Effects of extremely low frequency magnetic fields on pain thresholds in mice: roles of melatonin and opioids

Magnetic field effects in biology from the perspective of the radical pair mechanism

Hundreds of studies have found that weak magnetic fields can significantly influence various biological systems. However, the underlying mechanisms behind these phenomena remain elusive. Remarkably, the magnetic energies implicated in these effects are much smaller than thermal energies. Here, we review these observations, and we suggest an explanation based on the radical pair mechanism, which involves the quantum dynamics of the electron and nuclear spins of transient radical molecules. While the radical pair mechanism has been studied in detail in the context of avian magnetoreception, the studies reviewed here show that magnetosensitivity is widespread throughout biology. We review magnetic field effects on various physiological functions, discussing static, hypomagnetic and oscillating magnetic fields, as well as isotope effects. We then review the radical pair mechanism as a potential unifying model for the described magnetic field effects, and we discuss plausible candidate molecules for the radical pairs. We review recent studies proposing that the radical pair mechanism provides explanations for isotope effects in xenon anaesthesia and lithium treatment of hyperactivity, magnetic field effects on the circadian clock, and hypomagnetic field effects on neurogenesis and microtubule assembly. We conclude by discussing future lines of investigation in this exciting new area of quantum biology.

Design and Construction of a Chamber Enabling the Observation of Living Cells in the Field of a Constant Magnetic Force

The aim of the work was to design and construct a microscopic stage that enables the observation of biological cells in a magnetic field with a constant magnetic force. Regarding the requirements for biological observations in the magnetic field, construction was based on the standard automatic stage of an optical microscope ZEISS Axio Observer, and the main challenge was to design a set of magnets which were the source of a field in which the magnetic force was constant in the observation zone. Another challenge was to design a magnet arrangement producing a weak magnetic field to manipulate the cells without harming them. The Halbach array of magnets was constructed using permanent cubic neodymium magnets mounted on a 3D printed polymer ring. Four sets of magnets were used, differing in their dimensions, namely, 20, 15, 12, and 10 mm. The polymer rings were designed to resist magnetic forces and to keep their shape undisturbed when working under biological conditions. To check the usability of the constructs, experiments with magnetic microparticles were executed. Magnetic microparticles were placed under the microscope and their movement was observed to find the acting magnetic force.

Analgesia for Sheep in Commercial Production: Where to Next?

Simple Summary

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on industry to alleviate pain associated with husbandry practices, injury and illness. Although a number of analgesic solutions are now available for sheep, providing some amelioration of the acute pain responses, this review has highlighted a number of potential areas for further research.

Abstract

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on livestock production industries to alleviate pain associated with husbandry practices, injury and illness. Over the past 15–20 years, there has been considerable research effort to understand and develop mitigation strategies for painful husbandry procedures in sheep, leading to the successful launch of analgesic approaches specific to sheep in a number of countries. However, even with multi-modal approaches to analgesia, using both local anaesthetic and non-steroidal anti-inflammatory drugs (NSAID), pain is not obliterated, and the challenge of pain mitigation and phasing out of painful husbandry practices remains. It is timely to review and reflect on progress to date in order to strategically focus on the most important challenges, and the avenues which offer the greatest potential to be incorporated into industry practice in a process of continuous improvement. A structured, systematic literature search was carried out, incorporating peer-reviewed scientific literature in the period 2000–2019. An enormous volume of research is underway, testament to the fact that we have not solved the pain and analgesia challenge for any species, including our own. This review has highlighted a number of potential areas for further research.

Electromagnetic field exposure (50 Hz) impairs response to noxious heat in American cockroach

Exposure to electromagnetic field (EMF) induces physiological changes in organism that are observed at different levels—from biochemical processes to behavior. In this study, we evaluated the effect of EMF exposure (50 Hz, 7 mT) on cockroach’s response to noxious heat, measured as the latency to escape from high ambient temperature. We also measured the levels of lipid peroxidation and glutathione content as markers of oxidative balance in cockroaches exposed to EMF. Our results showed that exposure to EMF for 24, 72 h and 7 days significantly increases the latency to escape from noxious heat. Malondialdehyde (MDA) levels increased significantly after 24-h EMF exposure and remained elevated up to 7 days of exposure. Glutathione levels significantly declined in cockroaches exposed to EMF for 7 days. These results demonstrate that EMF exposure is a considerable stress factor that affects oxidative state and heat perception in American cockroach.

Biological effects of the hypomagnetic field: An analytical review of experiments and theories

During interplanetary flights in the near future, a human organism will be exposed to prolonged periods of a hypomagnetic field that is 10,000 times weaker than that of Earth's. Attenuation of the geomagnetic field occurs in buildings with steel walls and in buildings with steel reinforcement. It cannot be ruled out also that a zero magnetic field might be interesting in biomedical studies and therapy. Further research in the area of hypomagnetic field effects, as shown in this article, is capable of shedding light on a fundamental problem in biophysics-the problem of primary magnetoreception. This review contains, currently, the most extensive bibliography on the biological effects of hypomagnetic field. This includes both a review of known experimental results and the putative mechanisms of magnetoreception and their explanatory power with respect to the hypomagnetic field effects. We show that the measured correlations of the HMF effect with HMF magnitude and inhomogeneity and type and duration of exposure are statistically absent. This suggests that there is no general biophysical MF target similar for different organisms. This also suggests that magnetoreception is not necessarily associated with evolutionary developed specific magnetoreceptors in migrating animals and magnetotactic bacteria. Independently, there is nonspecific magnetoreception that is common for all organisms, manifests itself in very different biological observables as mostly random reactions, and is a result of MF interaction with magnetic moments at a physical level-moments that are present everywhere in macromolecules and proteins and can sometimes transfer the magnetic signal at the level of downstream biochemical events. The corresponding universal mechanism of magnetoreception that has been given further theoretical analysis allows one to determine the parameters of magnetic moments involved in magnetoreception-their gyromagnetic ratio and thermal relaxation time-and so to better understand the nature of MF targets in organisms.

Activation of glial glutamate transporter via MAPK p38 prevents enhanced and long-lasting non-evoked resting pain after surgical incision in rats

Pain after surgery has recently become a major issue not only due to lack of treatment success in the acute phase; even more alarming is the large number of patients developing prolonged pain after surgery. Because spinal glutamate as well as spinal glia plays a major role in acute incisional pain, we investigated the role of the spinal glial glutamate transporters (GT), GLAST, GLT-1, for acute and prolonged pain and hyperalgesia caused by an incision. Spinal administration of the GT-inhibitor DL-TBOA increased non-evoked pain but not evoked pain behavior (hyperalgesia) up to 2 weeks after incision. In accordance, spinal GLAST (and to a lesser degree GLT-1) were upregulated after incision for several days. Long-term incision induced GT upregulation was prevented by long-lasting p38-inhibitor administration but not by long-lasting ERK1/2-inhibition after incision. In accordance, daily treatment with the p38-inhibitor (but not the ERK1/2 inhibitor) prolonged non-evoked but not evoked pain behavior after incision. In electrophysiological experiments, spontaneous activity of high threshold (HT) (but not wide dynamic range (WDR)) neurons known to transmit incision induced non-evoked pain was increased after prolonged treatment with the p38-inhibitor. In conclusion, our findings indicate a new spinal pathway by which non-evoked pain behavior after incision is modulated. The pathway is modality (non-evoked pain) and neuron (HT) specific and disturbance contributes to prolonged long-term pain after surgical incision. This may have therapeutic implications for the treatment of acute and - even more relevant - for prevention of chronic pain after surgery in patients.

Acute behavioural responses to nicotine and nicotine withdrawal syndrome are modified in GABA(B1) knockout mice

Nicotine is the main active component of tobacco, and has both acute and chronic pharmacological effects that can contribute to its abuse potential in humans. The aim of the present study was to evaluate a possible role of GABA(B) receptors in acute and chronic responses to nicotine administration, by comparing GABA(B1) knockout mice and their wild-type littermates. In wild-type mice, acute nicotine administration (0.5, 1, 3 and 6 mg/kg, sc) dose-dependently decreased locomotor activity, and induced antinociceptive responses in the tail-immersion and hot-plate tests. In GABA(B1) knockout mice, the hypolocomotive effect was observed only with the highest dose of nicotine, and the antinociceptive responses in both tests were significantly reduced in GABA(B1) knockout mice compared to their wild-type littermate. Additionally, nicotine elicited anxiolytic- (0.05 mg/kg) and anxiogenic-like (0.8 mg/kg) responses in the elevated plus-maze test in wild-type mice, while selectively the anxiolytic-like effect was abolished in GABA(B1) knockout mice. We further investigated nicotine withdrawal in mice chronically treated with nicotine (25 mg/kg/day, sc). Mecamylamine (1 mg/kg, sc) precipitated several somatic signs of nicotine withdrawal in wild-type mice. However, signs of nicotine withdrawal were missing in GABA(B1) knockout mice. Finally, there was a decreased immunoreactivity of Fos-positive nuclei in the bed nucleus of the stria terminalis, basolateral amygdaloid nucleus and hippocampal dentate gyrus in abstinent wild-type but not in GABA(B1) knockout mice. These results reveal an interaction between the GABA(B) system and the neurochemical systems through which nicotine exerts its acute and long-term effects.

Perioperative melatonin use

Melatonin is a substance chiefly produced by the pineal gland and has a key role in the sleep-wake cycle. It also has an important antioxidant role. Exogenous melatonin has a short half-life and is available in a range of preparations. Newer analogues targeted for the recently discovered melatonin MT1 and MT2 receptors have also been developed. Exogenous melatonin is used as a resynchronisation agent in jet lag and for other sleep disturbances. Perioperatively, melatonin has been used as a premedicant, sedative and analgesic. It decreases paediatric emergence delirium. The antioxidant properties of melatonin are being investigated for use in sepsis and reperfusion injuries. It would appear that patients on melatonin supplements should continue taking them perioperatively because there may be benefits. Melatonin and its analogues will be increasingly encountered in the perioperative setting.

Emerging synergisms between drugs and physiologically-patterned weak magnetic fields: implications for neuropharmacology and the human population in the twenty-first century

Synergisms between pharmacological agents and endogenous neurotransmitters are familiar and frequent. The present review describes the experimental evidence for interactions between neuropharmacological compounds and the classes of weak magnetic fields that might be encountered in our daily environments. Whereas drugs mediate their effects through specific spatial (molecular) structures, magnetic fields mediate their effects through specific temporal patterns. Very weak (microT range) physiologically-patterned magnetic fields synergistically interact with drugs to strongly potentiate effects that have classically involved opiate, cholinergic, dopaminergic, serotonergic, and nitric oxide pathways. The combinations of the appropriately patterned magnetic fields and specific drugs can evoke changes that are several times larger than those evoked by the drugs alone. These novel synergisms provide a challenge for a future within an electromagnetic, technological world. They may also reveal fundamental, common physical mechanisms by which magnetic fields and chemical reactions affect the organism from the level of fundamental particles to the entire living system.

Melatonin: a hormone that modulates pain

AIMS

Melatonin is a hormone synthesized principally in the pineal gland that has been classically associated with endocrine actions. However, several lines of evidence suggest that melatonin plays a role in pain modulation. This paper reviews the available evidence on melatonin's analgesic effects in animals and human beings.

MAIN METHODS

A medline search was performed using the terms "melatonin", "inflammatory pain", "neuropathic pain", "functional pain", "rats", "mice", "human", "receptors", "opioid" and "free radicals" in combinations.

KEY FINDINGS

The antinociceptive effect of melatonin has been evaluated in diverse pain models, and several findings show that melatonin receptors modulate pain mechanisms as activation induces an antinociceptive effect at spinal and supraspinal levels under conditions of acute and inflammatory pain. More recently, melatonin induced-antinociception has been extended to neuropathic pain states. This effect agrees with the localization of melatonin receptors in thalamus, hypothalamus, dorsal horn of the spinal cord, spinal trigeminal tract, and trigeminal nucleus. The effects of melatonin result from activation of MT(1) and MT(2) melatonin receptors, which leads to reduced cyclic AMP formation and reduced nociception. In addition, melatonin is able to activate opioid receptors indirectly, to open several K(+) channels and to inhibit expression of 5-lipoxygenase and cyclooxygenase 2. This hormone also inhibits the production of pro-inflammatory cytokines, modulates GABA(A) receptor function and acts as a free radical scavenger.

SIGNIFICANCE

Melatonin receptors constitute attractive targets for developing analgesic drugs, and their activation may prove to be a useful strategy to generate analgesics with a novel mechanism of action.

A randomized, double-blind, placebo-controlled clinical trial using a low-frequency magnetic field in the treatment of musculoskeletal chronic pain

Exposure to a specific pulsed electromagnetic field (PEMF) has been shown to produce analgesic (antinociceptive) effects in many organisms. In a randomized, double-blind, sham-controlled clinical trial, patients with either chronic generalized pain from fibromyalgia (FM) or chronic localized musculoskeletal or inflammatory pain were exposed to a PEMF (400 microT) through a portable device fitted to their head during twice-daily 40 min treatments over seven days. The effect of this PEMF on pain reduction was recorded using a visual analogue scale. A differential effect of PEMF over sham treatment was noticed in patients with FM, which approached statistical significance (P=0.06) despite low numbers (n=17); this effect was not evident in those without FM (P=0.93; n=15). PEMF may be a novel, safe and effective therapeutic tool for use in at least certain subsets of patients with chronic, nonmalignant pain. Clearly, however, a larger randomized, double-blind clinical trial with just FM patients is warranted.

Pain perception and electromagnetic fields

A substantial body of evidence has accumulated showing that exposure to electromagnetic fields (EMFs) affects pain sensitivity (nociception) and pain inhibition (analgesia). Consistent inhibitory effects of acute exposures to various EMFs on analgesia have been demonstrated in most studies. This renders examinations of changes in the expression of analgesia and nociception a particularly valuable means of addressing the biological effects of and mechanisms underlying the actions of EMFs. Here we provide an overview of the effects of various EMFs on nociceptive sensitivity and analgesia, with particular emphasis on opioid-mediated responses. We also describe the analgesic effects of particular specific EMFs, the effects of repeated exposures to EMFs and magnetic shielding, along with the dependence of EMF effects on lighting conditions. We further consider some of the underlying cellular and biophysical mechanisms along with the clinical implications of these effects of various EMFs.

Extremely low frequency magnetic field induces hyperalgesia in mice modulated by nitric oxide synthesis

We investigated an effect of extremely low frequency magnetic field (ELF-MF, 60 Hz) on hyperalgesia using hot plate test. The level of nitric oxide (NO) and the expression of nitric oxide synthase (NOS) were measured to determine if ELF-MF is engaged in NO mediated pain mechanism. Additionally, the involvement of Ca2+-dependent NO pathway in ELF-MF induced hyperalgesia was evaluated by blocking Ca2+ sources with NMDA receptor antagonist and Ca2+ channel blocker. The exposure of mice to ELF-MF lowered pain threshold and elevated NO synthesis in brain and spinal cord. An NOS inhibitor blocked these effects of ELF-MF with attenuating the reduction of pain threshold and the rise of NO level in brain and spine by the exposure of ELF-MF. The hyperalgesic effects of ELF-MF were also blocked by a Ca2+ channel blocker, nimodipine, but not by a NMDA receptor antagonist, MK-801. The expression of Ca2+ -dependent nNOS and eNOS and Ca2+ -independent iNOS were not changed by ELF-MF. These results indicated that the exposure of ELF-MF might cause Ca2+ -dependent NOS activation, which then induces hyperalgesia with the increase in NO synthesis. In conclusion, ELF-MF may produce hyperalgesia by modulating NO synthesis via Ca2+ -dependent NOS.

The influence of extremely low frequency magnetic fields on cytoprotection and repair

Ischemia-reperfusion injuries, such as those suffered from various types of cardiovascular disease, are major causes of death and disability. For relatively short periods of ischemia, much of the damage is potentially reversible and in fact, does not occur until the influx of oxygen during the reperfusion stage. Because of this, there is a window of opportunity to protect the ischemic tissue. Here, we review several mechanisms of protection, such as heat shock proteins, opioids, collateral blood flow, and nitric oxide induction, and the evidence indicating that magnetic fields may be used as a means of providing protection via each of these mechanisms. While there are few studies demonstrating direct protection with magnetic field therapies, there are a number of published reports indicating that electromagnetic fields may be able to influence some of the biochemical systems with protective applications.

Possíveis efeitos adversos dos campos eletromagnéticos (50/60 Hz) em humanos e em animais

Os avanços tecnológicos têm aumentado o número de equipamentos elétricos e eletrônicos, seja nas residências ou mesmo no ambiente de trabalho, fazendo com que a população conviva com grande número de fontes de irradiação eletromagnética, com os mais diversos níveis de potência e freqüência. Por muitos anos, alguns cientistas e engenheiros acreditaram que o campo eletromagnético (CEM) com freqüência extremamente baixa não pudesse causar efeitos e alterações significantes no material biológico. O objetivo deste trabalho é verificar os possíveis efeitos adversos dos CEMs em humanos e animais, que foram publicados nos últimos anos, através de uma revisão da literatura disponível em Medline, revistas nacionais e internacionais e catálogos de obras de referência na área dos CEM (50/60 Hz). Como resultado foi observado que o CEM (50/60 Hz) é capaz de produzir diversos efeitos adversos em humanos e animais, como por exemplo: distúrbios na reprodução, doenças degenerativas, efeitos psiquiátricos e psicológicos, alterações citogenéticas, alterações no sistema cardiovascular, nervoso e neuroendócrino, bem como nos parâmetros biológicos e bioquímicos. Apesar de todas estas constatações e devido a muitas controvérsias entre vários autores, faz-se necessário um estudo mais específico e aprofundado sobre o assunto.

Extremely Low Frequency Magnetic Fields Modulate Bicuculline-lnduced-Convulsion in Rats

The effect of extremely low frequency (ELF, 60 Hz) magnetic fields (MFs) on convulsions was investigated in rats. We determined the onset and duration of convulsions induced by bicuculline alone or by co-exposure to MFs and bicuculline. In addition, we measured the GABA concentrations in the rat brains using HPLC-ECD. MFs strengthened the convulsion induced by bicuculline (0.3, 1, and 3 microg, i.c.v.), with a shortening of the onset time, but lengthening of the duration time. Co-exposure to MFs and bicuculline decreased the GABA levels in the cortex, hippocampus and hypothalamus, whereas MFs alone reduced the level of GABA only in the hippocampus. These results suggest that the exposure to MFs may modulate bicuculline-induced convulsions due to GABA neurotransmissions in rat brains.

Daily repeated magnetic field shielding induces analgesia in CD-1 mice

We have recently observed that a single exposure of mice to a magnetically shielded environment can attenuate opioid induced analgesia. Here, we report the effect of repeated exposures to the same magnetically shielded environment. Adult male Swiss CD-1 mice were placed in a Mu-metal lined box or an opaque Plexiglas box (sham condition) for 1 h per day for 10 consecutive days. Nociception was measured as the latency time to a foot lift/lick in response to an aversive thermal stimulus (hotplate analgesiometer, 50 +/- 1 degrees C) before and immediately after exposure. Multiple experiments were conducted in which thermal latency was tested on each of the 10 days or on days 1, 5, and 10, with some utilizing post-exposure testing only. It was shown that mice can detect and will respond to the repeated absence of the ambient magnetic field, with a maximum analgesic response occurring over days 4-6 of exposure and returning to baseline thereafter. The effect was robust, independent of pre-exposure and intermittent testing, and seems to be opioid related, since the results obtained on day 5 were similar to those from a 5 mg/kg dose of morphine and were abolished with the opioid antagonist, naloxone.

Benzodiazepine system is involved in hyperalgesia in rats induced by the exposure to extremely low frequency magnetic fields

Many reports demonstrate that extremely low frequency magnetic fields (ELF MFs, 60 Hz) may be involved in hyperalgesia. In a previous investigation, we suggested that MFs may produce hyperalgesia and such a response may be regulated by the benzodiazepine system. In order to further confirm this effect of MFs, we used diazepam and/or flumazenil with MFs exposure. When testing the pain threshold of rats using hot plate tests, MFs or diazepam (0.5 microg, i.c.v.; a benzodiazepine receptor agonist) induced hyperalgesic effects with the reduction of latency. These effects were blocked by a pretreatment of flumazenil (1.5 mg/kg, i.p.; a benzodiazepine receptor antagonist). When the rats were exposed simultaneously to MFs and diazepam, the latency tended to decrease without statistical significance. The induction of hyperalgesia by co-exposure to MFs and diazepam was also blocked by flumazenil. However, the pretreatment of GABA receptor antagonists such as bicuculline (0.1 microg, i.c.v.; a GABA(A) antagonist) or phaclofen (10 microg, i.c.v.; a GABA(B) antagonist) did not antagonize the hyperalgesic effect of MFs. These results suggest that the benzodiazepine system may be involved in MFs-induced hyperalgesia.

Low frequency therapeutic EMF differently influences experimental muscle pain in female and male subjects

Effects of a pulsating, half sine wave magnetic field (MF) with a frequency of 100 pps and 15 mT rms flux density, generated by the MD TEMF device (EMF Therapeutics, Inc., Chattanooga), on subjective pain rating, heart rate, and arterial blood pressure were tested in a double blind, crossover design study employing experimental muscle pain. Each of 24 healthy volunteers (12 females and 12 males, 24.7 +/- 3.2 years of age) received painful stimulation induced by the infusion of 5% hypertonic saline (HS) into the erector spinae muscle during real and sham MF exposure, in counterbalanced order. Exposure to MF differently affects subjective pain estimates in females and males. MF exposure increased averaged pain level and time integral of pain ratings in females, whereas no statistically significant difference for these characteristics was found in males. Pain related elevation of systolic and diastolic blood pressure was observed during both real and sham EMF exposure in female and male subjects.

Light alters nociceptive effects of magnetic field shielding

Orientation and nociception (pain sensitivity) are affected by exposure to geomagnetic or low frequency (<1,000 Hz) magnetic fields of approximately the earth's field strength, i.e., 50 microT. However, these effects are often dependent on the simultaneous presence of visible light. Recently, it was shown that nociception was affected in mice acutely exposed to an electromagnetic-shielded environment in the dark (<0.05 W/m(2)) during the mid-light phase of the diurnal cycle. Here, we report for the first time that if mice are exposed to magnetic shielding in the presence of visible light (0.6 W/m(2), 400-750 nm) that most of the effects of shielding are eliminated. This simple experimental protocol may be useful in investigating the role that light plays in the detection of ambient electromagnetic fields.

Thermal analgesia induced by 30-min exposure to 1 μT burst-firing magnetic fields is strongly enhanced in a dose-dependent manner by the α2 agonist clonidine in rats

Most of the research concerning analgesia following brief exposures to physiologically patterned weak magnetic fields has focused upon their morphine-related properties. However, the alpha-adrenergic system interacts with morphine-induced analgesia. In the present study we found that prazosin, phenylephrine, and yohimbine did not augment the robust analgesia to thermal stimuli in rats evoked by whole-body exposures to a 1 microT, burst-firing magnetic field presented once every 4s for 30 min. However, the alpha2 agonist clonidine enhanced the field-induced analgesia in a dose-dependent manner that reflected a receptor-saturation response. Potentiation between the field and clonidine was evident at 0.2 mg/kg and approached asymptote at 1 mg/kg. The combination of the effects from exposure to the magnetic field and the clonidine explained more than 75% of the variance in the change in nociceptive thresholds from baseline levels. The possibility that properly patterned weak magnetic fields could be a powerful adjunct to pharmacological treatments of pain is considered.

Diurnal changes of tonic nociceptive responses in mice: evidence for a proalgesic role of melatonin

Diurnal variations in tonic pain reactions have been described in mice tested in Spring, but the underlying mechanisms are still unknown. We tested the potential role of melatonin, a key hormone in the control of neuro-endocrine circadian rhythms. The experiments were performed in male CBA/J mice housed under controlled temperature, humidity, and light (12/12 dark/light cycle) conditions, during the Light (7-10a.m.) or Dark (7-10p.m.) phases of the diurnal cycle. In a first group of experiments, animals were either pretreated with i.p. saline (controls) or with the melatonin receptor antagonist, luzindole (30 mg/kg), before the s.c. injection of a dilute formalin solution into a hindpaw. In control animals, pain-related behavioral reactions (licking and flinching) were higher in the evening (Dark) than in the morning (Light), both during the first (0-10 min) and the second (11-55 min) phase of the response to s.c. formalin. In animals pre-treated with luzindole, no diurnal changes occurred, pain reactions in the Dark being similar to those of the Light Control group. In a second group of experiments, artificial pinealectomy, obtained by exposing animals to continuous light for 48 h, also reduced pain reactions in the evening to levels comparable to those in the morning. Receptor autoradiography showed lower binding availability at spinal cord level in mice sacrificed during the Dark, as expected from the circadian pattern of melatonin secretion. A further significant decrease of melatonin receptor binding was induced by noxious stimulation. These results suggest a proalgesic role of endogenous melatonin in tonic pain.

Analgesic and behavioral effects of a 100 μT specific pulsed extremely low frequency magnetic field on control and morphine treated CF-1 mice

Diverse studies have shown that magnetic fields can affect behavioral and physiological functions. Previously, we have shown that sinusoidal extremely low frequency magnetic fields and specific pulsed magnetic fields (Cnps) can produce alterations in the analgesia-related behavior of the land snail. Here, we have extended these studies to show an induction of analgesia in mice equivalent to a moderate dose of morphine (5 mg/kg), and the effect of both Cnp exposure and morphine injection on some open-field activity. Cnp exposure was found to prolong the response latency to a nociceptive thermal stimulus (hot plate). Cnp+morphine offset the increased movement activity found with morphine alone. These results suggest that pulsed magnetic fields can induce analgesic behavior in mice without the side effects often associated with opiates like morphine.

Human head exposure to a 37 Hz electromagnetic field: Effects on blood pressure, somatosensory perception, and related parameters

Previous studies have shown that exposure to an electromagnetic field (EMF) of 37 Hz at a flux density of 80 microT peak enhances nociceptive sensitivity in mice. Here we examined the effects on pain sensitivity and some indexes of cardiovascular regulation mechanisms in humans by measuring electrical cutaneous thresholds, arterial blood pressure, heart rate and its variability, and stress hormones. Pain and tolerance thresholds remained unchanged after sham exposure but significantly decreased after electromagnetic exposure. Systolic blood pressure was significantly higher during electromagnetic exposure and heart rate significantly decreased, both during sham and electromagnetic exposure, while the high frequency (150-400 mHz) component of heart rate variability, which is an index of parasympathetic activity, increased as expected during sham exposure but remained unchanged during electromagnetic exposure. Cortisol significantly decreased during sham exposure only. These results show that exposure to an EMF of 37 Hz also alters pain sensitivity in humans and suggest that these effects may be associated with abnormalities in cardiovascular regulation.

Effects of magnetic field exposure on open field behaviour and nociceptive responses in mice

Results of previous studies have shown that nociceptive sensitivity in male C57 mice is enhanced by exposure to a regular 37 Hz or an irregularly varying (<1 Hz) electromagnetic field. In order to test whether these fields affect more generally mouse behaviour, we placed Swiss CD-1 mice in a novel environment (open field test) and exposed them for 2 h to these two different magnetic field conditions. Hence, we analysed how duration and time course of various behavioural patterns (i.e. exploration, rear, edge chew, self-groom, sit, walk and sleep) and nociceptive sensitivity had been affected by such exposure. Nociceptive sensitivity was significantly greater in magnetically treated mice than in controls. The overall time spent in exploratory activities was significantly shorter in both magnetically treated groups (< 1 Hz, 33% and 37 Hz, 29% of total time), than in controls (42%). Conversely, the time spent in sleeping was markedly longer in the treated groups (both 27% of total time) than in controls (11%). These results suggest that exposure to altered magnetic fields induce a more rapid habituation to a novel environment.

The influences of extremely low frequency magnetic fields on drug-induced convulsion in mouse

This study investigated the effects of extremely low frequency magnetic fields (ELF-MFs) on the sensitivity of seizure response to bicuculline, picrotoxin and NMDA in mice. The mice were exposed to either a sham or 20 G ELF-MFs for 24 hours. Convulsants were then administered i.p. at various doses. The seizure induction time and duration were measured and lethal dose (LD50) and convulsant dose (CD50) of the clonic and tonic convulsion were calculated. The analysis of glutamate, glycine, taurine and GABA of mouse brain was accomplished by HPLC. The mice exposed to ELF-MFs showed moderately higher CD50, LD50 and onset time on the bicuculline-induced seizure. However, the ELF-MFs did not influence them in the NMDA and picrotoxin-induced seizures. After the exposure to MFs exposure, the glutamate level was increased and GABA was decreased significantly in NMDA and picrotoxin-induced seizure. The level of glutamate and GABA were not changed by MFs in bicuculline-induced seizure. These results suggest that ELF-MFs may alter the convulsion susceptibility through GABAergic mechanism with the involvement of the level of glutamate and GABA.

Human electrophysiological and cognitive effects of exposure to ELF magnetic and ELF modulated RF and microwave fields: a review of recent studies

The investigation of weak (<500 microT), extremely low frequency (ELF, 0-300 Hz) magnetic field (MF) exposure upon human cognition and electrophysiology has yielded incomplete and contradictory evidence that MFs interact with human biology. This may be due to the small number of studies undertaken examining ELF MF effects upon the human electroencephalogram (EEG), and the associated analysis of evoked related potentials (ERPs). Relatively few studies have examined how MF exposure may affect cognitive and perceptual processing in human subjects. The introduction of this review considers some of the recent studies of ELF MF exposure upon the EEG, ERPs and cognitive and perceptual tasks. We also consider some of the confounding factors within current human MF studies and suggest some new strategies for further experimentation.

The influences of extremely low frequency magnetic fields on clonidine-induced sleep in 2-day-old chicks

1. It has been shown that magnetic fields (MFs) affect a variety of biological effects in animal brains. There have been few experiments on the effects of MFs on sleep. Therefore, we investigated whether extremely low frequency (ELF) MFs affect the sleep induced by clonidine, a central alpha(2)-adrenoceptor agonist. Clonidine produced dose-related increase of the sleeping time and dose-related decrease of the onset time in 2-day-old chicks. 2. Exposure of chicks to MFs (5, 10, 20 G; for 3, 6, 9, 12 h) significantly increased the clonidine-induced sleep time as a direct function of intensity and duration of MF application. Clonidine reduced noradrenaline or tyrosine in the brain, an effect which was not further changed in animals exposed to MF. 3. To determine whether the gamma amino butyric acid A (GABA(A))/benzodiazepine (BZD) receptor system is involved in the decrease in clonidine-induced sleep caused by activation of central alpha(2)-adrenergic systems, we examined exposure of chicks to the effects of the BZD receptor antagonist flumazenil (0.5 mg kg(-1), i.p.) and GABA(A) antagonist bicuculline (0.1 mg kg-1, i.p.) on clonidine-induced sleep. Bicuculline and flumazenil inhibited the increase of clonidine-induced sleep time by MFs. Clonidine or MFs did not change GABA levels in the brain. 4. These results suggest that MFs can increase clonidine-induced sleep via a change of GABA(A) and BZD receptor system irrespective of the concentration of GABA or noradrenaline in the brain of 2-day-old chicks.