Fine structural evaluation of altered Schmidt-Lanterman incisures in human sural nerve biopsies

KATP channel subunits in rat dorsal root ganglia: alterations by painful axotomy

Background

ATP-sensitive potassium (K_ATP) channels in neurons mediate neuroprotection, they regulate membrane excitability, and they control neurotransmitter release. Because loss of DRG neuronal K_ATP currents is involved in the pathophysiology of pain after peripheral nerve injury, we characterized the distribution of the K_ATP channel subunits in rat DRG, and determined their alterations by painful axotomy using RT-PCR, immunohistochemistry and electron microscopy.

Results

PCR demonstrated Kir6.1, Kir6.2, SUR1 and SUR2 transcripts in control DRG neurons. Protein expression for all but Kir6.1 was confirmed by Western blots and immunohistochemistry. Immunostaining of these subunits was identified by fluorescent and confocal microscopy in plasmalemmal and nuclear membranes, in the cytosol, along the peripheral fibers, and in satellite glial cells. Kir6.2 co-localized with SUR1 subunits. Kir6.2, SUR1, and SUR2 subunits were identified in neuronal subpopulations, categorized by positive or negative NF200 or CGRP staining. K_ATP current recorded in excised patches was blocked by glybenclamide, but preincubation with antibody against SUR1 abolished this blocking effect of glybenclamide, confirming that the antibody targets the SUR1 protein in the neuronal plasmalemmal membrane.

In the myelinated nerve fibers we observed anti-SUR1 immunostaining in regularly spaced funneled-shaped structures. These structures were identified by electron microscopy as Schmidt-Lanterman incisures (SLI) formed by the Schwann cells. Immunostaining against SUR1 and Kir6.2 colocalized with anti-Caspr at paranodal sites.

DRG excised from rats made hyperalgesic by spinal nerve ligation exhibited similar staining against Kir6.2, SUR1 or SUR2 as DRG from controls, but showed decreased prevalence of SUR1 immunofluorescent NF200 positive neurons. In DRG and dorsal roots proximal to axotomy SLI were smaller and showed decreased SUR1 immunofluorescence.

Conclusions

We identified Kir6.2/SUR1 and Kir6.2/SUR2 K_ATP channels in rat DRG neuronal somata, peripheral nerve fibers, and glial satellite and Schwann cells, in both normal state and after painful nerve injury. This is the first report of K_ATP channels in paranodal sites adjacent to nodes of Ranvier and in the SLI of the Schwann cells. After painful axotomy K_ATP channels are downregulated in large, myelinated somata and also in SLI, which are also of smaller size compared to controls.

Because K_ATP channels may have diverse functional roles in neurons and glia, further studies are needed to explore the potential of K_ATP channels as targets of therapies against neuropathic pain and neurodegeneration.

Effects of nucleus pulposus on nerve root neural activity, mechanosensitivity, axonal morphology, and sodium channel expression

STUDY DESIGN

This study analyzed the effects of autografted nucleus pulposus on nerve root axon morphology, neurophysiologic function, and sodium channel expression.

OBJECTIVES

To investigate the chronic effects of the epidural implantation of nucleus pulposus on nerve root morphology, neural activity, ectopic discharge, mechanosensitivity, and sodium channel expression.

SUMMARY OF BACKGROUND DATA

It has been reported that ectopic discharges were recorded antidromically from sural nerve on compressing nucleus pulposus exposed spinal nerves. However, it is not clear what the effects of nucleus pulposus are on ectopic discharges recorded directly from the spinal nerve roots. It is also not clear what the effects of nucleus pulposus are on the threshold pressure to provoke ectopic discharges in the spinal nerves. Sodium channel content increases in remodeling axons after nerve injury, but it is not clear what the effects of nucleus pulposus are on sodium channel expression in spinal nerve.

METHODS

Forty-six male Sprague-Dawley rats were used, 20 in a nucleus pulposus-implanted group, 18 in a fat-implanted group, and 8 in a normal group. Fresh autografted nucleus pulposus or fat tissue was implanted into the dorsal epidural space at the L4-L5 disc level. On the 7th, 21st, or 42nd day, neurophysiologic recordings were made to determine nerve root response to compression. Nerve roots were then harvested to determine sodium channel protein concentration and histologic changes in the nerve root. The correlations between sodium channel density and neural activity and mechanosensitivity of dorsal root were analyzed statistically.

RESULTS

Ectopic discharge rate was higher in nucleus pulposus 7-day group. Threshold pressure to evoke ectopic discharges was lower in the nucleus pulposus 7-day group, and higher in the nucleus pulposus 42-day group compared to the normal group. Sodium channel protein density increased in the nucleus pulposus 7-day and nucleus pulposus 21-day group compared to normal nerve. Sodium channel density changes were not correlated to threshold pressure. Ectopic discharge rate increased with increase of sodium channel density in the nerve roots. The number of axons with neuropathy increased in the nucleus pulposus 7-day and 21-day groups.

CONCLUSIONS

Acute exposure of nerve root to nucleus pulposus resulted in increased number of axons with neuropathy, higher intensity of ectopic discharges on compression, and nerve mechanosensitization. Chronic exposure resulted in mechanical desensitization. Changes of sodium channel density were correlated to ectopic discharge rate.

Increased CSF protein in chloroquine-induced axonal polyneuropathy and myopathy

OBJECTIVES

Few data are available about myopathy and polyneuropathy as rare side effects of chloroquine treatment. Even more rarely are cerebrospinal fluid (CSF) abnormalities in chloroquine polyneuropathy/myopathy.

CASE DESCRIPTION

The patient is an 81-year-old woman with a 30-year history of chronic polyarthritis. As a basic therapy, she received chloroquine (250 mg per day) since 1997. Already, 1 year later she developed slowly progressive gait disturbance, which led to recurrent falls, and forced her to use crutches and other orthotic devices. Since March 2001, she was no longer able to climb stairs. Since then she also developed sensory disturbances in both lower limbs. Clinical neurological investigation revealed weakness and wasting of all four limbs and reduced tendon reflexes and stocking-type sensory disturbances. Nerve conduction studies were indicative of an axonal polyneuropathy. Electromyography was non-specifically abnormal. Muscle biopsy of the gastrocnemius muscle disclosed neuropathic and myopathic features and frequent fibers with partially rimmed vacuoles, containing concentrically or parallelly sliced inclusions. CSF investigations disclosed increased protein but otherwise normal findings. Five months after discontinuation of chloroquine and replacement by leflunomid, there was marked clinical improvement.

CONCLUSIONS

Chloroquine polyneuropathy/myopathy may go along with increased CSF protein. Discontinuation of the causative agent results in prompt recovery of the described abnormalities.

X-linked dominant Charcot-Marie-Tooth neuropathy: clinical, electrophysiological, and morphological phenotype in four families with different connexin32 mutations(1)

The sensorimotor neuropathy of the Charcot-Marie-Tooth type (CMT) is the most common hereditary disorder of the peripheral nervous system. The X-linked dominant form of CMT (CMTX) is associated with mutations in the gene for the gap junction protein connexin32. We examined four CMTX pedigrees two of which had potentially novel mutations in the only coding exon of connexin32. One previously unreported missense mutation, Ala39Val, was found in a family displaying a CMT phenotype with additional upper limb postural tremor reminiscent of a Roussy-Lévy syndrome. A novel single base insertion, 679insT, is among the first mutations found in the fourth transmembrane domain of connexin32. Frameshift and premature stop of translation are supposed to result in a non-functional carboxy-terminus. Two further families had the known missense mutations Arg15Trp and Arg22Gln. Several female carriers were found normal on clinical presentation, however, the genotype was paralleled by decreased nerve conduction velocities (NCV) and slowed central conduction of brain stem auditory evoked responses (BAER). Median motor NCVs showed mild (in women) to intermediate (in males) reduction, indicating a peripheral neuropathy with a predominating axonal component. Nerve biopsy findings were consistent with the electrophysiological data showing a marked loss of large myelinated fibres and clusters of regenerating axons. Electron microscopy revealed various alterations of the axoglial attachment zone. This suggests defective axon-Schwann cell interactions which may induce the axonopathy in CMTX.

Clinically distinct codon 69 mutations in major myelin protein zero in demyelinating neuropathies

Mutations in the major peripheral myelin protein zero (P0) gene on chromosome 1q21-q23 have been found with the hereditary demyelinating polyneuropathy Charcot-Marie-Tooth type 1B. Here, we describe 2 patients with distinct neurological characteristics, carrying different substitutions at the same codon--Arg69His and Arg69Cys. The patients were heterozygous for the mutation, which in both appeared to be de novo. Histological examination of sural nerve biopsy specimens revealed defective myelin as well as marked differences, confirming the importance of P0 in the compaction of myelin.

Developmental and pathological changes at the node and paranode in human sural nerves

The nodes and paranodes of peripheral nerve fibers are complex structures that are especially prone to artificial and pathological changes which have to be distinguished from normal developmental changes. Alterations during normal development are mainly caused by an increase in axonal diameter and myelin sheath thickness. The nodal, and paranodal axon diameters in human sural nerves reach their adult values at 3-5 years of age, simultaneously to the internodal diameter. The ratio between internodal and paranodal axon diameters remain relatively constant, with an average value of 1.8 to 2.0 (range: 1.6 to 2.5). Despite a considerable increase of the number of myelin lamellae, the length of the paranodal myelin sheath attachment zone at the axon does not increase correspondingly, because of (1) attenuation of the terminal myelin loops, (2) separation of some of these from the axolemma, and their piling up in the paranode. Separation of variable numbers of terminal myelin loops from the underlying axolemma results in the formation of the spines on the "double bracelet épineux" of Nageotte, while the transverse bands of these loops disappear. The adaptation of the paranodal myelin sheath to axonal expansion during development probably occurs by uneven gliding of the paranodal myelin loops simultaneously with internodal slippage of myelin lamellae. Artificial changes are caused by insufficient fixation or mechanical stress during excision and further handling (cutting, dedydrating, embedding) of nerves whereas pathological changes may be induced by a multitude of causes. An attempt to classify these changes is presented in Table 2.

Peripheral nerve elongation by laser Doppler flowmetry controlled expansion: morphological aspects

Peripheral nerve elongation by a tissue expander may offer an alternative to nerve grafting in the management of segmental nerve loss. We investigated the morphological changes in peripheral nerve following slow nerve elongation by laser Doppler flowmetry controlled expansion in a rabbit sciatic nerve model. The animals were randomly assigned to one of four groups, with an expander volume of 0, 5, 10 or 15 cm3, respectively. An elongation of up to 40% was possible with preservation of clinical function. Nerve conduction velocity decreased in relation to elongation. Paranodal widening, followed by remyelination of the node, were early and constant morphological features. Demyelination and remyelination of whole internodes, and axonal degeneration occurred sporadically and did not correlate with elongation, rate of elongation or neurophysiological parameters. The model of laser Doppler flowmetry controlled nerve expansion provides a method for remodelling of myelin sheaths and lengthening of nerve fibers without axonal damage.