摘要:

AbstractA brief summary is presented of electroreception and magnetoreception mechanisms in bacteria and in more complex organisms such as avians, bees, and various aquatic animals. This article is a prologue to the series of three reviews written by specialists in the field of electroreception and magnetoreception that appear in this issue ofBioelectromagnetics.

ISSN:0197-8462    

DOI:10.1002/bem.2250100302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractMagnetotactic bacteria from freshwater and marine sediments orient and navigate along geomagnetic field lines. Their magnetotactic response is based on intracellular, single magnetic domains of ferrimagnetic magnetite, which impart a permanent magnetic dipole moment to the cell.

ISSN:0197-8462    

DOI:10.1002/bem.2250100303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractMagnetite, the only known biogenic material with ferromagnetic properties, has been identified as a biochemical precipitate in three of the five kingdoms of living organisms, with a fossil record that now extends back nearly 2 billion years. In the magnetotactic bacteria, protoctists, and fish, single‐domain crystals of magnetite are arranged in membrane‐bound linear structures called magnetosomes, which function as biological bar magnets. Magnetosomes in all three of these groups bear an overall structural similarity to each other, which includes alignment of the individual crystallographic [111] directions parallel to the long axis. Although the magnetosomes represent only a small volume fraction in higher organisms, enough of these highly energetic structures are present to provide sensitivity to extremely small fluctuations and gradients in the background geomagnetic field. Previous experiments with elasmobranch fish are reexamined to test the hypothesis that gradients played a role in their successful geomagnetic conditioning, and a variety of four‐turn coil designs are considered that could be used to test the various hypotheses proposed for

ISSN:0197-8462    

DOI:10.1002/bem.2250100304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractA central problem in the study of magnetic sensitivity in animals has been the lack of behavioral techniques sufficiently powerful for the systematic psychophysical work required for an understanding of magnetosensory capacity and of the transduction mechanism. In recent experiments, free‐flying honeybees have been conditioned to discriminate the presence and absence of localized magnetic dipole anomalies superimposed on the uniform background field of the earth. The results obtained thus far suggest that movement is necessary for conditioned responding to magnetic field stimuli and support the hypothesis that magnetic field transduction is based on single‐domain particles of magnetite found in the anterodorsal abdomen of honeyb

ISSN:0197-8462    

DOI:10.1002/bem.2250100305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractWe exposed pigtailed macaques (Macaca nemestrina) to electric (E) and magnetic (B) fields at strengths of 3 kV/m and 0.1 G, 10 kV/m and 0.3 G, and 30 kV/m and 0.9 G for three 21 day segments. These three exposure segments were preceded and followed by 21 day sham exposure segments. Additional animals received only sham exposure for five 21 day segments. Detailed description of the exposure chamber and field generation apparatus is given. We evaluated measures of animal well‐being, including weight, blood chemistry, blood cell counts, and performance on a simple motor task, and performed postmortem examinations. Reliable and consistent results were obtained throughout data collection. None of the measures evaluated was significantly affected by E‐ and B‐field exposures. Data obtained during actual exposure segments were not distinguishable from those obtained during the initial and final sham exposure segments, nor were they different from data obtained from the sham‐exposed animals. Thus, field exposure had no apparent effects on general health or perf

ISSN:0197-8462    

DOI:10.1002/bem.2250100306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractWe exposedMacaca nemestrina(pig‐tailed macaques) to electric (E) and magnetic (B) fields ranging in intensity from 3 kV/m and 0.1 G to 30 kV/m and 0.9 G for three 21‐day (d) periods. Experimental animals were exposed to sham E and B fields for two 21‐d periods, one prior to and one following actual exposure to E and B fields, resulting in a total of five 21‐d periods. Control animals were exposed to sham E and B fields for the entire 105‐d interval. At the end of each 21‐d period cerebrospinal fluid (CSF) was obtained by lumbar puncture and analyzed for concentrations of homovanillic acid (HVA) and 5‐hydroxyindoleacetic acid (5‐HIAA), metabolites of dopamine and serotonin neurotransmitters, respectively, by high‐performance liquid chromatography with electrochemical detection (HPLC‐ECD). Results are based on an examination of six experimental and four control animals.Exposure to E and B fields at all strengths was associated with a significant decline in CSF concentrations of both HVA and 5‐HIAA when statistical comparisons were made against values obtained at the end of the preexposure interval. However, HVA returned to preexposure levels during the postexposure period, while 5‐HIAA did not. No significant change in the concentrations of HVA or 5‐HIAA was noted in the control animals.These results strongly suggest that exposure of the nonhuman primate to E and B fields can significantly affect specific biochemical estimates of nervous system function. These effects may involve alterations either in neuronal activity or in the activity of enzymes that catabol

ISSN:0197-8462    

DOI:10.1002/bem.2250100307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe neurophysiologic effects of combined 60‐Hz electric (E) and magnetic (B) fields, of magnitudes comparable to those produced by high‐voltage powerlines, were investigated in 10 monkeys (Macaca nemestrina). Six animals (experimental group) were each exposed to three different levels of E and B fields: 3 kV/m and 0.1 G, 10 kV/m and 0.3 G, and 30 kV/m and 0.9 G. Field exposures were preceded and followed by sham exposures, during which factors of field generation were present (e.g., heat, vibration, noise, etc.) without E and B fields. Each of the five segments (i.e., the three exposure segments and the initial and final sham exposure segments) lasted 3 weeks. Animals were exposed for 18 h/day (fields on at 1600 h, off at 1000 h). Four other animals (external control group) were given sham exposure for the entire 15‐week period. Auditory, visual, and somatosensory evoked potentials were recorded twice a week, during the daily 6‐h field‐off period.E‐ and B‐field exposure had no effect on the early or mid‐latency evoked potential components, suggesting that exposure at these levels has no effect on peripheral or central sensory afferent pathways. However, there was a statistically significant decrease in the amplitudes of late components of the somatosensory evoked potential during the 10kV/m and 0.3 G, and 30 kV/m and 0.9 G exposure levels. This result is possibly related to the opiate antagonist effect of electromagnetic field exposure rep

ISSN:0197-8462    

DOI:10.1002/bem.2250100308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe threshold intensity for detection of an AC electric field was studied in human subjects at several different temperatures and humidities. The dorsum and palm of the hand were exposed to fields, representing hairy and hairless skin, in order to clarify whether hair movement is critical for field detection. Experiments were carried out on human subjects (seven men and four women) during hot humid weather of July–August and dry cool air of October–November. Threshold values obtained in the summer were 30–65 kV/m for the hairy skin on the dorsum of the hand, while for the hairless skin on the palm the threshold was>115 kV/m (highest field available due to limitations of the power supply). During the fall, the threshold was much higher than during the summer. We sought possible reasons for the difference and found that humidity was the main factor. Relative permittivity of woman's hair was then estimated by measuring capacitance of the hairs under dry (35% RH) and wet (85% RH) conditions at 20 °C. The values of relative permittivity obtained under these two conditions differed by several times the average. The differences in detection thresholds may be attributable to the different relative permittivities of the hairs under dry and wet cond

ISSN:0197-8462    

DOI:10.1002/bem.2250100309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractFemale rats were implanted with mammary adenocarcinoma tissue and 25 days later exposed to 2,000‐Hz magnetic fields 1 h a day for 9 days. Analysis showed that tumor weights and the levels of several reproductive hormones were not significantly different between treated and control animals. Other studies with a similar design have also reported no significant effects from magnetic field exposure. However, vaginal smear data from all animals revealed that handling and restraint stress may have confounded the detection of subtle magnetic field effect

ISSN:0197-8462    

DOI:10.1002/bem.2250100310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

ISSN:0197-8462    

DOI:10.1002/bem.2250100301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY