Endoneurial Connective Tissue Research Articles

The Effects of Adipose-Derived Mesenchymal Stem Cells and Adipose-Derived Mesenchymal Stem Cell-Originating Exosomes on Nerve Allograft Regeneration: An Experimental Study in Rats.

Nerve regeneration has been the subject of many studies because of its complex mechanism and functional outcome. Mesenchymal stem cells and exosomes are promising factors in regeneration in many areas. Reconstruction of nerve defects is a controversial issue, and nerve allografts are promising alternatives with many advantages. In this study, it is aimed to evaluate the nerve regeneration in cellularized and decellularized nerve allografts and whether it is possible to accelerate this process with adipose-derived mesenchymal stem cells (ad MSC) or ad MSC-originating exosomes. This study was performed with 36 Lewis and 18 Brown Norway isogenic male rats aged 10 to 12 weeks and weighing 300 to 350 g. The Lewis rats were divided into 6 groups. Nerve allografts at a length of 12 mm that were obtained from the Brown Norway rats' proximal portion of both sciatic nerve branching points were coapted as cellularized in group A and decellularized in group B to the sciatic nerve defects of the Lewis rats. Group A received oral tacrolimus (0.2 mg/kg) for 30 days. Perineural saline (A1-B1), ad MSC (A2-B2), or ad MSC-originating exosomes (A3-B3) were applied to these groups. Walking track analysis, pinch-prick test and electromyelography were applied at the 8th and 16th weeks following surgery. Nerves were examined histopathologically at the 16th week. Between cellularized groups, better results were shown in A3 about axon-myelin regeneration/organization (P = 0.001), endoneural connective tissue (P = 0.005), and inflammation (P = 0.004). Better results were shown in the B2 and B3 groups electromyelographicaly about latency period (P = 0.033) and action potential (P = 0.008) at late period, and histomorphologicaly at vascularization (P = 0.012). It is argued that regeneration is accelerated with decellularization of nerve allografts by removing the chondroidin sulfate proteoglycans. The positive effects of stem cells are derived by exosomes without the cell-related disadvantages. In this study, better results were obtained by decellularization and perineural application of ad MSC and/or ad MSC exosome.

Schwann Cell Precursors; Multipotent Glial Cells in Embryonic Nerves.

The cells of the neural crest, often referred to as neural crest stem cells, give rise to a number of sub-lineages, one of which is Schwann cells, the glial cells of peripheral nerves. Crest cells transform to adult Schwann cells through the generation of two well defined intermediate stages, the Schwann cell precursors (SCP) in early embryonic nerves, and immature Schwann cells (iSch) in late embryonic and perinatal nerves. SCP are formed when neural crest cells enter nascent nerves and form intimate relationships with axons, a diagnostic feature of glial cells. This involves large-scale changes in gene expression, including the activation of established glial cell markers. Like early glia in the CNS, radial glia, SCP retain developmental multipotency and contribute to other crest-derived lineages during embryonic development. SCP, as well as closely related cells termed boundary cap cells, and later stages of the Schwann cell lineage have all been implicated as the tumor initiating cell in NF1 associated neurofibromas. iSch are formed from SCP in a process that involves the appearance of additional differentiation markers, autocrine survival circuits, cellular elongation, a formation of endoneurial connective tissue and basal lamina. Finally, in peri- and post-natal nerves, iSch are reversibly induced by axon-associated signals to form the myelin and non-myelin Schwann cells of adult nerves. This review article discusses early Schwann cell development in detail and describes a large number of molecular signaling systems that control glial development in embryonic nerves.

Morphometric analysis of connective tissue sheaths of sural nerve in diabetic and nondiabetic patients.

One of the most common complications of diabetes mellitus is diabetic neuropathy. It may be provoked by metabolic and/or vascular factors, and depending on duration of disease, various layers of nerve may be affected. Our aim was to investigate influence of diabetes on the epineurial, perineurial, and endoneurial connective tissue sheaths. The study included 15 samples of sural nerve divided into three groups: diabetic group, peripheral vascular disease group, and control group. After morphological analysis, morphometric parameters were determined for each case using ImageJ software. Compared to the control group, the diabetic cases had significantly higher perineurial index (P < 0.05) and endoneurial connective tissue percentage (P < 0.01). The diabetic group showed significantly higher epineurial area (P < 0.01), as well as percentage of endoneurial connective tissue (P < 0.01), in relation to the peripheral vascular disease group. It is obvious that hyperglycemia and ischemia present in diabetes lead to substantial changes in connective tissue sheaths of nerve, particularly in peri- and endoneurium. Perineurial thickening and significant endoneurial fibrosis may impair the balance of endoneurial homeostasis and regenerative ability of the nerve fibers. Future investigations should focus on studying the components of extracellular matrix of connective tissue sheaths in diabetic nerves.

Scientific Letter: Sodium valproate for the treatment of mania in a patient with Charcot-Marie-Tooth disease

?? Charcot-Marie-Tooth disease (CMT), also known as Hereditary Sensory Motor Neuropathy (HSMN) is the most common inherited peripheral neuropathy and it can follow autosomal dominant, Xlinked, autosomal recessive and even a sporadic inheritance pattern. 1Very few studies have evaluated psychiatric problems in this disease 2,3 , but there is a 30% lifetime prevalence of psychiatric disorder in patients with CMT. 2 Depression and phobic disorder are commonly occurring psychiatric comorbidities. 3After obtaining informed consent, we report the case of a patient with Charcot-Marie‐Tooth disease presenting with a manic episode and the treatment thereof with sodium valproate. Mr. L, a 28 year old male, presented with a two month history of talkativeness, irritable mood, increased physical activity and disturbed sleep. At the time of presentation, he was noted to be singing religious songs and had grandiose plans for the future. There was an increased physical activity throughout the day without associated fatigue. At times, he would even dance and he frequently cracked jokes with other patients. He had a history of several similar episodes in the past 10 years, almost one per year. In addition to this, he experienced generalized tonic-clonic seizures as a consequence of a head injury he sustained at the age of 14 years. He received antiepileptic medications (initially Phenytoin sodium and later Divalproex sodium) and remained seizure free for 8 years. There is also a history of progressive weakness and atrophy of his limbs, which had initially started in the distal, followed by the proximal aspects of both lower limbs, and later progressed to affect the upper limbs. As a result, he had difficulty in climbing stairs and getting up from a seated position. The patient’s younger sister, who had a similar history of weakness, atrophy and deformity of her limbs, had suffered from several depressive episodes over a period of 8 years. Investigations of patient i.e. haematology and biochemical tests were found to be normal. Magnetic resonance imaging of the patient’s brain as well as visual evoked potential and brainstem auditory evoked response were normal. The nerve conduction studies showed decreased conduction velocity of < 20m/s; with prolonged distal latencies, decreased compound muscle action amplitude and non-recordable sensory nerve axonal potential. Biopsy of the left sural nerve revealed “onion bulb” formation, fibrocystic proliferation, and increased endoneurial connective tissue. After psychiatric evaluation, he was diagnosed as a case of bipolar affective disorder, current episode mania with psychotic symptoms. The diagnosis of Charcot-Marie-Tooth disease was also entertained after consultation with a team of neurologists and psychiatrists. The patient was commenced on sodium valproate 1000mg per day for treatment of mania. Initially, risperidone 4mg was added to control aggression. Over a period of four weeks, his manic symptoms improved significantly and he achieved

Sexual Dimorphism in the Human Vocal Fold Innervation

This study investigated the sexual dimorphism in the recurrent laryngeal nerve (RLN) and thyroarytenoid (TA) muscle, which control the vocal fold. The RLN and TA were bilaterally studied in human specimens obtained from necropsies (seven men and seven women). Analysis of the morphometric parameters showed that the RLN of the men were significantly larger, as shown by the intraperineural area (42.5%) (P=0.006), total number of fibers (38.0%) (P=0.0002), axonal area (34.3%) (P=0.0001), axonal diameter (19.0%) (P=0.0001), and the area of the nerve occupied by myelinated fibers (34.9%) (P=0.001). By contrast, in women, our results showed that the area of the RLN occupied by endoneurial connective tissue was larger (5.7%) (P=0.001). Estimation of the fiber area and shape coefficient showed that the histologic organization of TA is similar in men and women. These results may contribute toward enhancing our understanding about the voice neurobiology.

The border between the central and the peripheral nervous system in the cat cochlear nerve: A light and scanning electron microscopical study

The transition between the central (CNS) and peripheral nervous system (PNS) in cranial and spinal nerve roots, referred to here as the CNS–PNS border, is of relevance to nerve root disorders and factors that affect peripheral-central regeneration. Here, this border is described in the cat cochlear nerve using light microscopical sections, and scanning electron microscopy of the CNS–PNS interfaces exposed by fracture of the nerve either prior to or following critical point drying. The CNS–PNS border represents an abrupt change in type of myelin, supporting elements, and vascularization. Because central myelin is formed by oligodendrocytes and peripheral myelin by Schwann cells, the myelinated fibers are as a rule equipped with a node of Ranvier at the border passage. The border is shallower and smoother in cat cochlear nerve than expected from other nerves, and the borderline nodes are largely in register. The loose endoneurial connective tissue of the PNS compartment is closed at the border by a compact glial membrane, the mantle zone, of the CNS compartment. The mantle zone is penetrated by the nerve fibers, but is otherwise composed of astrocytes and their interwoven processes like the external limiting membrane of the brain surface with which it is continuous. The distal surface of the mantle zone is covered by a fenestrated basal lamina. Only occasional vessels traverse the border. From an anatomical point of view, the border might be expected to be a weak point along the cochlear nerve and thus vulnerable to trauma. In mature animals, the CNS–PNS border presents a barrier to regrowth of regenerating nerve fibers and to invasion of the CNS by Schwann cells. An understanding of this region in the cochlear nerve is therefore relevant to head injuries that lead to hearing loss, to surgery on acoustic Schwannomas, and to the possibility of cochlear nerve regeneration.

Microanatomical structure of the human sciatic nerve

Sciatic nerve is the largest peripheral nerve of the human body. It gives motor and sensitive innervation for the most of lower limb. The aim of the present investigation was revealing his fascicular pattern in relation to microanatomic morphometric characteristics of its connective tissue sheaths. The material consisted of sciatic nerve slices, excised from 17 cadavers of humans aging 8-93 years. After routine histologic processing and light microscopic examination of the preparations, morphometric analysis was performed at magnifications of 40 and 630x. Sciatic nerve showed to be polyfascicular nerve type, with the group pattern of nerve fascicless distribution. The number of fascicless ranged from 27 to 70, whereas the number of fascicless per square millimeter was 1-4. Morphometric and correlation analysis confirmed the significant increase of whole sciatic nerve cross section area, which was associated with the significant increase of its epi- and perineural connective tissue sheaths. Interfascicular sciatic nerve domains of elderly persons contained more adipose tissue. Moreover, already detected loss and degeneration of the large myelinated nerve fibers within fascicles was accompanied by the significant increase of endoneural connective tissue. In conclusion, our study revealed comparative connective tissue enlargement of human sciatic nerve in the course of aging. These phenomena might influence on result of injured nerve's surgical reparations. We interpret this finding as non-specific compensatory phenomenon elicited by loss of thickest myelinated nerve fibers, higher vulnerability of remaining ones, and age-dependent decrease of connective tissue elasticity.

Endurance and Resistance Exercise Training Programs Elicit Specific Effects on Sciatic Nerve Regeneration After Experimental Traumatic Lesion in Rats

Objective. To evaluate the effects of endurance, resistance, and a combination of both types of exercise training on hindlimb motor function recovery and nerve regeneration after experimental sciatic nerve lesion in rats. Methods. Sciatic nerve crush was performed on adult male rats, and after 2 weeks of the nerve lesion, the animals were submitted to endurance, resistance, and a combination of endurance-resistance training programs for 5 weeks. Over the training period, functional recovery was monitored weekly using the Sciatic Functional Index (SFI) and histological and morphometric nerve analyses were used to assess the nerve regeneration at the end of the trainings. Results. The SFI values of the endurance-trained group reached the control values from the first posttraining week and were significantly better than both the resistance-trained group at the first, second, and third posttraining weeks and the concurrent training group at the first posttraining week. At the distal portion of the regenerating sciatic nerve, the endurance-trained group showed a greater degree of the myelinated fiber maturation than the sedentary, resistance-trained, and concurrent training groups. Furthermore, the endurance-trained group showed a smaller percentage area of endoneurial connective tissue and a greater percentage area of myelinated fibers than the sedentary group. Conclusion . These data provide evidence that endurance training improves sciatic nerve regeneration after an experimental traumatic injury and that resistance training or the combination of 2 strategies may delay functional recovery and do not alter sciatic nerve fiber regeneration.

A novel nerve bundle containing thin muscle fibers in the posterior cricoarytenoid muscle of the marmoset

We examined a novel nerve bundle in the posterior cricoarytenoid muscle of the marmoset. This intramuscular nerve bundle contained two thin muscle fibers about 10 microm in diameter, like intrafusal muscle fibers in the muscle spindle. These thin muscle fibers were individually surrounded by nerve bundles consisting of numerous nonmyelinated nerve fibers. Individual nerve axons contained clear synaptic vesicles and large granulated vesicles, being possibly cholinergic (parasympathetic) in nature. These nerve axons were often in contact with the muscle fiber with and without an interposing basal lamina. Two thin muscle fibers gradually terminated in the endoneural connective tissue around myelinated and nonmyelinated nerve fibers during their course. The innervation of thin muscle fibers in the novel nerve bundle is briefly discussed.

Role of N‐cadherin in Schwann cell precursors of growing nerves

In the present paper, we determine the localization and developmental regulation of N-cadherin in embryonic rat nerves and examine the role of N-cadherin in this system. We also identify a major transition in the architecture of embryonic nerves and relating it to N-cadherin expression. We find that in early embryonic nerves, N-cadherin is primarily expressed in Schwann cell precursors. Pronounced expression is seen at distal nerve fronts where these cells associate with growth cones, and the proximal nerve ends, in boundary cap cells. Unexpectedly, N-cadherin is downregulated as precursors generate Schwann cells, coinciding with the time at which most axons make target connections. Therefore, glial N-cadherin expression is essentially restricted to the period of axon outgrowth. We also provide evidence that N-cadherin supports the formation of contacts between Schwann cell precursors and show that these cells are a favorable substrate for axon growth, unlike N-cadherin-negative Schwann cells. Induction of N-cadherin expression in Schwann cells by neuregulin-1 restores their ability to form contacts and support axon growth. Finally, we show that the loss of glial N-cadherin during embryonic nerve development is accompanied by a transformation of nerve architecture, involving the appearance of endoneurial connective tissue space, fibroblasts, Schwann cell basal lamina, and blood vessels. Because N-cadherin is likely to promote the extensive glial contacts typical of the compact embryonic nerve, we suggest that N-cadherin loss at the time of Schwann cell generation allows endoneurial space to appear between the glial cells, a development that eventually permits the extensive interactions between connective tissue and individual axon-Schwann cell units necessary for myelination.

Histopathologic features of the vagus nerve after electrical stimulation in swine.

This paper describes the histological features of the vagus nerve after its stimulation with an electrostimulation system that is being developed for morbid obesity treatment. An electrostimulation system was implanted laparoscopically around the ventral vagal trunk of five Large White female pigs (49.63+/-1.94 kg.). Vagal nerve stimulation was performed by continuous constant voltage current pulses. Thoracic samples of both ventral and dorsal vagal trunks were obtained thoracoscopically one month after implantation. Animals were sacrificed one month after thoracoscopic vaguectomy. Tissue samples were then harvested from the vagal nerve at the implantation site, 1cm cranial to it, thoracic portion of ventral and dorsal vagal trunks, sub-diaphragmatic dorsal vagal trunk, left and right vagus nerves. Specimens were analysed with light microscope. The severity of the lesions was graded from 0 to 4 (0: no lesion, 1: mild, 2: moderate, 3: severe and 4: extremely severe), taking into account fibrosis, vascularization, necrosis, fiber degeneration and inflammation. Electrode implantation resulted in thickened epineurium and endoneural connective tissue. The greatest lesion score was evidenced at the leads implantation site in the ventral vagal trunk, followed by, in order of decreasing lesion severity, left vagus nerve, thoracic portion of ventral vagal trunk, subdiaphragmatic dorsal vagal trunk, thoracic portion of dorsal vagal trunk and right vagus nerve. The stimulation device used in this study caused connective tissue growth, greatest in the samples located closer to the implantation site. However, there was no sign of altered vascularization in any studied specimen.

Neuromuscular function of the latissimus dorsi muscle in goats after dynamic cardiomyoplasty.

Skeletal muscle deterioration is emerging as a limitation to long-term cardiac assist by dynamic cardiomyoplasty. Chronic electrical stimulation of in situ skeletal muscle showed that ischemia, decreased muscle preload, muscle overuse, and chronic electrical stimulation are factors for muscle deterioration. Transposition around the heart has been associated with signs of muscle denervation after chronic electrical stimulation. To evaluate latissimus dorsi muscle neuromuscular function after longterm dynamic cardiomyoplasty, we performed neuromuscular functional analysis and histology on the latissimus dorsi muscle and thoracodorsal nerve of six normal goats and six goats after 6 months of dynamic cardiomyoplasty. Electromyographic analysis showed positive sharp waves and fibrillation potentials in the latissimus dorsi of three goats from the dynamic cardiomyoplasty group. Conduction velocity of the thoracodorsal nerve of goats from the dynamic cardiomyoplasty group (58.32+/-9.80 m/s) was reduced compared to the goats from the control group (71.48+/-5.71 m/s, P = 0.02). Histologic changes in skeletal muscle were compatible with denervation. Loss of myelin sheaths, collapse of endoneurial connective tissue, and solitary foci of axonophagia and myelinophagia further documented severe injury to the thoracodorsal nerve in goats from the dynamic cardiomyoplasty group. The latissimus dorsi muscle wrap was denervated after long-term dynamic cardiomyoplasty. Traction on the neurovascular pedicle at each contraction of the transposed muscle may induce afferent axonal injury of the thoracodorsal nerve resulting in diminished muscular function.

Extracellular fluid pathway inside the facial nerve fascicles.

The extracellular fluid pathway in the facial nerve and the diffusion of a tracer from the facial nerve to other cranial nerves was examined in the rabbit. Sodium fluorescein solution was injected into either the facial nerve fascicles or the epineurial connective tissue as a tracer at the stylomastoid foramen and then localized by fluorescence microscopy. In the facial nerve, fluorescence was observed in the endoneurium and external nerve sheath (epineurium and perineurium) through the geniculate ganglion following injection into the nerve fascicles. The vestibular, trigeminal, and glossopharyngeal ganglia also showed fluorescence on the injection side in ganglion cells and intercellular connective tissues. The results suggested that the endoneurial connective tissue constitutes a diffusion pathway inside the facial nerve fascicles and that the extracellular fluid pathway from the facial nerve to these cranial ganglia may be related to the neural spread of inflammation or neoplastic metastasis.

Vascular permeability to sodium fluorescein in the rabbit cranial nerve root: possible correlation with normal cranial nerve enhancement on gadolinium-enhanced magnetic resonance imaging.

Vascular permeability in cranial nerve roots was examined after intravenous injection of sodium fluorescein in the adult rabbit. Fluorescence was observed in the distal nerves through the following portions: intracavernous portion of the oculomotor nerve, distal internal auditory canal segment of the facial nerve, and ganglionic portions of the trigeminal, glossopharyngeal and vagus nerves. In the acoustic nerve, the vestibular ganglion showed fluorescence. No fluorescence was observed in the olfactory or optic nerves. During in vivo gadolinium-enhanced magnetic resonance imaging (Gd-MRI) of two separate animals, trigeminal nerve enhancement was observed in the region showing fluorescence. Histologically, intense fluorescence was observed in ganglia and external nerve sheaths of the cranial nerves showing macroscopic fluorescence. A slight fluorescence was also seen in endoneurial connective tissue but not observed within the nerve fibers. The results of this study suggest that the physiological enhancement of human cranial nerves seen on Gd-MRI may correlate with vascular permeability.

Effects of intraoperative hyperthermia on canine sciatic nerve: histopathologic and morphometric studies.

Failure to achieve local control in the treatment of pelvic and retroperitoneal tumours results in a high rate of recurrences. The objective of intraoperative hyperthermia (IOHT) is to enhance the effect of intraoperative radiation therapy and to increase local tumour control. The tolerance of peripheral nerves to heat may limit the heat dose that can be applied to tumours. Histopathologic and histomorphometric changes of canine sciatic nerve after 60-min IOHT were studied in three groups of five dogs each for temperatures of 43, 44 and 45 degrees C. IOHT was performed using a water-circulating hyperthermia device with a multichannel thermometry system on surgically exposed sciatic nerve. Histopathologic and histomorphometric studies were done immediately, 3 weeks and 12 months after IOHT. Histologic changes observed immediately after treatment were minimal but at 3 weeks following 60-min 45 degrees C IOHT both axon and myelin loss and an increase in endoneurial fibrous tissue were observed. Twelve months after treatment a statistically significant decrease in axon, myelin and small vessel percentages as well as an increase in endoneurial and epineural connective tissue were observed for dog treated to 45 degrees C. Dog treated to 44 degrees C for 60 min had similar statistically significant but less severe changes. Twelve months after 43 degrees C IOHT for 60 min, nerve fibres appeared normal and endoneurial connective tissue was only increased mildly around small and medium-sized vessels. These results suggest that temperatures to the peripheral nerve > 44 degrees C for 60 min are likely to cause significant histopathologic changes that can be found 12 months after treatment. A hypothesis of the mechanism of heat injury to peripheral nerves was developed.

Localization of protein kinase C in human skeletal muscle.

The immunolocalization of protein kinase C (PKC) isozymes alpha, beta I and beta II, was investigated in human skeletal muscle. All three isozymes were present on the muscle fiber surface membrane and within the muscle fibers. The alpha-isozyme was most clearly delineated on the surface membrane of the muscle fiber and on small blood vessels in the connective tissue. The axons of myelinated intramuscular nerves stained intensely for the beta I isozyme, whereas the endoneurial connective tissue reacted more strongly for the alpha- and beta II-isozymes. PKC isozymes may regulate intracellular signal transduction in human skeletal muscle, as in the other tissues, but their exact role in muscle remains unknown.

Progression of regeneration after nerve infarction

We performed morphologic studies on the progression of regeneration in cat hind limb nerves after acute ischemic injury. None of the damaged nerve trunks showed a major increase in endoneurial connective tissue. Despite this fact, regeneration of nerve with transfascicular infarct was far from complete even 16 months after injury as manifested by a striking increase in the small myelinated fibers (MF) number and decrease in large MF number. Restoration of infarcted nerves was less complete than that previously reported after a nerve crush. Changes in the necrotic nerve segment and difficulty in making target contact with muscle and other tissues damaged by ischemia may be limiting factors in the regeneration of infarcted nerves.

Immunohistochemical findings in the vestibular ganglion from a patient with Meni�re's disease

Immunofluorescent staining techniques were performed on a series of cryostat sections of the vestibular ganglion taken during ganglionectomy from a patient with Menière's disease. The direct technique using FITC-labelled antiserum proved the presence of immunoglobulins in the patient's blood vessels and endoneural connective tissue. Preincubation with unlabelled antiserum blocked this reaction. An additional positive reaction of ganglion cells was demonstrated by incubating tissue with the patient's serum. These findings prove antibodies in the patient's serum against the autologous ganglion cells. The vestibular ganglion from a patient with dizziness following a skull base fracture served as a control specimen. No autoimmune reaction was found in the ganglion cells when incubation was carried out with the patient's serum. A positive reaction in the blood vessels and connective tissue was less pronounced. The findings of the present study underline the occurrence of immunological reactions in the vestibular ganglion of patients with Menière's disease. A subsequent degeneration of ganglion cells could provoke clinical Menière's attacks.

Histologic and physiologic evaluation of electrically stimulated peripheral nerve: Considerations for the selection of parameters

Helical electrodes were implanted around the left and right common peroneal nerves of cats. Three weeks after implantation one nerve was stimulated for 4-16 hours using charge-balanced, biphasic, constant current pulses. Compound action potentials (CAP) evoked by the stimulus were recorded from over the cauda equina before, during and after the stimulation. Light and electron microscopy evaluations were conducted at various times following the stimulation. The mere presence of the electrode invariably resulted in thickened epineurium and in some cases increased peripheral endoneurial connective tissue beneath the electrodes. Physiologic changes during stimulation included elevation of the electrical threshold of the large axons in the nerve. This was reversed within one week after stimulation at a frequency of 20 Hz, but often was not reversed following stimulation at 50-100 Hz. Continuous stimulation at 50 Hz for 8-16 hours at 400 microA or more resulted in neural damage characterized by endoneurial edema beginning within 48 hours after stimulation, and early axonal degeneration (EAD) of the large myelinated fibers, beginning by 1 week after stimulation. Neural damage due to electrical stimulation was decreased or abolished by reduction of the duration of stimulation, by stimulating at 20 Hz (vs. 50 Hz) or by use of an intermittent duty cycle. These results demonstrate that axons in peripheral nerves can be irreversely damaged by 8-16 hours of continuous stimulation at 50 Hz. However, the extent to which these axons may subsequently regenerate is uncertain. Therefore, protocols for functional electrical stimulation in human patients probably should be evaluated individually in animal studies.

Ultrastructural findings on human Scarpa's ganglion.

The morphology of human Scarpa's ganglion from two surgically removed specimens as well as from four autopsy preparations from patients without clinical evidence of vestibular dysfunction was investigated. Ganglion cell circumference varied between 45 and 160 microns. More than half of the nerve cells ranged between 90 and 110 microns. The arrangement of ganglion cells, nerve fibres and endoneural connective tissue appeared better preserved in autopsy preparation than in biopsy specimens. Electron microscopy revealed that in half of the investigated specimens, neuroglial tissue was present as far distal as the vestibular ganglion. Almost all ganglion cells were surrounded by one or several layers of satellite cells, and did not reveal myelination. From the present study we cannot predict if neuronal function in human beings differs from that in other animals, although morphological differences do exist.