-4 mm, and single fibres were identified up to 10 mm away from the implants. Axonal growth of this length within host white matter has not previously been observed from intraspinal grafts of rat CNS tissue.