PEASE DC: DEGENERATIVE CHANGES IN RAT DORSAL ROOTS DURING WALLERIAN DEGENERATION

Degenerative and regenerative changes in the trochlear nerve of goldfish

The features of unlesioned and lesioned trochlear nerves of goldfish have been examined electron microscopically. Lesioned nerves were studied between 1 and 107 days after cutting or crushing the nerve. Unlesioned nerves contained, on average, 77 myelinated axons and 19 unmyelinated axons. The latter were found in 1-2 fascicles per nerve. A basal lamina surrounded each myelinated axon and fascicle of unmyelinated axons. The numbers of myelinated axons, fascicles of unmyelinated axons and basal laminae varied by less than 5% over the intraorbital extramuscular segment of the nerve. Following interruption of the nerve, by either cutting or crushing, all of the axons and their myelin sheaths began to degenerate by 4 days in the distal nerve-stump. Both abnormally electron-dense and electron-lucent axons were observed. Both Schwann cells and macrophages appeared to phagocytose the myelin sheaths. Following a lesion, the Schwann cells and their basal laminae persisted in the distal nerve-stump. In crushed nerves, the basal laminae surrounding myelinated axons formed 97%, on average, of the Schwann tubes in the distal stump. The perimeters of the basal laminae were of similar size to those in the proximal stump, at least for the first 8 days after crush. In crushed nerves, single myelinated axons in the proximal nerve-stump gave rise to multiple sprouts, some of which reached the site of crush by 2 days, the distal stump by 4 days and the superior oblique muscle by 8 days. The regeneration of the unmyelinated axons was not examined. In both crushed and transected nerves, nearly all of the sprouts in the proximal and distal stumps were found within the basal laminae of Schwann cells, even though the spouts were disorganized in the transected region where there were no basal laminae. The growth cones of the regenerating axons were always found apposed to the inner surface of the basal laminae, which may have provided an adhesive substrate that directed their growth. Terminal sprouts from the ends of myelinated axons in the proximal stump accounted for the majority of the regenerating axons in the distal stump, as only a few collateral sprouts were found in the proximal stump, and only a small amount of axonal branching was found within the distal stump itself. The largest axons in the distal stump were remyelinated first, and the number of remyelinated axons increased progressively between 8 and 31 days after crush, at which time there were about twice as many as in unlesioned nerves.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent and efferent axons in the medial and posterior articular nerves of the cat

The goal of this study is to determine the average numbers of afferent axons and postganglionic autonomic (sympathetic) efferent axons supplying the cat knee joint through the medial and posterior articular nerves. Interestingly, both nerves are composed primarily of unmyelinated axons. Only 20% of the axons in the medial articular nerve are myelinated, with the overwhelming majority, 80%, being unmyelinated. The posterior articular nerve has 78% unmyelinated and 22% myelinated axons. Neither nerve contains ventral root efferent axons. The sympathetic chain, in both nerves, contributes no myelinated and only 50% of the unmyelinated axons. The medial and posterior articular nerves are therefore predominantly afferent, since all myelinated and the remaining 50% of the unmyelinated axons arise from the dorsal root ganglion cell. The ratio of afferent unmyelinated to myelinated axons is 2:1. The roles of these afferent unmyelinated axons must now be considered in regard to joint kinesthetics and pain.

An electron microscopic analysis of the left phrenic nerve in the rat

In this electron microscopic study, the axonal categories in the left phrenic nerve at its entrance to the diaphragm have been determined. At a level 3 mm rostral to the diaphragm, the left phrenic nerve contains approximately 700 axons: 57% are myelinated and 43% are unmyelinated. The dorsal root ganglion cells give rise to 31% of the myelinated axons and the ventral root contributes 69%. Of the unmyelinated axons, the dorsal root ganglion cell contributes 59%, the cervical sympathetic chain 24%, and 17% course through the ventral roots. These ventral root unmyelinated axons are presumably preganglionic efferents since the proximal stump of the ventral root showed no decrease in unmyelinated axons after ventral rhizotomy.

Ultrastructural changes in rat peripheral nerve following pneumatic tourniquet compression

The sciatic nerves of 12 male rats were examined in the electron microscope 14 days after pneumatic tourniquet compression. Tourniquet pressure was maintained at 300 mmHg for varied lengths of time (30 minutes to 3 hours). Nerves compressed for 30 minutes showed very mild fissuring of the myelin without axonal degeneration. Examination of nerves compressed for 1 to 3 hours showed progressively more varied and extensive damage. Changes included splaying of myelin lamellae, axonal shrinkage with periaxonal edema. Schwann cell hypertrophy, and an increase in the number of microtubules and mitochondria per unit area. The myelin sheaths of some fibers, compressed for more than 2 hours, were completely ruptured. These changes resemble nerve lesions which could be induced by a variety of experimental procedures. Ultrastructural changes produced by tourniquet compression are apparently time-related and affect large-diameter nerves more profoundly than smaller-diameter nerves. The data reported provide an explanation for delayed muscle rehabilitation experienced by patients who have undergone extremity surgery with pneumatic tourniquet application. The evidence presented suggests that the incidence of tourniquet palsy may be far greater than previously recognized.

Nerve regeneration--evidence for early sprout formation

Following microneurorrhaphy, sharply transected rat sciatic nerves were harvested 2, 5, 12, 16, 21, and 30 days after repair. Transverse sections of these specimens were made 3, 5, 7, 9 and 11 mm distal to the repair and examined with the scanning electron microscope. Myelinated sprouts were found 3 mm distal to the repair on the fifth day. Sprout migration occurred even though old myelin sheaths were present. Sprouts did not appear in old myelin sheath lumens. Many 5 U myelinated sprouts were found 11 mm distally 21 and 30 days after repair. This study demonstrates that nerve regeneration begins early, before degeneration is complete.

Non-neuronal cell cultures from dorsal root ganglia of the adult cat: production of Schwann-like cell lines

There are several methods available for the production of Schwann cell cultures from fetal and neonatal peripheral nervous tissue. We have investigated methods for producing Schwann cell-rich cultures from adult tissue. Dorsal root ganglia from normal adult cats were used to initiate explant cultures or subjected to primary dissociation. The resulting cultures were compared in terms of growth, the proportions of fibroblastic and Schwann-like cells in primary cultures and the effects of subculture on the relative frequency of these cell types. We found that excision and transfer of explanted ganglion pieces after 14 days in culture produced a secondary outgrowth rich in small, bipolar, spindle-shaped Schwann-like cells. Subculture of this outgrowth produced secondary cultures of predominantly Schwann-like cells with typical spindle-shaped morphology. The use of antimitotic agents in the media to inhibit fibroblast growth was not observed to be necessary or beneficial with this adult tissue. Primary dissociation of ganglia with enzymes (trypsin or collagenase) and mechanical agitation was even more effective in producing secondary cultures and cell lines that were, by morphological criteria, predominantly or exclusively Schwann-like cells. One of these Schwann-like cell lines, designated GSA, has been carried over 24 subcultures while retaining characteristic Schwann cell morphology. Cells of this line have been examined by scanning and transmission electron microscopy. Karyotype analysis indicates a chromosome complement consistent with the species of origin, a normal cat.

Cultures enriched in Schwann-like cells from dissociated nerve segments of the adult cat

Methods for producing Schwann cell-rich cultures from nerve segments of the adult cat were investigated. Efficient dissociation was achieved with a combination of collagenase and trypsin. Differential attachment of elements within the resulting suspension allowed production of Schwann cell-rich cultures derived by outgrowth from slowly attaching segments of degenerating myelin sheath tube containing Schwann-like cells. Rapid trypsinization during subculture further increased the proportion of Schwann-like cells in these cultures to 90% or more.

Retardation of Schwann cell division and axonal regrowth following nerve crush in experimental lead neuropathy

In experimental lead neuropathy, Schwann cells undergo segmental demyelination and possible cell death and, concurrently, remyelination and multiplication to create new internodes of myelin and onion bulb formations. In rats fed 4% lead carbonate for three months, the ability of Schwann cells to divide (percentage showing mitotic figures, labeling index, n total number per millimeter of fascicular length of nerve) was studied serially for four weeks. Schwann cell events were also compared in sural nerve distal to crush with and without resection of an intervening length of nerve. In both cases, Schwann cell multiplication as a result of axotomy was retarded in lead-intoxicated as compared to control animals. On the average, regrown myelinated axons four weeks after and 10 mm below the point of crush in lead-treated animals were similar in number and smaller in caliber, but they exhibited a normal relationship of myelin thickness to axonal area compared with control animals. These studies provide evidence that Schwann cell division and axonal regrowth after crush are retarded in experimental lead neuropathy.

An ultrastructural study of spinal nerve roots and dorsal root ganglia in aging rats with spontaneous radiculoneuropathy

The spinal nerve roots and dorsal ganglia of 104- to 135-week-old rats with spontaneous radiculoneuropathy were examined by light and electron microscopy. Demyelination was common in myelinated fibers of various diameters of both ventral and dorsal roots. The most striking alteration was wide distention of myelin sheaths, which extended throughout the entire internode. The spaces formed between separated lamellae frequently were invaded by macrophages. Subsequent vesicular degeneration of myelin seemed to be mediated by invading macrophages. These processes caused complete myelin destruction, but most axons showed no degenerative changes except for obvious reduction in diameter. Occasionally, there were clumping and partial degradation of neurofilaments and ruptured axolemma in the severely demyelinated axons. A few fibers also were undergoing wallerian-type degeneration, perhaps secondary to the severe demyelinative changes. Remyelinating fibers in various phases of repair were coexistent with markedly demyelinated ones. Demyelinative changes described above also developed within some of these remyelinated internodes. There were no remarkable changes in neurons of the dorsal root ganglia, though accumulation of lipofuscin was common. Our findings suggest that the changes in the nerve roots are essentially a primary segmental demyelination in aging rats with radiculoneuropathy.

Long-term survival of centrally projecting axons in the optic nerve of the frog following destruction of the retina

A significant number of unmyelinated axons and their synaptic endings in the frog, Rana pipiens, were found to retain a normal morphology long after separation from their cell bodies. At the end of various survival periods following unilateral removal of the retina, horseradish peroxidase (HRP) was administered to the optic nerve stump by a fiber-filling method. In frogs maintained at 20 degrees C, unmyelinated optic nerve axons conducted HRP from the site of application in the orbit to layers A, C, and E of the contralateral optic tectum, even though their retinas had been removed up to 69 days earlier. Such fiber-filling was absent beyond 19 days in other frogs surviving at 35 degrees C. No labeled fibers were continuous with any intracerebral neurons. The HRP was always localized intraaxonally, and the marked axons and terminals were ultrastructurally normal. Counts of surviving axons from electron micrographs of the optic nerves showed that, at 20 degrees C, more than half of the normal complement of unmyelinated axons disappeared in the first 10 days. All the myelinated axons degenerated during the first 6 weeks survival. However, approximately 55,000 normal-appearing unmyelinated axons (12% of the unmyelinated fiber population) persisted in the optic nerve at 10 weeks following removal of the retina. The survival rate was lower at 35 degrees C. In other frogs, one eye was injected with 3H-leucine to initiate axonal transport into the retinal ganglion cell axons. That eye was removed 48 hours later. Autoradiographic analysis of brain sections of frog surviving an additional 31 to 61 days at 20 degrees C showed strong labeling of the optic tract and layers A, C, and E of the contralateral optic tectum. The absence of displaced ganglion cells that might exist within the optic nerve was verified by other observations. It is hypothesized that the potential shown by frog optic axons for long-term survival in the absence of the cell-body expresses a general property of vertebrate (and invertebrate) axons, rather than a special property of the frog optic nerve.

Degenerative changes in the distal stump of the severed human facial nerve

Specimens of distal segments of the human facial nerve obtained at reinnervation surgery (hypoglossal-facial anastomosis) were studied by light and electron microscopy. Severance of the facial nerve led to the Wallerian degeneration in the distal segment. When the lesion was made at the intracranial level of the nerve, the sensory bundle remained intact. In a specimen 17 days after section, motor fibers either had disappeared or had loss of axons and advanced stage of myelin breakdown. Sensory fibers appeared intact. In two specimens three months after severance, many Schwann cells of degenerated fibers still possessed degraded myelin; most Schwann cells had ingested myelin and formed endoneurial tubes (bands of Büngner). Endoneurium showed proliferation of fibroblasts and increased collagen deposition. A specimen obtained seven months after section showed fibrosis only. The fifth specimen obtained 30 months after severance of the tympanic segment showed only mild collagenization and well formed, not appreciably shrunken Schwann tubes. The distal stump of human facial nerve appears to undergo less denervation atrophy than demonstrated in the peripheral nerves of experimental animals. The collagenization process appears to be essentially completed already after three months denervation with little change after that. The distal stump of the human facial nerve appears to provide a good structural basis for reinnervation even after prolonged denervation.

Degeneration of axons in the ureteric and duodenal nerve plexuses of the adult rat following in vivo treatment with capsaicin

The fine structure of the ureteric and duodenal nerve plexuses was studied in specimens taken from adult rats 24 h after subcutaneous injection of 50 mg/kg capsaicin and in specimens taken from rats injected with the vehicle used to emulsify the capsaicin. In specimens from capsaicin-treated rats, there was extensive degeneration of axons in the ureteric plexuses and widespread, but much smaller amounts of degeneration of axons in the duodenal plexuses. Comparison of the fine structure of the plexuses in the capsaicin-treated rats with that of the plexuses in the control rats indicated that the degeneration was confined to axons with terminals containing mainly large dense-cored vesicles.

Pattern of myelin breakdown during sciatic nerve Wallerian degeneration: reversal of the order of assembly

Myelin sheaths of rapidly growing rats were sequentially labeled with the 3H and 14C isotopes of leucine as precursors of protein synthesis. The two injections were separated by time intervals ranging from 2 to 12 d. Wallerian degeneration was initiated by sciatic nerve neurotomy at 2 or 10 d after the second injection of radioactivity. After 5 d of degeneration, myelin was purified and the ratio of isotopes was determined in the delipidated protein. Regardless of the order in which the two isotopes were administered, the relative recovery of radioactivity resultant from the second injection was greatly reduced in degenerating nerves compared with sham-operated controls. Radioactivity incorporated from the first injection was also reduced, but to a lesser extent. Consequently, the isotope ratio corresponding to the first/second injection was greater in degenerating nerves than in controls, and the ratio increased in proportion to the time interval separating the two injections. The magnitude of the effect of degeneration was only slightly greater when degeneration was initiated 2 d after the second injection than when initiated 10 d after the last injection. Consequently, myelin disintegration rather than diminished incorporation of radioactivity accounts for the losses of radioactivity. Furthermore, the pattern of myelin degeneration preferentially involves the last myelin to be formed.

Studies of Schwann cell proliferation. II. Characterization of the stimulation and specificity of the response to a neurite membrane fraction

When prepared by methods utilized in our laboratory, pure populations of Schwann cells in culture do not divide, but, after recombination with peripheral sensory neurons or their processes, proliferate rapidly (Wood and Bunge, 1975, Nature (Lond.) 256:661--664). In this paper, we demonstrate that a membrane fraction prepared from sensory ganglion neurites is also mitogenic for Schwann cells and increases the labeling index (assessed by autoradiography after incubation of cells with tritiated thymidine) from less than 0.2 to 10% for primary cells, and from 0.4 to 18--19% for replated cells. The increased responsiveness of replated cells may reflect their greater access to the neurite membranes which is a consequence of the elimination of multiple cell layers after replating and the removal of the basal lamina. This stimulation was specific; addition of membrane preparations from other cell types (3T3, C1300, etc.) was not mitogenic. Ultrastructural analysis demonstrated apparent binding of neurite membranes to Schwann cells as well as significant phagocytosis of the membranes by the cells. The uptake of nonmitogenic membranes suggests that phagocytosis per se is not the stimulus of proliferation.

Multiple granular-cell tumors

Granular-cell tumors are uncommon dermal tumors. Recent studies favor a neural, Schwann-cell derivation. Approximately 10% of cases have multiple lesions and a like percentage have tender lesions. We report a case of multipe (9) small, dermal tumors in which tenderness was associated with perineural infiltration. The need for therapy is discussed.

Morphology of cardiac nerves in experimental infarction of rat hearts. II. Electron microscopical findings

Alterations of cardiac nerves in myocardial infarction were investigated by electron microscopy after differing intervals in 28 rats. During the first 4 h there are, in non-myelinated nerves within the myocardium, a swelling of the axoplasm with the occurrence of 'pale' axons and swelling of axonal mitochondria and neurosecretory granules. After bursting of the axolemma, these are spilled into the adjacent interstitial space. After 4 h first myelin figures are observed, and in some axons an accumulation of neurofilaments takes place. During the second to seventh day an extensive vesicular disintegration of axonal structures develops. Because of regressive changes, axons cannot be identified with certainty within the necrosis. After two or three weeks nerves with lamellar enfoldings of cytoplasmic processes corresponding to Büngner bands can be seen at the infarction border. These nerves may contain only a few residual axons. Myelinated nerves show a mainly vesicular disintegration. The results are discussed with regard to their functional significance and the special conditions of the animal model, in which ligature of the coronary artery may not only produce ischemia, but may also, by simultaneous ligature of the adjacent cardiac nerves, induce Wallerian degeneration.

The fine structure of stumps of transected nerve fibers in subserial sections

The proximal stumps of five rat sciatic fibers, transected 72 hr earlier, were reconstructed on the basis of morphometry in subserial electron micrographs of isolated fibers. Three fibers showed extensive axon sprouting; 2 had no sprouts but were excessively swollen. The total volume of axoplasm in the axon swellings approximated the volume of axoplasm in all sprouts of any given fiber. Axonal swelling therefore may ensur when sprouting is frustrated. Axon sprouts originated mostly at nodes from where they descended or ascended along the fiber, running within its lamina basalis. Sprouting began soon after injury, usually within the first day. Counts of microtubules showed an approximately 10-fold increase in the total number of tubules per fiber toward the injured end. Schwann cells showed asymmetric hypertrophy, having distinctly more cytoplasm distally than proximally to the nucleus. The increase in Schwannian cytoplasm occurred roughly pari-passu with the increases in axoplasm. Hypertrophy of Schwann cells was associated with cytoplasmic islands or strands having an extremely variable content of organelles. Such islands of Schwannian cytoplasm may be confused with axon sprouts. Retraction of the myelin sheaths at nodes results in fiber profiles suggestive of partial demyelination. Retraction of nodal pseudopodia produces redundant loops of lamina basalis. Migratory cells are seen outside the fibers or underneath their lamina basalis having a preference for nodal regions or for the fiber stump. They behave differently toward axon or myelin: they encompass axon sprouts as do immature Schwann cells; simultaneously the same cell may invade myelin sheaths like a macrophage. Other curious overlaps of degenerative and regenerative phenomena were noted, including an axon sprout tunneling through the lumen of the sequester of the myelin sheath of its parent axon.

Endoneurial fluid pressure in wallerian degeneration

Endoneurial fluid pressure (EFP) was recorded by an active, servo-null pressure system after a glass micropipette was inserted into rat sciatic nerve undergoing wallerian degeneration. The lesions were produced by crushing the left sciatic nerve of the anesthetized animal at its point of entry into the thigh. Eighty-four animals were employed in this experiment, in which EFP was recorded from sham-operated rats and other controls as well as from rats with wallerian degeneration. The experiment was designed so that EFP could be recorded from 2 or more experimental animals at daily intervals starting at day 0 and concluding on day 28. Pressure progressively increased during the first week, reaching a peak elevation four to five times normal. The subsequent decline in EFP was more gradual, with values approaching normal during the third week after injury. Linear regression analysis showed the progressive increase in EFP to be statistically significant (p less than or equal to 0.01). To determine the time at which EFP was maximum, we used the Marquardt computer algorithm for lease-squares estimation of nonlinear variables. By this procedure the peak value for EFP occurred at six days. These biophysical observations were correlated with subsequent microscopic examination of 1 mu thick sections of Araldite-embedded sciatic nerve. Microscopy confirmed the presence of wallerian degeneration associated with edema, which was observed in every instance of elevated EFP.

Anin vivo method to prepare normal Schwann cells free of axons and myelin

A viable population of undifferentiated Schwann cells may be prepared from chronically denervated peripheral nerves. Nerve transection stimulates a sequence of cellular events in distal stumps leading to removal of axons and myelin, and proliferation of Schwann cells. Sealing the ends of nerve stumps prevents reinnervation and leaves daughter Schwann cells residing in longitudinal columns. Schwann cells may be harvested from the endoneurial tissue of the nerve stumps 5-12 weeks after nerve transection. Unlike myelinating cells prepared from intact tissue, where function has been specified by associated axons, Schwann cells obtained from denervated stumps are functionally naive. Their usefulness in analyzing axonal regulation of myelinogenesis and mitosis is therefore suggested.

An ultrastructural study of Schwann cell response to axonal degeneration

Adult Sprague-Dawley rats were used to prepare isolated and distal segments of ovarian, vagus and saphenous nerves. Isolated segments were prepared by cutting between double ligatures followed by retracting and anchoring the proximal and distal segments 0.5 cm or more away from the isolated piece. After various intervals between 3 and 123 days and rats were perfused with buffered glutaraldehyde and nerves were processed for electron microscopic examination. Cross sections of isolated and distal segments of all nerves displayed an abundance of mostly circular profiles containing microtubules and filaments that were indistinguishable from those in unmyelinated nerve fibers. Many such profiles were nested against perinuclear Schwann cell cytoplasm, others were present in isolated clusters enclosed only by basement membrane. Examples of continuity between the nerve-like profiles and perinuclear cytoplasm of Schwann cells were found in longitudinal sections. In time, the number of such processes gradually diminished, but 123 days after transection they still could be found. It was concluded that Schwann cells in isolated and distal segments of transected nerves develop great numbers of small cylindrical processes that are arranged in bundles parallel to the long axis of the degenerated nerve. These processes had an arrangement of cytoplasmic organelles similar to axons of the proximal segment and the contralateral nerve. However the processes differed from most mature axons in that they were not ensheathed by Schwann cell cytoplasm with a mesaxon.

Ultrastructural changes of the nerve elements following disruption of the organ of Corti. II. Nerve elements outside the organ of Corti

Various stages of changes in the nerve fibers, spiral ganglion cells, and satellite cells from the guinea pig cochlea 3 to 137 days after perilymphatic perfusion with streptomycin solution (2 and 20%) were observed electron microscopically. Initially, the axoplasms of the cochlear nerve fibers became swollen or pyknotic. Then, the axons disappeared and myelin lamellae disrupted. The Schwann cells shrank and degenerated, though their basement membranes survived for a time. Regeneration of the cochlear nerve fibers began with extension of axonal sprouts into the tube of the basement membrane and surviving Schwann cells, which still contained myelin debris. Only one of the axonal sprouts matured for myelination. These regenerating cochlear nerve fibers were found in the osseous spiral lamina, modiolus and internal auditory meatus, but these fibers atrophied and disappeared afterward. Retrograde degeneration occurred in the olivo-cochlear bundle. Some of the efferent myelinated fibers also showed temporary regeneration.

Ultrastructural sequence of myelin degradation. I. Wallerian degeneration in the rat optic nerve

The ultrastructural events in myelin degradation in the rat optic nerve following transection have been studied. Myelin debris was found in cells similar to multipotential glia cells (Vaughn and Peters, 1968) as well as in astrocytes and in few oligodendrocytes. The different types of inclusions found during myelin degradation were described in their quantitative relations. Similarities to inclusions described in adrenoleukodystrophy adn multiple sclerosis are discussed. By comparison of the ultrastructural findings with histochemical and biochemical data available a hypothetical model of myelin degradation is presented. The process starts with the degradation of digestible proteins resulting in uniformly layered lipid inclusions. Lipid degradation leads to the formation of unstructured lipid droplets and crystals. During the late stages of Wallerian degeneration numerous polymorph inclusion typed can be found, probably representing poorly digestible lipids or lipoproteins.

Ultrastructural sequence of myelin degradation. II. Wallerian degeneration in the rat femoral nerve

Myelin degradation in Wallerian degeneration of rat femoral nerves has been studied with the electron microscope. In the initial stages, a decrease of myelin periodicity from 115 A to 88 A was noted, followed by the transformation of the myelin structure into uniformly layered lipid inclusions. 10--14 days after nerve section, most of the inclusions found represented unstructured lipid droplets or crystals. In the later stages of degeneration, numerous pleomorphic lamellar inclusions were found, some of them resembling the structure of pi and micron-granules. Lysosomal enzyme activity was found especially in pleomorphic inclusions during the late stages of myelin degradation. Normal myelin sheaths, as well as unstructured lipid droplets and crystals, were devoid of enzyme activity. The results are compared with alterations found in Wallerian degeneration of the central nervous system.

The response of the satellite and other non-neuronal cells to the degeneration of neuroblasts in chick embryo spinal ganglia

The responses of non-neuronal cells to the degeneration of neuroblasts were studied in the spinal ganglia of the chick embryo. Reactive changes of the non-neuronal cells were not apparent during the early stage of degeneration of the neuroblast, but during the later stages of degeneration evidence was found suggesting that non-neuronal cells subdivided and phagocytosed the affected neuroblasts. Three types of non-neuronal cells appeared to participate in the phagocytosis: satellite cells, cells resembling undifferentiated elements, and macrophages. The appearance of the latter coincided with the beginning of the vascularization of the ganglionic rudiment. The phagocytic capacity of satellite cells is discussed in the light of these and other studies by light and electron microscopy.

Ultrastructural identification of a benign perineurial cell tumor

A solitary tumor which by light microscopy was calssified as a neurofibroma was found by electron microscopic study to be composed of parallel, elongate cells with collagen rich intervening matrix. The cells showed thin, polar cytoplasmic processes which extended long distances, frequent junctional complexes between cell processes, numerous surface vesicles, and either no or fragmented and variable basement membrane. Perineurial cells from small peripheral nerves of skin were demonstrated to have similar morphologic characteristics as the tumor cells. The present study, together with previous ultrastructural findings, indicate that benign peripheral nerve sheath tumors should be placed in at least three categories: Schwannoma, neurofibroma and perineurioma.

Study on the ultrastructure and acetylcholinesterase activity in von Recklinghausen's neurofibromatosis

The cutaneous nodules obtained from seven patients with von Recklinghausen's neurofibromatosis were investigated by electron microscopy, and ultrastructural localization of acetylcholinesterase activity was demonstrated in the nerve fibers of this tumor for the first time using Karnovsky's thiocholine method. The enzymatic activity was mainly found in unmyelinated fibers, exactly associated with their axonal membranes, the interspace between the apposing axonal and Schwann cell membrane, and some different mesaxons, which indicated their cholinergic nature. Almost all myelinated fibers and some unmyelinated fibers did not possess the activity. The relationship between axon and Schwann cell was quite similar to that of normal peripheral nervous system, but two striking alterations of the nerves existed: One is the dissociation of unmyelinated fibers, and the other is the degenerative changes of the axon and the myelin sheath. As the evidence of schwannian proliferation, onion bulb formations and collagen pockets were observed. Some signs of fibroblastic proliferation were also found. From the present study and the review of the literature, the probable histogenesis of this disease was discussed.

Effect of ischemia on axonal transport of choline acetyltransferase and acetylcholinesterase and on ultrastructural changes of isolated segments of rabbit nerves in situ

Axonal transport of acetylcholinesterase (AChE) and choline acetyltransferase (ChAc) and ultrastructural degenerative changes were compared in isolated nerve segments of rabbit peroneal nerves kept in vivo for 22 h, either with preserved blood supply (control segments) or under conditions of ischemia (ischemic segments). Ischemia abolished the proximo-distal and disto-proximal axonal transport of AChE and the proximo-distal transport of ChAc which, in control segments, were revealed by accumulations of the enzymes at corresponding ends of the segments. Total activities of AChE and ChAc recovered in isolated segments with intact blood supply corresponded to the activities in normal nerves; in ischemic segments, 50% of ChAc activity was lost in 22 h, whereas all AChE activity was preserved. Ultrastructural changes were found in few fibres in control segments and in many fibres in ischemic segments 22 h after nerve interruption. The early changes in control segments correspond to those described in the literature for peripheral stump of severed nerves. The microtubules, neurofilaments and mitochondria were not affected. In ischemic segments, various stages of axoplasmic disintegration occurred in the myelinated and unmyelinated axons:flocculation and clumping of axoplasmic material, decomposition of neurofilaments and microtubules, swelling, formation of amorphous densities and breakdown of mitochondrial cristae. Swelling, amorphous densities, clumping of nuclear chromatin and necrotic mitochondrial changes appeared also in Schwann cells. It is concluded that ischemia blocks axonal transport and brings about, within 22 h, ultrastructural changes both in nerve fibres and in Schwann cells. Cytoplasmic ChAc is affected earlier by necrotic degeneration of the axons than membrane-bound AChE.

Histological studies of trophic dependencies in crayfish giant axons

Medial giant (MGA) and lateral giant (LGA) axons of crayfish were doubly cut in order to selectively isolate axonal segments from perikaryal and transsynaptic sources of trophic input. Isolated MGA segments remained morphologically intact for over 43 days, whereas isolated LGA segments usually degenerated within one week. The glial sheaths around isolated MGA segments had significantly increased in thickness within one week, but severed LGA segments showed no increase in sheath thickness at any time after lesioning. These data suggest that cells of the surrounding glial sheath can provide trophic support to isolated MGA segments but not to isolated LGA segments. Extent of glial hypertrophy seems dependent upon specific spatiotemporal parameters. The diameters of isolated MGA segments decreased more rapidly than the diameters of singly cut MGA segments. These data suggest that the MGA also receives some trophic support from pre- or postsynaptic sources. Conversely, some singly cut LGA segments completely degenerated within one week, whereas other singly cut LGA segments remained intact for at least 43 days after lesioning. Such results suggest that the LGA receives a significant trophic input from pre- or postsynaptic structures.

Structural alterations of peripheral nerve induced by the calcium ionophore A23187

Desheathed segments of rat peripheral nerve were incubated at 37 degrees C in oxygenated Ringer's solution with and without the addition of calcium ionophore, A23187, 10 microgram/ml. Nerve fibers incubated in the presence of both ionophore and calcium revealed extensive granular disintegration of their axonal microtubules and neurofilaments after 30 and 60 min incubation intervals. These changes were not seen following control incubations in Ringer's solution without ionophore or in calcium-free Ringer's solution containing ionophore and EGTA, 1 mmole/1. Ionophore-induced alterations were also noted in Schwann cell cytoplasm. The granular degradative alteration of axoplasm caused by exposure of nerve fibers to ionophore and calcium were believed to be due to an ionophore-mediated influx of calcium into the axoplasm with resultant elevation of intra-axoplasmic calcium concentration. These axoplasmic changes were indistinguishable from the axoplasmic alteration occurring in the distal portions of transpected neurites during Wallerian degeneration. The findings support the view that abnormal calcium influxes are determinants in the degeneration of peripheral nerve.

Alterations of fast axoplasmic transport in experimental methyl n-butyl ketone neuropathy

Methyl n-butyl ketone (MBK) is known to produce a giant axonal neuropathy in man and experimental animals characterized pathologically by a gradual increase in the number of neurofilaments which become associated with focal areas of axonal swelling and thinning of the myelin sheath. Fast axoplasmic transport was studied in rats exposed to MBK. In 10 severely paralyzed rats exposed to MBK there was a significant impediment of fast axoplasmic transport following dorsal root ganglion injections (x +/- S.D. = 283.2 +/- 20.34 mm/day) compared to normal controls (417.6 +/- 23.78 mm/day). In rats undergoing injections into the ventral horn of the spinal cord there was a gradual impairment of the mean down flow rate for transport of [3H]leucine which correlated with the severity of the MBK induced neuropathy. Quantitative morphological determinations showed that the total number of neurotubules per unit cross-sectional myelin area and the number of neurotubules associated with mitochondria in swollen axons was unchanged from normal. The total number of mitochondria in randomly sampled axons varied significantly from controls but the absolute number of mitochondria associated with neurotubules was unchanged from normal. The results of these studies suggest that the impediment of fast axoplasmic transport may be related to the increased neurofilaments producing focal areas of axonal blockage.

The ultrastructure of oral neuromas in multiple mucosal neuromas, pheochromocytoma, medullary thyroid carcinoma syndrome

The ultrastructure of oral neuromas from 2 patients with multiple mucosal neuromas, pheochromocytoma, medullary thyroid carcinoma syndrome reveals numerous hypertrophic unmyelinated and myelinated axons, hyperplastic neurilemmal cells and associated collagen fiber formation. These tumors are described and compared ultrastructurally with neurilemmomas and neurofibromas as described by other authors. On the basis of this comparison, these tumors are not considered to be of neurilemmal origin. On the basis of light and electron microscopic histology it is postulated that these tumors represent hypertrophy of axons similar to that noted in amputation neuromas.

Unmyelinated and small myelinated axons in rat ventral roots

The present study is an analysis of the ventral roots in the rat. The smallest myelinated fibers are found in segments T1-L2 and L6-S1. These fibers are regarded as preganglionic efferents and the L6-S1 outflow is more cranial than the sacral parasympathetic outflow in other animals. Large numbers of unmyelinated axons are seen in segments T1-L2 and L6-S1, the same segments that contain the smallest myelinated fibers. This data will be used as a baseline for determining the functional categories of the unmyelinated axons.

The ultrastructure of cutaneous type I mechanoreceptors (Haarscheiben) in cats following denervation

Denervation of specialized cutaneous mechanoreceptors (Haarscheiben or domes) in cats was followed after 20 and 25 days by the following alterations in receptor structure: (1) reduced numbers of Merkel cells, (2) Merkel cells degenerating in situ, (3) fewer dense-core granules in the cytoplasm of Merkel cells, (4) an increased number of agranular dendritic cells and Langerhans cells in the dome, (5) the apparent phagocytosis of Merkel cells by Schwann and Langerhans cells, (6) fewer epithelial cell layers over the dome, and (7) a decrease in the number of transitional cells. Skin excised between the domes in the denervated nerve field appeared normal when compared to innervated skin, and it was considered unlikely that the alterations in dome structure were due to generalized nutritional changes in the skin caused by transection of sympathetic axons or to some other side effect of denervation. Since domes are formed in new locations on the skin after nerves have regenerated (Burgess et al., '74), changes in dome structure following nerve transection are probably due to loss of the "trophic" influence of the nerves supplying the dome.

The early stages of Wallerian degeneration in the severed optic nerve of the newt (Triturus viridescens)

The initiation of Wallerian degeneration in the severed optic nerve of the newt (Triturus viridescens) was very rapid and intense. Significant degeneration of nonmyelinated axons was observed as early as six hours after lesion (h.a.l.) and was almost complete by 48 h.a.l. Initial degeneration of non-myelinated axons began in "extracellular digestion chambers" formed between burgeoning ependymoglial processes. The remaining fragments and debris were later phagocytized by surrounding ependymoglial processes. Many axons of myelinated fibers have degenerated as early as 6 h.a.l. However, the overall population of myelinated axons degenerates at a much slower rate than nonmyelinated ones, for many of them appear intact as late as 48 h.a.l. Some myelin sheaths show significant signs of degeneration by 6 h.a.l. Indeed, by this time a number of myelinated fibers have completely degenerated leaving only large vacuolated spaces in the nerve parenchyma. Swelling and vacuolization of the sheath are among the earliest signs of myelin degeneration. The ependymoglial cell response to optic nerve lesion is manyfold and dramatic. By 6 h.a.l. there are signs of burgeoning ependymoglial processes which begin to resemble scar formation (gliosis) by 48 h.a.l. The morphological evidence is consistent with the concept of an important phagocytic role of ependymoglial cells during the early stages of optic nerve degeneration.

A light and electron microscope study of changes occurring at the cut ends following section of the dorsal roots of rat spinal nerves

Rat dorsal spinal nerve roots were cut; 20 h later the axons in the vicinity of the cut were examined by light and electron microscopy. The changes in the cut tip distant from the ganglion were largely degenerative. On the ganglionic side of the cut a cap of free unmyelinated sprouts was formed. These sprouts contained clear and dense-core vesicles 40-150 nm in diameter, smooth endoplasmic reticulum and mitochondria. Some of the unmyelinated sprouts were extensions of myelinated axons, others arose from myelinated axons by lateral budding. In both myelinated and non-myelinated axons there was an accumulation of mitochondria, tubulo-vesicular smooth endoplasmic reticulum and large and small dense-core vesicles for a distance of approximately 500 mum behind the tip. Dense-core vesicles were more common in non-myelinated axons than in their myelinated counterparts. In areas of intense accumulation the non-myelinated fibres were grossly swollen and distorted. The myelinated axons and some of the sprouts contained an unusual type of mitochondrion. The similarity between these sprouts and pre-synaptic terminals is discussed.

Fiber analysis of the feline inferior cardiac sympathetic nerve

The left inferior cardiac nerves of nine adult cats were examined with the electron microscope. Electrical recordings were also made from four of these nerves. Most of the nerves contained between 25,000 and 40,000 unmyelinated fibers and 30 to 150 myelinated fibers. The diameters of the unmyelinated fibers ranged from 0.1 mu to 1.8 mu with mean diameters ranging from 0.47 to 0.78 mu in the various nerves. The myelinated fibers ranged in diameter from 1 mu to 9 mu with a mean difference of approximately 3 mu. Electrical recordings showed two peaks in both the C fiber and the Adelta fiber compound action potentials. Conduction velocities of the two C fiber peaks were approximately 0.7 and 0.9 m/sec. The two groups of A delta fibers had conduction velocities of approximately 7 and 16 m/sec.

Some electron microscopic and autoradiographic results concerning cutaneous neurofibromas in von Recklinghausen's disease

The cutaneous tumors of 5 patients with clinical symptoms of Recklinghausens neurofibromatosis were investigated by light and electron microscopy. Special reference was given to the study of initial changes of the disease and the structure of the nerve fascicles which end in the tumor. In 2 patients the proliferating cells were determined by using an autoradiographic technique. It was discovered that all cellular elements of a peripheral nerve are involved by the tumor formation. The results were discussed and compared with the alterations during nerve regeneration after traumatic injury.