Graded inhibition of retrograde axonal transport by compression of rabbit vagus nerve

Quantitative mass spectrometry analysis of the injured proximal and distal human digital nerve ends

Introduction

Proteomic analysis of injured human peripheral nerves, particularly focusing on events occurring in the proximal and distal nerve ends, remains relatively underexplored. This study aimed to investigate the molecular patterns underlying a digital nerve injury, focusing on differences in protein expression between the proximal and distal nerve ends.

Methods

A total of 26 human injured digital nerve samples (24 men; 2 women; median age 47 [30-66] years), harvested during primary nerve repair within 48 h post-injury from proximal and distal nerve ends, were analyzed using mass spectrometry.

Results

A total of 3,914 proteins were identified, with 127 proteins showing significant differences in abundance between the proximal and the distal nerve ends. The downregulation of proteins in the distal nerve end was associated with synaptic transmission, autophagy, neurotransmitter regulation, cell adhesion and migration. Conversely, proteins upregulated in the distal nerve end were implicated in cellular stress response, neuromuscular junction stability and muscle contraction, neuronal excitability and neurotransmitter release, synaptic vesicle recycling and axon guidance and angiogenesis.

Discussion

Investigation of proteins, with functional annotations analysis, in proximal and the distal ends of human injured digital nerves, revealed dynamic cellular responses aimed at promoting tissue degeneration and restoration, while suppressing non-essential processes.

Carpal tunnel syndrome

Carpal tunnel syndrome (CTS) is the most common nerve entrapment disorder worldwide. The epidemiology and risk factors, including family burden, for developing CTS are multi-factorial. Despite much research, its intricate pathophysiological mechanism(s) are not fully understood. An underlying subclinical neuropathy may indicate an increased susceptibility to developing CTS. Although surgery is often performed for CTS, clear international guidelines to indicate when to perform non-surgical or surgical treatment, based on stage and severity of CTS, remain to be elucidated. Neurophysiological examination, using electrophysiology or ultrasonography, performed in certain circumstances, should correlate with the history and findings in clinical examination of the person with CTS. History and clinical examination are particularly relevant globally owing to lack of other equipment. Various instruments are used to assess CTS and treatment outcomes as well as the effect of the disorder on quality of life. The surgical treatment options of CTS - open or endoscopic - offer an effective solution to mitigate functional impairments and pain. However, there are risks of post-operative persistent or recurrent symptoms, requiring meticulous diagnostic re-evaluation before any additional surgery. Health-care professionals should have increased awareness about CTS and all its implications. Future considerations of CTS include use of linked national registries to understand risk factors, explore possible screening methods, and evaluate diagnosis and treatment with a broader perspective beyond surgery, including psychological well-being.

The Unpredictable Ulnar Nerve-Ulnar Nerve Entrapment from Anatomical, Pathophysiological, and Biopsychosocial Aspects

Peripheral nerves consist of delicate structures, including a rich microvascular system, that protect and nourish axons and associated Schwann cells. Nerves are sensitive to internal and external trauma, such as compression and stretching. Ulnar nerve entrapment, the second most prevalent nerve entrapment disorder after carpal tunnel syndrome, appears frequently at the elbow. Although often idiopathic, known risk factors, including obesity, smoking, diabetes, and vibration exposure, occur. It exists in all adult ages (mean age 40-50 years), but seldom affects individuals in their adolescence or younger. The patient population is heterogeneous with great co-morbidity, including other nerve entrapment disorders. Typical early symptoms are paresthesia and numbness in the ulnar fingers, followed by decreased sensory function and muscle weakness. Pre- and postoperative neuropathic pain is relatively common, independent of other symptom severity, with a risk for serious consequences. A multimodal treatment strategy is necessary. Mild to moderate symptoms are usually treated conservatively, while surgery is an option when conservative treatment fails or in severe cases. The decision to perform surgery might be difficult, and the outcome is unpredictable with the risk of complications. There is no consensus on the choice of surgical method, but simple decompression is relatively effective with a lower complication rate than transposition.

T2-weighted MRI defines critical compression in the distal carpal tunnel that is relieved after decompressive surgery

Introduction

Despite Carpal Tunnel Syndrome (CTS) being the most common entrapment neuropathy, its pathophysiology remains debated. Sub-synovial connective tissues (SSCT) within the carpal tunnel are thought to play a role but are poorly characterised. MRI analysis offers potentially novel insights into SSCT characteristics.

Methods

A pilot study of T2-weighted MRI was performed in healthy controls (n=7), and in CTS patients (n=16) pre- and 6 months post-surgical decompression. Image analysis was performed to quantify SSCT cross-sectional area, SSCT signal intensity ratio, and wrist index (depth/width) at distal, middle and proximal wrist landmarks.

Results

Median SSCT signal intensity was lower in the distal carpal tunnel of CTS patients pre-operatively (0.96) compared to controls (1.13; P = 0.008) and normalised post-operatively (1.13, P = 0.001). Median wrist index was also lower in CTS patients pre-operatively (0.60) compared to controls (0.67, P = 0.022), and again normalised post-operatively (0.74, P =0.001). This was attributed to changes in carpal depth in the antero-posterior axis with decompression surgery.

Conclusion

This pilot study successfully demonstrated MRI assessment of SSCT in patients with CTS. The decreased SSCT signal intensities suggest predominant changes at the distal tunnel, potentially indicating reduced SSCT perfusion pre-surgery which normalised post-surgery. Our preliminary findings merit further investigation in a larger cohort.

State of the Art and Advances in Peripheral Nerve Surgery

This review is intended to describe and actualize the basic knowledge of the three basic entities that affect the peripheral nerve system and can be treated by surgery: nerve trauma, chronic nerve compressions, and tumors.Regarding trauma, emphasis is given on the timing of surgery, given the fact that the moment in which the surgery is performed and the employed microsurgical reconstruction technique are the most important factors in the final result. Open lesions with associated nerve injury should be managed with an early exploration carried out before 7 days. Closed injuries are usually deferred, with few exceptions, from 3 to 6 months after the trauma.In turn, chronic compressions require an appropriate clinical, neurophysiological, and imaging diagnosis. Isolated sensory symptoms can be treated actively though without surgery: motor signs like atrophy should be regarded as a sign for immediate surgery, as a deferred treatment might cause an irreversible nerve and muscular damage. Endoscopic approaches are a valuable tool for treatment in selected neuropathies.Finally, nerve tumors demand a thorough preoperative evaluation, as benign tumors are treated in a very different way when compared to malignant lesions. Benign tumors can usually be safely and completely resected without sacrificing the nerve of origin. When malignancy is confirmed, extensive resection to optimize patient survival is the main objective, potentially at the expense of neurological function. This may then be followed by adjuvant radiation and/or chemotherapy, depending on the nature of the tumor and the completeness of resection attained. The role of nerve biopsy remains controversial, and several modern diagnostic techniques might be helpful.

[Entrapment neuropathies: a contemporary approach to pathophysiology, clinical assessment, and management : German version]

Entrapment neuropathies such as carpal tunnel syndrome, radiculopathies, or radicular pain are the most common peripheral neuropathies and also the most common cause for neuropathic pain. Despite their high prevalence, they often remain challenging to diagnose and manage in a clinical setting. Summarising the evidence from both preclinical and clinical studies, this review provides an update on the aetiology and pathophysiology of entrapment neuropathies. Potenzial mechanisms are put in perspective with clinical findings. The contemporary assessment is discussed and diagnostic pitfalls highlighted. The evidence for the noninvasive and surgical management of common entrapment neuropathies is summarised and future areas of research are identified.

Entrapment neuropathies: a contemporary approach to pathophysiology, clinical assessment, and management

Entrapment neuropathies such as carpal tunnel syndrome, radiculopathies, or radicular pain are the most common peripheral neuropathies and also the most common cause for neuropathic pain. Despite their high prevalence, they often remain challenging to diagnose and manage in a clinical setting. Summarising the evidence from both preclinical and clinical studies, this review provides an update on the aetiology and pathophysiology of entrapment neuropathies. Potential mechanisms are put in perspective with clinical findings. The contemporary assessment is discussed and diagnostic pitfalls highlighted. The evidence for the noninvasive and surgical management of common entrapment neuropathies is summarised and future areas of research are identified.

Patient Characteristics in Ulnar Nerve Compression at the Elbow at a Tertiary Referral Hospital and Predictive Factors for Outcomes of Simple Decompression versus Subcutaneous Transposition of the Ulnar Nerve

Patient characteristics and predictive factors for outcomes were analysed in 202 cases undergoing simple decompression, primary subcutaneous transposition, or secondary subcutaneous transposition for ulnar nerve compression at the elbow at a tertiary referral hospital. Data from medical charts and a survey were evaluated. The mean patient age was 49 years with revision surgery cases being significantly younger. Sixty-one percent of cases were female, and 31% were smokers. The comorbidity was extensive, including other nerve compression lesions as well as neck and shoulder problems. Overall, 53% reported being pleased with the result of surgery and 57% of the cases rated function as better or completely recovered after surgery. The median postoperative DASH (Disabilities of the Arm, Shoulder and Hand) score was 26 (IQR 11–49), which is in accordance with unpublished national data. No significant differences in DASH scores were found between surgical groups, but a higher preoperative McGowan grade was significantly associated with a poorer postoperative DASH score. Women scored greater disability postoperatively than men. There was a significantly increased risk of complications, which was doubled for smokers, following primary and secondary transposition compared to simple decompression. Surgical cases with ulnar nerve compression treated at a tertiary referral hospital constitute a heterogeneous group with great comorbidity and frequent concomitant nerve compression lesions. We suggest simple decompression as the procedure of first choice. Transposition can be used in selected cases or when simple decompression fails. All patients should be strongly recommended to stop smoking considering the remarkably increased risk for complications among smokers.

A genome-wide association analysis identifies 16 novel susceptibility loci for carpal tunnel syndrome

Carpal tunnel syndrome (CTS) is a common and disabling condition of the hand caused by entrapment of the median nerve at the level of the wrist. It is the commonest entrapment neuropathy, with estimates of prevalence ranging between 5-10%. Here, we undertake a genome-wide association study (GWAS) of an entrapment neuropathy, using 12,312 CTS cases and 389,344 controls identified in UK Biobank. We discover 16 susceptibility loci for CTS with p < 5 × 10^-8. We identify likely causal genes in the pathogenesis of CTS, including ADAMTS17, ADAMTS10 and EFEMP1, and using RNA sequencing demonstrate expression of these genes in surgically resected tenosynovium from CTS patients. We perform Mendelian randomisation and demonstrate a causal relationship between short stature and higher risk of CTS. We suggest that variants within genes implicated in growth and extracellular matrix architecture contribute to the genetic predisposition to CTS by altering the environment through which the median nerve transits.

Multifocal Neuropathy: Expanding the Scope of Double Crush Syndrome

Double crush syndrome (DCS), as it is classically defined, is a clinical condition composed of neurological dysfunction due to compressive pathology at multiple sites along a single peripheral nerve. The traditional definition of DCS is narrow in scope because many systemic pathologic processes, such as diabetes mellitus, drug-induced neuropathy, vascular disease and autoimmune neuronal damage, can have deleterious effects on nerve function. Multifocal neuropathy is a more appropriate term describing the multiple etiologies (including compressive lesions) that may synergistically contribute to nerve dysfunction and clinical symptoms. This paper examines the history of DCS and multifocal neuropathy, including the epidemiology and pathophysiology in addition to principles of evaluation and management.

Effects of simulated neural mobilization on fluid movement in cadaveric peripheral nerve sections: implications for the treatment of neuropathic pain and dysfunction

BACKGROUND AND PURPOSE

Neural mobilization techniques are used clinically to treat neuropathic pain and dysfunction. While selected studies report efficacy of these techniques, the mechanisms of benefit are speculative. The purpose of this study was to evaluate the effects of in vitro simulated stretch/relax neural mobilization cycles on fluid dispersion within sections of unembalmed cadaveric peripheral nerve tissue.

METHODS

Bilateral sciatic nerve sections were harvested from six cadavers. Matched pairs of nerve sections were secured in a tissue tester and injected with a plasma/Toluidine Blue dye solution. Once the initial dye spread stabilized, the experimental nerve sections underwent 25 stretch/relaxation cycles (e.g. simulated neural mobilization) produced by a mechanical tissue tester. Post-test dye spread measurements were compared to pre-test measurements as well as control findings (no simulated mobilization). Data were analyzed using paired t-tests.

RESULTS

Individual dye spread measurements were reliable [ICC(3,1) = 0·99]. The post-test intraneural fluid movement (dye spread) in the experimental section increased significantly with simulated neural mobilization compared to pre-test measurements (3·2±2·1 mm; P = 0·015) and control measurements (3·3±2·7 mm; P = 0·013).

CONCLUSION

Repetitive simulated neural mobilization, incorporating stretch/relax cycles, of excised cadaveric peripheral nerve tissue produced an increase in intraneural fluid dispersion. Neural mobilization may alter nerve tissue environment, promoting improved function and nerve health, by dispersing tissue fluid and diminishing intraneural swelling and/or pressure.

Radial nerve mobilization reduces lateral elbow pain and provides short-term relief in computer users

Study Design :

Prospective Experimental Study.

Background :

Computer users may be at risk of lateral elbow pain. It is theorized that adverse mechanical tension can arise in the radial nerve with sustained keyboarding due to sustained static work of the elbow extensor muscles. Neural mobilization has been suggested as a potential treatment.

Purpose :

The purpose of this study was to evaluate the effect of neural mobilization of the radial nerve on a single occasion in terms of its ability to reduce lateral elbow pain.

Methods and Analysis :

Forty-one computer professionals (Mean age 46.7; S.D. 12.77), who had experienced lateral elbow pain for a mean of 2.87 months were recruited. The participants rated the pain using a verbal, numeric rating scale (NRS). Radial nerve tension was tested using the Upper limb Tension Test (ULTT) for radial nerve in both upper extremities. The radial nerve was mobilized using a series of 8 oscillations and repeated 3 times with a one minute rest in between. The NRS and ULLT were repeated after treatment and the scores compared using a paired t-test by the first author.

Results :

The mean NRS scores decreased significantly from 5.7 (1.1) to 3.8 (1.4) (p<0.000; t value=8.07).

Conclusion :

A single session of 3 neural mobilization resulted in a reduction of pain in computer users with lateral elbow pain. A long-term randomized trial is needed to determine the effects sustained over-time.

The effects of neurodynamic mobilization on fluid dispersion within the tibial nerve at the ankle: an unembalmed cadaveric study

OBJECTIVE

To evaluate the effects of neurodynamic mobilization on the fluid dynamics of the tibial nerve in cadavers.

BACKGROUND

Evidence showing patients benefit from neural mobilization is limited. Mechanisms responsible for changes in patient symptoms are unclear.

METHODS

Bilateral lower limbs of six unembalmed cadavers (n = 12) were randomized into matched pairs and dissected to expose the tibial nerve proximal to the ankle. Dye composed of Toulidine blue and plasma was injected into the nerve. The longitudinal dye spread was measured pre- and post-mobilization. The experimental group received the intervention consisting of 30 repetitions of passive ankle range of motion over the course of 1 minute. The matched control limb received no mobilization. Data were analysed using a 2×2 repeated measures ANOVA with subsequent t-tests for pairwise comparisons.

RESULTS

Mean dye spread was 23.8±10.2 mm, a change of 5.4±4.7% in the experimental limb as compared to 20.7±6.0 mm, a change of -1.5±3.9% in the control limb. The ANOVA was significant (P⩽0.02) for interaction between group (experimental/control) and time (pre-mobilization/post-mobilization). t-test results were significant between pre- and post-mobilization of the experimental leg (P = 0.01), and between control and experimental limbs post-mobilization (P⩽0.02).

CONCLUSION

Passive neural mobilization induces dispersion of intraneural fluid. This may be clinically significant in the presence of intraneural edema found in pathological nerves such as those found in compression syndromes.

Changes in NGF and NT-3 protein species in the superior cervical ganglion following axotomy of postganglionic axons

Mature sympathetic neurons in the superior cervical ganglion (SCG) are regulated by target-derived neurotrophins such as nerve growth factor (NGF) and neurotrophin-3 (NT-3). High molecular weight NGF species and mature NT-3 are the predominant NGF and NT-3 protein isoforms in the SCG, yet it is unknown whether the presence of these species is dependent on intact connection with the target tissues. In an attempt to determine the role of peripheral targets in regulating the neurotrophin species found in the SCG, we investigated the NGF and NT-3 protein species present in the SCG following axotomy (transection) or injury of the post-ganglionic axons. Following a 7 day axotomy, the 22-24 kDa NGF species and the mature 14 kDa NT-3 species in the SCG were significantly reduced by 99% and 66% respectively, suggesting that intact connection with the target is necessary for the expression of these protein species. As expected, tyrosine hydroxylase (TH) protein in the SCG was significantly reduced by 80% at 7 days following axotomy. In order to distinguish between the effects of injury and loss of target connectivity, the SCG was examined following compression injury to the post-ganglionic nerves. Following injury, no reduction in the 22-24 kDa NGF or 14 kDa mature NT-3 species was observed in the SCG. TH protein was slightly, yet significantly, decreased in the SCG following injury. The findings of this study suggest that the presence of the 22-24 kDa NGF and mature 14 kDa NT-3 species in the SCG is dependent on connection with peripheral targets and may influence, at least in part, TH protein expression in adult sympathetic neurons.

Structure and biomechanics of peripheral nerves: nerve responses to physical stresses and implications for physical therapist practice

The structural organization of peripheral nerves enables them to function while tolerating and adapting to stresses placed upon them by postures and movements of the trunk, head, and limbs. They are exposed to combinations of tensile, shear, and compressive stresses that result in nerve excursion, strain, and transverse contraction. The purpose of this appraisal is to review the structural and biomechanical modifications seen in peripheral nerves exposed to various levels of physical stress. We have followed the primary tenet of the Physical Stress Theory presented by Mueller and Maluf (2002), specifically, that the level of physical stress placed upon biological tissue determines the adaptive response of the tissue. A thorough understanding of the biomechanical properties of normal and injured nerves and the stresses placed upon them in daily activities will help guide physical therapists in making diagnoses and decisions regarding interventions.

Changes in expression of PACAP in rat sensory neurons in response to sciatic nerve compression

In the present study, expression of pituitary adenylate cyclase-activating polypeptide (PACAP) in rat dorsal root ganglion (DRG) neurons and sciatic nerve following experimental sciatic nerve compression was studied with the use of quantitative immunohistochemistry and in situ hybridization. Previously, we have investigated changes in PACAP expression after nerve transection and, here, the far more frequently encountered condition of nerve compression injury is examined. Nerve compression was performed unilaterally on the rat sciatic nerve, at mid-thigh level, by application of a narrow silicone tube around the nerve for 3, 7, 14 or 28 days, respectively. We detect a statistically significant upregulation in the number and density of PACAP mRNA expression in both small and large DRG neurons in response to nerve compression. An increased number of PACAP-immunoreactive neurons is also found in the ipsilateral DRG. In addition, PACAP immunoreactivity is observed in the compressed sciatic nerve segment and adjacent nerve tissue after nerve compression. The present findings can be compared with previous studies where we have shown that PACAP expression is upregulated in DRG; in response to peripheral inflammation (primarily in small-medium neurons), and after axotomy (dramatic upregulation in medium-large neurons). In view of the recent findings of an increased PACAP expression in DRG after nerve compression, as well as the previous findings of a modulation of PACAP expression in response to axotomy and inflammation, it is likely that PACAP is also involved in the modulation of the response to peripheral nerve compression.

MR imaging of entrapment neuropathies at the elbow

MR imaging has a valuable role in the evaluation of compressive neuropathies at the elbow. Specific MR signs in association with clinical findings can supply an accurate diagnosis. A review of normal anatomy, clinical features, and MR assessment of nerve entrapment syndromes at the elbow is presented.

MR myelography of the spine and MR peripheral nerve imaging

MRM is a useful imaging technique that can be incorporated into routine spine MR imaging protocols without a significant increase in imaging time or patient discomfort. When combined with high quality, sequential (no inter-slice gap), axial images of the spine, the authors have found that it decreases the surgeon's need for conventional contrast enhanced myelography by showing the etiology of compression and degree of compressive effect, particularly in cases of degenerative spine disease. In select cases where greater bone detail is desired, an unenhanced CT is often sufficient. MRPNI also is a useful imaging technique that is primarily used in the evaluation of patients with radicular symptoms not explained by spine MR imaging findings. Selective MRPNI is performed based on clinical and electrodiagnostic results to evaluate extra-spinal causes of peripheral neuropathy. It is easily performed using phase array coils and is primarily used to detect traumatic axonal disruption and compressive neuropathy.

Yasargil-Phynox aneurysm clip: a simple and reliable device for making a peripheral nerve injury

A great number of devices were used to make a peripheral nerve injury. In the scientific literature, experimental crush injuries have been usually created using forceps or hemostatic forceps, neither of which allows quantitative or standard application of compression. Therefore, we used a Yasargil-Phynox aneurysm clip to make a reliable and standardized peripheral nerve injury. The advantages and disadvantages of this clip were discussed. In particular, we think that standardization of the compression is necessary to compare interlaboratory results.

Experimental nerve compression and upregulation of CPON in DRG

Expression of C-terminal flanking peptide of neuropeptide Y (CPON) in DRG and cell proliferation (incorporation of BrdU) in sciatic nerve of rats following chronic nerve compression (silicone tubes with different internal diameters) was studied by immunocytochemistry. An increased number of CPON-positive neurons and cells incorporating BrdU was induced on the compressed side, most pronounced when a tight tube was used, while no cells expressed CPON or BrdU in intact nerves. The increase was transient and declined with time. Nerve compression induces transient cell proliferation in the nerve and expression of CPON in nerve cell bodies, but this is of a lesser magnitude than those following nerve transection.

Evaluation of an acute nerve compression injury with magnetic resonance neurography

Although magnetic resonance (MR) imaging is performed routinely, current techniques offer little for evaluation of the peripheral nervous system. An animal model was developed to evaluate the appearance and geographic changes associated with an acute nerve compression injury by MR neurography. Several measurements of signal intensity were made for the contralateral noninjured nerve and each sciatic nerve proximal to the site of compression (PN), at the site of compression (CN), and distal to the site of compression (DN) injury. Mean (+/-SEM) values of the MR nerve/muscle signal intensity ratio were 2.24 +/- 0.08 for normal nerve, 2.29 +/- 0.12 for PN, 3.11 +/- 0.31 for CN, and 4.33 +/- 0.47 for DN. There was a statistically significant geographic variation of nerve/muscle signal intensity ratios along the course of the nerve relative to the site of injury that MR neurography could detect. Magnetic resonance neurography may have significant potential to provide more information about problems such as brachial plexus injuries and peripheral nerve compression.

C-terminal flanking peptide of neuropeptide Y in DRG following nerve compression

The C-terminal flanking peptide of neuropeptide Y (CPON) was studied in dorsal root ganglia (DRG) by immunocytochemistry after different recovery periods (3, 6,14 and 28 days) following tourniquet compression of the rat hindlimb (sciatic nerve; 150 or 300 mmHg; 2 h). Compression induced a transient increase in the number of CPON-positive DRG-neurons (the contralateral uninjured side was devoid of CPON-positive cells). The compression-induced increase in CPON was less than that observed in separate rats subjected to sciatic nerve transection. The results show that compression induces regenerative changes in peripheral neurons and that such an injury of the nerve trunk is not limited to the site of the compression but results in the activation of the entire neuron.

Assessing Adverse Neural Tension in Athletes

Sports medicine assessment and treatment techniques are ever developing and becoming more holistic. Traditional musculoskeletal assessment is changing to incorporate neural tissue pathology. Neural tension tests assess the mobility of neural tissue in the extremities and spinal canal. Positive adverse neural tension tests suggest poor mobility of neural tissue. Athletes with adverse neural tension often present with pain and decreased range of motion. These disorders can occur individually or can be associated with sports injuries. Ankle sprains, hamstring strains, tennis elbow, and thoracic outlet syndrome are some conditions that respond well to treatment of adverse neural tension. Reports of improved treatment outcomes following neural tension assessment and treatment suggest that adverse neural tension should be considered as a possible source of pain and dysfunction. This paper outlines concepts necessary to understand adverse neural tension including neuroanatomy, pathology, assessment techniques, and common sports injuries that may have an adverse neural tension component.

Transient damage to the axonal transport system without Wallerian degeneration by acute nerve compression

The aim of this study was to examine whether acute nerve compression damages an axonal transport system based on microtubules and how the fibers recover after the compression. A 5-mm segment of the tibial nerve of male wistar rat was compressed with a specially designed clip. Functional recovery was assessed using Tibial Nerve Functional Index (TFI). Rats were sacrificed each day from Day 0 to Day 2 and every 2 days between Day 4 and Day 10. For immunohistochemical analysis of the tibial nerve, the proximal uncompressed, the middle compressed, and the distal uncompressed segments of each section were assessed under immunofluoroscent microscopy for anti-dynein, anti-tubulin, and anti-neurofilament antibodies staining. In rats whose tibial nerve was compressed by 25 g/mm2 of pressure for 5 min, staining of dynein and mirotubules in the compressed portion were obscure on Days 4-8, suggesting that the microtubules based axonal transport system was temporarily damaged, while neurofilaments were retained. In contrast, in the distal portion, anti-neurofilament staining showed no abnormality throughout the experimental period, indicating that Wallerian degeneration did not occur. We conclude that acute nerve compression can cause transient damage to the axonal transport system in nerve fibers without Wallerian degeneration.

Acute stretching of peripheral nerves inhibits retrograde axonal transport

The conjugation of horseradish peroxidase with wheat germ agglutinin was used to identify the effect on retrograde axonal transport of stretching the rat sciatic nerve indirectly by 10% and 20% femoral lengthening with a unilateral external fixator. To investigate the relationship between retrograde axonal transport and blood flow in the stretched nerve, nerve blood flow in the sciatic nerve was measured by a hydrogen washout technique. At 11% strain (20% femoral lengthening), the numbers of horseradish peroxidase-labelled motor neuron cells and nerve blood flow had decreased by 43% and 50%, respectively. Histological examination demonstrated ischaemic changes, but not mechanical damage. However, at 6% strain (10% femoral lengthening) there were no significant abnormalities. These findings suggest that the inhibition of retrograde axonal transport can be induced by acute stretching of the peripheral nerve and that circulatory disturbance is the main cause of the inhibition of retrograde axonal transport at the low strain.

Axonal transport and morphological changes following nerve compression. An experimental study in the rabbit vagus nerve

Axonal transport and morphological changes were studied in the rabbit vagus nerve after the nerves had been subjected to compression at either 0, 50 or 200 mmHg for two hours. Slow axonally transported proteins, tubulin and actin, were radiolabelled with 35S-methionine two, seven or 14 days after the injury and the distribution of radiolabelled tubulin and actin within component b of slow transport was measured three days later by densitometric analysis of fluorographs of polyacrylamide gel. No significant differences were found in the distribution of tubulin two (50 and 200 mmHg) or seven (200 mmHg) days after injury, but at 14 days (200 mmHg) there was significantly increased radiolabelling of tubulin relative to actin in the nerve 60 to 70 mm from the nodose ganglion. Morphometric measurements of the nerve cell bodies two days after the compression injury at 200 mmHg revealed no significant changes. Previous work has shown that morphological changes, similar to those found after axotomy, were present in nerve cell bodies seven days after a compression injury. This, taken together with the present results, indicates that compression can induce both morphological and biochemical changes in the neurone. The altered axonal transport of tubulin associated with nerve injury follows a slower time course and does not precede the morphological changes. The findings may be of relevance when discussing the double crush syndrome.

Conditioning effect induced by chronic nerve compression. An experimental study of the sciatic and tibial nerves of rats

To find out if chronic nerve compression could affect the peripheral nerve by acting as a "conditioning lesion", silicone tubes (internal diameter 0.8-1.6 mm) were placed round the sciatic or tibial nerves of adult rats for different time periods. After the period of compression the tubes were removed and a test crush lesion was made on the sciatic nerve in the thigh. Regeneration distances of the sensory nerve fibres were analysed by the pinch reflex test after a further three or six days. Compression of sciatic or tibial nerves induced a significant increase in outgrowth length compared with nerves subjected to mobilisation and crush lesion alone. All the tubes tested had a conditioning effect, but only tubes with a small internal diameter seemed to induce nerve fibre degeneration as assessed by immunocytochemistry. The results showed that chronic compression induced a regenerative response in the peripheral nerve. The mechanism by which this was accomplished remains obscure but it may involve both the neurons and the non-neuronal cells.

Pressure-induced inhibition of fast axonal transport of proteins in the rabbit vagus nerve in galactose neuropathy: prevention by an aldose reductase inhibitor

Fast and slow anterograde axonal transport and retrograde axonal transport of proteins were studied in the mainly non-myelinated sensory fibres of the vagus nerve of rabbits fed a diet of 50% galactose over a period of 29 days. Galactose feeding had no effect on the rate or protein composition of slow transport nor on the amount of retrogradely transported proteins. There was a slight retardation of fast transported proteins although their composition was unchanged. The galactose feeding led to a significant increase (p less than 0.005) in nerve water content and nerve galactitol but no significant change in myo-inositol. When 20 mm Hg pressure was applied locally to the cervical vagus nerve, fast transported proteins accumulated proximal to the compression zone in the galactose-fed but not in control rabbits. Administration of the aldose reductase inhibitor Statil (ICI 128436) throughout the experiment prevented the increased susceptibility to pressure and the increase in nerve galactitol and water content. The effects of pressure are similar to those found in the streptozotocin-diabetic rat although the underlying mechanisms may differ.

Morphologic changes in nerve cell bodies induced by experimental graded nerve compression

The effects of experimental nerve fiber compression on the morphology of nerve cell bodies were studied. Rabbit cervical vagus nerves were crushed or subjected to compression at 0 (sham compression), 30, 200, or 400 mm Hg for 2 h. Morphometric measurements and light microscopical evaluation of the nerve cell bodies in the nodose ganglion were carried out 7 days after the injury on the injured and control sides. Crush and compression at 30, 200, or 400 mm Hg induced a slight decrease in total cell profile area compared with the control side, but it was not related to degree of injury. There was a marked decrease in the ratio between nuclear and total cell profile area (nuclear volume density) after compression at 200 and 400 mm Hg, as well as after crush, and to a lesser extent after compression at 30 mm Hg. Compression at 30, 200, or 400 mm Hg as well as crush of the vagus nerve induced migration of the nucleus to the periphery and dispersion of Nissl substance in the cytoplasm of the nerve cell bodies. Sham compression induced no obvious changes in total cell profile area, nuclear volume density, or migration of nucleus. There was a somewhat increased percentage of cells showing dispersion of Nissl substance in sham-compressed animals than in controls. The results show that nerve fiber compression induced pronounced reactive changes in nerve cell bodies, even at low pressures, corresponding to those found in human carpal tunnel syndrome. Such pressures are known to induce reversible inhibition of fast axonal transport as well as inhibition of retrograde axonal transport. The nerve cell body changes in the nodose ganglion may thus be a reaction to disturbances in axonal transport.