Knockout of p75(NTR) impairs re-myelination of injured sciatic nerve in mice

Remyelination is an important aspect of nerve regeneration after nerve injury but the underlying mechanisms are not fully understood. The neurotrophin receptor, p75(NTR), in activated Schwann cells in the Wallerian degenerated nerve is up-regulated and may play a role in the remyelination of regenerating peripheral nerves. In the present study, the role of p75(NTR) in remyelination of the sciatic nerve was investigated in p75(NTR) mutant mice. Histological results showed that the number of myelinated axons and thickness of myelin sheath in the injured sciatic nerves were reduced in mutant mice compared with wild-type mice. The myelin sheath of axons in the intact sciatic nerve of adult mutant mice is also thinner than that of wild-type mice. Real-time RT-PCR showed that mRNA levels for myelin basic protein and P0 in the injured sciatic nerves were significantly reduced in p75(NTR) mutant animals. Western blots also showed a significant reduction of P0 protein in the injured sciatic nerves of mutant animals. These results suggest that p75(NTR) is important for the myelinogenesis during the regeneration of peripheral nerves after injury.     

三叉神经对去运动神经支配面肌肌萎缩的影响

本文用组织化学、电镜以及肌球蛋白和肌动蛋白电泳分析了在单纯性面神经切断和三叉神经、面神经同时切断后面肌萎缩的病理改变--肌纤维的显微结构改变以及面肌收缩蛋白质在手术后不同时期的降解变化。实验证明,面部肌肉在不同的神经切断情况下其病理改变不同,正常的三叉神经支配可以延缓面瘫后肌肉蛋白质的降解,减少胶原纤维结缔组织的增生,较好地保护肌纤维的显微结构,延缓和减轻去运动神经支配面肌肌萎缩。本研究结果可以为临床治疗面瘫提供一定的理论指导。     

PATTERN OF RNA SYNTHESIS IN THE SCIATIC NERVE OF THE HEN DURING WALLERIAN DEGENERATION

The pattern of synthesis of rapidly-labelled RNA of hen sciatic nerve was studied during Wallerian degeneration. At 2,4,8, 16 and 30 days of degeneration the proximal and distal stumps of the severed nerve as well as the intact contralateral sciatic nerve (functional control) were excised and incubated with either [5-³H]uridine or [2-¹⁴C]uridine for 0.5 h. The electrophoretic pattern of RNA from the normal adult sciatic nerve showed that most of the radioactivity was incorporated into RNA species migrating between the 18 S and 4 S components of the bulk RNA. The synthesis of RNA was sensitive to actinomycin-D, an indication that it was directed by a DNA template. The electrophoretic patterns of the rapidly-labelled RNA in the proximal and distal nerve stumps demonstrated a change following nerve section. After 2–4 days of Wallerian degeneration the degenerating distal nerves incorporated more radioactivity in the 4 S region than the corresponding controls, but at 8 and 16-days after degeneration relatively more label appeared in higher molecular weight RNA species. In the intact sciatic nerve of the operated hens progressively more radioactivity was detected in the 4 S region with increasing time after the contralateral nerve section. At each stage of Wallerian degeneration the specific radioactivities of RNA in the control nerves from experimental hens were higher than those of the normal adult sciatic nerve. These results indicated a change of RNA metabolism in increased functional activity and during Wallerian degeneration.     

Desert hedgehog-patched 2 expression in peripheral nerves during Wallerian degeneration and regeneration

Hedgehog proteins are important in the development of the nervous system. As Desert hedgehog (Dhh) is involved in the development of peripheral nerves and is expressed in adult nerves, it may play a role in the maintenance of adult nerves and degeneration and regeneration after injury. We firstly investigated the Dhh-receptors, which are expressed in mouse adult nerves. The Dhh receptor patched(ptc)2 was detected in adult sciatic nerves using RT-PCR, however, ptc1 was undetectable under the same experimental condition. Using RT-PCR in purified cultures of mouse Schwann cells and fibroblasts, we found ptc2 mRNA in Schwann cells, and at much lower levels, in fibroblasts. By immunohistochemistry, Ptc2 protein was seen on unmyelinated nerve fibers. Then we induced crush injury to the sciatic nerves of wild-type (WT) and dhh-null mice and the distal stumps of injured nerves were analyzed morphologically at different time points and expression of dhh and related receptors was also measured by RT-PCR in WT mice. In dhh-null mice, degeneration of myelinated fibers was more severe than in WT mice. Furthermore, in regenerated nerves of dhh-null mice, minifascicular formation was even more extensive than in dhh-null intact nerves. Both dhh and ptc2 mRNA levels were down-regulated during the degenerative phase postinjury in WT mice, while levels rose again during the phase of nerve regeneration. These results suggest that the Dhh-Ptc2 signaling pathway may be involved in the maintenance of adult nerves and may be one of the factors that directly or indirectly determines the response of peripheral nerves to injury.     

Functional properties of factor Va subunits after proteolytic alterations by activated protein C

The two-subunit structure of the factor Va molecule is essential to its function in the prothrombinase complex. In the presence of phospholipids, the cleavage of the light chain of bovine factor Va by activated protein C proceeded at the same rate as the cleavage of the heavy chain. The limited proteolysis of factor Va is accompanied by a parallel loss of factor Va activity. Evidence that loss of activity was solely the result of the cleavage of the heavy chain, was obtained from reconstitution experiments utilizing cleaved and intact chains. The pseudo first-order rate constant of factor Va inactivation by activated protein C was found to be dependent on the amount of phospholipid-bound activated protein C and not on the amount of phospholipid-bound factor Va. However, phospholipids enhance the rate of proteolysis of the phospholipid-binding subunit, i.e. the light chain, and not the cleavage of the heavy chain. Cleavage of the heavy chain and as a consequence the inactivation of factor Va by activated protein C is mediated by phospholipid-bound light chain. After cleavage of the light chain, the 'two-subunit' structure, as well as the phospholipid-binding properties of factor Va were found to be conserved.     

Partial glycosylation at asparagine-2181 of the second C-type domain of human factor V modulates assembly of the prothrombinase complex.

Thrombin-activated factor Va exists as two isoforms, factor Va(1) and factor Va(2), which differ in the size of their light chains and their affinity for biological membranes. The heterogeneity of the light chain remained following incubation of factor Va with N-glycanase. However, we found that the factor V C2 domain, which contains a single potential glycosylation site at Asn-2181, was partially glycosylated when expressed in COS cells. To confirm the structural basis for factor Va(1) and factor Va(2), we mutated Asn-2181 to glutamine (N2181Q) and expressed this mutant using a B domain deletion construct (rHFV des B) in COS cells. Thrombin activation of N2181Q released a light chain with mobility identical to that of factor Va(2) on SDS-PAGE. The functional properties of purified N2181Q were similar to those of factor Va(2) in prothrombinase assays carried out in the presence of limiting concentrations of phosphatidylserine. The binding of human factor Va(1) and factor Va(2) to 75:25 POPC/POPS vesicles was also investigated in equilibrium binding assays using proteins containing a fluorescein-labeled heavy chain. The affinity of human factor Va(2) binding to POPC/POPS vesicles was approximately 3-fold higher than that of factor Va(1). These results indicate that partial glycosylation of factor V at asparagine-2181 is the structural basis of the light chain doublet and that the presence of this oligosaccharide reduces the affinity of factor Va for biological membranes.     

Expression of neutrophil gelatinase-associated lipocalin (NGAL) in peripheral nerve repair

Introduction: Trauma is one of the causes of peripheral nerve injuries. Free radicals increase after tissue damage. Free radicals are usually scavenged and detoxi?ed by antioxidants. In this study, we assessed the antioxidative role of the NGAL molecule in sciatic nerve repair in rats. Materials and methods: The sciatic nerves of 40 rats were crushed and the total mRNA of samples from day 1 and 3 and week 1, 3, 5 post injury was extracted. The expression of the NGAL gene was confirmed by RT-PCR. For immunohistochemistry analysis, the samples were ?xed in paraformaldehyde and cut in 20 micrometer slices by cryostat. Results: The expression of NGAL signi?cantly upregulated in day 1, 3 and week 1 following the crushing of sciatic nerves in comparison with the intact nerves. Immunohistochemistry results also confirmed the protein expression of this gene. Discussion: The NGAL molecule showed upregulation in the degeneration process after nerve injury, so it may play an important role in nerve repair.     

Expression of specific sheath cell proteins during peripheral nerve growth and regeneration in mammals

Protein synthesis in the nerve sheath of injured as well as intact mature and developing sciatic nerves from rat and rabbit was investigated by incubating segments of nerve with [35S]methionine in vitro. The composition of labeled proteins under the different conditions of nerve growth was analyzed by two-dimensional gel electrophoresis and fluorography. The expression of six secreted proteins in rat sciatic nerve with the apparent molecular weights of 70,000 (70 kD), 54,000 (54 kD), 51,000 (51 kD), 39,000 (39 kD), 37,000 (37 kD), and 30,000 (30 kD) was of particular interest because of the correlation of their synthesis and secretion with aspects of nerve growth and regeneration. The synthesis of the 37-kD protein was significantly stimulated during both sciatic nerve development as well as regeneration but not in the intact mature nerve. The expression of this protein appears to be regulated by signal(s) from the axon but not the target. The 70-kD protein was exclusively synthesized in response to axotomy, thus confining its role to some aspect(s) of nerve repair. In contrast, the 54- and 51-kD proteins were expressed in the intact mature nerve sheath. Their synthesis and release was rapidly inhibited upon axotomy but returned to normal or higher levels towards the end of sciatic nerve regeneration, suggesting a role in the maintenance of the integrity of the mature (nongrowing) rat nerve. The 39- and 30-kD proteins were only transiently synthesized within the first week after axotomy. Two proteins with the apparent molecular masses of 70 and 37 kD were synthesized in denervated rabbit sciatic nerve. The similar molecular weights, net charges, and time-courses of induction suggest a homology between these proteins in rabbit and rat, indicating common molecular responses of peripheral nerve sheath cells to axon injury in both mammalian species.     

Effect of Wallerian Degeneration on Histamine Concentration of the Peripheral Nerve

One sciatic nerve of a White Leghorn hen was severed and the distal portion was allowed to undergo Wallerian degeneration. The change in histamine and DNA concentration and mast cell number was measured at different times following nerve sectioning in the proximal regenerating, distal degenerating, and intact, contralateral nerves. The experimental results revealed a significant accumulation of histamine in the proximal desheathed segment and in the contralateral “functional nerve,” whereas the biogenic amine in the distal desheathed nerve significantly decreased. The pattern of change of histamine in the distal and proximal nerve sheaths was different: it dropped at 2 h and then rose in the later stages of Wallerian degeneration. In the distal desheathed nerves and in both the proximal and distal nerve sheaths DNA increased significantly by 14 days. The number of mast cells appeared to be highest in the 14-day distal nerve and in the 7-day proximal nerve sheaths. These results support a dual localization of histamine in the peripheral nerve, and are consistent with the interpretation that the amine has either some role in neurotransmission or in the process of growth and regeneration.     

In vivo USPIO magnetic resonance imaging shows that minocycline mitigates macrophage recruitment to a peripheral nerve injury

ABSTRACT: BACKGROUND: Minocycline has proven anti-nociceptive effects, and delays the development of allodynia/hyperalgesia after peripheral nerve injury. However, the mechanism by which this occurs remains unclear. Inflammatory cells, in particular macrophages, are critical components of the response to nerve injury. Using ultrasmall superparamagnetic iron oxide-magnetic resonance imaging (USPIO-MRI) to monitor macrophage trafficking, the purpose of this project is to determine whether minocycline modulates macrophage trafficking to the site of nerve injury in vivo and, in turn, results in altered pain thresholds. RESULTS: Animal experiments were approved by Stanford IACUC. A model of neuropathic pain was created using the Spared Nerve Injury (SNI) model that involves ligation of the left sciatic nerve in the left thigh of adult Sprague-Dawley rats. Animals with SNI and uninjured animals (control) were then injected with/without USPIOs (300umol/kg IV) and with/without minocycline (50mg/kg IP). Bilateral sciatic nerves were scanned with a volume coil in a 7T magnet 7 days after USPIO administration. Fluid-sensitive MR images were obtained, and ROIs were placed on bilateral sciatic nerves to quantify signal intensity. Pain behavior modulation by minocycline was measured using the Von Frey filament test. Sciatic nerves were ultimately harvested at day 7, fixed in 10% buffered formalin and stained for the presence of iron oxide-laden macrophages. Behavioral measurements confirmed the presence of allodynia in the neuropathic pain model while the uninjured and minocycline-treated injured group had significantly higher paw withdrawal thresholds (p<0.011). Decreased MR signal is observed in the SNI group that received USPIOs (3.3+/-0.5%) compared to the minocycline-treated SNI group that received USPIOs (15.2+/-4.5%) and minocycline-treated group (no USPIOs; 41.2+/-2.3%) (p<0.04). Histology of harvested sciatic nerve specimens confirmed the presence USPIOs at the nerve injury site in the SNI group without minocycline treatment. CONCLUSION: Animals with neuropathic pain in the left hindpaw show increased trafficking of USPIO-laden macrophages to the site of sciatic nerve injury. Minocycline appears to retard the migration of macrophages to the nerve injury site, which may partly explain its anti-nociceptive effects. USPIO-MRI is an effective in vivo imaging tool to study the role of macrophages in the development of neuropathic pain.     

On the location of the divalent metal binding sites and the light chain subunits of vertebrate myosin.

The divalent metal ion binding sites of skeletal myosin were investigated by electron paramagnetic resonance (EPR) spectroscopy using the paramagnetic (Mn(II) ion as a probe. Myosin possesses two high affinity sites (K less than 1 muM) for Mn(II), which are located on the 5,5'-dithiobis(2-nitrobenzoate) (DTNB) light chains. Mn(II) bound to the isolated DTNB light chain gives rise to an EPR spectrum similar to that of Mn(II) bound to myosin and this indicates that the metal binding site comprises ligands from the DTNB light chain alone. Myosin preparations in which the DTNB light chain content is reduced by treatment with 5,5'-dithiobis(2-nitrobenzoate) show a corresponding reduction in the stoichiometry of Mn(II) binding, but the stoichiometry is recovered on reassociation of the DTNB light chain. Chymotryptic digestion of myosin filaments in the presence of ethylenediaminetetraacetic acid yields subfragment 1, but digestion in the presence of divalent metal ions produces heavy meromyosin. Myosin with a depleted DTNB light chain content gives rise to subfragment 1 on proteolysis, even in the presence of divalent metal ions. It is proposed that saturation of the DTNB light chain site with divalent ions protects this subunit against proteolysis, which, in turn, inhibits the cleavage of the subfragment 1-subfragment 2 link. Either the DTNB light chain is located near the region of the link and sterically blocks chymotryptic attack, or it is bound to the subfragment 1 moiety and affects the conformation of the link region. When the product heavy meromyosin was examined by sodium dodecyl sulfate gel electrophoresis, an apparent anomaly arose in that there was no trace of the 19 000-dalton band corresponding to the DTNB light chain. This was resolved by following the time course of chymotryptic digestion of the myosin heavy chain, the DTNB light chain, and the divalent metal binding site. The 19 000-dalton DTNB light chain is rapidly degraded to a 17 000-dalton fragment which comigrates with the alkali 2 light chain. The divalent metal site remains intact, despite this degradation, and the 17 000 fragment continues to protect the subfragment 1-subfragment 2 link. In the absence of divalent metal ions, the 17 000-dalton fragment is further degraded and attack of the subfragment 1 link ensues. Mn(II) bound to cardiac myosin gives an EPR spectrum basically similar to that of skeletal myosin, suggesting that their 19 000-dalton light chains are analogous with respect to their divalent metal binding sites, despite their chemical differences. The potential of EPR spectroscopy for characterizing the metal binding sites of myosin from different sources and of intact muscle fibers is discussed.     

Unique in vivo modifications of coagulation factor V produce a physically and functionally distinct platelet-derived cofactor: characterization of purified platelet-derived factor V/Va

Platelet- and plasma-derived factor Va (FVa) serve essential cofactor roles in prothrombinase-catalyzed thrombin generation. Platelet-derived FV/Va, purified from Triton X-100 platelet lysates was composed of a mixture of polypeptides ranging from approximately 40 to 330 kDa, mimicking those visualized by Western blotting of platelet lysates and releasates with anti-FV antibodies. The purified, platelet-derived protein expressed significant cofactor activity such that thrombin activation led to only a 2-3-fold increase in cofactor activity yet expression of a specific activity identical to that of purified, plasma-derived FVa. Physical and functional differences between the two cofactors were identified. Purified, platelet-derived FVa was 2-3-fold more resistant to activated protein C-catalyzed inactivation than purified plasma-derived FVa on the thrombin-activated platelet surface. The heavy chain subunit of purified, platelet-derived FVa contained only a fraction ( approximately 10-15%) of the intrinsic phosphoserine present in the plasma-derived FVa heavy chain and was resistant to phosphorylation at Ser(692) catalyzed by either casein kinase II or thrombin-activated platelets. MALDI-TOF mass spectrometric analyses of tryptic digests of platelet-derived FV peptides detected an intact heavy chain uniquely modified on Thr(402) with an N-acetylglucosamine or N-acetylgalactosamine, whereas Ser(692) remained unmodified. N-terminal sequencing and MALDI-TOF analyses of platelet-derived FV/Va peptides identified the presence of a full-length heavy chain subunit, as well as a light chain subunit formed by cleavage at Tyr(1543) rather than Arg(1545) accounting for the intrinsic levels of cofactor activity exhibited by native platelet-derived FVa. These collective data are the first to demonstrate physical differences between the two FV cofactor pools and support the hypothesis that, subsequent to its endocytosis by megakaryocytes, FV is modified to yield a platelet-derived cofactor distinct from its plasma counterpart.     

Purification and properties of intracellular clotting factor, factor B, from horseshoe crab (Tachypleus tridentatus) hemocytes

An intracellular clotting factor, factor B, which is closely associated with the hemolymph coagulation system of horseshoe crab (Tachypleus tridentatus), was purified and characterized. The purified preparation gave a single band (Mr = 64,000) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in the absence of 2-mercaptoethanol, while three bands (Mr = 64,000, 40,000, and 25,000) were detected on SDS-PAGE after reduction. This preparation was converted by limulus clotting factor C to an activated form, factor B, with Mr = 56,000 consisting of a heavy chain (Mr = 32,000) and a light chain (Mr = 25,000) bridged by disulfide linkage(s). The factor B, which was produced separately by treating the partially purified factor B with factor C, was also purified. It gave a single band on unreduced SDS-PAGE and two bands on reduced SDS-PAGE. The purified factor B had Mr of 56,000 consisting of a heavy chain (Mr = 32,000) and a light chain (Mr = 25,000). These results indicated that the purified factor B zymogen is a mixture of single-chain and two-chain forms, both of which have the same molecular weight of 64,000, and that these two forms are converted to factor B by factor C. The diisopropyl phosphorofluoridate-sensitive site of factor B was found in the heavy chain. The reconstitution studies using purified factor C, factor B, proclotting enzyme and coagulogen in the presence of lipopolysaccharide indicated that factor B is an essential component to complete sequential activation of the limulus clotting system, and that it specifically activates proclotting enzyme to the active clotting enzyme.     

Sulfation of Rat Apolipoprotein E

The synthesis of a 37-kilodalton (kDa) protein which has been shown recently to be identical with apolipoprotein E (apo-E) was increased after sciatic nerve injury of the rat. When regeneration of the nerve was allowed, its synthesis returned to control levels at about 8 weeks post injury. In this report it is shown that similar time-course studies of the protein in the rat optic nerve revealed a delayed increase of the protein but a comparably high level of synthesis at 3 weeks post injury. This level was maintained up to at least 18 weeks after crush. Furthermore, two-dimensional electrophoresis revealed that the characteristic "trailing" of the protein is due to its sialylation, because it was reduced after neuraminidase treatment. This treatment, however, detected a neuraminidase-resistant heterogeneous form in CNS tissue and a homogeneous form in peripheral nervous tissue. The trailing persisted up to 18 days of culture of optic nerve explants, of CNS glial cells, and of peritoneal macrophages, but disappeared during the first culture days of sciatic nerve explants and was not observed in Schwann cell culture media. Incorporation studies with 35SO4 revealed that apo-E was the major sulfated protein in culture media conditioned by CNS glial cells, whereas sulfation of the protein was undetectable in Schwann cell cultures. Because macrophages are likely to be the major source of apo-E in both peripheral and central glial cell cultures as well as in injured optic and sciatic nerves, it is hypothesized that resident cells of sciatic nerves secrete potent sulfatases. As a result, sialic acid residues may be more susceptible to degradation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Peripheral nerve lesion-induced uptake and transport of choleragenoid by capsaicin-sensitive c-fibre spinal ganglion neurons

In the present experiments the effect of systemic capsaicin treatment on the retrograde labelling of sensory ganglion cells was studied following the injection of choleratoxin B subunit-horseradish peroxidase conjugate (CTX-HRP) into intact and chronically transected peripheral nerves. In the control rats CTX-HRP injected into intact sciatic nerves labelled medium and large neurons with a mean cross-sectional area of 1,041 +/- 39 gm2. However, after injection of the conjugate into chronically transected sciatic nerves of the control rats, many small cells were also labelled, shifting the mean cross-sectional area of the labelled cells to 632 +/- 118 microm2. Capsaicin pretreatment per se induced a moderate but significant decrease in the mean cross-sectional area of the labelled neurons (879 +/- 79 microm2). More importantly, systemic pretreatment with capsaicin prevented the peripheral nerve lesion-induced labelling of small cells. Thus, the mean cross-sectional areas of labelled neurons relating to the intact and transected sciatic nerves, respectively, did not differ significantly. These findings provide direct evidence for a phenotypic switch of capsaicin-sensitive nociceptive neurons after peripheral nerve injury, and suggest that lesion-induced morphological changes in the spinal cord may be related to specific alterations in the chemistry of C-fibre afferent neurons rather than to a sprouting response of A-fibre afferents.     

Axonal Contact Regulates Expression of α2 and β2 Isoforms of Na+,K+-ATPase in Schwann Cells: Adhesion Molecules and Nerve Regeneration

Abstract: Three isoforms of catalytic α subunits and two isoforms of β subunits of Na⁺,K⁺-ATPase were detected in rat sciatic nerves by western blotting. Unlike the enzyme in brain, sciatic nerve Na⁺,K⁺-ATPase was highly resistant to ouabain. The ouabain-resistant α1 isoform was demonstrated to be the predominant form in rat intact sciatic nerve by quantitative densitometric analysis and is mainly responsible for sciatic nerve Na⁺,K⁺-ATPase activity. After sciatic nerve injury, the α3 and β1 isoforms completely disappeared from the distal segment owing to Wallerian degeneration. In contrast, α2 and β2 isoform expression and Na⁺,K⁺-ATPase activity sensitive to pyrithiamine (a specific inhibitor of the α2 isoform) were markedly increased in Schwann cells in the distal segment of the injured sciatic nerve. These latter levels returned to baseline with nerve regeneration. Our results suggest that α3 and β1 isoforms are exclusive for the axon and α2 and β2 isoforms are exclusive for the Schwann cell, although axonal contact regulates α2 and β2 isoform expressions. Because the β2 isoform of Na⁺,K⁺-ATPase is known as an adhesion molecule on glia (AMOG), increased expression of AMOG/β2 on Schwann cells in the segment distal to sciatic nerve injury suggests that AMOG/β2 may act as an adhesion molecule in peripheral nerve regeneration.     

Characterization of MSH/ACTH-like immunoreactivity in sciatic nerves of Xenopus laevis by immunocytochemistry,Western blotting and radioimmunoassay

Summary Previous studies have indicated that rat neurofilament protein may contain an endogenous MSH-like epitope with neuroregenerative properties. The presence of such an epitope has now been studied in nerve tissue from Xenopus laevis. Western blot analyses of sciatic nerve tissue using an assortment of sequence-specific MSH/ACTH antisera revealed the presence of two major immunoreactive protein bands of 52 and 50 kDa, which contained a mid-region MSH-like epitope. Weaker staining occurred in another protein band at 135 kDa. Immunocytochemistry revealed the immunoreactivity to reside in the axis cylinders of the nerve fibers. Other antisera, recognizing other regions of MSH/ACTH produced strong staining of Xenopus intermediate lobes, but failed to stain sciatic nerves. Thus, the proteins detected have no clear relation to either Xenopus neurofilament proteins or proopiomelanocortin.     

Slow flow in axons detached from their perikarya

Slow flow was followed in unmyelinated olfactory axons, severed from their cell bodies, at 14 degrees C, 21 degrees C, and 31 degrees C. Slow flow does not stop after axotomy but rather accelerates to a value 3.3 times faster than the rates measured in an intact nerve. These velocities are equivalent to the rates of slow flow characteristic of regenerating fibers. The injury appears to have an influence on the contralateral intact nerve, where slow flow velocity increases to severed nerve values for several days before reverting to intact nerve rates. It can be hypothesized that the increase in the rate of slow flow is triggered by a factor repressed in intact nerve but released into the blood stream following injury.     

Age-Related Changes of Myelin Proteins in the Rat Peripheral Nervous System

Age-related changes in amounts of myelin proteins from rat sciatic nerve or spinal root were analyzed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE). In the aged peripheral nerve myelin, the relative amounts of band 105K and proteins X and Y increased, whereas those of proteins P0 and P1 and band 190K decreased. Band 105K purified by preparative SDS-PAGE exhibited three bands of 105K, 28K, and 21K at the second electrophoresis. A repeated SDS-PAGE did not improve the purity of bank 105K, but increased the ratio of 21K to 28K. Compared with P0 protein, band 105K has a very similar peptide map pattern and amino acid composition, as well as the identical NH2 terminal residue, isoleucine. These findings suggest that band 105K is an aggregate form of P0 protein and its fragment, 21K. The 21K protein is a distinct entity from X protein. The quantitative and qualitative alterations in myelin proteins, as we report here, may reflect continuing demyelination and remyelination in aged peripheral nerves.