Sciatic Nerve Myelin Research Articles

Polypeptide components of myelin from rat peripheral nerve

Myelin was isolated from rat sciatic nerve and its composition determined. Peripheral nerve myelin contained 21% protein and the polypeptide-chain components were analyzed on polyacrylamide gels in presence of sodium dodecylsulfate. Sciatic nerve myelin contained at least seven polypeptide components ranging in molecular weight from 50 000 to 16 000. The two major polypeptides had a molecular weight of 28 000 and 22 000 and they were shown to be glycoproteins as they also stained with periodic acid—Schiff reagent for carbohydrates.

Recurrent experimental allergic polyganglioradiculoneuritis. Multiple demyelinating episodes in rhesus monkey sensitized with rabbit sciatic nerve myelin.

Seven rhesus monkeys immunized with 60 to 70 mg of rabbit sciatic nerve myelin developed neurological symptoms (ptosis, strabismus, paresis, or paralysis). In two animals clinical episodes of the disease recurred. Morphologic studies of the animals between 21 and 70 days after immunization showed that all monkeys developed demyelinating polyganglioradiculoneuritis. Cranial nerves myelinated by Schwann cells were also involved; however, the central nervous system did not display any demyelinating lesions. In all animals, irrespective of postimmunization time lapse and occurrence of clinical symptoms, chronic demyelinating plaques and acute lesions with cellular infiltration, active stripping, and phagocytosis of myelin were observed. Coexistence of active and chronic demyelinating plaques is especially important, particularly in animals that survived long after appearance of clinical symptoms; it indicates that experimental allergic neuritis is not a monophasic disease.

Evidence that the major protein in rat sciatic nerve myelin is a glycoprotein.

AbstractEvidence is presented that the major protein of rat sciatic nerve myelin is a glycoprotein. When myelin proteins were separated by polyacrylamide gel electrophoresis, the major band which was stained with amido black–Coomassie blue was also stained with periodic acid‐Schiff reagents for carbohydrate. Radioactive labelling of myelin in vivo with [3H]leucine and [14C]fucose, followed by electrophoresis of the proteins, indicated that with both isotopes the major labelled peak corresponded to the major stained band. In addition, a second smaller peak of [14C]fucose migrated ahead of the major peak. Delipidated myelin contained galactose, mannose, fucose and sialic acid.

Myelination of rat sciatic nerve: comparison of undernutrition and cholesterol biosynthesis inhibition.

The effects of partial feeding and subsequent free feeding on myelination of rat sciatic nerve were investigated and compared with the effects of daily i.p. administration of AY9944 (trans-1, 4-bis-(2-chlorobenzylaminomethyl)-cyclohexane dihydrochloride), a cholesterol biosynthesis inhibitor. The frequency distributions of myelin sheath thicknesses in electron micrographs of sciatic nerves of experimental and control littermates were compared together with the relationships of axon circumference to myelin sheath thickness. Undernutrition and administration of a hypocholesteremic drug (AY9944) had dissimilar effects on myelinating rat sciatic nerve. Myelination of rat sciatic nerve was retarded more than the circumferential growth of the axon by undernutrition from 4 to 12, 4 to 18, and 12 to 26 days of age. The retardation of myelination caused by undernutrition from 4–12 days of age was still evident at 26 days of age but not at 34 days of age, whereas retardation of myelination after undernutrition from 4 to 18 days of age was still present at 46 days of age. AY9944 had no effect on the frequency distributions of myelin sheath thickness although 22% of Schwann cells in the 11 day old rats injected daily from 2 days of age contained crystalline and lamellar inclusions; and the AY9944 treated rats gained weight less quickly than their littermates. Undernutrition during a critical period in the development of rat peripheral nerve can cause deficits in myelin accumulation not fully accounted for by generalized growth retardation.

Developmental changes in lipid composition of chick sciatic nerve myelin.

AbstractMyelin isolated from the sciatic nerves of chicks by centrifugation on a discontinuous sucrose gradient was found to undergo marked changes in lipid composition during development from the 18 day embryonic to the adult stage, particularly in the phospholipid and cerebroside content. Significant changes in the content of individual phospholipids were also noted.

The proposed amino acid sequence of the P1 protein of rabbit sciatic nerve myelin

A basic protein (P1 protein) exists in rabbit sciatic nerve myelin that appears to have the same amino acid sequence as the rabbit A1 protein, a basic protein of central nervous system myelin. The amino acid sequences proposed for the two rabbit proteins are compared with the bovine and human A1 proteins; differences (substitutions, deletions, additions) in approximately 15 residues are observed. The amino acid sequence of each rabbit protein (168 amino acids, M r 18,100) was assessed by amino acid analysis of each tryptic peptide obtained by elution of the ninhydrin-positive spots from the tryptic peptide map. Peptides were judged to have the same or similar sequence if they migrated to the same position on the peptide map as the analogous peptide from the bovine A1 protein, and if they had the same or similar composition as the bovine peptides. Several characteristic features of the bovine A1 protein are preserved in the two rabbit proteins: the region surrounding the molecules single tryptophan residue; the rare triproline sequence; the methylated arginine derivatives localized exclusively at position 107 of the bovine A1 protein; and the reactive threonine residue which serves as an acceptor for glycosylation by the polypeptide: N-acetylgalactosaminyl transferase.

Incorporation of Cholesterol into Peripheral Nerve Myelin

Several speculations exist as to the site of incorporation of preformed molecules into myelin. The possibility that an autoradiographic analysis of cholesterol-1,2-H3 incorporation at very short times after injection might shed some light in the solution of that problem led to the present experiment.Cholesterol-1,2-H3 was injected intraperitoneally into 24 tenday old mice. The animals were then sacrificed at 10,20,30,40,60,90,120 and 180 min after the injection and the sciatic nerves were processed for electron microscope autoradiography. To analyze the grain distribution in the autoradiograms of cross and longitudinal sections from each sciatic nerve myelin sheaths were subdivided into three compartments named: outer 1/3, middle 1/3 and inner 1/3 compartments.It was found that twenty min. after the injection of cholesterol -1.2-H3 (Figs. 1 and 2), 55% of the total number of grains (t.n.g) found in myelin were within the outer 1/3 compartment, 9% were within the middle 1/3 and 36% within the inner 1/3 compartment

Isolation and characterization of a protein from sciatic nerve myelin responsible for experimental allergic neuritis.

EXPERIMENTAL allergic encephalomyelitis (EAE) is an autoimmune demyelinating disease1,2 of the central nervous system (CNS) induced by the basic Al protein3 of the myelin membrane (30% of the total protein). The complete aminoacid sequences of the human and bovine A1 proteins have been determined4,5. The open conformation6–8 of the A1 protein (18,400 molecular weight) emphasizes the role of the primary structure in determining its immunological properties. From isolated peptide fragments, disease-inducing sites of the A1 protein have been identified and subsequently synthesized9–11.

Structure of the nerve myelin membrane: Proof of the low-resolution profile

In analyzing the low-angle X-ray diffraction patterns recorded from the normal and swollen myelin in frog sciatic nerve, a precise value is found for the center-to-center distance between the pair of membranes constituting the repeating structure in the myelin. The previously reported large increase in period when the nerve is put in hypotonic Ringer's solution is shown to be accompanied by a small decrease in the center-to-center distance of the membranes within one pair. Thus both a large amplitude swelling at the extracellular interface between membrane pairs and a moderate one at the cytoplasmic interface within the pair are observed. The two kinds of swelling—cytoplasmic and extracellular—are sufficient to demonstrate crystallographically the correctness of the bilayer profile for a single myelin membrane. The existence of a lipid bilayer within the membrane is confirmed by the scale of absolute electron density derived from the swelling experiments, and hydrated surface layers of protein are postulated.

X-Ray Diffraction of Myelin Membrane: I. Optimal Conditions for Obtaining Unmodified Small-Angle Diffraction Data from Frog Sciatic Nerve

The X-ray diffraction pattern of myelin of frog sciatic nerve has been investigated, using a Kratky small angle slit camera to obtain the electron density distribution across the membrane. All major reflections observed were related to a fundamental repeat distance of 171 +/- 2.8 A. There was no further increase in the number of reflections on varying the experimental conditions (varying pH, applying tension, immersion in various isotonic buffer solutions, etc.) or by varying the camera slit arrangement. The degree of disorder within the myelin sheath was examined by comparing the crystallite size to the half-width of the diffraction peak at half-height. The limiting of the diffraction spectra to five major reflections was determined not to be caused by disorder. It is concluded that the observed X-ray diffraction pattern is a consequence of the particular electron density distribution of the membrane. Therefore, the membrane cannot contain sharply distinct step-function regions of electron density, but approaches a modified cosine distribution.

Electron density model for nerve myelin.

THE swelling of freshly dissected frog sciatic nerve myelin in sucrose solutions has been studied by low-angle X-ray diffraction. Our analysis of the X-ray data leads to a choice between two possible triple layered membrane units and also allows us to assign an absolute electron density scale to the favoured model.

Electron microscope and x-ray diffraction studies of the effects of dehydration on the structure of nerve myelin. II. Optic nerve.

The dehydration of rat optic nerve has been studied by allowing specimens to become partially or fully dried before fixation and preparation for electron microscopy. A correlation is established between electron micrographs of the myelin sheath and corresponding small-angle x-ray diffraction patterns. The modifications of the optic nerve myelin layers during drying were very similar to those described in more detail for the myelin of frog sciatic nerve. The most striking difference was that the system of fine layers characteristic of the fully dried myelin was much more extensive in the case of the optic nerve, and the layer thickness was significantly greater than the corresponding layer in the frog sciatic nerve preparation. The significance of these correlations is discussed.

The effects of osmium tetroxide fixation on the structure of myelin in sciatic nerve

A study has been made of the effects of osmium tetroxide on the X-ray diffraction patterns of normal and modified sciatic nerve. Intense and well-defined diffraction patterns were obtained from OsO 4-fixed fresh nerve but not from nerve which had been initially modified by temperature changes, or treatment with lipid solvents or formalin. The effect is thought to emphasize the precise arrangement of reactive groups in fresh myelin and the disorganization of such groups which accompanies modifications. OsO 4-fixed fresh nerve appears to resist further modifications, and the structure revealed by the electron microscope probably resembles very closely the normal structure. Detailed correlation of E.M. and X-ray diffraction data is not possible because of lack of knowledge of the precise chemical action of OsO 4, but some tentative suggestions are made.