RESUMO
Effects of a static magnetic field (SMF) with strong gradient components were studied in black Swiss mice. Exposure to SMF (100-220 mT, 15-40 T/m for 1h) did not affect the threshold for detecting auditory brainstem responses. Serial seizures elevated the hearing threshold at some frequencies, but there was no difference between SMF-exposed and unexposed control mice. EEG changes were recorded during audiogenic seizures. Pretreatment with SMF prolonged seizure latency in response to stimulation with white noise of increasing intensity from 74 to 102 dBA (1 min interval between 2 and 4 dBA increments) without significant effects on seizure severity. Gender-related differences were not statistically significant. Stimulation with 10 min sound steps revealed prolongation of latency and reduction of seizure severity in SMF-exposed, but not unexposed, mice. Pretreatment with phenytoin (5 mg/kg) in combination with SMF had significantly greater effects on seizure latency and severity than either pretreatment alone. These findings indicate that the SMF studied here under different conditions elevated seizure threshold and had anticonvulsant properties in Black Swiss mice and increased the efficacy of a conventional anticonvulsant drug.
Assuntos
Campos Eletromagnéticos , Epilepsia Reflexa/fisiopatologia , Epilepsia Reflexa/terapia , Potenciais Evocados Auditivos do Tronco Encefálico/efeitos da radiação , Estimulação Acústica/métodos , Animais , Animais Recém-Nascidos , Anticonvulsivantes/uso terapêutico , Comportamento Animal/efeitos da radiação , Modelos Animais de Doenças , Relação Dose-Resposta à Radiação , Eletroencefalografia , Potenciais Evocados Auditivos do Tronco Encefálico/efeitos dos fármacos , Camundongos , Fenitoína/uso terapêutico , Psicoacústica , Tempo de Reação/efeitos dos fármacos , Tempo de Reação/efeitos da radiação , Índice de Gravidade de DoençaRESUMO
We describe devices designed for magnetic field exposures in which field amplitude and gradients are controlled simultaneously. Dosimetry based on field continuation of high resolution magnetic field scans and numerical models is compared with validation measurements. The dosimetry variables we consider are based on the assumption that the biological or chemical system under study has field transducers that are spatially isotropic, so that absolute field amplitude and two gradient components fully describe local exposure.
Assuntos
Técnicas de Cultura de Células/instrumentação , Ambiente Controlado , Exposição Ambiental , Magnetismo/instrumentação , Radiometria/instrumentação , Desenho Assistido por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Doses de Radiação , Radiometria/métodosRESUMO
A magnetic field transduction mechanism based on an ion oscillator model is derived from an explicit quantum mechanical description. The governing equation prescribes how the electric dipole moment of an ion oscillating in a symmetric potential well evolves under the influence of an arbitrary magnetic field. The resulting equation is an analog of the Bloch equation, a well-studied model for magnetic resonances in atomic and molecular spectroscopy. The differential equation for this ion oscillator model is solved numerically for a few illustrative magnetic field exposures, showing when those resonances occur with single frequency, linearly polarized fields. Our formulation makes explicit the conditions that must be present for magnetic fields to produce observable biological effects under the ion oscillator model. The ion's potential well must have symmetry sufficient to produce a degenerate excited state, e.g., octahedral or trigonal bipyramid potentials. The impulse that excites the ion must be spatially correlated with the orientation of the detector that reads off the final state of the oscillator. The orientation between the static and oscillating magnetic fields that produces resonance is a complicated function of the field magnitudes and frequency. We suggest several classes of experiments that could critically test the validity of the model presented here.
Assuntos
Biopolímeros/química , Biopolímeros/efeitos da radiação , Campos Eletromagnéticos , Íons/química , Íons/efeitos da radiação , Modelos Biológicos , Modelos Químicos , Relógios Biológicos , Simulação por Computador , Relação Dose-Resposta à Radiação , Teoria Quântica , Doses de RadiaçãoRESUMO
The effect on myosin phosphorylation from exposure to a magnetic field generated by an array of four permanent magnets was investigated. Two lateral positions in the non-uniform field over the array were explored, each at four vertical distances over the surface of the device. The rate of myosin phosphorylation was found to depend on the position laterally over the array as well as the distance from the device surface. The square magnet array was comprised of axially magnetized, cylindrical NdFeB permanent magnets arranged with poles of alternating polarity in a plane (MagnaBloc trade mark therapeutic device). Detailed dosimetry of the magnet array was compiled: the magnetic flux density averaged over the exposure volume spanned the range 0.7-86 mT for the eight different exposure positions. The corresponding range for the absolute field gradient was 0.4-20 T/m. Comparing the dosimetry to the experimental outcome, our results imply that magnetic field amplitude alone is not sufficient to describe the influence of the field in this preparation.
