Tonic sympathetic activity in the rabbit sciatic nerve

Tonic activity of sympathetic nerve fibers of the tibial and peroneal nerves was investigated in rabbits anesthetized with urethane by the multichannel coherent recording technique. Activity of stochastic character was shown to predominate in the tonic activity of these fibers. A component of activity with the frequency of the heart beat also is frequently observed, but the power of this component is never more than half the total power of activity. Activity with a frequency of 10 Hz, observed by other workers, and also modulation of tonic activity in the rhythm of respiration were not recorded in these experiments. Slow changes in the power of activity from zero to a level several times above average were observed when the blood pressure was stable.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 351–358, May–June, 1985.     

Glycolipids of peripheral nerve: isolation and characterization of glycolipids from rabbit sciatic nerve

Besides cerebreside and sulfatide four other glycolipids were isolated from rabbit sciatic nerve and analyzed by chemical and chromatographic methods. Three of the glycolipids were shown to be fatty acid esters of cerebroside; the fourth was characterized as diacyl glycerol galactoside and its alkyl ether analog. In the ester linkage mainly unsubstituted acids with chain length C(16) to C(18) were present. Both hydroxy and unsubstituted acids were found in amide linkage. They varied in chain length from C(16) to C(24) and were typical of cerebrosides. The long-chain base fraction contained sphingosine and dihydrosphingosine as the main components.     

Changes in the sciatic nerve of the rabbit and its tissue constituents during development

Abstract— A segment, defined by gross anatomic boundaries, which comprises most of the sciatic nerve was dissected from rabbits aged from birth to 1 yr. The mean and standard deviation of the variance determined for the weights of pairs of nerve units removed from single animals of an age group did not exceed 2·7 per cent and 12·3 per cent respectively of the average weight of the two nerve units which were the values determined for a group of newborn animals. During the period from birth to one year of age, the weight and length of the nerve unit increased 47- and 6-fold respectively while the animal's weight increased 78-fold. Whereas the nerve unit length increased little after 8 weeks, its weight and that of the whole animal continued to increase up to 1 year. Estimations of nucleic acids in the nerve unit from adult animals gave values of 54 μg DNA-P and 25 μg RNA-P per g fresh weight. During the period birth to 1 yr the absolute amount of DNA in the nerve unit increased 11-fold, 71 per cent of this having occurred by 6 weeks of age. The absolute amount of RNA increased 11 -fold by 8 weeks of age and remained constant thereafter. During the period birth to 1 yr, the proportion of the nerve constituents accounted for by lipid-free solids remained constant at 10 per cent, while lipids increased from 5 to 18 per cent and tissue water declined from 84 to 71 per cent. Changes in some lipid classes were examined also. Increases of absolute content in the nerve unit over the first year and concentrations on a fresh weight basis attained in year-old animals were as follows: cholesterol, 132-fold and 86 mg/g; triglyceride 554-fold and 43·2 mg/g; total phospholipid, 85-fold and 61 mg/g; cerebroside 205-fold and 28 μmol/g; sulphatide, 154-fold and 10 μmol/g; monogalactosyl diglyceride, 31-fold and 0·6 μmol/g. The ratio cholesterol/phospholipid/galactolipid in whole nerve units from adult animals was 2·0/2·1/1·0 and the change in this ratio in the first year was compatible with enrichment of myelin in galactolipid during myelination. The ratio of cerebroside to sulphatide increased from 2·0 to 2·6 during this period. Increases in absolute content and concentrations attained for sialic acid-containing components representing cell surface constituents were as follows: ganglioside sialic acid, 33-fold, and 83 μg/g; glycoprotein sialic acid, 57-fold and 371 μg/g. The quantitative pattern of ganglioside fractions separated by thin-layer chromatography in one direction resembled that of whole brain and was the same at all ages studied. The changes reported reflect a composite picture of changes in a variety of cell membranes indicative of marked variation during development in quantity and composition of membranes.     

Localization and irregular distribution of Na,K-ATPase in myelin sheath from rat sciatic nerve

Sodium, potassium adenosine triphosphatase (Na,K-ATPase) is a membrane-bound enzyme that maintains the Na(+) and K(+) gradients used in the nervous system for generation and transmission of bioelectricity. Recently, its activity has also been demonstrated during nerve regeneration. The present study was undertaken to investigate the ultrastructural localization and distribution of Na,K-ATPase in peripheral nerve fibers. Small blocks of the sciatic nerves of male Wistar rats weighing 250-300g were excised, divided into two groups, and incubated with and without substrate, the para-nitrophenyl phosphate (pNPP). The material was processed for transmission electron microscopy, and the ultra-thin sections were examined in a Philips CM 100 electron microscope. The deposits of reaction product were localized mainly on the axolemma, on axoplasmic profiles, and irregularly dispersed on the myelin sheath, but not in the unmyelinated axons. In the axonal membrane, the precipitates were regularly distributed on the cytoplasmic side. These results together with published data warrant further studies for the diagnosis and treatment of neuropathies with compromised Na,K-ATPase activity.     

The in vivo synthesis of myelin proteins in rabbit sciatic nerve

Rabbits were injected into the sciatic nerves with either ³⁵S-methionine, or ³H-fucose. After times ranging from 45 min to 15 days the nerves were removed and the total particulate material from the nerves fractionated to give seven subfractions with densities between 0.2 and 1.2 M sucrose. The patterns of radio-labelled proteins were examined by SDS-PAGE and quantitative fluorography. The results showed that the P₂ basic protein was metabolically far more active than either the major P₀ glycoprotein, or the basic protein BP. The P₂ protein also entered the myelin fractions more rapidly than either P₀, or BP components. The net synthesis of P₀ was slower than P₂ and BP and this intrinsic membrane protein remained associated with the denser membrane fractions (>0.7 M sucrose) for longer than the basic proteins prior to entering myelin. Newly synthesized high molecular weight proteins remained concentrated in the denser membrane fractions and turned over faster than the myelin proteins.

A low density myelin fraction (B) was detected in which both the P₂ protein and certain high molecular weight proteins became more rapidly labelled than in compact myelin. In this fraction the specific activity remained higher than that of compact myelin for up to five days after the injection of ³⁵S-methionine into the nerve.

The results indicate that the major PNS myelin proteins are incorporated into and turn over in the various compartments of the Schwann cell plasma membrane—myelin continuum at very different rates.     

The freezing threshold of the peripheral motor nerve: an electrophysiological and light-microscopical study on the sciatic nerve of the rabbit.

Fifty sciatic nerves of 39 rabbits are treated at different temperatures (+5, +1, 0, ?3, ?5, ?10, ?15 and ?20 °C), for different freezing times (10, 20, 30, 60 and 120 sec), and for different numbers of freeze-thaw cycles (1, 2 and 4). After electric supramaximal stimulation (3.8 V) action potentials of the sciatic nerve are measured before, immediately after, and 1, 3, 5, 10, 20, 30, 60, 90 min, 2, 5 and 10 days after freezing. Two or ten days after freezing, the nerves are examined in a light microscope. The cold threshold of the sciatic nerve was determined, i.e., the temperature at which after supramaximal stimulation it is still possible to measure an action potential within 1.5 hr after freezing. On application of one freeze-thaw cycle, the cold threshold is ?15 °C after a freezing time of 10 sec, ?10 °C after 20 sec and 30 sec, and ?5 °C after 60 and 120 sec. After application of two and four freeze-thaw cycles, the cold threshold is elevated, and after a super-cooling time of 10 sec it is ?10 °C, after 30 sec ?5 °C. The longer the freezing time and the more freeze-thaw cycles, the higher is the cold threshold. At ?20 °C (superthreshold temperature) an action potential can no longer be measured and all myelinated nerve fibres have decayed, except some small-caliber ones.Electrophysiologically, it is evident that some of the myelinated nerve fibres become functionally damaged for 1.5 hr, while other parts of the nerve fibres will degenerate and later regenerate. The amplitudes of the measured action potentials correlate with the decay of myelin sheaths and axons of large- and medium-caliber nerve fibres. Action potentials between 0 and 40% show a gradual paresis, above 40% a physiological motor function. The pathophysiological mechanism of this reversible functional loss after super-cooling and freezing may be a consequence of a disturbed membrane permeability.It is of clinical importance that, if the cold threshold of a peripheral motor nerve is known, the nerve can be frozen concomitantly for a short time at application of low temperatures without suffering any functional loss. This is achieved by controlling during freezing the motor function of the corresponding nerve situated on the periphery of cryolesion, and, if there is a loss of motor function, the freezing process has to be interrupted immediately.     

Remyelination in the chicken sciatic nerve

Remyelination in the chicken sciatic nerve occurring after the injection of diphtheria toxin was studied. The rates of fast axonal transport and conduction velocities were measured sixty days after the injection of the toxin. Fast axonal transport rates were found to have returned to normal in the remyelinated nerves, but conduction velocity was markedly reduced even though the birds appeared to walk normally. The remyelinated nerve fibres had on histological examination relatively thin myelin sheaths. Of greater interest was the number of Schmidt-Lanterman clefts observed in both the control and remyelinated nerves when viewed in the electron microscope.     

Freeze-fracture study of the junctional complexes of human and rabbit thyroid follicles

Summary Zonulae occludentes, gap junctions and desmosomes have been demonstrated in replicas of freeze-fractured follicular cells of normal human and rabbit thyroid glands. The zonulae occludentes between the human follicular cells are composed of two to eight strands, which completely separate the intercellular space from the follicular lumen. Four to twelve or more strands are visible between the follicular cells of the rabbit thyroid gland.In the meshes of the zonulae occludentes as well as below them, gap junctions are present. They are numerous on the fracture faces of the human follicular cell membranes, but infrequent in those of the rabbit.Aggregates of particles related to desmosomes are found in the deeper meshes of the zonulae occludentes or close to them.     

Freeze-fracture study of taste bud pores in the foliate papillae of the rabbit

Summary In freeze-fractured specimens of taste buds from the foliate papillae of rabbits, the intercellular spaces are separated from the pore of the taste bud by zonulae occludentes of the tight-type. Below these tight junctions numerous desmosomes are found at irregular intervals. The epithelial cells adjacent to the pore are also joined by single strands of fusion. The microvilli arising from the neck of the type I cells have a high particle density. The microvilli of type II cells and especially the short microvilli of peripherally situated cells have a lower intramembranous particle density. The single microvillus of type III cells has a very large diameter and is longer than the other microvilli. It contains a few larger intramembranous particles and vesicle-like protrusions of the membrane facing the cytoplasm. Transverse fracturing reveals a filamentous fine structure in all microvilli. The physiological implications of these observations are discussed.Supported by grants from the Deutsche Forschungsgemeinschaft (Ja 205/5+6)     

Adrenergic nerve fibers in the human fetal sciatic nerve.

The adrenergic innervation was studied in the human sciatic nerve at the gestational age of 16, 17, 18 and 21 weeks. Formaldehyde-induced catecholamine fluorescence, tyrosine hydroxylase (TH) and neuropeptide Y (NPY) peroxidase-antiperoxidase immunohistochemistry methods were used. At the gestational age of 16, 17 and 18 weeks no adrenergic or NPY-positive nerve fibers were seen. At 21 weeks both fluorescence microscopy and TH immunohistochemistry showed adrenergic nerve fibers around arterioles in the epiperineurium and single nerve fibers in the endoneurium not related to blood vessels. The number of adrenergic nerve fibers appeared to be higher in the sciatic than in the tibial segment of the nerve. At this age, as at earlier stages of gestation, no NPY-positive nerve fibers were seen either in the epiperineurium or in the endoneurium. The results suggest that adrenergic nerve fibers may be associated with the epiperineurial blood vessels in the human sciatic nerve, and that the innervation starts to develop between 18 and 21 weeks of gestational age.