Effect of procaine on electrical activity of the ranvier node in solutions with high and low pH

The effect of procaine on generation of the action potential and its derivative in solutions with different pH values was studied in experiments on single Ranvier nodes. Minimal concentrations of procaine depressing the action potential were increased in solutions with low pH and reduced in solutions with high pH. The calculated concentrations of the basic and cationic forms of procaine changed regularly: With an increase in pH of the medium the basic decreased and the cationic increased. Excitability of the membrane (the number of sodium channels capable of excitation) did not change regularly in accordance with a change in pH of the medium: It fell on both a decrease and an increase in the pH of the solution. It was concluded from the results that the two forms of procaine interact with the membrane, but with different effectiveness.A. V. Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 161–167, March–April, 1974.     

After-depolarization of the frog nerve and single nerve fiber

Experiments on frogs (Rana ridibunda) showed that, unlike in the whole nerve, prolonged after-depolarization and the associated phase of summation are absent in the single node of Ranvier of isolated nerve fibers. If, however, special measures are taken to prevent the stretching of the Ranvier node of single fibers, prolonged after-depolarization can be found in them. It is concluded that the absence of prolonged after-depolarization in single Ranvier nodes of nerve fibers isolated without additional precautions is the result of injury to the excitable membrane or to disturbance of the integrity of the ionic barrier surrounding it as a result of stretching of the fibers during dissection.     

Effect of changes in pH of the medium on electrical activity of the Ranvier node

The effect of changes in pH of the medium from 4 to 10 on the action potential and its first derivative was studied at the original resting potential and during hyperpolarization of the membrane in experiments on single nodes of Ranvier. Raising the pH of the medium from 7 to 9 led to a decrease in amplitude of the action potential and of its derivative (V_max). During hyperpolarization of the membrane these parameters were fully restored. Lowering the pH of the solution led to an increase in the action potential and a decrease in V_max. During hyperpolarization of the membrane the action potential and its derivative were not completely restored. Under the influence of solutions with low and high pH values the duration of the action potential was increased. Changes in the action potential and in V_max with an increase in pH can be attributed to increased inactivation of the sodium permeability of the membrane, and in solutions with low pH to a decrease in the maximal sodium permeability and to weakening of its inactivation.A. V. Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 6, No. 2, pp. 205–210, March–April, 1974.     

Comparison of morphological and physiological characteristics of the Ranvier node

Variations in the structure of Ranvier nodes and of the paranodal region of frog nerve fibers were examined in an intravital light-optical investigation. Several morphological characteristics of the degree of disturbance of the structures of the paranodal zone (myelin cones and bulbs of the node) are compared. Morphological characteristics for the same isolated nerve fibers were compared with electrophysiological characteristics obtained by the voltage clamp method. A definite parallel was found between the degree of morphological changes in the paranodal myelin and the fall in the maximal sodium and potassium conductances of the membrane, while the leakage conductance remained relatively constant. The lower resistance of the sodium and potassium systems to injurious factors evidently reflects the more complex molecular organization of the excitable (sodium and potassium) than of the leakage channels. Considerable changes in the properties of the sodium channels caused by batrachotoxin were not accompanied by any visible changes in the paranodal regions of the myelin sheath. The results are examined from the standpoint of modern views regarding the nature of axo-glial relations in the nerve fiber.A. V. Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR, Moscow. I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 10, No. 4, pp. 400–406, July–August, 1978.     

A mathematical model of a myelinated nerve fiber for analysis of impulse conduction mechanisms during the relative refractory period

It was shown by means of a mathematical model of a myelinated nerve fiber (Frankenhaeuser — Huxley) that an increase in threshold and decrease in the amplitude of the action potential (AP) during the relative refractory period are due mainly to sodium inactivation. The contribution of increased potassium permeability to these changes is small, for the chief component of the outgoing ionic current in the node of Ranvier is not the potassium current, but the leak current. Given the ratio between these currents the increase in threshold and graduation of the action potential in the node membrane are less marked than in the membrane of the squid giant axon. At the beginning of the relative refractory period the AP evoked by strong stimulation is conducted only to the next node. Later in the refractory period impulses are conducted incrementally, and the threshold for the spreading impulse is higher than the threshold for spike excitation in the stimulated node. Delay in impulse conduction between refractory nodes leads to the formation of a retrograde depolarization wave. The reasons for differences in the mechanisms of impulse conduction along unmyelinated and myelinated refractory fibers are discussed.Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 201–207, March–April, 1972.     

Effect of potassium ions on firing pattern of ampullae of Lorenzini in rays

The effect of a change in potassium ion concentration in the region of the basal membranes of the ampullae of Lorenzini of the thornback ray on spontaneous and evoked discharges of the receptors was investigated. A decrease in potassium ion concentration in the solution of perfusion with potassium-free solution led to a decrease in firing rate. Conversely, an increase in the potassium ion concentration caused an increase in discharge frequency followed by a decrease; thresholds of the receptors to the action of electrical stimuli were unchanged. When synaptic transmission was blocked by magnesium ions, an increase in the potassium ion concentration did not cause the appearance of activity in nerve fibers. If, however, activity of the nerve fibers in solution with a high magnesium ion concentration was restored with L-glutamic acid (10^–4 M), an increase in the potassium ion concentration caused an increase in firing rate. The role of potassium ions in the activity of receptors of the lateral-line system is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 493–497, July–August, 1984.     

神经退变和再生过程中郎氏结构筑的变化

将夹伤的大鼠坐骨神经分离成单根纤维,在光镜、扫描和透射电镜下观察伤后９８天内郎氏结的构筑变化。发现损伤使细胞器的轴浆转运阻断,积累的退变细胞器使结区的轴突外凸,郎氏结构构筑变形,髓鞘板层失序,轴膜崩解,积累的细胞器逸出,并看到仅残存的郎氏结近心端构筑、由近心端的母体神经和远心端的再生神经共同构筑的新生郎氏结,以及新生郎氏结构的发育过程等特征性图象。再生轴突中转运的微管等细胞器和施旺细胞中富含的线粒     

Miniature potentials in fast and slow muscle fibers in locusts

Excitatory miniature postsynaptic potentials were studied by an intracellular recording method in fast and slow muscle fibers ofLocusta migratorioides. Statistical analysis showed that liberation of mediator in both types of fibers can be predicted by the formula for a negative binomial distribution with a probability of 85%. This correlation is evidence of some degree of interaction between consecutive liberations of quanta of mediator by nerve endings. It is shown that the fraction of miniature potentials depending on the external calcium concentration is greater in fast muscle fibers. An increase in the magnesium ion concentration from 2 to 40 mM led to a decrease in the frequency of miniature potentials, and this decrease was greater in fast fibers; an increase in the magnesium ion concentration from 1 to 10 mM in calcium-free solutions, on the other hand, led to some increase in frequency, and this also was greater in fast muscle fibers. It is concluded that nerve endings in fast and slow muscle fibers differ in their sensitivity to changes in the ionic composition of the medium.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 210–217, March–April, 1981.     

Hydrogen ion block of single sodium channels in neuroblastoma cells

The effects of pH of the external medium on amplitude of currents through single sodium channels at the membrane of cultured neuroblastoma cells were investigated in mice belonging to strain C 1300, clone N18A-1. Currents through single sodium channels in isolated membrane segments (outside-out configuration) were registered with normal (7.2) and reduced (5.4) pH levels in the external medium. Reducing the pH to 5.4 was found to decrease current amplitude reversibly by about twofold (–10 to –30 mV for test potentials). Findings would confirm that the depression of macroscopic sodium currents produced by reducing the pH of the extracellular solution is due to a decline in ionic flow through single open sodium channels.Institute of Cytology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 101–105, January–February, 1989.     

Complex nerve terminal formation in the phasic muscles of frogs

Synapses with complex nerve terminals consisting of several terminal arbors of a single axon divided by myelin segments were investigated using histological and electrophysiological techniques during experiments on the cutaneous-pectotoralis muscles of different aged frogs. Numbers of synapses with complex nerve terminals were shown to increase during the postnatal developmental process. The relationship between the complexity of nerve terminals, summated length of terminals, and size of muscle fiber is described. Some terminal arborizations at complex nerve terminals originate from nodes of Ranvier; these are marked by low quantal secretion and a distinctive pattern of sodium current decay along the path of the terminals. The causes and mechanisms governing increased complexity of nerve endings in phasic muscles are discussed, together with transmitter release patterns at these endings. It is postulated that growth and myelination processes occur in parallel at the nerve terminal.A. A. Ukhtomskii Physiological Institute, Leningrad State University; S. A. Kurashov Medical Institute, RSFSR Ministry of Health, Kazan'. V. I. Ul'yanov State University, Kazan'. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 99–107, January–February, 1990.     

Excitation and inhibition in the visual center of Rana temporaria

Analysis of postsynaptic unit responses in the visual center ofRana temporaria showed that optic nerve fibers with high and low conduction velocities usually converge on a single neuron of the tectum opticum (TO). In response to stimulation of the optic nerve a complex depolarization potential consisting of 3 (or possibly 4) EPSPs was recorded in one group of neurons; these EPSPs were probably generated through excitation of several groups of afferent fibers. Either an increase or a decrease in the EPSPs can be observed in the TO neurons in response to repetitive and paired stimulation of the optic nerve. Postsynaptic inhibitory responses of some TO neurons, probably of direct and recurrent origin, are discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 637–643, November–December, 1971.     

The Fine Anatomy of the Optic Nerve of Anurans—An Electron Microscope Study

In the optic nerve of Anurans numerous myelinated and unmyelinated axons appear under the electron microscope as compact bundles that are closely bounded by one or several glial cells. In these bundles the unmyelinated fibers (0.15 to 0.6 µ in diameter) are many times more numerous than the myelinated fibers, and are separated from each other, from the bounding glial cells, or from adjacent myelin sheaths, by an extracellular gap that is 90 to 250 A wide. This intercellular space is continuous with the extracellular space in the periphery of the nerve through the numerous mesaxons and cell boundaries which reach the surface. Numerous desmosomes reinforce the attachments of adjacent glial membranes. The myelinated axons do not follow any preferential course and, like the unmyelinated ones, have a sinuous path, continuously shifting their relative position and passing from one bundle to another. At the nodes of Ranvier they behave entirely like unmyelinated axons in their relations to the surrounding cells. At the internodes they lie between the unmyelinated axons without showing an obvious myelogenic connection with the surrounding glial cells. In the absence of connective tissue separating individual myelinated fibers and with each glial cell simultaneously related to many axons, this myelogenic connection is highly distorted by other passing fibers and is very difficult to demonstrate. However, the mode of ending of the myelin layers at the nodes of Ranvier and the spiral disposition of the myelin layers indicate that myelination of these fibers occurs by a process similar to that of peripheral nerves. There are no incisures of Schmidt-Lantermann in the optic myelinated fibers.     

MORPHOLOGICAL CORRELATES OF FUNCTIONAL DIFFERENTIATION OF NODES OF RANVIER ALONG SINGLE FIBERS IN THE NEUROGENIC ELECTRIC ORGAN OF THE KNIFE FISH STERNARCHUS

Electric organs in Sternarchidae are of neural origin, in contrast to electric organs in other fish, which are derived from muscle. The electric organ in Sternarchus is composed of modified axons of spinal neurons. Fibers comprising the electric organ were studied by dissection and by light- and electron microscopy of sectioned material. The spinal electrocytes descend to the electric organ where they run anteriorly for several segments, turn sharply, and run posteriorly to end blindly at approximately the level where they enter the organ. At the level of entry into the organ, and where they turn around, the axons are about 20 µ in diameter; the nodes of Ranvier have a typical appearance with a gap of approximately 1 µ in the myelin. Anteriorly and posteriorly running parts of the fibers dilate to a diameter of approximately 100 µ, and then taper again. In proximal and central regions of anteriorly and posteriorly running parts, nodal gaps measure approximately 1 µ along the axon. In distal regions of anteriorly and posteriorly running parts are three to five large nodes with gaps measuring more than 50 µ along the fiber axis. Nodes with narrow and with wide gaps are distinguishable ultrastructurally; the first type has a typical structure, whereas the second type represents a new nodal morphology. At the typical nodes a dense cytoplasmic material is associated with the axon membrane. At large nodes, the unmyelinated axon membrane is elaborated to form a closely packed layer of irregular polypoid processes without a dense cytoplasmic undercoating. Electrophysiological data indicate that typical nodes in proximal regions of anteriorly and posteriorly running segments actively generate spikes, whereas large distal nodes are inactive and act as a series capacity. Increased membrane surface area provides a morphological correlate for this capacity. This electric organ comprises a unique neural system in which axons have evolved so as to generate external signals, an adaptation involving a functionally significant structural differentiation of nodes of Ranvier along single nerve fibers.     

Histochemical localization of galactose-containing glycoconjugate at peripheral nodes of Ranvier in the rat

Lectin-horseradish peroxidase conjugates were used to study glycoconjugates in paraffin sections of dorsal roots of the rat spinal cord. Griffonia simplicifolia-B4 isolectin (GSA I-B4) and peanut agglutinin (PNA) stained strongly the nodes of Ranvier, localizing, respectively, terminal alpha- and beta-D-galactose. Sialidase digestion did not increase staining with PNA at the node of Ranvier, suggesting the presence of a neutral glycoconjugate. Staining of the nodal but not the internodal axolemma was observed with PNA. The outer surface of the myelin sheath in axons of the dorsal root stained strongly with GSA I-B4 but only weakly with PNA, demonstrating an abundance of terminal alpha-galactose. PNA staining was enhanced in this site by sialidase digestion, showing terminal sialic acid-beta-galactose dimers. The presence of sialic acid here was further evidenced by labeling of these membranes with the lectin derived from the slug, Limax flavus (LFA). Affinity for a high iron diamine-Alcian blue (pH 2.5) sequence demonstrated, in addition, the presence of sulfate esters in glycoconjugates on the outer myelin membrane. GSA I-B4 imparted strong reactivity to nonmyelinated fibers in the dorsal root and the spinal nerve. The present findings appear to reflect several localizations of biochemically described nervous system glycoproteins containing O-glycosidically linked side chains terminated by alpha- and beta-D-galactose.     

Effect of preliminary mechanical and antidromic influences on orthodromic activity in C fibers from mechanoreceptors of the cat skin

Analysis of afferent activity in unmyelinated fibers of a cutaneous nerve was carried out by the colliding impulses method in cats. The effect of antidromic excitation of the nerve and mechanical stimulation of the receptors on subsequent orthodromic activity during stretching of the skin was investigated. Both these factors were shown to reduce subsequent orthodromic activity evoked by testing stimulation. The reduction in activity was greatest 10–15 sec after stimulation. The duration of the inhibitory effect was greater after mechanical than after antidromic stimulation. Combined mechanical stimulation and antidromic excitation resulted in a greater decrease of afferent activity and an increase in the time of its recovery. An increase in the frequency of antidromic excitation potentiated the inhibitory effect of preliminary stimulation on orthodromic activity in C fibers.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii Gor'kii State University. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 307–312, May–June, 1977.     

The effect of subthreshold prepulses on the recruitment order in a nerve trunk analyzed in a simple and a realistic volume conductor model

 The influence of subthreshold depolarizing prepulses on the threshold current-to-distance and the threshold current-to-diameter relationship of myelinated nerve fibers has been investigated. A nerve fiber model was used in combination with both a simple, homogeneous volume conductor model with a point source and a realistic, inhomogeneous volume conductor model of a monofascicular nerve trunk surrounded by a cuff electrode. The models predict that a subthreshold depolarizing prepulse will desensitize Ranvier nodes of fibers in the vicinity of the cathode and thus cause an increase in the threshold current of a subsequent pulse to activate these fibers. If the increase in threshold current of the excited node is large enough, the excitation will be accompanied by a strong hyperpolarization of adjacent nodes, preventing the propagation of action potentials in these fibers. As fibers close to the electrode are more desensitized by prepulses than more distant ones, it is possible to stimulate distant fibers without stimulating such fibers close to the electrode. Moreover, as larger fibers are more desensitized than smaller ones, smaller fibers have lower threshold currents than larger fibers up to a certain distance from the electrode. The realistic model has provided an additional condition for the application of this method to invert nerve fiber recruitment, i.e., real or virtual anodes should be close to the cathode. When using a cuff electrode for this purpose, in the case of monopolar stimulation the cuff length (determining the position of the virtual anodes) should not exceed twice the internodal length of the fibers to be blocked. Similarly, the distance between cathode and anodes should not exceed the internodal length of these fibers when stimulation is to be applied tripolarly. Received: 15 May 2000 / Accepted in revised form: 9 February 2001     

Isolation and characterization of axolemma-enriched fractions from rabbit and bovine peripheral nerve

Axolemma-enriched fractions were isolated from bovine spinal accessory nerves, bovine intradural dorsal roots, and rabbit sciatic nerve by differential centrifugation and separation on a linear 10–40% sucrose (w/w) gradient. The fractions were enriched 4 to 10 fold in acetylcholinesterase, a biochemical marker for axolemma. Axolemma-enriched fractions isolated from uniformly well-myelinated fibers (bovine spinal accessory nerve) contained lower CNPase activity and higher acetylcholinesterase activity than comparable fractions isolated from variably myelinated fibers (rabbit sciatic nerve and bovine intradural roots). Separation by polyacrylamide electrophoresis showed that the molecular weight distribution of all peripheral nerve axolemma-enriched fractions was similar and ranged from 20 to over 150 kilodaltons. All axolemma-enriched fractions appeared to contain a small but variable amount of myelin-specific proteins. Based on biochemical properties, peripheral nerves containing uniformly well-myelinated fibers yield an axolemma-enriched fraction which is least contaminated with myelin-related membranes.     

Conditions for Ethanol Production during Bioconversion of Cellulose-Containing Raw Material

Several natural associations composed of thermophilic anaerobic bacteria capable of utilizing various cellulose materials at 60 ± 2°C and pH 6.0–7.0 were isolated from the sludge of Kamchatka geothermal springs. The rate of ethanol production (up to 1.7 g/l per day) and the concentration of ethanol in the medium (up to 1.2%), as well as the fermentation period (10–15 days), were determined under anaerobic conditions in the presence of cellulose, coniferous sawdust, newsprint, or paper pulp as a carbon source. Microorganisms were found that inhibited the production of ethanol. The initial pH value was found to influence both the ethanol production rate and ethanol/acetate ratio. A pH decrease from 7.0 to 5.0 led to a 6.7-fold increase in ethanol production and caused a 23.8-fold increase in the ethanol/acetate ratio.     

Effect of phytate on aflatoxin formation by Aspergillus parasiticus and Aspergillus flavus in synthetic media

The effect of phytate on the production of aflatoxins by Aspergillus parasiticus and Aspergillus flavus grown on synthetic media was examined. In the absence of pH control (initial pH 4.5–6.5) for A. parasiticus, phytate (14.3 mM) caused a six-fold decrease in aflatoxins in the medium and a ten-fold decrease in those retained by the mycelia. When the initial pH of the medium was adjusted to 4.5 no effect on aflatoxin production was observed. With A. flavus or A. parasiticus grown on media with a higher initial pH value (6 to 7), the presence of phytate in the media caused an increase in aflatoxin production. These results are inconsistent with previous studies which indicated that phytate depresses aflatoxin production by rendering zinc, a necessary co-factor for aflatoxin biosynthesis, unavailable to the mold.     

Effect of ouabain on electrical activity of the isolated frog muscle spindle

Changes in electrical activity of the isolated frog muscle spindle were studied in Ringer's solution containing ouabain. The presence of ouabain in the solution increased the spontaneous firing rate of the receptors up to a maximum and then reduced it quickly to zero. The amplitude of the action potentials was reduced on the average to 40% of normal. Ouabain causes initial disappearance of the hyperpolarization phase of the receptor potential and a subsequent decrease in amplitude of its dynamic phase to zero. The decrease in amplitude of the receptor potential and action potential and also the changes in firing rate in the solution with ouabain depend on the frequency of their spontaneous activity. The changes observed can be explained by depolarization of the membrane of the nerve endings and the first node of Ranvier, developing as a result of blocking of the sodium pump by ouabain.Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 576–582, November–December, 1973.