Changes in peripheral nerve fibres distal to a constriction

Outcomes of ulnar nerve decompression for double crush syndrome

BACKGROUND

Double crush syndrome (DCS) of the ulnar nerve, including cubital tunnel syndrome with ulnar tunnel syndrome (UTS), is uncommon. This study compares the postoperative outcomes of patients with isolated ulnar tunnel syndrome versus those with double crush syndrome of the elbow and ulnar tunnel.

METHODS

This study enrolled 22 patients: 12 underwent cubital tunnel surgery and ulnar tunnel surgery (double crush group); and 10 underwent only ulnar tunnel decompression (isolated UTS group). Postoperative effect evaluation of patients in both groups after at least 2.6 years (mean, 5.1 years and 5.7 years, respectively). Statistical analysis compared postoperative function, physical examination, and patient-reported satisfaction between groups.

RESULTS

In terms of postoperative grip strength, there was no difference between the postoperative states of the two groups (0.88 ± 0.04 versus 0.87 ± 0.05), while there was statistical difference in terms of the increment of the grip strength (p = 0.036); the two-point discrimination of isolated UTS group is better than the double crush group (90% versus 83.3%); double crush patients reported lower satisfaction than the UTS group (90% versus 83.3%).

CONCLUSIONS

At a minimum of 2.6 years after the nerve decompression, the patients of isolated UTS group are likely to have superior grip strength increment than patients with a history of double crush surgery, and there is no big difference in the final recovery situation. The sensation and satisfaction of isolated UTS group after nerve release were better compared with patients following double crush surgery.

10 Hypotheses in Hand Surgery

I have put together 10 topics and labeled them as hypotheses, which outline my preferred practices. The topics relate to questionable nerve compression, double crush syndrome of nerves, motion therapy after surgery, delayed primary tendon repair, proximal pole fracture of the scaphoid, short splint, and indications for postoperative hand elevation. I found no proof whether my preferred methods are better than or inferior to alternative methods that others use. The 10 hypotheses are presented to stimulate thinking, clinical observation, or investigations and highlight several areas of research. Investigation into these hypotheses may avoid unnecessary treatment or improve postsurgical comfort for patients and long-term outcomes of treatment.

Double Crush Syndrome of the Lower Limb in L5 Radiculopathy and Peroneal Neuropathy: A Case Report

Double crush syndrome (DCS) is a clinical condition involving impingement of the spinal and peripheral nerves. DCS of the lower limbs has been recognized; however, no detailed reports have been published. Herein, we report a rare case of the coexistence of L5 radiculopathy and peroneal nerve entrapment neuropathy. The patient suffered from pain in the left lower leg and left foot combined with muscle weakness in the left leg without a Tinel-like sign in the peroneal tunnel area. MRI showed a deficit in the left L5 nerve root sleeve, and X-ray imaging revealed L5 spondylolysis. Lumbar fusion surgery was performed at L5-S1. Subsequently, the patient’s symptoms were partially improved, but the pain and toe and ankle motor weakness persisted. In addition, a Tinel-like sign appeared at the entrapment point of the peroneal nerve. The entrapped peroneal nerve was decompressed, and the patient’s symptoms improved. The patient had L5 radiculopathy owing to the improvement in his symptoms in the upper leg before and after lumbar surgery. It is unclear why no Tinel-like sign was detected before the first surgery, but we hypothesized that L5 nerve disorder may mask the symptoms triggered by compression of the peroneal nerve due to the complex pathology of DCS and dynamic factors. Distinguishing between radiculopathy and relative peripheral neuropathy should always be a consideration. DCS may mask characteristic symptoms, and it is important to carefully follow up the patient to detect changes in his or her condition.

Electrophysiological investigation of motor axonal excitability in a mouse model of nerve constriction injury

Peripheral nerve injuries caused by focal constriction are characterised by local nerve ischaemia, axonal degeneration, demyelination, and neuroinflammation. The aim of this study was to understand temporal changes in the excitability properties of injured motor axons in a mouse model of nerve constriction injury (NCI). The excitability of motor axons following unilateral sciatic NCI was studied in male C57BL/6J mice distal to the site of injury at the acute (6 hours-1 week) and chronic (up to 20 weeks) phases of injury, using threshold tracking. Multiple measures of nerve excitability, including strength-duration properties, threshold electrotonus, current-threshold relationship, and recovery cycle were examined using the automated nerve excitability protocol (TRONDNF). Acutely, injured motor axons developed a pattern of excitability characteristic of ischemic depolarisation. In most cases, the sciatic nerve became transiently inexcitable. When a liminal compound muscle action potential could again be recorded, it had an increase in threshold and latency, compared to both pre-injury baseline and sham-injured groups. These axons showed a greater threshold change in response to hyperpolarising threshold electrotonus and a significant upward shift in the recovery cycle. Mathematical modelling suggested that the changes seen in chronically injured axons involve shortened internodes, reduced myelination, and exposed juxtaparanodal fast K⁺ conductances. The findings of this study demonstrate long-term changes in motor excitability following NCI (involving alterations in axonal properties and ion channel activity) and are important for understanding the mechanisms of neurapraxic injuries and traumatic mononeuropathies.

Double crush syndrome: Epidemiology, diagnosis, and treatment results

BACKGROUND

Double Crush Syndrome (DCS) is a clinical condition that involves multiple compression sites along a single peripheral nerve. The present study aims to describe the epidemiology of DCS and surgical results.

METHODS

A retrospective observational analytic study included patients with clinical diagnosis of cervical radiculopathy and carpal tunnel syndrome who underwent surgery between January 2009 and January 2019. General demographic characteristics were noted, and 3 groups were distinguished: spinal surgery, carpal tunnel release, and bimodal decompression (BD); statistical differences were analyzed between them.

RESULTS

The sample comprised 32 patients. DCS prevalence was 10.29%. Mean age at presentation was 59.25±10.98 years. There was female predominance (75%). Paresthesia was the main symptom (65.6%). Post-surgical results of BD showed significant improvement in sensory nerve conduction velocity, motor nerve conduction velocity (both P=0.008), and disability on Douleur Neuropathique 4 questions, Neck Disability Index, and Boston Carpal Tunnel Questionnaire (P=0.001, 0.004, 0.008, respectively).

CONCLUSIONS

Diagnosis and management of DCS are a challenge. It is necessary to determine the site with maximal compression and risk of complications to decide on treatment. If first-line surgery is adequate, proximal and distal symptomatology can be improved. To maximize success, we recommend BD, according to the present results.

Shoulder Double Crush Syndrome: A Retrospective Study of Patients With Concomitant Suprascapular Neuropathy and Cervical Radiculopathy

Purpose

While the double crush phenomena (compression along two points on a nerve) has been established between median neuropathy and cervical radiculopathy, combined suprascapular neuropathy (SSN) and cervical C5/C6 radiculopathy-so-called shoulder double crush syndrome-has not been well examined. We aim to identify the incidence of shoulder double crush syndrome in patients undergoing arthroscopic suprascapular nerve release for SSN.

Methods

One hundred consecutive patients >18 years of age who were positive for SSN on electromyography and motor nerve conduction studies (EMG/NCS) and underwent a suprascapular nerve release were included. Patients with evidence of shoulder double crush syndrome were identified based on x ray, cervical spine magnetic resonance imaging (MRI) and examination findings. Demographics, electrodiagnostics results, treatment courses, and clinical outcomes (visual analog scores and rotator cuff strength) following arthroscopic suprascapular nerve release were compared between patients with double crush syndrome versus isolated SSN.

Results

Thirty one percent of patients had evidence of shoulder crush syndrome. Two significant electrophysiologic differences were noted in shoulder double crush patients compared to isolated SSN patients. Patients with double crush had an increased incidence of median neuropathy (51% vs 30%, P = .04). Double crush patients had less supraspinatus motor amplitude difference between the affected side and non-affected side compared to isolated SSN patients (2.62 mV vs 3.44 mV, P = .03). In general, most double crush patients were treated conservatively with regard to their cervical spine pathology.

Conclusion

A significant percentage of patients with SSN have evidence of shoulder double crush syndrome. Patients with SSN and concomitant median neuropathy should have a detailed neck examination performed.

W, Fazan VPS. Sensory and Motor Conduction Velocity in Spontaneously Hypertensive Rats: Sex and Aging Investigation

The literature is extensive on how hypertension affects the morphology and function of the central nervous system (CNS) and is being focused on multiple organ damage involving the kidneys, heart, endothelium and retina. Hypertension damage to the peripheral nervous system is less explored in the literature. We have previously shown morphometric alterations in large and small caliber myelinated fibers of nerves in the adult spontaneously hypertensive rat (SHR). However, the functional correlation of these findings has not been explored. We performed an electrophysiological investigation of hind limb nerves in SHR of both genders in different ages. Normotensive Wistar-Kyoto (WKY) rats were used as controls. Electrophysiological recordings and determination of motor (MCV) and sensory (SCV) nerve conduction velocity were performed in the same animals at four different ages: 5, 8, 20 and 40 weeks after birth. Comparisons were made between ages, genders and animal strain. We showed a continuous body weight increase in adult life in all animals studied. MCV got stable at 20-week old hypertensive animals and continued to increase in normotensive ones. The SCV was constant between the ages of 20 and 40 weeks old in female SHR and decreased in male SHR while it continued to increase in WKY animals. The electrophysiological investigation of the nerves in WKY and SHR from both genders and different ages, associated with morphological and morphometric data from the literature suggest that hypertension affects the nerve function and might corroborate the development of a peripheral neuropathy.

A translational framework for peripheral nerve stimulating electrodes: Reviewing the journey from concept to clinic

The purpose of this review article is to describe the underlying methodology for successfully translating novel interfaces for electrical modulation of the peripheral nervous system (PNS) from basic design concepts to clinical applications and chronic human use. Despite advances in technologies to communicate directly with the nervous system, the pathway to clinical translation for most neural interfaces is not clear. FDA guidelines provide information on necessary evidence which should be generated and submitted to allow the agency evaluate safety and efficacy of a new medical device. However, a knowledge gap exists on translating neural interfaces from pre-clinical studies into the clinical domain. Our article is intended to inform the field on some of the key considerations for such a transition process specific to neural interfaces that may not be already covered by FDA guidances. This framework focuses on non-penetrating peripheral nerve stimulating electrodes that have been proven effective for motor and sensory neural prostheses and successfully transitioned from pre-clinical through first-in-human and chronic clinical deployment. We discuss the challenges of moving these neural interfaces along the translational continuum and ultimately through FDA approval for human feasibility studies. Specifically, we describe a translational process involving: quantitative human anatomy, neural modeling and simulation, acute intraoperative testing and verification, clinical demonstration with temporary percutaneous access, and finally chronic clinical deployment and functional performance. To clarify and demonstrate the importance of each step of this translational framework, we present case studies from electrodes developed at Case Western Reserve University (CWRU), specifically the spiral cuff, the Flat Interface Nerve Electrode (FINE), and the Composite FINE (C-FINE). In addition, we demonstrate that success along this translational pathway can be further expedited by: appropriate selection of well-characterized materials, validation of fabrication and sterilization protocols, well-implemented quality control measures, and quantification of impact on neural structure, health, and function. The issues and approaches identified in this review for the peripheral nervous system may also serve to accelerate the dissemination of any new neural interface into clinical practice, and consequently advance the performance, utility, and clinical value of new neural prostheses or neuromodulation systems.

Electrophysiologic evaluation of facial nerve functions after oxaliplatin treatment

PURPOSE

This study analyzes the effect of oxaliplatin treatment on the facial nerve. The facial nerve is the most commonly paralyzed cranial motor nerve because it advances through a long, curved bone canal. Electroneurography and blink reflex are the electrophysiological measurements used for evaluating facial nerve function. Oxaliplatin is a cytotoxic agent used in adjuvant or palliative systemic therapy for colorectal cancer treatment.

METHODS

This study was performed on 20 individuals who were at least 18 years old at Hacettepe University Ear Nose Throat Department, Audiology and Speech Disorders Unit, and Neurology Division EMG Laboratory as they received oxaliplatin treatment from Hacettepe University Oncology Hospital. Electroneurography and blink-reflex values were recorded and examined. The parameters taken during the second and fourth months were compared for this purpose.

RESULTS

This study shows that the prolongation of distal latencies of compound muscle action potential is statistically significant, the amplitudes showed no difference. The ENoG results were analyzed, the prolongation of latency measurements between pre-treatment and the fourth month after treatment were statistically significant. The blink-reflex results showed that comparison with the baseline values, the prolongation of latencies in R1 measurements between pre-treatment, the second month, and the fourth month were significant.

CONCLUSIONS

The facial nerve is affected asymptomatically by oxaliplatin treatment. During oxaliplatin treatment, the evaluation of facial nerve function could be beneficial for patients by improving their quality of life. Electroneurography and blink-reflex tests can be used in the early evaluations of different medicines to determine their neurotoxicity.

Iron prevents demyelination of frog sciatic nerves

Metal ions are of particular importance in nervous system function, notably iron. However, very little has been done to investigate its physiological role in frog peripheral nervous system. The present research aim to evaluate i) the time-effect of sciatic nerve ligation and/or ii) iron sulphate (1.50mg/kg, in lymphatic sac) on frog myelin sheaths. Histological sections following ligation shows degeneration of some fibres with axonal and myelin breakdown associated to a decrease of Schwann cells number following 2h (45.00±0.30, p<0.0001), 24h (28.00±0.020, p<0.0001). Interestingly, iron administration reduces the degeneration of myelin sheaths classically observed in frog ligated sciatic nerve associated with an increase of Schwann cells number (139.00±0.50, p<0.0001). Thus, iron could prevent degeneration or promote regeneration induced by ligation in frog sciatic nerve.

The design of and chronic tissue response to a composite nerve electrode with patterned stiffness

OBJECTIVE

As neural interfaces demonstrate success in chronic applications, a novel class of reshaping electrodes with patterned regions of stiffness will enable application to a widening range of anatomical locations. Patterning stiff regions and flexible regions of the electrode enables nerve reshaping while accommodating anatomical constraints of various implant locations ranging from peripheral nerves to spinal and autonomic plexi.

APPROACH

Introduced is a new composite electrode enabling patterning of regions of various electrode mechanical properties. The initial demonstration of the composite's capability is the composite flat interface nerve electrode (C-FINE). The C-FINE is constructed from a sandwich of patterned PEEK within layers of pliable silicone. The shape of the PEEK provides a desired pattern of stiffness: stiff across the width of the nerve to reshape the nerve, but flexible along its length to allow for bending with the nerve. This is particularly important in anatomical locations near joints or organs, and in constrained compartments. We tested pressure and volume design constraints in vitro to verify that the C-FINE can attain a safe cuff-to-nerve ratio (CNR) without impeding intraneural blood flow. We measured nerve function as well as nerve and axonal morphology following 3 month implantation of the C-FINE without wires on feline peripheral nerves in anatomically constrained areas near mobile joints and major blood vessels in both the hind and fore limbs.

MAIN RESULTS

In vitro inflation tests showed effective CNRs (1.93  ±  0.06) that exceeded the industry safety standard of 1.5 at an internal pressure of 20 mmHg. This is less than the 30 mmHg shown to induce loss of conduction or compromise blood flow. Implanted cats showed no changes in physiology or electrophysiology. Behavioral signs were normal suggesting healthy nerves. Motor nerve conduction velocity and compound motor action potential did not change significantly between implant and explant (p  >  0.15 for all measures). Axonal density and myelin sheath thickness was not significantly different within the electrode compared to sections greater than 2 cm proximal to implanted cuffs (p  >  0.14 for all measures).

SIGNIFICANCE

We present the design and verification of a novel nerve cuff electrode, the C-FINE. Laminar manufacturing processes allow C-FINE stiffness to be configured for specific applications. Here, the central region in the configuration tested is stiff to reshape or conform to the target nerve, while edges are highly flexible to bend along its length. The C-FINE occupies less volume than other NCEs, making it suitable for implantation in highly mobile locations near joints. Design constraints during simulated transient swelling were verified in vitro. Maintenance of nerve health in various challenging anatomical locations (sciatic and median/ulnar nerves) was verified in a chronic feline model in vivo.

Neuropathy in the spontaneously hypertensive rat: An electrophysiological and histological study

INTRODUCTION

Hypertension is identified as a risk factor for development of polyneuropathy. In this study we examined nerve conduction and morphological alteration of peripheral nerves in spontaneously hypertensive rats (SHR).

METHODS

Motor nerve conduction velocity (MNCV) in the sciatic-tibial nerve and sensory nerve conduction velocity (SNCV) in the sural nerve were measured. Pathological investigations included spinal cord, dorsal root ganglion, and hindlimb nerves in SHR and Wistar-Kyoto rats (WKY) aged 4-64 weeks.

RESULTS

Blood pressure was significantly higher in SHR than WKY animals at 4 weeks and elevated further with aging. MNCV and SNCV were significantly slower in SHR compared with WKY after age 24 weeks. Prominent morphological changes in SHR nerves included axonal atrophy and myelin splitting. SHR also had endoneurial microangiopathy with reduplication of basement membrane.

CONCLUSIONS

SHR showed slowed nerve conduction velocity and pathological abnormalities of hindlimb nerves. Sustained severe hypertension may cause axonal atrophy and endoneurial microangiopathy. Muscle Nerve 54: 756-762, 2016.

Double Crush Syndrome

Double crush syndrome is a distinct compression at two or more locations along the course of a peripheral nerve that can coexist and synergistically increase symptom intensity. In addition, dissatisfaction after treatment at one site may be the result of persistent pathology at another site along a peripheral nerve. Double crush syndrome is a controversial diagnosis; some scientists and surgeons believe it is an illness construction that may do more harm than good because it emphasizes an objective pathophysiologic explanation for unexplained symptoms, disability, and dissatisfaction that may be more psychosocially mediated. However, peripheral neuropathy may coexist with compressive neuropathy and contribute to suboptimal outcomes following nerve decompression. To better manage patients' expectations, treating practitioners should be aware of the possibility of concomitant cervical radiculopathy and carpal tunnel syndrome, as well as the presence of underlying systemic neuropathy.

Noninvasive peroneal sensory and motor nerve conduction recordings in the rabbit distal hindlimb: feasibility, variability and neuropathy measure

The peroneal nerve anatomy of the rabbit distal hindlimb is similar to humans, but reports of distal peroneal nerve conduction studies were not identified with a literature search. Distal sensorimotor recordings may be useful for studying rabbit models of length-dependent peripheral neuropathy. Surface electrodes were adhered to the dorsal rabbit foot overlying the extensor digitorum brevis muscle and the superficial peroneal nerve. The deep and superficial peroneal nerves were stimulated above the ankle and the common peroneal nerve was stimulated at the knee. The nerve conduction studies were repeated twice with a one-week intertest interval to determine measurement variability. Intravenous vincristine was used to produce a peripheral neuropathy. Repeat recordings measured the response to vincristine. A compound muscle action potential and a sensory nerve action potential were evoked in all rabbits. The compound muscle action potential mean amplitude was 0.29 mV (SD ± 0.12) and the fibula head to ankle mean motor conduction velocity was 46.5 m/s (SD ± 2.9). The sensory nerve action potential mean amplitude was 22.8 μV (SD ± 2.8) and the distal sensory conduction velocity was 38.8 m/s (SD ± 2.2). Sensorimotor latencies and velocities were least variable between two test sessions (coefficient of variation  =  2.6-5.9%), sensory potential amplitudes were intermediate (coefficient of variation  =  11.1%) and compound potential amplitudes were the most variable (coefficient of variation  = 19.3%). Vincristine abolished compound muscle action potentials and reduced sensory nerve action potential amplitudes by 42-57% while having little effect on velocity. Rabbit distal hindlimb nerve conduction studies are feasible with surface recordings and stimulation. The evoked distal sensory potentials have amplitudes, configurations and recording techniques that are similar to humans and may be valuable for measuring large sensory fiber function in chronic models of peripheral neuropathies.

Neurophysiological approach to disorders of peripheral nerve

Disorders of the peripheral nerve system (PNS) are heterogeneous and may involve motor fibers, sensory fibers, small myelinated and unmyelinated fibers and autonomic nerve fibers, with variable anatomical distribution (single nerves, several different nerves, symmetrical affection of all nerves, plexus, or root lesions). Furthermore pathological processes may result in either demyelination, axonal degeneration or both. In order to reach an exact diagnosis of any neuropathy electrophysiological studies are crucial to obtain information about these variables. Conventional electrophysiological methods including nerve conduction studies and electromyography used in the study of patients suspected of having a neuropathy and the significance of the findings are discussed in detail and more novel and experimental methods are mentioned. Diagnostic considerations are based on a flow chart classifying neuropathies into eight categories based on mode of onset, distribution, and electrophysiological findings, and the electrophysiological characteristics in each type of neuropathy are discussed.

Ultrasonography in patients with ulnar neuropathy at the elbow: comparison of cross-sectional area and swelling ratio with electrophysiological severity

The aim of this study was to determine the diagnostic value of ultrasonographic measurements in ulnar neuropathy at the elbow (UNE) and to assess the relationship between the measurements and the electrophysiological severity. The largest anteroposterior diameter (LAPD) and cross-sectional area (CSA) measurements of the ulnar nerve were noted at multiple levels along the arm, and the distal-to-proximal ratios were calculated. Almost all of the measurements and swelling ratios between patients and controls showed statistically significant differences. The largest CSA, distal/largest CSA ratio, CSA at the epicondyle, and proximal LAPD had larger areas under the curve than other measurements. The sensitivity and specificity in diagnosing UNE were 95% and 71% for the largest CSA, 83% and 85% for the distal/largest CSA ratio, 83% and 81% for the CSA at the epicondyle, and 93% and 43% for the proximal LAPD, respectively. There was a statistically significant correlation between the electrophysiological severity scale score (ESSS) and the largest CSA, the CSA at the epicondyle and 2 cm proximal to the epicondyle, and the LAPD at the level of the epicondyle (P < 0.05). None of the swelling ratios showed a significant correlation with the ESSS. The largest CSA measurement is the most valuable ultrasonographic measurement both for diagnosis and determining the severity of UNE.

High-resolution ultrasound in the evaluation and prognosis of Bell's palsy

INTRODUCTION

Bell's palsy is a commonly encountered paralysis of the facial nerve occurring worldwide. Prognosis for Bell's palsy is good, but the proportion of patients with poor outcomes may reach 30%. Ultrasound (US) may provide a novel approach for evaluating and prognosticating Bell's palsy, in comparison with known electrophysiological techniques.

METHODS

In this study, we measured the diameter of the distal facial (VII) nerve using US in patients with Bell's palsy treated with prednisolone, in comparison with healthy controls. Blink reflex and VII nerve conduction studies were also performed. Studies were prospective and performed within 1 week of disease onset.

RESULTS

Our results have shown that diameter of the distal VII nerve is a good predictor of favorable (positive predictive value: 100%) and bad outcomes (negative predictive value: 77%) in Bell's palsy at 3 months after clinical presentation. Furthermore, we also noted the lack of correlation of VII diameter with conventional VII nerve conduction studies (NCS) and blink reflex studies. US was superior to VII nerve conduction and blink reflex studies in outcome prediction.

CONCLUSIONS

This first study utilizing US in Bell's palsy highlights its role in outcome prediction and contributes to our understanding of recovery processes in this common neurological disorder.

Neurophysiological study to assess the severity of each site through the motor neuron fiber in entrapment neuropathy

Background

The double crush hypothesis (DCH) that had been widely accepted seems to have been dismissed recently. Prior to the DCH, retrograde changes in the proximal median nerve in carpal tunnel syndrome (CTS) were reported. There has been no report of quantitative analyzing about the effect of one site's compression on another site all through the same peripheral nerve in CTS patients.

Methods

We measured the central motor conduction time (CMCT), motor conduction latency of the cervical root region (CRL), peripheral path latency from the rootlet to the wrist (PL) and motor distal latency (MDL) in the median nerve and ulnar nerves, respectively in CTS patients.

Results

MDL, PL and CRL were prolonged selectively in the median nerve, but not in the ulnar nerve of CTS patients. And in the median nerve measurement, MDL was high (r = 0.59, p < 0.0001) while PL showed a significant (r = -0.28, p < 0.05) relationship with CRL. MDL was large (r = 0.58, p < 0.0001) and showed a close (r = 0.59, p < 0.0001) relationship with the amplitude of CMAP. There was no significant difference between the amplitude of the normal CRL group and that of the prolonged CRL group. This quantitative analysis showed a linear relationship among MDL, CRL and CMAP amplitude.

Conclusion

Dual entrapment lesions did not unexpectedly exaggerate the vulnerability or total damage. The vulnerability and the damage were proportional to the severity of each lesion. If the DCH term presented to an unexpectedly exaggerated degree, the cases of double crush symdrome in the CTS patients were rare, but if the term DCH refers to only this linear relationship, the DCH should not be dismissed.

Sox11 transcription factor modulates peripheral nerve regeneration in adult mice

The ability of adult peripheral sensory neurons to undergo functional and anatomical recovery following nerve injury is due in part to successful activation of transcriptional regulatory pathways. Previous in vitro evidence had suggested that the transcription factor Sox11, a HMG-domain containing protein that is highly expressed in developing sensory neurons, is an important component of this regenerative transcriptional control program. To further test the role of Sox11 in an in vivo system, we developed a new approach to specifically target small interfering RNAs (siRNAs) conjugated to the membrane permeable molecule Penetratin to injured sensory afferents. Injection of Sox11 siRNAs into the mouse saphenous nerve caused a transient knockdown of Sox11 mRNA that transiently inhibited in vivo regeneration. Electron microscopic level analysis of Sox11 RNAi-injected nerves showed that regeneration of myelinated and unmyelinated axons was inhibited. Nearly all neurons in ganglia of crushed nerves that were Sox11 immunopositive showed colabeling for the stress and injury-associated activating transcription factor 3 (ATF3). In addition, treatment with Sox11 siRNAs in vitro and in vivo caused a transcriptional and translational level reduction in ATF3 expression. These anatomical and expression data support an intrinsic role for Sox11 in events that underlie successful regeneration following peripheral nerve injury.

Double crush syndrome: an analysis of age, gender and body mass index

OBJECTIVES

The aim of this study is to evaluate the role of age, gender, body mass index (BMI), wrist ratio and median sensory nerve conduction velocity as independent risk factors for double crush syndrome (DCS) and to analyze the strength of association of these factors.

PATIENTS AND METHODS

We have undertaken a case-control study in 142 patients (125 females) with carpal tunnel syndrome (CTS) and 109 controls. Based on clinical and electrophysiologic criteria 106 pure CTS patients and 36 DCS patients as well as 62 female and 47 male control subjects were selected from patients and their relatives referred to our tertiary referral hospital. Totally nerve conduction studies and electromyographic examination were done in 201 hands. Height, weight, BMI, wrist width, depth, circumference and ratio were measured in all patients and control group. Mean values of different risk factors for DCS group and controls were measured. A logistic regression analysis was conducted to evaluate odds ratio of different risk factors.

RESULTS

The mean values for age was greater in DCS patients than CTS group. Male gender and increasing age had odds ratio of 4.19 (CI 95%: 1.35-12.96) and 1.13 (CI 95%: 1.07-1.19), respectively.

CONCLUSION

Our study confirms that male gender and increased age are independent risk factors for DCS. We suggest that in elderly men presenting with CTS, electrophysiologic screening for cervical radiculopathy should be considered because the treatment of DCS differs from pure CTS.

Prolonged ischemic conduction failure after reperfusion in diabetic nerve

Diabetic nerve exhibits morphological vulnerability to ischemia and reperfusion, in contrast to its physiological resistance to ischemic conduction failure (RICF). To examine the sequence of ischemic conduction failure after reperfusion in diabetic nerve, we measured sciatic-tibial nerve conduction before and during 30-180 min of ischemia and after reperfusion for up to 1 week in streptozocin (STZ)-induced diabetic rats. RICF in diabetic rats was confirmed during ischemia. After reperfusion, control nerves showed an immediate recovery in amplitude of compound muscle action potential (CMAP) following ischemia for 120 min or less, and delayed recovery after 150 min of ischemia. In contrast, recovery in diabetic nerves was delayed even after 1 h of ischemia. Ischemia for 75 min in diabetic nerve resulted in either delayed or no recovery of the CMAP upon reperfusion. Following ischemia for 90 or 120 min, axonal degeneration was observed in diabetic nerve. Thus, severe ischemia for 60 or 75 min causes prolonged ischemic conduction failure in diabetic nerve, compared with 150 min in control nerve. In conclusion, diabetic nerve shows delayed recovery of ischemic conduction failure after brief ischemia, compared to controls, suggesting that patients with diabetic neuropathy have a worse prognosis when faced with nerve ischemia.

Double-crush syndrome after acetabular fractures. A sign of poor prognosis

Injury to the sciatic nerve is one of the more serious complications of acetabular fracture and traumatic dislocation of the hip, both in the short and long term. We have reviewed prospectively patients, treated in our unit, for acetabular fractures who had concomitant injury to the sciatic nerve, with the aim of predicting the functional outcome after these injuries. Of 136 patients who underwent stabilisation of acetabular fractures, there were 27 (19.9%) with neurological injury. At initial presentation, 13 patients had a complete foot-drop, ten had weakness of the foot and four had burning pain and altered sensation over the dorsum of the foot. Serial electromyography (EMG) studies were performed and the degree of functional recovery was monitored using the grading system of the Medical Research Council. In nine patients with a foot-drop, there was evidence of a proximal acetabular (sciatic) and a distal knee (neck of fibula) nerve lesion, the double-crush syndrome. At the final follow-up, clinical examination and EMG studies showed full recovery in five of the ten patients with initial muscle weakness, and complete resolution in all four patients with sensory symptoms (burning pain and hyperaesthesia). There was improvement of functional capacity (motor and sensory) in two patients who presented initially with complete foot-drop. In the remaining 11 with foot-drop at presentation, including all nine with the double-crush lesion, there was no improvement in function at a mean follow-up of 4.3 years.

Alterations in neurofilament protein(s) in human leprous nerves: morphology, immunohistochemistry and Western immunoblot correlative study

Using a specific antibody (SMI 31), the state of phosphorylation of high and medium molecular weight neurofilaments (NF-H and NF-M) was studied in 22 leprous and four nonleprous human peripheral nerves by means of immunohistochemistry, sodium dodecyl sulfate-poly acrylamide gel electrophoresis (SDS-PAGE) and Western immunoblot (WB). The results thus obtained were compared with morphological changes in the respective nerves studied through light and electron microscopy. Many of the leprous nerves showing minimal pathology revealed lack of or weak staining with SMI 31, denoting dephosphorylation. Remyelinated fibres stained intensely with SMI 31 antibody. The WB analysis of Triton X-100 insoluble cytoskeletal preparation showed absence of regular SMI 31 reactive bands corresponding to 200 and 150 kDa molecular weight (NF-H and NF-M, respectively) in 10 nerves. Three of the 10 nerves revealed presence of NF protein bands in SDS-PAGE but not in WB. Presence of additional protein band (following NF-M) was seen in four nerves. Two nerves revealed NF-H band but not NF-M band and one nerve showed trace positivity. In the remaining five nerves presence of all the three NF bands was seen. Thus, 77.3% (17/22) of human leprous nerves studied showed abnormal phosphorylation of NF protein(s). The ultrastructural study showed abnormal compaction and arraying of NF at the periphery of the axons in the fibres with altered axon to myelin thickness ratio (atrophied fibres) as well as at the Schmidt-Lantermann (S-L) cleft region. Such NF changes were more pronounced in the severely atrophied axons suggesting a direct correlation. The observed well-spaced NF in the remyelinated fibres under ultrastructural study was in keeping with both intense SMI 31 staining and presence of NF triplet bands seen in WBs in four of leprous nerves that showed a large number of regenerating fibres suggesting reversal of changes with regeneration. Findings in the present study suggest that atrophy, that is, the reduction in axonal calibre and paranodal demyelination, seen in leprous nerves may result from dephosphorylation of NF-H and NF-M proteins.

Acute motor axonal neuropathy rabbit model: immune attack on nerve root axons

Macrophages in the periaxonal space and surrounding intact myelin sheath are the most prominent pathological feature of acute motor axonal neuropathy (AMAN). We describe this characteristic in nerve roots from paralyzed rabbits immunized with bovine brain ganglioside or GM1. IgG was deposited on nerve root axons. Distal nerve conduction was preserved, and late F wave components were absent during the acute phase. Initial lesions were located mainly on nerve root axons, as in human AMAN. This study thus provides supportive evidence that the rabbits constitute a model of AMAN.

Vulnerability of the gradually elongated nerve to compression injury

The purpose of this study is to clarify the vulnerability of the gradually elongated peripheral nerve. Rabbit's sciatic nerves were gradually elongated to 30 mm at the rate of 2.0 mm/day and 4.0 mm/day. Immediately after elongation, the sciatic nerve was exposed and compressed for 30 minutes at various forces, 15, 30 and 60 g/0.1 cm(2). Immediately after elongation and compression, 2, 4 and 8 weeks after compression, each group was electrophysiologically and histologically estimated--15 g/0.1 cm(2) caused no damage to the control group, neurapraxia to the 2.0 mm/day group, and axonotmesis to the 4.0 mm/day group; 30 g/0.1 cm(2) caused neurapraxia to the control group and axonotmesis to the 2.0 mm/day group; 60 g/0.1 cm(2) caused axonotmesis to the control group and slowly recovered axonotmesis to the 2.0 mm/day group. This study shows that though mild compression, does not cause nerve injury to the intact nerve, it can sometimes cause severe damage to the gradual elongated nerve.

Amplitude-dependent slowing of conduction in amyotrophic lateral sclerosis and polyneuropathy

The mechanism of motor nerve conduction slowing in amyotrophic lateral sclerosis (ALS) is thought primarily to be loss of large, fast-conducting motor fibers; this is less certain in axonal polyneuropathy. We compared motor conduction studies in 64 patients with axonal polyneuropathy with 72 patients with ALS. Compound motor action potential amplitude, distal motor latency, and conduction velocity were converted to a percentage of the upper or lower limit of normal and then represented as a square root (SQRT) transformation, plotted with SQRT amplitude as the independent variable and SQRT latency or SQRT conduction velocity as the dependent variables. Regression analysis of the lower extremity nerve data showed that prolongation of latency and slowing of velocity were amplitude-dependent and were virtually identical in ALS and polyneuropathy. In the upper extremity, amplitude-dependent prolongation of latency was similar in both groups, but amplitude-dependent slowing of velocity was seen in ALS and not in axonal polyneuropathy. Our data support the hypothesis that the major mechanism of slowing is similar in both polyneuropathy and ALS and is the loss of large, fast-conducting fibers. However, the presence of distal but not proximal slowing in the upper extremity of axonal polyneuropathy suggests that additional mechanisms may be contributory.

A noninvasive method of neurography in meralgia paraesthetica

The lateral femoral cutaneous nerve (LFCN) becomes superficial 10 cm distal to the anterior superior iliac spine, where it can be located and stimulated by superficial electrodes. This is not the case in the inguinal region. In the present study the LFCN compound nerve action potential (NAP) was recorded with a pair of 8-cm-long strip electrodes placed on the anterolateral aspect of the thigh 25 cm distal to the stimulating electrodes. Normative values were obtained in 58 healthy nerves. The conduction velocity (CV) was 62.3 +/- 5.5 m/s for NAP onset and 55.3 +/- 4.1 m/s for the negative NAP peak. The CV variability was comparable to that obtained with needle recordings despite a relatively low NAP amplitude (2.0 +/- 1.0 muV). This method provided definite neurophysiological evidence of the disorder in 12 of 13 patients with meralgia paraesthetica. According to our results, a slowing of CV is a more reliable sign of the condition than a decrease of NAP amplitude alone.

Time course of degeneration and regeneration of myelinated nerve fibres following chronic loose ligatures of the rat sciatic nerve: can nerve lesions be linked to the abnormal pain-related behaviours?

This study of a mononeuropathy of 1-15 weeks (W) duration was induced in rats by setting 4 loose ligatures around the common sciatic nerve. This chronic lesion, in which the continuity of the nerve was maintained, has been introduced as a model for experimental pain. Quantitative analyses of teased nerve fibres and a morphometric analysis of semi-thin transverse sections, were performed and completed by electron microscopic examination. Morphological changes were observed mainly distal, but also proximal, to the ligatures, indicating significant axonopathy with simultaneous degeneration and regeneration. The lesions were analysed in parallel with the time course of the pain-related behaviours. Both were at their maximum 2 weeks after ligature with progressive recovery beginning between W3 and W4. However, the largest fibres had not totally recovered by W15, contrasting with the disappearance of abnormal nociceptive reactions between W8 and W10. Although the damage to unmyelinated fibres is of importance, the abnormal pain-related behaviours seen in these rats appeared to be closely linked to the presence of both degenerative and regenerative changes in the A delta-range fibres, which did not necessarily correspond to initial A delta fibres.

Slowly conducting myelinated fibers in peripheral neuropathy

The main component of the compound sensory action potential reflects the activity of large myelinated sensory fibers with diameters of greater than 9 micron(s). By recording the averaged potential using a needle electrode placed close to the nerve, small late components can be measured. The latency of these late components can be used to calculate minimum conduction velocity (CV); in normal subjects, average minimum CV is 15 m/s, corresponding to conduction in fibers of about 4 micron(s) in diameter. Minimum CV was measured in median, ulnar, and sural nerves of 187 patients with mild to severe neuropathic symptoms. A reduction in minimum CV was a sensitive measure of peripheral nerve dysfunction, often showing abnormalities when measures derived from the main component were normal. Patients with isolated abnormalities in minimum CV tended to have neuropathic symptoms but no signs of neuropathy. In addition, reduced minimum conduction velocity has implications for the pathology of different types of neuropathy. Slowing conducting potentials may originate from regenerating fibers, which may be of particular relevance in patients with neuropathic pain.

Nerve conduction studies in experimental non-freezing cold injury: I. Local nerve cooling

In rabbits, the tibial nerve was exposed in the lower thigh under general anesthesia and cooled in a metal trough at 1 to 2 degrees C or 5 degrees C for 2, 3, or 4 hours. Nerve conduction studies showed local failure of conduction at the site of cooling which persisted after rewarming, and which was followed by distal degeneration of affected fibers. No persistent conduction block was seen. Changes in maximal velocity indicated that the fastest-conducting motor and afferent axons had been preferentially affected. Histological findings in nerves examined at different intervals after cooling confirmed the physiological evidence of primary axonal damage, affecting particularly large diameter fibers. Paranodal demyelination was inconspicuous and restricted to regions just proximal to sites of axonal degeneration. No segmental demyelination was seen. These results clarify previous uncertainties as to the time-course and distribution of nerve damage after local cooling at temperatures just above freezing point.

The role of thoracic outlet syndrome in the double crush syndrome

The association between thoracic outlet syndrome (TOS) and carpal tunnel syndrome (CTS) (40 cases), ulnar neuropathy (UN) (19 cases) and radial tunnel syndrome (29 cases) is investigated. The possibility of a double crush syndrome is considered with reference to the difficulties in diagnosis. It is demonstrated that in approximately half of all cases the proximal neuropathy precedes the distal one. Despite the fact that surgical treatment of the thoracic outlet syndrome appears to improve the distal neuropathy it is still difficult to decide, in a given case, which decompression takes priority with the exception of carpal tunnel release which is generally to be performed first. The historical background and theoretical basis of the management of double crush syndrome is outlined and arguments for and against the association of the various neuropathies are presented.

Conduction studies in peripheral cat nerve using implanted electrodes: III. The effects of prolonged constriction on the distal nerve segment

Electrophysiological properties were monitored in detail in chronically constricted peripheral nerves by implanted, multicontact nerve cuff electrodes and correlated with morphometric histology in selected cases. The physiological and histological responses in nerve to a range of constricting cuffs of standard sizes were readily graded. The initial response to any significant constriction was a transient, focal conduction slowing or block at the constriction, followed by more protracted distal effects; the latter ranged from loss of excitability consistent with "dying-back" degeneration to reductions in conduction velocity consistent with histologically observed atrophy. Smaller myelinated fibers tended to have similar but less pronounced changes than larger diameter fibers. Recordings from ventral and dorsal roots showed that distal degeneration was more pronounced in motor than in sensory fibers of similar caliber. Electronmicroscopical measurements showed that basal laminas were relatively preserved around even the most atrophic and demyelinated axons. Perimeter measurements of the basal lamina could be used to estimate the diameter of the original nerve fiber.

Number, size, and class of peripheral nerve fibers regenerating after crush, multiple crush, and graft

Morphometric characterization of fiber regeneration in a distal nerve after focal proximal nerve injury may provide useful clinical information and insights about underlying neurobiologic mechanisms. The myelinated (MF) and unmyelinated (UF) fibers of peroneal nerve of groups of mice were assessed 9 months after crush, graft, and multiple crush injury of the proximal sciatic nerve: number and size distribution of axon areas, myelin areas, and fiber diameters. After crush, number of regenerated MF and UF was almost identical to that of controls. Their size distribution had almost returned to normal. After graft and multiple crush, fiber number had returned to normal or was significantly increased beyond normal but there were only a few large fibers present. This may be explained by: (a) disproportionate regeneration of small-diameter compared to large-diameter classes of fibers; (b) misdirected regrowth of fibers, so that functional reinnervation was not established, resulting in failure of development or retrograde atrophy and degeneration; or (c) cellular alterations at the site of injury or in the distal nerve which inhibited neural outgrowth or elongation or did not inhibit outgrowth but retarded or prevented maturation. We conclude that explanation (b) is involved, and that there is some evidence favoring the roles of (a) and (c).

The pathology of early leprous neuropathy

A qualitative and quantitative study was made of early changes in nerves from 10 patients with tuberculoid or lepromatous type of leprosy. Five nerve biopsies, taken from sites remote from skin lesions, were considered to be unaffected when examined by paraffin histology but showed abnormalities in semi-thin resin sections and by electron microscopy; 5 showed mild to moderate involvement by paraffin histology. Changes in 'unaffected' nerves in both types of leprosy included the presence of subperineurial oedema; occasional evidence of fibre regeneration, sometimes with atypical features; increased numbers of small myelinated fibres, possibly a consequence of axonal atrophy; a few thinly remyelinated fibres, probably due to secondary demyelination, and some loss of unmyelinated axons. In more affected nerves there was variable loss of axons, both myelinated and unmyelinated. Demyelination was not a conspicuous feature; there was evidence of axonal atrophy in some fibres. Similarities in some of the changes observed in tuberculoid and lepromatous types of leprosy suggest a common mechanism of nerve damage, at least in the early stages. The presence of abnormalities in nerves at a distance from skin lesions implies a more diffuse nerve involvement than might have been expected in both types of leprosy.

Conduction studies in peripheral cat nerve using implanted electrodes: I. Methods and findings in controls

Silicone rubber cuff and patch electrodes with multiple contacts were implanted along the sciatic-tibial-plantar nerves in cat for repeated studies of conduction properties of normal peripheral nerve over periods of time. The contacts were used in various combinations for precise localization of changes in conduction velocities and excitability along the extent of normal nerves. In this paper the particular characteristics and limitations associated with cuff-electrode recordings of neural activity are discussed. The nerve action potential was recorded using a tripolar configuration with a central lead flanked by two shunted leads at symmetrical distances. This configuration records the spatial derivative of the action potential and rejects potentials from sources outside the cuff. The voltage changes are restricted by the silicone cuff, and the dynamic range is therefore very high, allowing detection from single myelinated fibers to whole nerve responses. The electrodes are well suited for following the development of regeneration and degeneration following experimental lesions.

Ultrastructural and morphometric analysis of long-term peripheral nerve regeneration through silicone tubes

Light and electron microscopy were used to investigate long-term regeneration in peripheral nerves regenerating across a 10 mm gap through silicone tubes. Schwann cells and axons co-migrated behind an advancing front of fibroblasts, bridging the 10 mm gap between 28 and 35 days following nerve transection. Myelination of regenerated fibres started between 14 and 21 days after transection and occurred in a manner similar to that reported during development. Although these early events were successful in producing morphologically normal-appearing regenerated fibres, complete maturation of many of these fibres was never achieved. Axonal distortion by neurofilaments, axonal degeneration and secondary demyelination were seen at 56 days following nerve transection. These changes progressed in severity with time as more axons advanced through the distal stump towards their peripheral target. Since regeneration occurs in the absence of endoneurial tubes, and because constrictive forces act on the nerve during regeneration, we suggest that these extrinsic factors limit the successful advancement of axons through the distal stump to their target organ.

Radiculoneuropathy of ageing rats: a quantitative study

A quantitative and morphometric study has been done on the effects of age on myelinated nerve fibres of the sciatic nerve of rats ranging from 100 to 824 days of age. Using 1.0 micron semi-thin sections and a particle size analyser (TGA 10, Zeiss) it was found that both myelin sheaths and their associated axons grew in diameter until about 400 days of age, but massive destruction and disappearance of myelinated nerve fibres became manifest only after 700 days of age. In addition, onset, development and distribution of degenerative changes of nerve fibres were studied in spinal roots, lumbar plexus and sciatic nerves. Analysis of the observed data suggests that two independent mechanisms are involved in the degenerative changes of myelinated peripheral nerve fibres with age: one is axonal atrophy or loss and the other is vacuole forming, segmental demyelination and remyelination. The former begins very early in a limited number of nerve fibres and in more distal parts of the nerve, while the latter begins at a significantly later age and from the most proximal (spinal root) region.

Susceptibility to pressure neuropathy distal to a constricting ligature in the guinea-pig

Silk ligatures were tied round the sciatic nerve in guinea-pigs and left in place in order to produce persistent nerve constriction. Serial nerve conduction studies over the following 9 weeks showed a reduction in motor conduction velocity distal to the ligature. The presence of axonal atrophy in tibial nerve fibres in the leg was subsequently confirmed by histological studies. These changes were not seen in a second group of animals in which similar ligatures were tied but removed after 6 hours. When the ligatures were left in place, the animals developed local plantar nerve lesions in the sole of the foot on the affected side, which were thought to be due to pressure from the floor of the cage. Local pressure changes of varying severity were seen in the foot in all the constricted nerves, but were only occasionally found in control nerves from the opposite foot, or in nerves which had been constricted for a few hours by ligatures which were then removed. These results suggest that atrophic nerve fibres distal to a persistent constriction may be particularly sensitive to local pressure.

Friedreich's ataxia: electrophysiologic and histologic findings in patients and relatives

Peripheral nerve conduction velocity and cortical evoked potentials were investigated in 48 patients with Friedreich's disease and in 35 relatives. There were 14 patients and 2 relatives who underwent sural nerve biopsy. In the patients sensory conduction velocity was moderately slowed, whereas sensory responses were markedly reduced. Nerve biopsy showed a severe loss of large myelinated fibers and no demyelination. On teased nerve fiber preparations, most fibers presented uniformly short internodes. No correlation was seen between sensory conduction findings or histologic abnormalities and clinical disability. In patients SSEP changes, which were constant, and VEPs, which were frequently involved, were unrelated to the severity or duration of clinical disability. There were 14 relatives who showed clinical signs of Friedreich's disease. Slightly decreased distal conduction velocity along sensory fibers was observed in more than half of the relatives. Nerve biopsy was noncontributory. In conclusion, we could not determine whether the abnormalities observed in the siblings were an expression of a heterozygotic condition, or whether they were early signs of the disease.

An experimental study on the "double crush" hypothesis

An experimental study investigated the vulnerability of peripheral nerves in the "double crush" situation. Canine sciatic nerves were studied by means of electrophysiologic and histologic examination. Compression was applied by the KEIO compression clamp, with compression force of 15 g (approximately, 27.6 mm Hg). An incomplete conduction block and mild axonal degeneration were induced by a single compression. However, a complete conduction block and severe axonal degeneration could be induced in half of the cases by the double compression. In these cases, the loss of nerve function after a double lesion was greater than the sum of the deficits after each separate lesion. A good therapeutic effect was obtained by removing all compression, but the effect was incomplete when either compression was retained. It is concluded that proximal compression of a nerve could lessen its ability to withstand further compression more distally.

Compression induced damage on in-situ severed and intact nerves

The effect of rapid as well as sustained compressive forces applied to the surface of intact and severed peroneal nerves of rabbits was studied. Considerable effort was taken to ensure a quantitative and consistent experimental paradigm. Stimuli were delivered to the sciatic nerve, and the compound action potential was recorded in the peroneal nerve, with compressive forces applied more proximally on the peroneal nerve. It was found that the conduction of action potentials on the larger nerve fibers was more sensitive to compressive force than that of the smaller nerve fibers, although all nerve fibers stopped conducting when sufficient compression was applied to the nerve. The effect on the conduction of action potentials on the nerve fibers appeared to be determined both by Laplace's law (as previously reported by others) and the viscoelastic properties of the entire nerve. Relatively low compressive forces (20 gm applied over approximately 7 sq mm) were found to decrease the neutral conduction of the larger nerve fibers for at least two hours, whereas stagnation of blood circulation was not found to affect measurably the neural conduction of all the nerve fibers for up to two hours.

Adaptation of the myelin sheath during axonal atrophy

Distal axonal atrophy was produced by proximal constriction of the tibial nerve in the rabbit. Single fibres were teased from the distal tibial nerve, and a selected internode from each fibre was measured and then cut transversely for electron microscopy, so that axon area and perimeter, myelin lamellar number and periodicity, and myelin spiral length could be related to the length of the internode which had been sectioned. When sections from atrophic and control internodes of similar length were compared, there was no difference in the mean number of myelin lamellae or their periodicity in the two groups, in spite of a mean reduction in axon cross-sectional area of 60% in the atrophic group. Mean values for axon perimeter and myelin spiral length were reduced by 14%-15% in atrophic fibres, compared with controls. The reduction in mean myelin spiral length might seem to imply that myelin had been lost from the atrophic internodes. However, there was also an increase in the length of individual lamellae in the long axis of the internode, due to the irregular folding of the sheath, and it is uncertain whether any overall change in internodal myelin volume had occurred.

Regeneration following tibial nerve crush in the rabbit: the effect of proximal constriction

In order to test the regenerative capacity of atrophic axons, a constricting ligature was placed around the proximal tibial nerve of the rabbit, and the nerve crushed at the ankle one week later. Axonal atrophy with altered g ratios was subsequently confirmed in fibres distal to the site of ligature and proximal to the site of crush. In nerves with tight proximal ligatures the reinnervation of plantar muscles and the subsequent recovery of distal motor latency were delayed, indicating impaired regeneration. This result may be relevant to the "double-crush" theory of nerve damage.

Structural correlates of physiological abnormalities in beta, beta'-iminodipropionitrile

beta, beta'-Iminodipropionitrile (IDPN) produces neurofilamentous giant axonal swellings in proximal internodes of large myelinated axons. Secondary demyelinative changes result from the production of these axonal enlargements. Electrophysiological studies have demonstrated profound alterations in the electrical properties of motor neurons (MN) within the spinal cord. On the basis of intracellular recordings, it has been suggested that electrical contacts may exist between swollen axons and neighboring MN. In addition, the possibility remained that synaptic contacts develop on demyelinated axonal swellings. In the present study, we report the lack of either synapses on demyelinated axonal swellings or direct electrical contacts between neighboring MN. Axonal swellings are surrounded by attenuated processes of glial cells (probably fibrillary astrocytes), a finding discussed in terms of its possible role in the production of ephaptic transmission. There was considerable variation in the degree of axonal enlargements and in the extent of secondary (passive and active) demyelination. It is suggested that these morphological changes may represent structural correlates of some electrophysiological alterations observed in IDPN neuropathy.

Conduction failure and nerve conduction slowing in experimental allergic neuritis induced by P2-specific T-cell lines

P2-specific T cells (LiP2/A) mediate experimental allergic neuritis (EAN) in the Lewis rat after adoptive transfer to naive recipients. After a latent period of 4 days, injection of 2 X 10(6) line cells induced fulminant paraplegia and complete conduction failure in the peripheral nerves and roots, resembling acute axonal breakdown. Injection with 10(6) cells caused milder clinical signs, nerve conduction failure, and conduction slowing. Clinical and electrophysiological recovery from adoptively transferred EAN was nearly complete and its time course was inversely correlated to the initial severity of EAN. These findings suggest that EAN induced by the P2-specific T-cell line can lead to a profound and rapidly evolving nerve dysfunction in a dose-dependent fashion.