Magnetic field modulation of receptor binding

Neurochemical effects of static magnetic field exposure

BACKGROUND

There has been considerable interest in both the lay and scientific media concerning the putative effects of exposure to electromagnetic fields. An assessment of the effects of static magnet exposure on neurochemistry was undertaken to determine potential risks to patients and staff involved with magnetic resonance imaging and spectroscopy.

METHODS

One set of rats were exposed to weak static field (800 gauss [G]) in an otherwise normal laboratory surrounding. Another set of rats were exposed to 7-Tesla fields, both with suitable controls.

RESULTS

Exposure of rats (n=8) to weak static fields for periods between 12 hours and 8 days produced no significant change in nighttime pineal or serum melatonin levels, as compared to controls, nor did it significantly influence levels of pontine medullary 5-hydroxytryptamine [5-HT] and hypothalamic 5-hydroxyindoleacetic acid [5-HIAA]. Placing rats in a 7-Tesla MRI magnet for 45 minutes produced similar results.

CONCLUSIONS

These experiments suggest that daily light/dark cycle has much greater influence on levels of melatonin, catecholamines, serotonin, or their metabolites than does exposure to a static magnetic field.

Blood-brain barrier permeability in rats is altered by exposure to magnetic fields associated with magnetic resonance imaging at 1.5 T

We have previously reported that exposure of rats to low-field (0.15 T) magnetic resonance imaging (MRI) increases blood-brain barrier (BBB) permeability. However, a number of investigators have failed to observe this effect when high-field MRI (1.5 T or higher) is used. Therefore, we investigated whether or not we would observe changes using our technique at these higher fields. Adult male Sprague-Dawley rats were anaesthetised and then exposed to a 22.5 min imaging or sham procedure. Immediately following exposure, rats were injected with 1 MBq of 153Gd-DTPA intracardially and then immediately re-exposed for an additional 22.5 min. The rats were killed 1h following the second MRI exposure, at which time the brain was resected and 3 ml of venous blood collected. The ratio of radioactivity per gram of brain to radioactivity per milliliter of blood, known as the brain-blood partition coefficient, was determined and used as a measure of BBB permeability. Groups of animals had different exposures. Group 1 (n = 9) was exposed to a clinically relevant MRI procedure. Group 2 (n = 20) was exposed to the same procedure except the rf specific absorption rate (SAR) was reduced to 25% and the animals were positioned 15 cm from imager centre to increase the time-varying magnetic field from 0.4 to 2.8 T/s. For the sham exposures (n = 21), the animals were placed in the imager with the static field ramped down to zero and exposed to a sound recording simulating a MRI examination.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimates for ELF effects: noise-based thresholds and the number of experimental conditions required for empirical searches

Interactions between physical fields and biological systems present difficult conceptual problems. Complete biological systems, even isolated cells, are exceedingly complex. This argues against the pursuit of theoretical models, with the possible consequence that only experimental studies should be considered. In contrast, electromagnetic fields are well understood. Further, some subsystems of cells (viz. cell membranes) can be reasonably represented by physical models. This argues for the pursuit of theoretical models which quantitatively describe interactions of electromagnetic fields with that subsystem. Here we consider the hypothesis that electric fields, not magnetic fields, are the source of interactions, From this it follows that the cell membrane is a relevant subsystem, as the membrane is much more resistive than the intra- or extracellular regions. A general class of interactions is considered: electroconformational changes associated with the membrane. Expected results of such as approach include the dependence of the interaction on key parameters (e.g., cell size, field magnitude, frequency, and exposure time), constraints on threshold exposure conditions, and insight into how experiments might be designed. Further, because it is well established that strong and moderate electric fields interact significantly with cells, estimates of the extrapolated interaction for weaker fields can be sought. By employing signal-to-noise (S/N) ratio criteria, theoretical models can also be used to estimate threshold magnitudes. These estimates are particularly relevant to in vitro conditions, for which most biologically generated background fields are absent. Finally, we argue that if theoretical model predictions are unavailable to guide the selection of experimental conditions, an overwhelmingly large number of different conditions will be needed to find, establish, and characterize bioelectromagnetic effects in an empirical search. This is contrasted with well-established chemical dosimetry, which is much simpler. Because of the large number of possible electromagnetic field conditions, we also conclude that in vitro studies, rather than in vivo studies, should be emphasized in studies aimed at discovering and characterizing mechanisms for bioelectromagnetic effects.

Evidence for the involvement of protein kinase C in the modulation of morphine-induced 'analgesia' and the inhibitory effects of exposure to 60-Hz magnetic fields in the snail, Cepaea nemoralis

There is substantial evidence that magnetic fields can reduce opiate-induced analgesia, with alterations in calcium channel function and/or calcium ion flux being implicated in the mediation of these inhibitory effects. The present experiments were designed to examine the effects of protein kinase C (PKC), a calcium/diacylglycerol/phospholipid-dependent protein kinase, on opiate-induced analgesia and its involvement in mediating the inhibitory effects of exposure to magnetic fields. We observed that morphine-induced antinociception, or 'analgesia', in the land snail, Cepaea nemoralis, as measured by the enhanced latency of response to a thermal (38.5 degrees C) stimulus, was reduced in dose-related manner by the PKC activator, SC-9. Exposure of snails for 2 h to a low intensity (1.0 gauss rms) 60-Hz magnetic field also reduced morphine-induced analgesia. The inhibitory effects of the 60-Hz magnetic field on morphine-induced analgesia were significantly reduced by the PKC inhibitors, H-7 and H-9, and significantly enhanced by the PKC activator, SC-9. The non-specific protein kinase inhibitor, HA-1004, and the preferential calmodulin inhibitor, W-7, had no significant effects on either morphine-induced analgesia or the inhibitory actions of exposure to the magnetic fields. These results suggest that: (1) PKC has antagonistic effects on opiate-mediated analgesia in the snail, Cepaea, and (2) that the inhibitory effects of magnetic fields on opiate-induced analgesia involve alterations in PKC.

Theoretical and experimental considerations linking an environmental stress to expression of endogenous retroviruses in a mammalian tumour

CBA mice, containing the transplantable CaNT adenocarcinoma were exposed to magnetic fields of 0.5T. Doubling times of the tumours were found to increase significantly from 71 to 123 hours. Electron microscopy of these tumours revealed that the numbers of intracisternal A-type viral-like particles increased from a total of 127 in control mice (counted in 97 fields from 4 different tumours), to 459 in mice exposed to magnetic fields (counted in 95 fields from 5 different tumours). Similarly, intra-cytoplasmic A-type particle numbers increased from 98 to 184. In contrast the number of budding and extracellular C-type virus particles did not differ significantly in mice exposed to the magnetic field. To our knowledge this is the first report linking an environmental stress (magnetic field) to the visible expression of endogenous retro-viral-like type-A particles. We therefore propose the hypothesis that environmental stress may be relevant to the expression of endogenous retroviruses in mammalian cells. Such a mechanism could be relevant in the mechanisms of carcinogenesis and in the rapid evolution of species.