Magnetic and electric characteristics of the electric fish Gymnotus carapó.

The fresh water fish Gymnotus carapó produces a continuous series of weak pulsed electric fields in its surroundings and senses disturbances of this field as part of its sensory system. The electric and magnetic properties of the electric organ of this fish were studied. Magnetic fields close to the fish on the order of nT are produced by currents on the order of 10(-4) A in the electric organ of the fish. The electromotive force, the internal resistance, the current, and the electric power of the equivalent circuit were determined noninvasively.     

Peripheral electrosense physiology: a review of recent findings.

Advances, since 1974, in understanding the physiology of electroreceptors are reviewed. In brief: 1. In fish that produce a weak electric discharge with electric organs, the tuberous electroreceptors are generally most sensitive to stimulus frequencies near the species', individual's, and even local, waveform of the electric organ discharge; there is a good match between receptor sensitivity and the normal stimulus. 2. The ability of tuberous electroreceptors to detect field distortions produced by reasonably sized objects is limited; an object must be closer than a body-length to be detected, and the afferent response is a negative power function of object distance. 3. The second major electroreceptor class, the ampullary electroreceptors, is sensitive to low frequency, low intensity electric fields, and this acute sensitivity results in the ability of the receptors in marine species to detect magnetic fields on the order of the Earth's. 4. The calcium ion is essential for normal functioning of ampullary electroreceptors.     

Thermal noise limit on the sensitivity of cellular membranes to power frequency electric and magnetic fields

Several authors have concluded that thermal electromagnetic noise will be of sufficient magnitude to overwhelm electric and/or magnetic fields induced by environmentally generated, power frequency electric and magnetic fields in the membranes of living cells located in the bodies of humans. Yet, there are research reports that indicate that living cells may respond to power frequency electric and/or magnetic field levels well below the limits set by these thermal noise arguments. The purpose of this study is to suggest that published thermal arguments may not make a full accounting of all membrane force fields of thermal origin, and that when such an accounting is made, the net thermal noise fields may be smaller in the power frequency range than previously thought. If this analysis is correct, there may be no thermal noise barrier that precludes the possibility of cellular membranes of human cells responding to environmental levels of power frequency electric or magnetic fields.     

Limiting electric fields of HVDC overhead power lines

As a consequence of the increased use of renewable energy and the now long distances between energy generation and consumption, in Europe, electric power transfer by high-voltage (HV) direct current (DC) overhead power lines gains increasing importance. Thousands of kilometers of them are going to be built within the next years. However, existing guidelines and regulations do not yet contain recommendations to limit static electric fields, which are one of the most important criteria for HVDC overhead power lines in terms of tower design, span width and ground clearance. Based on theoretical and experimental data, in this article, static electric fields associated with adverse health effects are analysed and various criteria are derived for limiting static electric field strengths.     

Circadian and Social Cues Regulate Ion Channel Trafficking

Electric fish generate and sense electric fields for navigation and communication. These signals can be energetically costly to produce and can attract electroreceptive predators. To minimize costs, some nocturnally active electric fish rapidly boost the power of their signals only at times of high social activity, either as night approaches or in response to social encounters. Here we show that the gymnotiform electric fish Sternopygus macrurus rapidly boosts signal amplitude by 40% at night and during social encounters. S. macrurus increases signal magnitude through the rapid and selective trafficking of voltage-gated sodium channels into the excitable membranes of its electrogenic cells, a process under the control of pituitary peptide hormones and intracellular second-messenger pathways. S. macrurus thus maintains a circadian rhythm in signal amplitude and adapts within minutes to environmental events by increasing signal amplitude through the rapid trafficking of ion channels, a process that directly modifies an ongoing behavior in real time.     

The functional characteristics of electroreceptive central neurons of the sea catfish Plotosus anguillaris

With the use of microelectrode techniques (extracellular recordings) and the method of post-stimulus histograms, the functional characteristics of medulla oblongata neurons of sea catfish Plotosus were investigated under stimulation of electroreceptors by a homogeneous electric field of different duration, intensity, and direction. Two types of the cells possessing, accordingly, tonic or phase activity were registered among 66 neurons investigated. The mode of responses (inhibition or acceleration) of tonic neurons to the direction of the applied electric current is typical for central neurons of fresh-water catfish connected with ampullae's electroreceptors. Neurons showing a substantial response to fields of an intensity less than 1 microV/cm were registered. The reactions were most pronounced with the duration of electric stimuli in the range of 20-200 ms; however, particularly sensitive neurons showed distinct responses to stimuli of duration of 5 and even 2 ms. Thus, for the first time a high sensitivity of ampullae's electroreceptors to high-frequency stimulus was discovered, which allows one to expand the range of studying electric signals used by weakly electric fish for electrolocation and communication.     

Insight into the mechanisms of neuronal processing from electric fish

Weakly electric fish use their electric fields to locate objects and communicate with each other. Their electric discharges vary with species, gender, and social status. This variation is mediated by steroid and peptide hormones that influence ion currents through changes in gene expression or phosphorylation state. Understanding how electric fish decode the perturbations of their electric fields that result from interactions with the discharges of other fish or prey is illuminating general mechanisms of neuronal processing. Their central sensory circuits are specialized to process amplitude modulated signals, to detect microsecond variations in spike timing, and are dynamically reconfigured depending on the stimulus parameters.     

Gauging the strength of power frequency fields against membrane electrical noise

The possible physiological effect of power frequency fields (60 Hz in the US, 50 Hz in most other countries) is still a hotly debated issue. These relatively slow fields distribute themselves across cell membranes and a common approach has been to compare the strength of these fields to the strength of the electric noise that the membrane generates itself through Brownian motion. However, there has been disagreement among researchers on how to evaluate the membrane electric noise. In the first part of this article three major models are discussed. In the second part an ab initio modeling of membrane electric fields finds that different manifestations of Brownian noise lead to an electric noise intensity that is many times larger than what conventional estimates have yielded. Finally, the legitimacy of gauging a nonequilibrium external signal against internal equilibrium noise is questioned.     

The possible role of contact current in cancer risk associated with residential magnetic fields

Residential electrical wiring safety practices in the US result in the possibility of a small voltage (up to a few tenths of a volt) on appliance surfaces with respect to water pipes or other grounded surfaces. This "open circuit voltage" (V(OC)) will cause "contact current" to flow in a person who touches the appliance and completes an electrical circuit to ground. This paper presents data suggesting that contact current due to V(OC) is an exposure that may explain the reported associations of residential magnetic fields with childhood leukemia. Our analysis is based on a computer model of a 40 house (single-unit, detached dwelling) neighborhood with electrical service that is representative of US grounding practices. The analysis was motivated by recent research suggesting that the physical location of power lines in the backyard, in contrast to the street, may be relevant to a relationship of power lines with childhood leukemia. In the model, the highest magnetic field levels and V(OC)s were both associated with backyard lines, and the highest V(OC)s were also associated with long ground paths in the residence. Across the entire neighborhood, magnetic field exposure was highly correlated with V(OC) (r = 0.93). Dosimetric modeling indicates that, compared to a very high residential level of a uniform horizontal magnetic field (10 mu T) or a vertical electric field (100 V/m), a modest level of contact current (approximately 18 mu A) leads to considerably greater induced electric fields (> 1 mV/m) averaged across tissue, such as bone marrow and heart. The correlation of V(OC) with magnetic fields in the model, combined with the dose estimates, lead us to conclude that V(OC) is a potentially important exposure with respect to childhood leukemia risks associated with residential magnetic fields. These findings, nonetheless, may not apply to residential service used in several European countries or to the Scandinavian studies concerned with populations exposed to magnetic fields from overhead transmission lines.     

Spectral sensitivity of the weakly discharging electric fish Gnathonemus petersi using its electric organ discharges as the response measure

The spectral sensitivity of the weakly electric mormyrid fish Gnathonemus petersi was investigated under dark- and light-adapted conditions using a transient change (startle) in its electric organ discharge (EOD) rate as response measure. The startle was resistant to habituation and graded with light intensity. Under both lighting conditions, the fish responded optimally to a monochromatic light of 525 nm. A porphyropsin pigment (520–540₂) appears to mediate spectral sensitivity over most of the visible spectrum. However, G. petersi responded more strongly to 625- and 675-nm lights (dark- and light-adapted fish) and a 725-nm light (light-adapted fish only) than predicted by the presence of a single rod pigment. These data suggest that at least one additional visual pigment (most likely of cone cells) maximally absorbing long wavelength light (600 nm or longer) is present. The spectral sensitivity data are consistent with the sensitivity hypothesis in that heightened sensitivity to long wavelength light is predicted for fish living in blackwater habitats which are characterized typically by low light levels and transmission of predominantly long wavelengths. Histology of the retina showed photoreceptors grouped into bundles and ensheathed by pigment epithelial cells. Our results demonstrated a functional visual sense in a species of fish much better known and studied for its electrosensory and electromotor abilities.     

Coaxial lines for multiphase power distribution

A coaxial cable can be used to reduce the magnetic and electric fields that extend into environments in the vicinity of transmission lines and distribution lines and in-house or building wiring for power distribution systems. The use of the coaxial geometry may prove useful in cases where there are environmental concerns with respect to health effects and in cases where there is a need to run high-speed data communications in close proximity to power distribution systems. © 1996 Wiley-Liss, Inc.     

Generation of strong magnetic fields by counterpropagating moderate-intensity laser pulses in a low-density plasma

A study is made of the generation of strong quasistatic magnetic fields by counterpropagating moderate-intensity laser pulses of different frequencies in a low-density plasma. Strong magnetic fields are generated by small-scale large-amplitude plasma waves excited at different frequencies by ponderomotive forces in the interaction region of laser pulses. It is shown that magnetic fields are generated most efficiently under resonance conditions such that the frequency difference between laser pulses coincides with the plasma frequency. The spatial distribution of quasistatic magnetic fields is investigated, and the pattern of the contour lines of the electric current is calculated.     

Numerical simulation of gel electrophoresis of DNA knots in weak and strong electric fields

Gel electrophoresis allows one to separate knotted DNA (nicked circular) of equal length according to the knot type. At low electric fields, complex knots, being more compact, drift faster than simpler knots. Recent experiments have shown that the drift velocity dependence on the knot type is inverted when changing from low to high electric fields. We present a computer simulation on a lattice of a closed, knotted, charged DNA chain drifting in an external electric field in a topologically restricted medium. Using a Monte Carlo algorithm, the dependence of the electrophoretic migration of the DNA molecules on the knot type and on the electric field intensity is investigated. The results are in qualitative and quantitative agreement with electrophoretic experiments done under conditions of low and high electric fields.     

Effects of turbidity and light intensity on foraging success of juvenile mandarin fish Siniperca chuatsi (Basilewsky)

This study aimed to evaluate the effects of turbidity and light intensity on foraging success of juvenile mandarin fish Siniperca chuatsi. Predation on crucian carp Carassius auratus by juvenile mandarin fish was tested at five levels of turbidity combined with two light intensities, imitating daylight and night in two turbidity types. Foraging success was significantly lower in clay-induced turbidity than in algal-induced turbidity. In clay-induced turbidity trials, there was a slight but insignificant increase in foraging success of mandarin fish with increasing turbidity under lighted conditions. In algal-induced turbidity trials, there were no significant differences in foraging success of mandarin fish among turbidity levels at both light and dark levels, but at 80 NTU turbidity level, foraging success was lower than in all the other turbidity levels. There was no significant difference in foraging success at different turbidities under darkness. These results suggest that piscivory of mandarin fish is influenced by different turbidity types but is not significantly influenced by increased turbidity combined with decreased light intensity.     

Perception and the Characteristics of the Response of Honey Bees,Paper Wasps,and Red Wood Ants to a Low-Frequency Electric Field

Bees, wasps, and ants have no specialized receptors for the perception of an electric field. An appropriate response to naturally occurring electric fields in bees and ants is associated with atmospheric exposure, amplified by the approach of the front of a thunderstorm. The primary transducers of mechanoreceptors that respond to displacement are related to the perception of low-frequency electric fields of high intensity by insects. The non-specific mechanism of perception of electric fields is based on irritation by induced currents that flow in the locations of their contact with each other and/or conductive surfaces. The frequency dependence of the electric field sensitivity is determined mainly by the magnitude of the current induced by it and the intensity of its contact action. The magnitude of the current induced in the outer part of the insect body is non-linearly related to the frequency of the electric field. The region with the highest sensitivity to electric fields is close to 500 Hz, which is consistent with the maximum magnitude of the induced current. At the same time, the threshold of the sensitivity to an electric field in wasps is approximately 0.04 kV/m, while in bees it is 0.45 kV/m. Ants react to the action of an electric field of 7–10 kV/m by slowing their movement. Magnetic fields and ionization, which accompany the generation of an electric field whose intensity reaches 15–20 kV/m, do not stimulate changes in the behavior of insects.

     

Nanosecond pulsed electric fields have differential effects on cells in the S-phase

Nanosecond pulsed electric fields (nsPEFs) are a type of nonthermal, nonionizing radiation that exhibit intense electric fields with high power, but low energy. NsPEFs extend conventional electroporation (EP) to affect intracellular structures and functions and depending on the intensity, can induce lethal and nonlethal cell signaling. In this study, HCT116 human colon carcinoma cells were synchronized to the S-phase or remained unsynchronized, exposed to electric fields of 60 kV/cm with either 60-ns or 300-ns durations, and analyzed for apoptosis and proliferative markers. Several nsPEF structural and functional targets were identified. Unlike unsynchronized cells, S-phase cells under limiting conditions exhibited greater membrane integrity and caspase activation and maintained cytoskeletal structure. Regardless of synchronization, cells exposed to nsPEFs under these conditions primarily survived, but exhibited some turnover and delayed proliferation in cell populations, as well as reversible increases in phosphatidylserine externalization, membrane integrity, and nuclei size. These results show that nsPEFs can act as a nonligand agonist to modulate plasma membrane (PM) and intracellular structures and functions, as well as differentially affect cells in the S-phase, but without effect on cell survival. Furthermore, nsPEF effects on the nucleus and cytoskeleton may provide synergistic therapeutic actions with other agents, such as ionizing radiation or chemotherapeutics that affect these same structures.     

Electric organ discharges of the gymnotiform fishes: III. Brachyhypopomus

We measured and mapped the electric fields produced by three species of neotropical electric fish of the genus Brachyhypopomus (Gymnotiformes, Rham phichthyoidea, Hypopomidae), formerly Hypopomus. These species produce biphasic pulsed discharges from myogenic electric organs. Spatio-temporal false-color maps of the electric organ discharges measured on the skin show that the electric field is not a simple dipole in Brachyhypopomus. Instead, the dipole center moves rostro-caudally during the 1st phase (P1) of the electric organ discharge, and is stationary during the 2nd phase (P2). Except at the head and tip of tail, electric field lines rotate in the lateral and dorso-ventral planes. Rostro-caudal differences in field amplitude, field lines, and spatial stability suggest that different parts of the electric organ have undergone selection for different functions; the rostral portions seem specialized for electrosensory processing, whereas the caudal portions show adaptations for d.c. signal balancing and mate attraction as well. Computer animations of the electric field images described in this paper are available on web sites http://www.bbb.caltech.edu/ElectricFish or http://www.fiu.edu/∼stoddard/electricfish.html. Accepted: 22 September 1998     

Growth assessment of children exposed to low frequency electromagnetic fields at the Abu Sultan area in Ismailia (Egypt)

A cross-sectional study was carried out to assess the growth of 780 children of both sexes, aged between 0-12 years, and living at two different areas in Ismailia, Egypt, with approximately similar socioeconomic standards. Based on a designed questionaire, the exposed group was formed of 390 children from the Abu Sultan area. They were chosen from families living within 50 meters nearby high voltage electric power lines. Another 390 children from the El-Sheikh Zayed area were chosen as the control group. Standard anthropometric measurements were carried out for each child. Plain X-ray was done on the hands of 200 randomly selected children from both groups (100 each) to assess their bone maturation. In the exposed group the weight was significantly decreased only at birth, while the circumferences of the head and chest as well as the height were significantly reduced at all studied ages. The radiological study revealed a significant delay in carpal bone ossification of the exposed children. In conclusion: Exposure to low frequency electromagnetic fields emerged from high voltage electric power lines increases the incidence of growth retardation of children. Isolating these power lines in a scientific way in order to shield both the magnetic and electric fields or removing them far away from the inhabitant areas is recommended.     

Active electric imaging: body-object interplay and object's "electric texture"

This article deals with the role of fish's body and object's geometry on determining the image spatial shape in pulse Gymnotiforms. This problem was explored by measuring local electric fields along a line on the skin in the presence and absence of objects. We depicted object's electric images at different regions of the electrosensory mosaic, paying particular attention to the perioral region where a fovea has been described. When sensory surface curvature increases relative to the object's curvature, the image details depending on object's shape are blurred and finally disappear. The remaining effect of the object on the stimulus profile depends on the strength of its global polarization. This depends on the length of the object's axis aligned with the field, in turn depending on fish body geometry. Thus, fish's body and self-generated electric field geometries are embodied in this "global effect" of the object. The presence of edges or local changes in impedance at the nearest surface of closely located objects adds peaks to the image profiles ("local effect" or "object's electric texture"). It is concluded that two cues for object recognition may be used by active electroreceptive animals: global effects (informing on object's dimension along the field lines, conductance, and position) and local effects (informing on object's surface). Since the field has fish's centered coordinates, and electrosensory fovea is used for exploration of surfaces, fish fine movements are essential to perform electric perception. We conclude that fish may explore adjacent objects combining active movements and electrogenesis to represent them using electrosensory information.     

Behavioral stochastic resonance: how the noise from a Daphnia swarm enhances individual prey capture by juvenile paddlefish.

Zooplankton emit weak electric fields into the surrounding water that originate from their own muscular activities associated with swimming and feeding. Juvenile paddlefish prey upon single zooplankton by detecting and tracking these weak electric signatures. The passive electric sense in this fish is provided by an elaborate array of electroreceptors, Ampullae of Lorenzini, spread over the surface of an elongated rostrum. We have previously shown that the fish use stochastic resonance to enhance prey capture near the detection threshold of their sensory system. However, stochastic resonance requires an external source of electrical noise in order to function. A swarm of plankton, for example Daphnia, can provide the required noise. We hypothesize that juvenile paddlefish can detect and attack single Daphnia as outliers in the vicinity of the swarm by using noise from the swarm itself. From the power spectral density of the noise plus the weak signal from a single Daphnia, we calculate the signal-to-noise ratio, Fisher information and discriminability at the surface of the paddlefish's rostrum. The results predict a specific attack pattern for the paddlefish that appears to be experimentally testable.