Microwave irradiation of peripheral nerve following injury: a structural analysis of degeneration and regeneration

Studies of the enhancement effect of pulsed energy irradiation on nerve regeneration following injury have produced variable results. The effect of microwave treatment on the rat peroneal nerve after transection and anastomosis was analyzed by light and electron microscopy. The hindquarters were irradiated 1 h/day during the first 10 days postoperative (dpo). The nerves were fixed in situ and prepared for microscopic analysis. At 10 dpo the distal segment of the degenerating nerve had several enlarged myelin sheath profiles devoid of axoplasm. The swelling was not significantly altered by microwave treatment, but the number and density of the empty myelin sheath profiles were three to four times greater in the treatment group. At 49 dpo the regenerating nerve segment had a 43% decrease in the nerve fiber diameter compared with a normal mean of 7 microns. The number and density of remyelinated fibers showed a 50% increase in both treatment and control groups. Histologic evidence indicated no permanent enhancement on nerve regeneration by microwave treatment, even though the treatment may have delayed Wallerian degeneration.

Changes in some myelin protein markers and in cytoskeletal components during Wallerian degeneration of mouse sciatic nerve

After transection of the mouse sciatic nerve, the sequence of events occurring in the distal degenerating segment was followed by the biochemical changes related to the cytoskeletal components and to the myelin protein markers. The components of the intermediate filaments and of the microtubules undergo early changes. Within 3 days, the neurofilament triplet and the peripherin disappear whereas many peptides bearing the antigenic determinant common to all classes of intermediate filaments accumulate. Several of them persist after 1 month. The tubulin pattern changes from a high level of microheterogeneity--reflecting mostly the axonal contribution--to a lower level displayed by the predominant Schwann cells. A decrease in the amount of the myelin markers is also observed. However, a month after transection, immunoreactive basic protein is still present in the degenerated segment homogenate.

An ultrastructural study of the response of traumatized rabbit tibial nerve to epineurial infection with Mycobacterium leprae

Crushed rabbit tibial nerves were inoculated with a suspension of living Mycobacterium leprae at and just distal to the site of nerve trauma. The resulting changes occurring over a period of time from 40 min to 72 hr post-inoculation were studied electron microscopically. Bacilli were seen in perineurial cells and in macrophages that had infiltrated the perineurium adjacent to epineurial deposits of M. leprae. It is suggested that trauma may weaken the perineurial barrier and facilitate the transperineurial passage of phagocytes, some of which may be laden with M. leprae, and may thus be a means whereby M. leprae enter the endoneurium of peripheral nerves.

Response of astrocytes in the visual system to Wallerian degeneration: an immunohistochemical analysis of laminin and glial fibrillary acidic protein (GFAP)

Eye removal in adult rats resulted in an increase in immunohistochemical staining with antibodies to glial fibrillary acidic protein in the optic nerve, optic tract, and primary visual nuclei. Astrocytes along the primary visual pathway did not stain with antibodies to laminin in response to eye removal. There was an increase in laminin immunoreactivity associated with blood vessels along the injured pathway. These blood vessels were also shown to have an increased size. The lack of laminin induction in astrocytes along the path of degenerating optic axons may be responsible in part for the inability of axons to regenerate in the primary visual system.

Ultrastructural alterations of perineurial cells in the early stage of Wallerian degeneration

Ultrastructural changes of the perineurium in the distal segment of the mouse phrenic nerve after crush were studied at various intervals of up to 56 days. In the control, the perineurium of the phrenic nerves was composed of multilayered perineurial cells joined together by tight junctions forming concentric laminae surrounding the endoneurium which mainly contained myelinated fibers with a relatively small amount of unmyelinated fibers. In the experiment, perineurial cells showed prominent morphological changes from day 3 to day 6 with the presence of proteinaceous exudate between the cellular laminae of the perineurium. Some of the perineurial cells appeared hypertrophic and often showed mitotic figures. Newly formed gaps between the perineurial cells forming the same lamina as well as between those of adjacent laminae were frequently observed. Intracellular microcavities in the perineurial cells associated with increased pinocytotic vesicles were also observed. In addition, debris-free macrophages were occasionally seen in the perineurium. At this stage, axonal degeneration, myelin breakdown and interstitial proteinaceous exudate, which were already noticed on day 2, were evident in the endoneurium, demonstrating the early stage of Wallerian degeneration. From day 7 on, however, mitotic figures of perineurial cells were not encountered. Perineurial cells of inner laminae contained lipid droplets which increased in number with time. Our observations strongly suggest that perineurial cells play an important role in the early stage of Wallerian degeneration of the peripheral nerve.

Acute swelling of nodes of Ranvier caused by venoms which slow inactivation of sodium channels

The venoms of the spider Phoneutria nigriventer and the scorpions Leiurus quinquestriatus and Centruroides sculpturatus cause acute, transient swelling of axons at nodes of Ranvier. The changes in the morphology of the node and paranode were studied in the mouse. Venom was injected into the sciatic nerve by means of a glass micropipette. After survival times ranging from 15 min to 3 weeks the nerves were examined by light and electron microscopy. The increase in nodal axoplasmic volume led within an hour to disruption of neurofilaments and microtubules, swelling of the paranodes and displacement of the terminal loops of myelin away from the node. Axonal calibre recovered within a few hours, but restoration of nodal width took several days and seemed to be accomplished by elongation and remodelling of the paranodal myelin. Occasional internodes were interrupted by node-like discontinuities in the myelin sheath. These developed within a few hours and persisted for the duration of the study.

Formation of oedema in transected rat sciatic nerve. A microgravimetric study

The formation of oedema in peripheral nerves was studied in rats at intervals varying from 6 h to 14 days after transection of the right sciatic nerve. Samples were removed proximal and distal to the injury, and the degree of oedema was determined by a microgravimetric method and by measurements of the water content and of the fascicular area. Distal to the lesion, decreased density values indicating the presence of oedema were observed in samples examined after a survival period of 6 h-14 days. The water content and fascicular area were both increased in samples taken 24 h after injury. Fourteen days postinjury the water content had increased further. Proximal to the lesion, the water content and the fascicular area were increased in samples examined after a survival period of 24 h. Fourteen days after the injury, the increase in water content was even more pronounced. No changes were detected with the microgravimetric technique 6 and 24 h after the injury. Unexpectedly, animals surviving 14 days showed increased density values. The microgravimetric technique used is a valuable adjunctive method for quantitation of peripheral nerve oedema in the acute phase after a traumatic nerve injury. Later on, loss of axons and of myelin components, together with regenerative phenomena, influence the density values obtained. Quantitative methods for studying chronic peripheral nerve oedema should, therefore, be supplemented with other techniques.

The role of Schmidt-Lanterman incisures in Wallerian degeneration

The number of the Schmidt-Lanterman incisures and their intrasegmental distribution were studied at 36 h after transection of the rat sciatic nerve. Examination of teased, proximo-distally oriented, myelinated nerve fibers revealed no difference between the distal and the proximal stump. The results indicate that no proliferation of the incisures is required for the fiber fragmentation: numerous incisures are normally available in the midinternodal area where the degeneration begins.

Laser injury of peripheral nerve: a model for focal endoneurial damage

A model of endoneurial oedema is presented which produces localised nerve fibre injury including Wallerian degeneration, endoneurial oedema and increased endoneurial fluid pressure. A carbon dioxide laser was used to irradiate rat sciatic nerve and quantitative results were collected 2 days and 6 days after irradiation. The increase in endoneurial fluid pressure is compared with other models of Wallerian degeneration in which the entire fascicle was involved to aid in a comparative study of the role of oedema in neuropathy.

Topography of the human corpus callosum

This study was undertaken to determine the topographical organization of fibers coursing through the human corpus callosum. We correlated the distribution of Wallerian degeneration in the corpus callosum with the anatomical sites of focal cortical lesions due to ischemic infarctions or circumscribed contusions. Fibers from the inferior frontal and anterior inferior parietal regions course through the rostrum and genu of the corpus callosum. Callosal connections from the temporo-parieto-occipital junctional region course through the splenium and caudal portion of the body of the corpus callosum. Both the superior parietal lobule and the occipital cortex give rise to interhemispheric fibers that course exclusively through the splenium of the corpus callosum. No callosal degeneration was associated with a cortical lesion in the anterior superior frontal region. The topographical organization of fibers in the human corpus callosum appears to be fairly similar to that found in the rhesus monkey (Macaca mulatta).

Quantitative method for detection of blood-nerve barrier alterations in experimental animal models of neuropathy

A solid phase radioimmunoassay was developed for measuring albumin concentrations in both endoneurium and serum, which were normalized to total endoneurium and serum protein to obtain a blood-nerve barrier index (BNB-index). The BNB-index in experimental lead neuropathy demonstrated barrier dysfunction beginning at 6 weeks of 4% lead carbonate ingestion and at 14 weeks was 5.2 times that of pair-fed controls. These data, therefore, confirmed investigations that indicated a gradual alteration of the BNB beginning at 6 weeks and were based on (i) direct measurement of endoneurial albumin concentration by densitometry after sodium dodecyl sulfate-pore gradient electrophoresis and (ii) intravenous injection of 125I-albumin (J. F. Poduslo, P. A. Low, A. J. Windebank, P. J. Dyck, C. T. Berg, and J. D. Schmeltzer, 1982. J. Neurosci. 2: 1507-1514). The BNB-index after crush injury was 2.2 times that of control nerves at 24 h and gradually decreased toward normal values but was still 1.6 times that of controls at 70 days, a value consistent with the prolonged time course for complete repair. The BNB-index, therefore, can be used to evaluate BNB alterations quantitatively in animal models of neuropathy. Furthermore, we suggest that the BNB-index can also be used on biopsied, neuropathic, human sural nerve for evaluation of blood-nerve barrier abnormality.

Ultrastructural sequence of myelin breakdown during Wallerian degeneration in the rat optic nerve

Adult albino rats were subjected to unilateral surgical removal of the eyeball. After survival times of 7-140 days, the numerical response of the neuroglial cells, and the progressive disintegration of the myelin sheaths in the optic nerves, were studied qualitatively and quantitatively in electron-microscopic montages. The distribution density of microglia and astroglia in degenerating optic nerve increased to peaks after 35 and 56 days respectively, whereas, the oligodendroglia gradually decreased. During the early stage of degeneration, microglial cells appeared and invaded the sheath at the intraperiod line, peeling off the outer lamellae, which were then engulfed by phagocytosis. Within the microglia, myelin sheath fragments were surrounded by a membrane curled to form a myelin ring. In the intermediate stage of degeneration, the paired electron-dense lines of the ring, made up of myelin basic protein, decomposed and formed a homogeneous or heterogeneous osmiophilic layered structure, the myelin body, which, in the final stages, disintegrated and transformed into globoid lipid droplets and needle shaped cholesterol crystals.

Selected recent advances in peripheral nerve injury research

Interactions between Schwann cells and growing neurites are reviewed as are the implications of axonal transport studies in shaping the regenerative process. Increased investigative attention will be required to study biochemical changes occurring in the local environment of the injury site even though continued study of the neuronal metabolic process remains critical. Important studies concerning the connective tissue structure of nerve and probable "blood-nerve barrier" sites are reviewed. Factors responsible for connective tissue proliferation and fibroblast alignment after injury are not well understood. Recent experimental studies relating to surgical repair of nerve are reviewed as are a few selected papers reflecting changes in clinical management of the patient with nerve injury.

Direct immunofluorescence findings in peripheral nerve from patients with diabetic neuropathy

Direct immunofluorescence examination was performed on peripheral nerve from 16 patients with diabetes mellitus and 53 additional patients with peripheral neuropathy of diverse cause. Six nerves from patients with diabetes mellitus yielded positive findings: 4 had granular and lamellar deposition of IgM within the perineurium (of which 2 also had fibrinogen, IgA, C3, and albumin and 1 also had IgG); 1 had IgM, C3, and C4, and perineurial fibrinogen; the sixth contained linear perineurial C3 and fibrinogen. These 6 nerves contained axonal degeneration (3), axonal degeneration with chronic demyelination (1), microvasculitis with wallerian degeneration (1), and no pathological change (1). Sixteen of 53 nerves from nondiabetics yielded positive findings with immunofluorescence, possibly as a result of vascular leakage or as a manifestation of impaired removal of plasma proteins. The deposition of immunoreactants, as well as other plasma proteins, in peripheral nerve from patients with diabetes mellitus probably represents a "trapping" phenomenon reflecting altered basement membrane permeability. Alternatively, the changes could reflect a defect in the blood-nerve barrier in diabetic microangiopathy.

The effect of sciatic nerve transection on myelinated fibers in the L5 dorsal root and lumbar dorsal column. A Marchi study in the rat

The occurrence of Marchi-positive structures (MPS) in the L5 dorsal root and lumbar dorsal column was examined 1-18 weeks after unilateral sciatic nerve transection in rats, and compared to the occurrence of MPS during Wallerian degeneration seen after transection of L4 and L5 dorsal roots. There was an increasing number of MPS centrally to the junction between the peripheral (PNS) and central nervous system (CNS) and in the lumbar dorsal column ipsilateral to sciatic nerve transection throughout the examined time period. In the portion of the root distal to the PNS-CNS junction MPS were rare before 12 weeks postoperatively after which time small groups of MPS appeared. At all stages the incidence of MPS was just a fraction of that seen during Wallerian degeneration. From these observations it is inferred that few ganglion cells with myelinated central processes undergo complete disintegration after peripheral nerve transection. In addition, some of the myelinated central ganglion cell processes appear to be more severely affected proximal to the PNS-CNS junction than distally to it.

Ultrastructure of the radial components of the mouse optic nerve and its changes during Wallerian degeneration

Radial components of the optic nerve of the mouse were studied by using thin sections and freeze-fracture replicas. The investigations were performed on normal optic nerves, as well as on those undergoing Wallerian degeneration following eyeball enucleation. Normal radial components in thin sections were observed as a series of light lines composed of small electron-lucent dots situated in the interperiod lines across the myelin sheath. They are frequently found in those parts of the myelin sheath lying near the outer and inner processes of the oligodendroglia. Radial components in freeze-fracture replica were observed as a parallel array of many ridges composed of a row of particles. The particles of radial components located in the deeper part of the myelin sheath lose their linear arrangement and fall into disorder in a relatively early post-operative period. The parallel array of rows of particles located closely beneath the outer processes of the oligodendroglia remained intact for a long period, even in a markedly distorted myelin sheath. The present observations suggest that the radial components are resistant against the disintegration of the myelin lamellae during Wallerian degeneration.

Central-peripheral distal axonopathy in the spontaneously diabetic BB-rat: ultrastructural and morphometric findings

Central sensory nerve fibers were examined at distal (C3) and proximal (D12) levels of the gracile tract in the spontaneously diabetic BB-rat. Ultrastructural findings included early occurring malorientation of axoplasmic neurofilaments, axonal sequestration by honeycombing, and ensuing progressive axonal atrophy followed by Wallerian degeneration. Quantification of qualitative findings revealed a proximal to distal gradient in severity. Morphometric analysis confirmed a progressive myelinated fiber atrophy, which was more severe at the distal level. These findings are similar to those earlier described in peripheral sensory nerves of this model. Taken in concert with these previous findings, we conclude that the distal mainly sensory polyneuropathy in the diabetic BB-rat can be classified as a central-peripheral distal axonopathy.

On the occurrence of the fenestrated vessels in Wallerian degeneration of the peripheral nerve

Ultrastructural studies were made on the distal segments of the mouse phrenic nerve after crush injury. In the control, endoneurium contained only unfenestrated capillaries. In the experiment, from day 2 to day 6, endoneurial capillaries occasionally showed fenestrations with the attenuation of its cytoplasm. At this stage, axonal degeneration and myelin breakdown became evident showing early stage of Wallerian degeneration. In addition, detachment of the neighboring endothelial cells concomitant with the invasion of macrophage was also observed. These findings were previously unobserved changes of the endoneurial endothelium in Wallerian degeneration. The significance of the early occurrence of fenestrae was discussed briefly.

Lesions in bovine progressive degenerative myeloencephalopathy ("Weaver") of Brown Swiss cattle

Gross changes and other necropsy findings in 36 purebred Brown Swiss cattle affected with bovine progressive degenerative myeloencephalopathy were nonspecific. Primary microscopic lesions were confined to the central nervous system, specifically the white matter of the spinal cord, axons in some brainstem nuclei, and Purkinje cells of the cerebellar cortex. Spinal cord lesions involved only the white matter and consisted of axonal degeneration, loss of axons and myelin, and status spongiosus. Axonal degeneration was characterized by swelling and fragmentation of the axoplasm or formation of large, discontinuous swellings referred to as spheroids. Lesions were qualitatively similar at all levels, but quantitatively dissimilar in the same funiculi at different levels. Both ascending and descending fibers were involved but correlation to specific fasciculi was not evident. Lesions always were most severe in thoracic spinal cord segments. Little or no astroglial response, no inflammatory response, and no involvement of gray matter were observed in the spinal cord. Cerebellar lesions were limited to selective degeneration and loss of Purkinje cells and occasional swelling of Purkinje cell axons (torpedos) in the granular layer of the cerebellar cortex. Brainstem lesions were inconsistent and limited to occasional axonal swelling in brainstem nuclei. The pathogenesis of bovine progressive degenerative myeloencephalopathy is unknown and possible mechanisms were discussed. The disease exhibits a familial pattern in Brown Swiss cattle and may be hereditary. Extraneural lesions were considered secondary to central nervous system lesions.

Polyarteritis nodosa and peripheral neuropathy. Ultrastructural study of 13 cases

Peripheral nerves from 13 patients suffering from polyarteritis nodosa with multiple mononeuropathy were studied by light and electron microscopy. In the majority of cases, the vascular lesions were associated with Wallerian-like degeneration. Myelinated fibers presenting a normal axon with a disproportionately thin myelin sheath were less numerous. Unusual abnormalities consisted of swollen axons with an accumulation of organelles. Unmyelinated fibers were also damaged. A quantitative estimation of myelinated fibers loss did not show any selective vulnerability of either the large or the small diameter group.

Sutures or fibrin glue for divided rat nerves: Schwann cell and muscle metabolism

Peripheral nerve anastomoses using either epiperineurial sutures or a fibrinogen adhesive technique have been compared in the rat sciatic nerve model. Evaluation of results was made using radiolabelling of the metabolically active acid-soluble phosphate fractions of both nerve and muscle. In none of the situations tested--traumatic degeneration and regeneration in the sciatic nerve proximal segment, Wallerian degeneration and regeneration in its distal segment, atrophy and regeneration of the fast gastrocnemius muscle, and atrophy and regeneration of the slow soleus muscle--was one repair method significantly superior to the other. A significant degree of cross-reinnervation was shown to take place after anastomosis, altering the characteristics of the regenerating muscles. Both repair methods were equally inferior to the spontaneous repair occurring after a simple nerve crush.

Effects of cryotherapy on the palmar and plantar digital nerves in the horse

The duration of anesthetic effect and the histopathologic changes resulting from a controlled freeze of the palmar and plantar digital nerves in the horse were evaluated. Two techniques were compared: (i) nerves were frozen by direct application of the cryoprobe after surgical exposure and (ii) nerves were frozen by percutaneous application of the cryoprobe to the overlying skin. Return of skin sensation and ability to detect a stimulus were used to determine return of nerve function. The duration of anesthetic effect was significantly (P less than 0.005) longer for nerves frozen after surgical exposure than for those frozen by the percutaneous technique (mean 156 days vs 47.5 days). At the termination of the study, horses were euthanatized and all nerves were examined histologically. Neuromas-in-continuity were observed in 10 of 28 frozen nerves. Classification was based on the involvement of the supporting fibrous connective tissues of the nerve, endoneurium, perineurium, and epineurium. The direct technique of freezing the nerve after surgical exposure was repeatable and could be used to provide temporary neurectomy in the horse. The percutaneous technique caused a temporary loss of pain perception, but could not be relied on to interrupt nerve function for longer than a few weeks.

[Morphological studies of gunshot wounds of the peripheral nerves in rabbits]

The author reports the results of morphological investigations in 48 experimental shot wounds of the peripheral nerves of rabbits. In 8 animals the missile hit directly the ischiadic nerve disrupting its continuity (neurotmesis). The microscopic picture of not discupted nerves differed from one animal to another. Three types of microscopic findings were distinguished: 1) normal microscopic appearance, 2) Wallerian degeneration, 3) axonal regeneration. Normal appearance of nervous fibres was observed in all three groups of animals studied at different time intervals after injury (8-10, 18 and 56 days after injury). In the first and second groups Wallerian degeneration prevailed, while axonal regeneration was a typical finding in groups II and III. Microscopic changes in the nerves were very similar to those observed in peripheral nerves subjected to traction injury. It may be assumed that the cause of shot injury was sudden stretching of the nerve trunk in the pulsating shot channel.