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.

Structural alterations of peripheral nerve monogalactosylceramides during development and Wallerian degeneration

The structural alterations of monogalactosylceramides in peripheral nerve were investigated during development, nerve fiber degeneration and regeneration. During early development, hydroxy cerebrosides and sulfatides were the main constituents of the monogalactosylceramides of immature rat sciatic endoneurium. The ratio of hydroxy to nonhydroxy cerebrosides decreased rapidly as myelination proceeded but remained fairly constant throughout adulthood. More than 50% of the adult content of endoneurial monogalactosylceramides was achieved before 21 days of age. The long-chain nonhydroxy fatty acids (above C21) had increased from under 20% to over 80% by day 20, while 24h:0 (h, hydroxy) had already reached approximately 50% of hydroxy cerebrosides by day 12. These results suggest that the biosynthesis of endoneurial monogalactosylceramides and fatty acid elongation take place preferentially at the time when peripheral nerve is undergoing active myelination. During Wallerian degeneration, the maximum decrease of monogalactosylceramides was associated temporally with axonal degeneration and demyelination and particularly with myelin conversion to sudanophilic lipids. By the time that nerve fiber regeneration was well established, both the cerebroside and sulfatide contents had returned to near control values. Cerebrosides and long-chain fatty acids (above C21) appear to be the most sensitive to fiber degeneration while fatty acid elongation is selectively increased during nerve regeneration.

Myelin proteins in Wallerian degeneration of the optic nerve

The development of changes in the protein spectrum of the rabbit optic nerve undergoing Wallerian degeneration was studied and compared with the time sequence of the previously established changes occurring in the lipid composition of the degenerating nerve. The myelin protein spectrum remained essentially unchanged till 32 days after enucleation to show a decrease of the relative content of basic myelin proteins accompanied by increased percentages of the Wolfgram protein during the forthcoming development of Wallerian degeneration. The occurrence of changes in the myelin protein spectrum was significantly delayed in comparison with the onset of enhanced esterification of myelin cholesterol, and thus the latter process, and not the hydrolysis of basic protein is considered as an early event, weakening the molecular structure of the myelin membrane that might initiate the demyelinating process.

[Fine structure of intrafusal and extrafusal nerve segments of the rat muscle spindle after sciatic nerve transsection]

Intrafusal and extrafusal nerve segments in muscle spindles from lumbricalis muscles of the hindpaw of the rat were studied by electron microscopy from 10 h to 5 days after severance of the sciatic nerve. In several spindles examined, nerve fascicles piercing the spindle capsule in the equatorial region contained a large myelinated, a smaller myelinated, and an unmyelinated fiber. Unmyelinated fibers were not present in small fascicles leading to the polar region. The changes in the extrafusal nerve segments followed the pattern of Wallerian degeneration. Intra-axonal glycogen deposits were prominent in sensory fibers. The unmyelinated fibers were the earliest to degenerate, the large myelinated ones the latest. Differences between motor and sensory fiber degeneration emerged in their preterminal intrafusal segments and were analogous to those of the nerve endings. Terminal nerve fibers in the spindle equator succumbed to attack of mesenchymal cells, leaving extensive basement membrane reduplications around myelin debris-laden Schwann cells, while polar fibers were engulfed by Schwann cell processes, leaving regular bands of Büngner.

Autologous peripheral nerve grafting into murine brain as a model for studies of regeneration in the central nervous system

Autologous sciatic nerve was grafted into rat brain by (i) passing an 8-mm segment of nerve tied to a straight surgical needle through two craniotomy holes ("through-and-through" model); (ii) inserting a small tube of polyethylene containing the 8-mm nerve piece ("nerve-within-tube" model). Longitudinally oriented neurofilament-positive fibers were consistently observed within the graft. Compared with the through-and-through model, axonal sprouting in the nerve-within-tube model followed a slow-motion pattern so that a growing front of regenerating axons could be easily identified and more easily related to the cellular events occurring in Wallerian degeneration. In the through-and-through model, regenerated axons at the brain-nerve interface followed a disorganized, tortuous course so that direct continuity between brain and graft was difficult to demonstrate. The reverse was true in the nerve-within-tube model, i.e., axons penetrated directly into the graft. The difference in orientation of axonal growth at the brain-graft interface appeared to be related to the glial reaction. In the through-and-through model, reactive astrocytes formed a mesh of randomly oriented fibers in the damaged brain tissue facing the graft (anisomorphic gliosis). Conversely, longitudinally oriented fibers extended directly from the brain to the graft in the nerve-within-tube model, where brain damage was substantially reduced (isomorphic gliosis). A different type of glial fibrillary acidic (GFA) protein-positive fibrous structures was identified in the graft. Compared with reactive astrocytes, these structures were more elongated, more uniform in diameter, and less brightly immunofluorescent. Moreover, they were present throughout the graft, whereas astrocytes were confined to the distal end of the transplant, i.e., the part of nerve close to the brain-graft interface. Based on previous reports in the literature we interpret these GFA protein-positive structures as reacting Schwann cells.

Spontaneous lower motor neuron disease with neurofibrillary accumulation in young pigs

A spontaneous neurologic disease occurred in six 5 weeks old Yorkshire pigs of both sexes from four litters sired by one boar. Clinically, the disease was characterized initially by bilateral posterior ataxia and weakness which rapidly progressed to tetraplegia by 10 weeks of age. By light microscopy, there was bilateral neuronal chromatolysis, degeneration and loss restricted to motor nuclei in the ventral horns of the spinal cord, in the medulla oblongata and midbrain. In addition to diffuse Wallerian-type degeneration in the spinal cord white matter and ventral peripheral nerve roots, there was prominent neurogenic atrophy of skeletal muscle. Ultrastructurally, the perikaryon and processes of affected neurons contained massive accumulations of single 10 nm diameter neurofilaments. Copper concentrations of both the commercially prepared ration and the livers were within normal limits.

The effects of acrylamide on beta-glucuronidase and acid phosphatase activities in rat sciatic nerve above and below a ligature

The enzymes beta-glucuronidase and acid phosphatase have been assayed by histochemical and by fluorimetric methods above and below a tightly tied ligature on the rat sciatic nerve over the subsequent 10 days. These findings have been compared with similarly treated animals also given four daily doses of acrylamide (50 mg/kg). The following have been found: 1 during this time, acrylamide at this dose causes slight increases in beta-glucuronidase in untied sciatic nerves, detectable both histochemically and fluorimetrically; 2 below the ligature both enzyme activities were greatly increased and this was slightly reduced in the acrylamide-dosed animals; 3 there was a mild rise in beta-glucuronidase activity in the 1.0 cm above the ligature in undosed animals demonstrable both histochemically and fluorimetrically; 4 that in the acrylamide-dosed animals there was a marked rise in beta-glucuronidase activity both 1.0 cm and 2.0 cm above the ligature which was intensified at 7 days and at 10 days after dosing. This was demonstrated both histochemically and fluorimetrically. These results are discussed in the light of the known sheath cell and axonal responses to acrylamide intoxication.

Protein turnover in normal and degenerating visual pathway of the frog and the rat, an autoradiographic study

Radioactivity above background level can be detected in the contralateral visual pathway of normal rats as long as 250 days after intraocular injection of tritiated proline. Silver grains disappear first from the retina, and last from the superior colliculus. In the optic tectum and the isthmic nucleus of the frog, more than 500 days are necessary to reach background level of radioactivity, when labelled retinal fibres are undergoing Wallerian degeneration. The intensity of label in tectal laminae formed by myelinated fibres is markedly reduced 12 days after the removal of the labelled eye. In the laminae of unmyelinated fibres, the decrease in the number of silver grains is less than 50% during a 150-day degeneration period. In the isthmic nucleus radioactivity was less intense, when labelled retinal fibres were degenerating in the tectum, as compared to that in normal animals. Radioactivity in the superior colliculus decreased 3 times faster than in the tectum after removal of the labelled eye. We conclude that proline is reutilized for protein synthesis. Unmyelinated fibres degenerate slower than myelinated ones in frogs, and transneuronal transport cannot be enhanced by increased protein breakdown.

The pathophysiology of compression injuries of the peripheral facial nerve

The buccolabial branches of guniea pig facial nerves were crushed to produce axonotmesis, Wallerian degeneration, and demyelination. The lesions were followed from 1 to 8 weeks by transmission electron microscopy, electrophysiological tests, and cytochemical staining methods for Na+ channels. The first week demonstrated the classic degenerative neural changes. At 2 weeks the axoplasmic side of the demyelinated axolemma demonstrated diffuse staining for Na+ channels at a distance of 1 micrometer. At 4 weeks multiple condensed areas of dense staining were noted along the demyelinated axolemma. These staining areas resemble in character and length a normal node of Ranvier and denote new Na+ channels. The internodal distance is shorter than for the normal facial nerve. At 6 weeks a thin layer of myelin covered the nerve fibers. At 8 weeks half of the nerves were normal sized and the myelin sheath was normal in width. Following nerve crushing, electrical activity is present for 24-48 hours in the axonotmetic distal stump. Then the axon becomes unresponsive to electrical stimulation. There is gradual resumption of electrical activity between 5 and 14 days. Normal conduction resumes by 8 weeks. This study provides ultrastructural and cytochemical evidence for nerve fiber reorganization, axolemmal plasticity and sodium channel production and redistribution following Wallerian degeneration and demyelination in axonotmesis. Resumption of electrical neural excitability is achieved by an increase in the density of sodium channels and reduction in the internodal distance as a means for impedence matching. Reduction of the cross sectional diameter of the regenerating axon facilitates electrical conduction.

Tight junction contact events and temporary gap junctions in the sciatic nerve fibres of the chicken during Wallerian degeneration and subsequent regeneration

Tight and gap junctions are described on the basis of freeze-fractures in normal chicken sciatic nerves as well as during Wallerian degeneration and subsequent regeneration. 1. Small calibre nerve fibres display a fairly continuous tight junction contact zone in the membranes of the mesaxons, paranodal loops and Schmidt-Lanterman incisures. Large fibres with more than 40 lamellae have only focal tight junction contacts in the mesaxonal membranes. 2. With the onset of Wallerian degeneration (days 2-4 post-crush, distal stump) myelinic tight junctions become arranged as maculae composed of one circular or several polygonally oriented strands that are criss-crossed by other tight junctional strands. These maculae are subsequently found in the membranes of cytoplasmic vacuoles of the Schwann cells, indicating an endocytotic mode of uptake. Tight junctions are not found between the 5th and 6th day after crush. 3. During the proliferation phase of the Schwann cells and the arrangement of these cells into Büngner cell bands (2 to 8 days post-crush) gap junctions appear between the Schwann cells of the bands. These junctions then disappear with the onset of remyelination (8 days post-crush). 4. With the onset of remyelination (from the 8th day onwards) short focal tight junctions appear in the membranes of the outer mesaxons. Shortly thereafter, when the sheaths possess 4 to 8 lamellae, tight junctions also appear in the membranes of the inner mesaxons, the paranodal loops and the cytoplasmic inclusions. The characteristic differences of tight junction elaboration in small versus large nerve fibres are re-established after three months of regeneration. The elaborated tight junctions in small and early remyelinating fibres point to a specific function; in small fibres (versus large fibres) the tight junctions might effect a separation of the intramyelinic extracellular space as a single compartment. The tight junction contacts in early remyelinating fibres support the hypothesis that myelin growth occurs within the myelin spiral and not by a free rotation and elongation of the Schwann cell tongues. It is assumed that the gap junctions between the Schwann cells contribute to the co-ordination of the Schwann cell band formation, which is involved in the guidance of sprouting axons.

Vimentin in the central nervous system. A study of the mesenchymal-type intermediate filament-protein in Wallerian degeneration and in postnatal rat development by two-dimensional gel electrophoresis

Intermediate filament proteins were identified by two-dimensional gel electrophoresis in urea extracts of rat optic nerves undergoing Wallerian degeneration and in cytoskeletal preparations of rat brain and spinal cord during postnatal development. The glial fibrillary acidic (GFA) protein and vimentin were the major optic nerve proteins following Wallerian degeneration. Vimentin was a major cytoskeletal component of newborn central nervous system (CNS) and then progressively decreased until it became barely identifiable in mature brain and spinal cord. The decrease of vimentin occurred concomitantly with an increase in GFA protein. A protein with the apparent molecular weight of 61,000 and isoelectric point of 5.6 was identified in both cytoskeletal preparations of brain and spinal cord, and in urea extracts of normal optic nerves. The protein disappeared together with the polypeptides forming the neurofilament triplet in degenerated optic nerves.

IDPN neuropathy in the cat: coexistence of proximal and distal axonal swellings

Administration of beta,beta'-iminodipropionitrile (IDPN) to rodents has previously been shown to produce neurofilament-filled axonal swellings in the proximal regions of motor and sensory nerve fibers. Because of the distinctive distribution of these swellings, IDPN has been classed as a proximal axonopathy and thereby distinguished from other disorders in which similar axonal swellings occur in the distal parts of the axon (distal axonopathies). This report describes the pathology in the peripheral nerves of cats which received intermittent injections of IDPN and calls attention to two previously undescribed pathological changes. First, in addition to the typical proximal swellings associated with IDPN, these animals developed numerous axonal swellings within the distal branches of the sciatic nerve. Distal swellings were present as early as 23 days after initiation of intoxication, indicating that they formed locally (rather than developing in the proximal axon and undergoing transport into the distal regions). The second finding was Wallerian-like degeneration within the affected nerve branches. These changes in the distal sciatic nerve and its branches closely resembled the pathology of the distal axonopathies produced by agents such as the neurotoxic hexacarbons and carbon disulfide. The pathological similarities suggest that IDPN may share with these agents pathogenetic mechanisms to an extent not previously suspected.

Peripheral nerve phospholipid composition: development in normal nerve and age-dependent changes in Wallerian degenerated nerve

The phospholipid composition of normal peripheral nerve as a function of developmental age as well as that of Wallerian-degenerated nerve as a function of age at nerve transection and duration of Wallerian degeneration have been quantitated in rabbit sciatic nerve. During development, increases in the proportions of ethanolamine plasmalogen, sphingomyelin, and combined phosphatidyl serine plus phosphatidyl inositol and decreases in the proportions of phosphatidyl choline and phosphatidyl ethanolamine correlated well with the concurrent myelin accretion. During Wallerian degeneration, age-dependent changes in phospholipid composition were observed. The large and statistically significant increase in the proportion of phosphatidyl choline and decrease in the proportion of ethanolamine plasmalogen were manifest promptly in nerves transected at 2 weeks of age but in a delayed manner in nerves transected at 8, 12, and 20 weeks of age. The rate of loss of individual phospholipids was greater in nerves transected at younger ages. The findings from normal developing peripheral nerve may well serve as baseline data for subsequent studies of phospholipid composition in pathological peripheral nerve. The findings from Wallerian-degenerated peripheral nerve provide additional evidence for age-dependent chemical changes occurring in Wallerian-degenerated peripheral nerve that may be of significance in explaining the superior functional recovery from peripheral nerve injury observed in younger compared with older subjects.

Evidence for glucocorticoid target cells in the rat optic nerve. Hormone binding and glycerolphosphate dehydrogenase induction

Biochemical evidence suggests that neuroglia are responsive to glucocorticoids, yet previous studies of glucocorticoid localization have typically failed to demonstrate significant uptake by neuroglial cells. To further investigate this problem, we measured glycerol-3-phosphate dehydrogenase (GPDH) activity and glucocorticoid receptor binding capacity in normal rat optic nerves and in those undergoing Wallerian (axonal) degeneration. Binding studies were also performed on hippocampus and anterior pituitary for comparison purposes. Normal optic nerve preparations possessed a high level of GPDH activity that was glucocorticoid-inducible and that increased further following axonal degeneration. Antibody inactivation experiments demonstrated the presence of more enzyme molecules in the degenerating nerve preparations. correlative immunocytochemical studies found GPDH-positive reaction product only in morphologically identified oligodendrocytes, a result that is consistent with the previously reported localization of this enzyme in rat brain. Optic nerve cytosol fractions displayed substantial high-affinity binding of both dexamethasone (DEX) and corticosterone (CORT) that, like GPDH, was elevated approximately two fold in degenerating nerves. Finally, in vivo accumulation of [3H]DEX and [3H]CORT by optic nerve and other myelinated tracts was examined using nuclear isolation and autoradiographic methods. Although neither steroid was found to be heavily concentrated by these tissues in vivo, a small preference for DEX was observed in the nuclear uptake experiments. These results are discussed in terms of the hypothesis that glial cells are targets for glucocorticoid hormones.

Progressive ultrastructural changes after peripheral nerve transection and repair

Six rhesus monkeys (Macaca mulatta) underwent sharp transection and repair of the intrinsic motor fascicles of both ulnar nerves in order to determine the sequential events during reinnervation of the distal stamp. Light and electron microscopic sections were made at 2.0 mm increments distal to the neurorrhaphy at weekly intervals in separate monkeys. Neurite sprouts could be identified distal to the neurorrhaphy by 1 week and were clearly evident 40 mm distal by 3 weeks. Although some old endoneurial tubules persisted, they were less often used as conduits or scaffolds for the regenerating neurites than previously described. Most new fibers, whether myelinated or unmyelinated, passed down new endoneurial tubules, thus precluding perfect end-organ specificity because the regenerating neurites seldom utilized old endoneurial tubules. The clinical implication suggested by this study is that the ideal situation is the immediate repair of transected nerves. This allows neurite sprouts to cross a neurorrhaphy rapidly and reinnervate end organs.

Effects of distal vagal ganglionectomy and midcervical vagotomy on the ultrastructure of axonal elements in the carotid body of the domestic fowl

The carotid body of the domestic fowl was examined with the electron microscope after either removal of the distal vagal ganglion or midcervical vagotomy. Almost all the axonal elements of the carotid body degenerated within 5-15 days after ganglionectomy. The degeneration was considered to be due to separation of these axonal elements from their cell bodies (Wallerian degeneration) and indicated that nearly all the nerve supply of the carotid body of Gallus is derived from the vagus nerve. Degeneration of many axonal elements of the carotid body was also seen after midcervical vagotomy, but it took longer (19-41 days) to begin and had greatly increased 207-214 days after operation. It was interpreted as transganglionic degeneration, i.e. severance of the central processes of the distal vagal ganglion cells (by vagotomy) had induced slow degeneration in their peripheral processes (axonal elements in the carotid body). We conclude that the vast majority of the axonal elements in the carotid body of Gallus belong to nerve cell bodies in the distal vagal ganglion and are therefore afferent.

A change in the cerebrosides and sulfatides in a demyelinating nervous system. Development of the methodology and study of multiple sclerosis and Wallerian degeneration

This report described a new method for the microanalysis of sphingolipids and its application for the characterization of cerebrosides and sulfatides in multiple sclerosis brain and rat sciatic nerves undergoing Wallerian degeneration. Tissue was extracted with isopropanol/hexane (20:78), and the total lipids obtained were subjected to benzoylation-desulfation. A portion of this was directly analyzed by silica-column high performance liquid chromatography for the determination of nonhydroxycerebroside, hydroxycerebroside, nonhydroxysulfatide, and hydroxysulfatide. Another portion was fractionated by thin-layer chromatography, and the spots corresponding to the sphingolipid derivatives were eluted. The material from each spot was analyzed by reverse phase high performance liquid chromatography for its homolog composition. With this new procedure the concentrations and homolog compositions of cerebrosides and sulfatides were measured in plaque, periplaque, and normal-appearing white matter from brains of multiple sclerosis patients and Wallerian degenerated rat sciatic nerves distal to the nerve transection. One piece of plaque studied contained only 1.86, 2.76, 0.60, and 0.45 nmol of nonhydroxycerebroside, hydroxycerebroside, nonhydroxysulfatide and hydroxysulfatide/mg of protein, respectively. These concentrations are less than 1% of those found in normal white matter. Periplaques were found to contain concentrations of these sphingolipids between those of plaque and normal white matter. The levels of these sphingolipids in degenerative nerves were 10-20% below normal the third day after the nerve was severed and about 70% below normal after 10 days. The rate of decrease lessened from ten days to 55 days. The homolog compositions of these sphingolipids in both multiple sclerosis brain and degenerating nerves were similar to those in the control. The implications of these findings and the advantages of this new analytical method are discussed.

Early stimulation of phosphatidylcholine biosynthesis during Wallerian degeneration of rat sciatic nerve

Phospholipid metabolism was studied in rat sciatic nerve during Wallerian degeneration induced by crush injury. Portions of crushed sciatic nerve, incubated with labeled substrates, showed significantly higher phosphatidylcholine synthesis than normal nerve, prior to any measurable alterations of phospholipid composition. Maximum synthesis occurred 3 days after crush injury, at which time the metabolism of other phospholipids was unchanged. After a rapid decrease in biosynthetic activity, a second phase of enhanced phosphatidylcholine synthesis occurred, beginning 6 days after crush injury. Increased incorporation of [33P]phosphate, [2-3H]glycerol, and [Me-14C]choline indicated stimulation of de novo synthesis of phosphatidylcholine 3 days after injury. Neither base exchange reactions nor sequential methylation of ethanolamine phospholipids contributed significantly to phosphatidylcholine synthesis. Assay of certain key enzymes under optimal conditions in subcellular fractions of sciatic nerve revealed higher activities of cholinephosphate cytidyltransferase, choline phosphotransferase, and acyl-CoA:lysophosphatidylcholine acyltransferase in injured nerve, while choline kinase activity remained unchanged. This indicates that stimulation of phosphatidylcholine synthesis occurs via the cytidine nucleotide pathway, as well as by increased acylation of lysophosphatidylcholine. Although the cause of stimulated phosphatidylcholine synthesis remains unexplained, it is possible that trace amounts of lysophospholipids or other metabolites produced by injury-enhanced phospholipase activity may be responsible.

[Peripheral neuropathies. Current data concerning nerve regeneration (author's transl)]

The peripheral neuropathies in humans could be classified both with clinical criteria and pathological aspects. Between these, only axonal neuropathies are subject to regeneration. Axonal neuropathies present two aspects: wallerian degeneration and dying-back neuropathy. Dying-back neuropathy is the commonest type of human neuropathy but wallerian degeneration has been the most studied model of axonal neuropathy. The regeneration in this case lead to two questions: what is the signal for regeneration and what are the factors which improve the nerve growth?

Patterns of Wallerian degeneration of myelinated fibres in short and long peripheral stumps and in isolated segments of rat phrenic nerve. Interpretation of the role of axoplasmic flow of the trophic factor

The topographical level of nerve transection influences the time of appearance of Wallerian degeneration in the peripheral stump. After transection made in the distal portion of the nerve, degeneration appears earlier and is, for equal times, stronger than that observed under similar conditions after transection made near the beginning of the nerve. In nerves transected in the proximal part, the spatial pattern of degeneration along the peripheral stump depends on the time after neurotomy. A time span exists, different for each size class of fibres, within which the degree of degeneration decreases linearly with increasing distance from the site of transection. Within this time span, at increasing hours, the intercepts of calculated regression lines increase but the slopes change only slightly, so that an array of quasi-parallel lines is obtained. Departures from linearity occur at early times when some degree of degeneration has already appeared in the proximal part of the stump, whereas in its distal part all fibres still look normal. Another type of departure from linearity appears at late times (over 34 h). In isolated nerve segments the degeneration is weaker than in the peripheral stumps remaining in continuity with the nerve terminals and the longitudinal pattern of changes is strikingly altered. A unitary interpretation of these phenomena in terms of redistribution of the trophic factor by the bidirectional axoplasmic transport is proposed.

Synthesis of myelin, particulate, and soluble protein subfractions of rat sciatic nerve during the early stage of Wallerian degeneration: a comparison of metabolic studies using double and single isotope methods and recovery

The recovery, electrophoretic composition and synthesis of the myelin, particulate protein and soluble protein subfractions of rat sciatic nerve were compared in normal, sham-operated, and degenerating rat sciatic nerve at one, three and five days after neurotomy. Both single and double isotope methods were used to measure changes in synthesis in vitro and double isotope methods were used in vivo. The wet weights of nerves undergoing Wallerian degeneration for 5 days increased by 40 percent compared to normal and sham-operated nerves. The recovery, specific radioactivity, and synthesis of the myelin was reduced. The effect on myelin protein synthesis was similar in vitro and in vivo. The myelin loss was relatively constant in amount (30-40 microgram) regardless of differences in nerve sizes of young and old rats, consequently the percentage of myelin loss was inversely proportional to nerve size. The recovery of particulate protein increased, its rate of synthesis remained unchanged, and accordingly the specific radioactivity was decreased. The recovery, specific radioactivity, and the rate of synthesis of the soluble protein fraction were all elevated. The protein composition of the three fractions, as analyzed qualitatively by polyacrylamide disc gel electrophoresis, remained essentially unchanged through five days of degeneration. With regard to comparisons of the single and double isotope methods, results shows that the latter are more ideally suited to measuring changes in synthesis during the non-steady state conditions that are characteristics of rapid degeneration.