Bioelectric properties of frog sciatic nerves during exposure to stationary magnetic fields

The bioelectric properties of frog sciatic nerves have been measured during exposure to homogeneous, stationary magnetic fields. The action potential amplitude, conduction velocity, absolute refractory period and relative refractory period were found to be unaffected by a continuous 4-h exposure to perpendicular or parallel 2.0 T (1 T equal 10(4) G) magnetic fields. These parameters also remained unchanged during a 1-h post-exposure period. The conduction velocity was similarly found to be unchanged when the field was applied continuously for 17 h. Exposure of sciatic nerves to a 1.0-T field led to no alteration in the threshold for neural excitation. The absence of magnetic field effects on nerve electrical activity observed in the present experiments contrasts with the positive findings reported previously by other investigators. These discrepancies may be attributable to an inadequate control of ambient temperature in the earlier studies.     

Effects of a Magnetic Field on the Growth of Primary Roots of Zea mays

Caryopses with primary roots of Zea mays L. (cv. Golden CrossBantam 70) were incubated on agar-solidified distilled water(0.4% agar) in a magnetic field of 5 k gauss or 0.01 k gauss(control), the direction of root growth corresponding to thedirection of magnetic field from the north- to the south-seekingpole. The rate of growth of the roots exposed to 5 k gauss wasincreased by about 25% over that of the controls (0.01 k gauss).When caryopses with primary roots were incubated on agar-solidifieddistilled water that had previously been exposed to a magneticfield of 5 k gauss or 0.01 k gauss, no differences in ratesof root growth were observed. The growth rate of the primaryroot increased with increased magnetic flux density (from 0.01k to 5 k gauss). The orientation of the root in terms of thedirection of the magnetic field (from the north- to the south-seekingpole) affected the rate of growth of the root. When the directionof root growth was in line with the direction of the magneticfield of 5 k gauss or in the direction opposite to that of thefield, growth rates increased by 27% and 22%, respectively,of the growth rate of the controls (magnetic field of 0.01 kgauss). When the direction of growth was perpendicular to thedirection the field, the growth rate increased by 15% of thatof the control (0.01 k gauss). It appears that a magnetic stimulusmay induce an increase in the rate of root growth in some plantmaterials. (Received March 23, 1988; Accepted August 9, 1988)     

七叶莲对蟾蜍坐骨神经动作电位的影响

目的：观察七叶莲水煎液对蟾蜍离体坐骨神经复合动作电位的幅度及传导速度的影响,研究其对坐骨神经电生理特性的作用。方法：将制备的蟾蜍坐骨神经干分为4组,分别在任氏液和浓度为10％,20％,40％的七叶莲水煎液中浸泡,用MedLab生物信号采集处理系统引导神经干复合双相动作电位,并分别测定各组不同浸泡时间的坐骨神经干动作电位的幅度和传导速度两项电生理指标。记录不同浓度的七叶莲水煎液对蟾蜍离体坐骨神经复合动作电位的幅度和传导速度的影响。结果：10％,20％,40％3种浓度的七叶莲水煎液均使坐骨神经复合动作电位的幅度变小（P〈0．01）,传导速度变慢（P〈0．01）并最终使坐骨神经动作电位消失,且经过一段时间后动作电位的幅度和传导速度均能恢复。结论：七叶莲能可逆地阻滞神经动作电位的传导。     

Alterations in the rat electrocardiogram induced by stationary magnetic fields

A field strength dependent increase in the amplitude of the T-wave signal in the rat electrocardiogram (ECG) was observed during exposure to homogeneous, stationary magnetic fields. For 24 adult Sprague-Dawley and Buffalo rats of both sexes, the T-wave amplitude was found to increase by an average of 408% in a 2.0 Tesla (1 Tesla = 10⁴ Gauss) field. No significant magnetically induced changes were observed in other components of the ECG record, including the P wave and the QRS complex. The minimum field level at which augmentation of the T wave could be detected was 0.3 Tesla. The magnetically induced increase in T-wave amplitude occurred instantaneously, and was immediately reversible after exposure to fields as high as 2.0 Tesla. No abnormalities in any component of the ECG record, including the T wave, were noted during a period of 3 weeks following cessation of a continuous 5-h exposure of rats to a 1.5-Tesla field. The heart rate and breathing rate of adult rats were not altered during, or subsequent to, application of fields up to 2.0 Tesla. The effect of animal orientation within the field was tested using juvenile rats 3–14 days old. The maximum increase in T-wave amplitude was observed when subjects were placed with the long axis of the body perpendicular to the lines of magnetic induction. These experimental observations, as well as theoretical considerations, suggest that augmentation of the signal amplitude in the T-wave segment of the ECG may result from a superimposed electrical potential generated by aortic blood flow in the presence of a stationary magnetic field.     

Search for frequency-specific effects of millimeter-wave radiation on isolated nerve function

Effects of a short-term exposure to millimeter waves (CW, 40–52 GHz, 0.24–3.0 mW/cm²) on the compound action potential (CAP) conduction were studied in an isolated frog sciatic nerve preparation. CAPs were evoked by either a low-rate or a high-rate electrical stimulation of the nerve (4 and 20 paired pulses/s, respectively). The low-rate stimulation did not alter the functional state of the nerve, and the amplitude, latency, and peak latency of CAPs could stay virtually stable for hours. Microwave irradiation for 10–60 min at 0.24–1.5 mW/cm², either at various constant frequencies or with a stepwise frequency change (0.1 or 0.01 GHz/min), did not cause any detectable changes in CAP conduction or nerve refractoriness. The effect observed under irradiation at a higher field intensity of 2–3 mW/cm² was a subtle and transient reduction of CAP latency and peak latency along with a rise of the test CAP amplitude. These changes could be evoked by any tested frequency of the radiation; they reversed shortly after cessation of exposure and were both qualitatively and quantitatively similar to the effect of conventional heating of 0.3–0.4°C. The high-rate electrical stimulation caused gradual and reversible decrease of the amplitude of conditioning and test CAPs and increased their latencies and peak latencies. These changes were essentially the same with and without irradiation (2.0–2.7 or 0.24–0.28 mW/cm²), except for attenuation of the decrease of the test CAP amplitude. This effect was observed at both field intensities, but was statistically significant only for certain frequencies of the radiation. Within the studied limits, this effect appeared to be dependent on the frequency rather than on the intensity of the radiation, but this observation requires additional experimental confirmation. Bioelectromagnetics 18:324–334, 1997. © 1997 Wiley-Liss, Inc.     

Nerve,spinal cord and brain somatosensory evoked responses: a comparative study during electrical and magnetic peripheral nerve stimulation

Somatosensory evoked potentials (SEPs) and compound nerve action potentials (cNAPs) have been recorded in 15 subjects during electrical and magnetic nerve stimulation. Peripheral records were gathered at Erb's point and on nerve trunks at the elbow during median and ulnar nerve stimulation at the wrist. Erb responses to electrical stimulation were larger in amplitude and shorter in duration than the magnetic ones when ‘electrical’ and ‘magnetic’ compound muscle action potentials (cMAPs) of comparable amplitudes were elicited. SEPs were recorded respectively at Cv7 and on the somatosensory scalp areas contra- and ipsilateral to the stimulated side. SEPs showed a statistically significant difference in amplitude only for the brachial plexus response and for the ‘cortical’ N20-P25 complex; differences were not found between the magnetic and electrical central conduction times (CCTs) or for the peripheral nerve response latencies. Magnetic stimulation preferentially excited the motor and proprioceptive fibres when the nerve trunks were stimulated at motor threshold intensities.     

Influence of weakened constant magnetic field on nerve cell excitability

Attenuation of the constant magnetic field by a factor of 200–250 (to ～0.2 μT) raised the excitation threshold and decreased the amplitude of the action potentials in the isolated frog sciatic nerve, and altered the conformation of carotenoids in the plasma membrane (sciatic axolemma) as well as in intracellular vesicles (cytosomes of snail ganglia). The variation in nerve excitability was supposedly caused by changes in the ordering of membrane lipids.     

The influence of pulsed magnetic fields (PMFs) on nonsynaptic potentials recorded from the central and peripheral nervous systems in vitro

The influence of pulsed magnetic fields (PMFs) on nonsynaptic potentials recorded from the central and peripheral nervous system in vitro has been investigated. The population spikes (PSs) recorded from hippocampal slices during antidromic stimulation and compound action potentials (CAPs) recorded from the segments of the sciatic nerve were used as indicators of neuronal activity. The potentials recorded from both preparations were significantly and permanently enhanced following PMF (0.16 Hz, 15 mT) exposure. The increase in the antidromic PS occurred even in the presence of potassium channel blocker tetraethylammonium (TEA) and was accompanied by multiple spiking. Among all frequencies of PMF tested (0.5, 0.16, 0.07, 0.03, 0.0 Hz), the frequency of 0.5 Hz was the most effective in enhancement of potential amplitude. The influence of PMF on the amplitude of two CAPs evoked by the pair of electrical stimuli applied in rapid succession has also been evaluated. In control conditions the potential triggered by the second stimuli was slightly smaller expressing the phenomenon of short‐term depression (STD). Although PMF exposure amplified the amplitude of both potentials, the increase in the size of the first potential was significantly greater increasing further the magnitude of STD. The blocking of potassium channels reversed STD into facilitation. One of the possible mechanisms involved in PMF action could be the modification of the axonal threshold, which was significantly reduced following exposure to PMF. Bioelectromagnetics 30:621–630, 2009. © 2009 Wiley‐Liss, Inc.     

Effect of weak static magnetic fields on the excitability of a neuron

Changes in the excitability of the neuron (amplitude, excitability threshold, rate of action potential transduction), as well as changes in the viscosity of the plasma membrane of the nerve and membranes of subcellular organelles, induced by the action of a weak magnetic field, have been studied by the methods of extracellular registration of membrane potential and combination scattering. It was found that only the threshold of excitability in intact nervous fibers increases by the action of this field. It was proven that the conformation of C40 carotenoids localized not only in plasma membranes but also in subcellular membranes of the neuron changes in a weak magnetic field. It is assumed that the changes in the excitability of the neuron by the action of weak magnetic field are due to changes in the orderliness of membrane lipids and the content of oxygen in the cytoplasm.     

Magnetic evoked field associated with transcortical currents in turtle cerebellum.

The neural basis of magnetic evoked fields of the brain was studied with an isolated turtle cerebellum as a model preparation. The turtle cerebellum is a nearly flat tissue with neural processes arranged along three orthogonal axes of symmetry. According to theoretical results, this geometry should enable us to selectively measure the magnetic field due to a subpopulation of nerve cells whose longitudinal axes are perpendicular to the cerebellar surface, by simply placing the cerebellum vertically in the bath so that these cells are horizontal and by measuring the field along the rostrocaudal axis perpendicular to the longitudinal axis of these nerve cells. To elicit neural activity in these cells the dorsal midline was electrically stimulated with a bipolar electrode. Consistent with our expectations, the one-dimensional profile of the field normal to bath surface (Bz) was antisymmetrical along the rostrocaudal axis, implying that the underlying currents were transcortical. Also, the Bz field at a field extremum varied as a cosine of the orientation of the cerebellum when it was rotated about its rostrocaudal axis with the amplitude being zero when the cerebellum was horizontal. The Bz field was dipolar as judged by statistically excellent fits of the dipolar field to the one-dimensional field profile and to the distance function relating the field magnitude at an extremum to measuring distance. This was the case even for the initial component thought to be due to antidromic action currents invading the soma and dendrites of Purkinje cells. We also showed that the dipolar term of the source could be localized within 1 mm of the actual source location in most cases.     

Does direction of induced electric field or current provide a test of mechanism involved in nerve regeneration?

We suggest an experimental comparison of two directions for applying the time-varying magnetic fields which have been found to speed spontaneous regeneration of injured peripheral nerves and in attempts to repair spinal cord injuries. Time-varying magnetic fields induce currents in a plane perpendicular to the magnetic field direction. The lower conductivity of the spinal cord's sheath (dura matter) or of the myelin sheath of peripheral nerves would seem to confine the induced electric fields and currents to the spinal cord or nerve itself. The proposed comparison could allow choosing between two possible modes of action of the fields: (1) Magnetically-induced electric fields or currents may be encouraging ion flow or otherwise helping enzyme, channel or other interactions at the cell membrane, as is thought to be the case in field stimulation of healing in bone. This mechanism should be independent of field direction. (2) Work in developing organisms and with fields applied to nerve cells in vitro has shown that neurite growth is guided parallel to both endogenous and external electric fields. This mechanism would be effective when induced electric fields are parallel, but not when they are perpendicular to the nerve. Any experimental test should seek to produce as close as possible to the same induced current intensity with both field directions. Possible confounding factors, as well as breakdowns in the assumptions of the simple model presented here, would have to be considered. This proposal was motivated by a recent report in which the authors listed a changed field direction as one of several possible reasons for an unsuccessful experiment.     

What is the time scale of magnetic field interaction in biological systems?

An experimental test constraining the intrinsic time scale of a primary physical mechanism that detects extremely-low-frequency (ELF) magnetic fields in biological systems is proposed. The suggested test postulates that a transductive mechanism operating on time scales much shorter than the period of an applied magnetic field cannot obtain any information about the exposure conditions other than the absolute magnitude of the field. By generating field exposures that differ in their vector properties but are equivalent in their time-varying absolute amplitude, it is possible to differentiate between two broad classes of mechanisms: 1) those with intrinsic time scales comparable with or longer than those of the external influence, and 2) those that are much faster than the period of the applied field. The hypothesis assumes an experimental model proven to respond to magnetic fields and sensitive to a change of about a factor of two in one of the field parameters (AC, DC amplitude or frequency). The case of general linearly polarized fields is discussed, and an analytical solution for the case of perpendicular AC/DC fields is given. Bioelectromagnetics 18:244–249, 1997 © 1997 Wiley-Liss, Inc.     

Pulsed magnetic fields enhance the rate of recovery of damaged nerve excitability

Pulsed magnetic fields (PMFs) have well‐known beneficial effects on nerve regeneration. However, little research has examined the nerve conduction characteristics of regenerating peripheral nerves under PMF. The main goal of this study was to examine the conduction characteristics of regenerating peripheral nerves under PMFs. The sucrose‐gap recording technique was used to examine the conduction properties of injured sciatic nerves of rats exposed to PMF. Following the injury, peripheral nerves were very sensitive to repetitive stimulation. When the stimulation frequency was increased, the amplitude of the compound action potential (CAP) decreased more at 15 days post‐crush injury (dpc) than at 38 dpc. PMF treatment for 38 days after injury caused significant differences in the conduction of CAPs. Moreover, application of PMF ameliorated the abnormal electrophysiological activities of nerves such as hyperpolarizing afterpotentials and delayed depolarizations that were revealed by 4‐aminopyridine (4‐AP). Consequently, characteristic findings in impulse conduction of recovered nerves under PMF indicate that the observed abnormalities in signaling or aberrant ion channel functions following injury may be restored by PMF application. Bioelectromagnetics 32:200–208, 2011. © 2010 Wiley‐Liss, Inc.     

Heat Pain Increases the Perceived Magnitude of an Innocuous Electrical Stimulus: Evidence for a Peripheral Mechanism

Painful heat produced an increase in the perceived magnitude of an innocuous electrical stimulus applied either to the sural nerve or to the skin of the dorsum of the foot. The increased sensitivity was observed when the painful heat was spatially coincident with the electrical stimulus, and when it was not coincident but adjacent within the same dermatome. Painful heat had no effect when it was applied to the contralateral foot, which makes it unlikely that attention or arousal played any role in the increased electrical sensitivity produced by ipsilateral heat. The painful heat also produced an increase in the amplitude of the sural nerve compound action potential (CAP). The heat-pain-related changes in the CAP and subjective magnitude ratings were in the same direction, which suggests that the latter were due at least in part to a temperature-dependent change in the electrical sensitivity of the peripheral afferents     

Determination of the resonant harmonics of the error field from dynamic magnetic measurements in a tokamak

The possibility is discussed of determining the amplitude and phase of a static resonant error field in a tokamak by means of dynamic magnetic measurements. The method proposed assumes measuring the plasma response to a varying external helical magnetic field with a small (a few gauss) amplitude. The case is considered in which the plasma is probed by square pulses with a duration much longer than the time of the transition process. The plasma response is assumed to be linear, with a proportionality coefficient being dependent on the plasma state. The analysis is carried out in a standard cylindrical approximation. The model is based on Maxwell’s equations and Ohm’s law and is thus capable of accounting for the interaction of large-scale modes with the conducting wall of the vacuum chamber. The method can be applied to existing tokamaks.     

Effect of prolonged exposure to a magnetic field on the haematopoietic stem cell.

The authors studied the effect of prolonged exposure (3, 4 and 5 months) to the action of a magnetic field of 180-200 gauss formed by the poles of a rotating permanent magnet on the haematopoietic stem cells of mouse bone marrow donors. The effect of the field was evaluated from the ability of the donors' bone marrow cells to form haematopoietic colonies in the spleen of lethally irradiated mice. It was found that the number of stem cells was not reduced by the action of the above magnetic field and that proliferative capacity was likewide unimpaired.     

Prostaglandin E1 modifies nerve conduction and interferes with local anaesthetic action

Prostaglandin E1 (PGE1) altered both the amplitude and conduction velocity of the compound action potential in frog sciatic nerve. Concentrations up to 1 ng/ml increased both amplitude and conduction velocity but at higher concentrations both effects were reversed. Procaine, chloroquine, indomethacin and SC19220 all reduced action potential amplitude and conduction velocity. These local anaesthetic type actions could be partially or completely prevented by PGE1.     

Prostaglandin E1 modifies nerve conduction and interferes with local anaesthetic action.

Prostaglandin E1 (PGE1) altered both the amplitude and conduction velocity of the compound action potential in frog sciatic nerve. Concentrations up to 1 ng/ml increased both amplitude and conduction velocity but at higher concentrations both effects were reversed. Procaine, chloroquine, indomethacin and SC19220 all reduced action potential amplitude and conduction velocity. These local anaesthetic type actions could be partially or completely prevented by PGE1.     

A testable theoretical model for magnetotherapy potentially applicative to such diverse concerns as oncogenic, CNS trophic factor and viral disorders

Physiologic magnetic fields of the order 10(-8) gauss have been unified with their propitiators: quantum genetic particles, the gravitational potential of which is about an erg. As these fields are applied to the equation for solenoidal models, B = micro NI/L, currents of about a microampere are derived; in perfect accord with recent clinical data indicating the therapeutic efficacy of weak currents in repair and growth of soft tissue, bone and nerve. The mechanism of reorientation of spin angular momentum of leptons and baryons influencing molecular magnetic domains to bring about 'particle jumps' is presented so that a clinical picture results. The clinical picture is that of an organism placed at right angles to flux lines in the midst of a solenoid immersed in water exposed then to exogenously applied resonant physiologic magnetic fields which convert malalligned atomic lattices of oncogenes and associated particles to homologous normal structures.