Neuroglia of the adult rat optic nerve in the course of wallerian degeneration

The neurological reactions in Wallerian degeneration have been studied by electron microscopy in the optic nerve of adult albino rats from 7 to 120 days after unilateral enucleation. Reactive astrocytes contained abundant dense bodies, numerous microtubules and hyperplastic glial filaments. These astrocytes also assisted phagocytosis of degenerated myelin sheaths and in glial scar formation. Oligodendrocytes disconnected their cytoplasmic extensions, which were phagocytosed by microglial cells and astrocytes, by increased production of lysosomes. Microglial cells consisted of crinkled, long, rough endoplasmic reticula, several highly-active Golgi complexes, laminar inclusions and globoid lipid droplets. Microglia engulfed and lysed the disintegrated axons and myelin sheaths.

Sutures of fibrin glue for divided rat nerves. Schwann cell and muscle metabolism

A comparative study using 32P-labeling techniques on Schwann cell and skeletal muscle metabolism after repair of divided rat sciatic nerve by anastomosis with either microneurosurgical sutures or fibrinogen tissue adhesive shows no significant difference between the two repair modes. The successful measurement of functional muscle regeneration in the experimental study of nerve repair techniques is still hampered by the absence of definitive functional and physiologic criteria, despite an apparent normal anatomic restitution of the muscle.

The role of non-resident cells in Wallerian degeneration

Wallerian degeneration was studied in the phrenic or sciatic nerves of mice following transplantation into Millipore diffusion chambers of 0.22 micron pore size which were implanted in the peritoneal cavity and kept for up to eight weeks. This method positively eliminates the access of nonresident cells to the tissue, at the same time providing proper conditions for tissue survival. Such nerves showed no proliferation of Schwann cells and no evidence for their active role in the removal or digestion of myelin. Schwann cells rejected their sheaths and the latter persisted for weeks, leading either to sheath distension (the sheath becoming wider and thinner) or to collapse (the sheath becoming thicker, collapsing upon the empty axis cylinder). The outer envelope of Schwann cytoplasm separated into pseudopodia rich in microtubules. Sheath rejection led to a slow decay of the myelin in the absence of active phagocytosis. There was profuse fibroblastic proliferation from the epineurium and perineurium, from which cells migrated into the chambers developing fatty change. No evidence was found to link the fatty change in fibroblasts to sheath decay. Diffusion chambers of 5.0 micron pore size were invaded by leukocytes and monocytes. Nerves kept in such chambers showed active phagocytosis of myelin leading to its removal, similar to Wallerian degeneration in situ. Phagocytes were shown to attack selectively the rejected myelin sheaths, distinguishing the latter from the surviving Schwann cells, even though both structures derive from the same cell. The activity of phagocytes in digesting myelin was mediated by a signal which diminished in intensity with time; there was very little active phagocytosis of myelin in nerves that had been predegenerated in 0.22 micron pore chambers. Various modifications of the experiment, including studies with co-cultured peritoneal macrophages or bone marrow, indicate a need for additional activating factors to induce myelin phagocytosis.

Alteration of sulfatide synthesis in control and Trembler mice during Wallerian degeneration and remyelination

Sulfatide synthesis from sulfate is much greater in the peripheral nerves of the Trembler mouse. After nerve transection, during Wallerian degeneration, this synthesis rate drops down very rapidly in both normal and Trembler mice. Twenty-four hours after permanent transection, the rate of synthesis is reduced by 80% in the mutant and 50% in the normal mouse. Four days after transection, the synthesis rate in the Trembler is only 9% of that observed in intact nerves, and 21% of that in the intact nerves of normal animals. After 5 d the synthesis remains constant. Thus, enhanced synthesis of sulfatides in the Trembler mouse is probably not caused by Wallerian degeneration. After crush of the sciatic nerve, the synthesis rate decreases very rapidly in the normal mouse as it does after permanent transection. But during regeneration, from the 7th day, it rises dramatically and 14 d after crush, a 2.5-fold increase in the synthesis rate is observed, compared to that in the contralateral control nerve. This synthesis rate returns to normal 1 mo after crush. In the Trembler, the synthesis decreases for 2 d after crush and increases from then on, eventually reaching the value of the contralateral control Trembler nerve within 2 mo. In the mutant there is no prominent peak of sulfatide synthesis during regeneration.

Peripheral nerve morphometry in stroke patients

Sural nerve biopsy specimens from affected and non-affected limbs of stroke patients were examined morphometrically. Two principle abnormalities of peripheral nerve were found in hemiparetic and hemiplegic limbs. First, the frequency of abnormal teased nerve fibers was significantly increased with abnormal internodes frequently "clustered" and showing a 50% or more reduction in myelin thickness. Second, the mean diameter of myelinated nerve fibers was reduced. These results suggest a primary atrophy of peripheral nerve fibers in the affected limbs of stroke patients with secondary demyelination. Possible aetiological factors include disuse, transynaptic degeneration, ischemia, pressure effect, and decreased axoplasmic flow. It would seem that the structural integrity of peripheral nerve is frequently compromised following a cerebral lesion.

Chronic nerve compression--an experimental model in the rat

This study reports a rat model of chronic nerve compression. The sciatic nerves of adult male Sprague Dawley rats were bonded with 1-cm lengths of tubing with varying internal diameters. Histological and electrical studies as well as studies to assess the blood-nerve barrier function were carried out at one through six months. With marked compression of the sciatic nerve, profound electrical changes were noted as early as one month, and histological findings were those of degeneration and regeneration. In the rats with minimal compression, nerve conduction studies remained normal. The earliest findings were alterations in the blood-nerve barrier, followed by histological changes in the large myelinated fibers at the periphery of the fascicles and changes about the nodes of Ranvier. This model appears to be a valid one with which to study other aspects of both the pathophysiology and treatment of chronic nerve compression.

The non-directional pattern of axonal changes in Wallerian degeneration: a computer-aided morphometric analysis

Wallerian degeneration was investigated to determine whether axonal changes occur progressively in a somatofugal or somatopetal direction or simultaneously along the length of the axon. Microtubule density was used as a measure of the extent of axonal degeneration and was assessed by a computer-aided analysis of electron micrographs. The left sural nerves of ten rats were crushed and 30 hours later axonal areas and axonal microtubule numbers were recorded from a large sample of axons at two sites 1 cm and 3 cm distal to the crush. The same recordings were made from the right unoperated nerve at two comparable sites. Statistical analysis of all the data provided no evidence for a somatofugal or reverse direction of degeneration. It is concluded therefore that in Wallerian degeneration axonal changes, as indicated by microtubule dissolution, occur simultaneously along the length of the axon. It is proposed that to interpret the conflicting published data on the direction of fibre degeneration, Schwann cell changes (e.g. myelin ovoid formation) and axonal changes (e.g. microtubule dissolution) should be considered independently since they have different aetiological mechanisms which may account for the differing experimental results reported.

[Clinical physiopathology of axoplasmic flow]

Anatomical, biological and patho-physiological characteristics of axoplasmic transport are described in normal conditions and experimental neuropathies.

Acute vs. chronic compressive neuropathy

Studies of the management of acute and chronic compressive peripheral neuropathies have not kept pace with advances in our understanding of the pathophysiology of these disorders. In this review, the pathophysiological differences between acute and chronic compressive neuropathy are reviewed from experimental models as well as from clinical examples in humans. It is concluded that surgical intervention is unlikely to alter significantly the course of recovery in acute compressive neuropathies. Similarly, in chronic compressive neuropathies without progressive weakness, conservative treatment is indicated because of the high incidence of spontaneous improvement. However, in patients with progressive weakness, especially in conjunction with electrophysiological evidence of partial denervation or conduction block (but not simply slowing of nerve conduction), surgical treatment is recommended.

Wallerian degeneration demonstrated by magnetic resonance: spectroscopic measurements on peripheral nerve

Wallerian degeneration of rat sciatic nerves was induced by nerve section. Fifteen days later the degenerated nerves were compared with the intact contralateral nerves from the same animal. Histological sections showed the changes typical of wallerian degeneration: axonal degeneration and secondary demyelination. The freshly dissected nerves were analyzed by magnetic resonance (MR) spectroscopy at 10 MHz, and the water content was determined by dehydration. In the degenerated nerves there was a marked prolongation of both T1 and T2 relaxation times, accompanied by an increase of water content. The results demonstrate the sensitivity of MR for detection of secondary demyelination and disintegration of nerve structures. These results suggest that it should be possible to detect wallerian degeneration in MR images; this will have an important impact on neuropathological diagnosis of central and peripheral nervous system lesions.

Cardiac adrenergic innervation after instrumentation of the coronary artery in dog

A fine methacrylate ring (not constricting the artery) was placed around the ramus interventricularis anterior (RIA) of the left coronary artery in dogs. By means of Falck's histochemical technique an extensive degeneration of the vasomotor and cardiomotor adrenergic innervation of ventricles was detected 14 days after the procedure. The innervation of atria remained intact. The surgical intervention as well as the scarring process (which compressed the conducting parts of axons composing the perivascular nerves) induced the degeneration. The results have important implications for experiments with instrumented arteries.

Myelin associated glycoprotein (MAG) in Wallerian degeneration of the optic nerve

The content of myelin associated glycoprotein (MAG) was studied in the rabbit optic nerves undergoing Wallerian degeneration after ophthalmectomy . MAG was estimated according to the method described by Matthieu and Quarles (1973). The results of the studies demonstrated only negligible changes in the content of MAG in the course of central Wallerian degeneration. These experiments do not support the assumption that the periaxionally localized MAG of the central myelin is as a rule seriously involved in subcellular mechanisms functioning in early stages of central demyelinating processes.

Laminin in rat sciatic nerve undergoing Wallerian degeneration. Immunofluorescence study with laminin and neurofilament antisera

Immunofluorescence with laminin antisera revealed a striking change in the localization of this basal membrane glycoprotein in rat sciatic nerve as a result of Wallerian degeneration. The staining was confined to the endoneurium in normal sciatic nerve and during the first days of degeneration. On day 11 endoneurial tubes were no longer identified in the distal stump of crushed nerves or of nerves that had been transected and tightly ligated to prevent regeneration. In both crushed and ligated nerves proliferating Schwann cells forming the cell-bands of Büngner were intensely laminin positive. With double-labeling experiments, laminin and neurofilament antisera revealed similar but not identical staining patterns in crushed nerves, which suggests a close relation between laminin and regenerating axons. Crushed nerves had recovered their normal appearance 18 days after operation while anti-laminin reactivity was decreased in parts of ligated nerves undergoing fibrosis. The localization of laminin in reactive Schwann cells was confirmed by electron microscopy using the indirect immunoperoxidase procedure. Axons did not contain reaction product.

[Recent data on Schwann cells]

Because of the role they play in the physiopathology of peripheral neuropathies, Schwann cells have been the subject of numerous studies for some ten years. Schwann cells originate in the ectoderm. They migrate along the myelinated and the unmyelinated axons of peripheral nerves, and lie on a basal lamina. They are responsible for the myelination of peripheral nerves; whether the Schwann cell does or does not form a myelin sheath is determined by the type of axon with which it associates. Recent techniques, such as chimaeric quail-chick embryos, biochemical analysis of human peripheral nerve biopsies, Schwann-cell cultures, nerve grafts, mouse mutants, have permitted some progress. The biochemical composition of peripheral myelin is almost completely known. In vitro, Schwann cells can synthesize myelin-specific molecules. Interactions between axons, Schwann-cells and extra-cellular space have been observed.

Dysautonomia in Guillain-Barré syndrome with dorsal root ganglioneuropathy, wallerian degeneration, and fatal myocarditis

An acute Guillain-Barré syndrome presenting as dysautonomia is described in a 12-year-old boy. The patient died of intractable cardiac arrhythmias and cardiac failure. A severe myocarditis with destruction of dorsal root ganglion cells and wallerian degeneration of dorsal roots and peripheral nerves was apparent postmortem. Segmental demyelination and inflammatory cellular infiltrations were not present at these sites.

Changes in the compact myelin of single internodes during axonal atrophy

Distal axonal atrophy was produced by proximal constriction of the tibial nerve in the rabbit. Transverse sections were studied by light and electron microscopy at 10 micron intervals along individual internodes of both atrophic and normal tibial nerve fibres. During axonal atrophy there were marked changes in axonal configuration at different levels within the territory of a single Schwann cell. These resulted in changes in the lengths of the axon perimeter and myelin spiral, without causing any alteration in the numbers of myelin lamellae or their spacing. Comparable changes in axon perimeter and myelin spiral length were seen in transverse sections through the paranodal and nuclear regions of normal fibres. These results show that local variations in axonal calibre or shape are associated with appropriate adjustments to the length of the myelin spiral, without a change in the number of lamellae, and thus of sheath thickness.

Wallerian degeneration of the corticospinal tract region of the brain stem: demonstration by computed tomography

Pathophysiological and CT aspects of wallerian degeneration of the corticospinal tract in the brain stem were studied in patients with old hemispheric infarcts. There was found to be a clear relationship between (a) the location and size of the infarcts and (b) the presence or absence of wallerian degeneration. When most of the motor cortex is involved, degeneration can be seen at least as far as the mesencephalic level and sometimes down to the pontine level. Isolated capsular infarcts which spare the motor cortex are also associated with degeneration. No degeneration could be seen in patients with small infarcts.

[14C]acetate metabolism in the peripheral nervous system

Lipid biosynthesis was studied by incorporation of [14C]acetate into different compartments of rat sciatic nerve during development, degeneration and regeneration. Acetate incorporation was over three times higher in the sciatic endoneurium (desheathed nerve) than in epi- and perineurium. The endoneurium contained much higher contents of radioactively labeled membrane lipids (cholesterol and phospholipids) than did the epi- and perineurium (mainly triacylglycerol), indicating a benefit of utilization of endoneurium in the study of the metabolic derangements of peripheral nerve lipids. When 3H2O was used as a precursor, no incorporation was found. Endoneurial lipid biosynthesis from [14C]acetate decreased rapidly as myelination proceeded. After 4 months, the decrease continued but at a much slower rate. The total acetate incorporation found in endoneurial lipids of 6-month-old rats was predominantly in the free fatty acid fraction (40%), but was only 5% of that found in 10-day-old rats, demonstrating the importance of age-matched controls for metabolic studies of diseased nerve. During Wallerian degeneration, a decreased acetate incorporation into endoneurial lipids was observed as early as 2 days after crush injury. The profile of labeled lipids in developing and degenerating nerve revealed that the rate of lipogenesis did not change to the same extent for each lipid subclass. Cholesterol biosynthesis appeared to be the most sensitive. During regeneration, an increase in the uptake of [14C]acetate and an altered profile of labeled lipids demonstrated that the metabolic state of adult peripheral nerve, which is normally relatively inactive, can be modified by an exogenous factor such as crush injury.

Retrograde axoplasmic transport of toxic lectins is useful for transganglionic tracings of the peripheral nerve

Wallerian degeneration in the primary afferents consequent to death of parental root ganglion cells was successfully traced up to the level of the nucleus gracilis, following intraneural injections of ricinus communis agglutinin (RCA 60 or RCA 120) into the sciatic nerve or its branches. This method serves as a novel way of tracing primary afferents in the CNS in strict concordance with their counterparts in the peripheral nerve.

Early histopathologic changes in experimentally replanted extremities

Early serial histologic changes in replanted extremities have not been well defined; their contribution to a suboptimal functional result is unknown. With the use of a rat hind limb replantation model to address this question, we studied tissues of the replanted legs by light microscopy from 1 to 60 days after replantation. Although early lesions were consistent with ischemic injury, the chronic preparations were remarkably normal, and the lesions were more consistent with denervation. Poor function in clinical replantations may be a reflection of more pronounced versions of these pathologic lesions.

Proper microsurgical nerve suture may impede Wallerian degeneration of completely transected nerves. An electron microscopic study

Electron microscopic findings on the nerve of the biventer cervicis muscle of the chick, which was completely transected and immediately after submitted to an adequate microsurgical nerve suture, confirmed our previous statement that proper microsurgical nerve suture may impede the Wallerian degeneration that normally occurs in the distal segment of a completely transected nerve.

Recovery of distal changes after nerve constriction by a ligature

When ligatures were used to constrict the proximal tibial nerve in rabbits, nerve fibres distal to the site of constriction underwent a reduction in axonal and external fibre diameter, and in conduction velocity. Distal changes could be detected within 7-12 days of the onset of constriction; removal of the ligatures was followed by partial recovery. When paranodal myelin damage occurred in the distal tibial nerve, it showed the typical non-random distribution of secondary demyelination, with multiple paranodal defects on some fibres and complete sparing of others. These findings emphasize the role of the axon in the genesis of paranodal demyelination.

Plasma membrane pores of the Schwann cell in Wallerian degeneration: a morphometric analysis

Using the freeze-fracture technique, myelinated fibres were examined from the rabbit sciatic nerve at 48 h after a proximal nerve crush. Employing computer-aided morphometric techniques the distribution of Schwann cell plasma membrane pores was analysed. In both normal control and crushed nerves membrane pores were restricted to the cytoplasmic circumferential bands and longitudinal columns, which characterize the surface of the myelinated nerve fibre, and were absent from the flat plaque-like areas delimited by the bands and columns. In approximately half of the myelinated fibres from the crushed nerves there was a five-fold increase in the density of plasma membrane pores. This response of the Schwann cell was interpreted in terms of an increase in pinocytosis and related to regenerative phenomena in the peripheral nerve.