摘要:

AbstractIn an effort to understand microwave heating better, regional brain and core temperatures of rats exposed to microwave radiation (2450 MHz) or elevated air temperatures were measured in two studies. In general, we have found no substantial evidence for temperature differentials, or “hot spots,” in the brain of these animals. In the first study, after a 30‐min exposure, no temperature differences between brain regions either after microwave or ambient air exposure were found. However, a highly significant correlation between brain and core temperatures was found and this correlation was the same for both microwave and ambient air heating. In the second study, time‐temperature profiles were measured in rats exposed to either 30 mW/cm2or 36.2°C. In this study, the 30‐min exposure period was divided into seven intervals and the change in temperature during each period was analyzed. Only the cortex showed significantly different heating rates between the air heating and microwave heating; however, this difference disappeared after the initial 5 min o

ISSN:0197-8462    

DOI:10.1002/bem.2250070302

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

年代:1986

数据来源: WILEY

摘要:

AbstractA new method for finding the dielectric parameters of biological substances is presented. The method makes use of the loss‐tangent as a function of frequency to identify the dominating relaxation process. The method was tested for a few cell suspensions (blood and lymphocytes) and two tissues (liver and spleen). The obtained parameters agree well with those calculated from Maxwell‐Wagner theory (β dispers

ISSN:0197-8462    

DOI:10.1002/bem.2250070303

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

年代:1986

数据来源: WILEY

摘要:

AbstractA method for simultaneous magnetic field application and intracellular recording is presented. A little used method for magnetic field application was exploited; the field generator consisted of a flat copper sheet through which current was passed to generate a magnetic field. The resultant magnetic field was relatively homogeneous, exhibiting a variation of ± 5%. This compact, current‐sheet field generator was mounted on the condensor of a microscope. The current induced in the intracellular electrode was reduced by injecting current equal and opposite to the induced current into the microelectrode. This step reduces the possibility of cellular effects and voltage artifacts due to the induced electrode current. The technique was used to conduct preliminary studies on the effects of extremely low frequency (ELF) linearly and circularly polarized magnetic fields (1.0 Gauss, 60 and 70 Hz) on miniature end plate potential (mepp) frequency (frequency of neurotransmitter release events) of rat flexor digitorum brevis muscle. The same synapse was utilized for both the sham‐exposed control and the exposed experimental halves of an experiment. After 10 min of exposure to a 60‐Hz linear field, mepp frequency was significantly increased by 12%, but exposure to a 60‐Hz circular field did not significantly alter mepp frequency. Exposure to a 70‐Hz linear field did not significantly change mepp frequency, but application of a 70‐Hz circular field appears to decrease mepp frequency by 4%. These results indicate that both types of magnetic fields can alter mepp frequency, depending upon the frequency and configuration

ISSN:0197-8462    

DOI:10.1002/bem.2250070304

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe effects of in vivo ultrasound irradiation of the spleen on immunological functions were assessed with an in vitro natural killer (NK) cell cytotoxic assay. Anesthetized hamsters were exposed to 1 MHz ultrasound at intensity levels currently being used clinically for therapeutic diathermy and hyperthermia (1–5 W/cm2, for 500 sec with constant beam scanning). Hyperthermic levels in the spleen ranged from 38–43°C. Significant depression of natural killer (NK) cell activity was seen 4 h after spleen irradiation as compared to sham irradited and normal animals. A return towards normal levels was observed in experimental groups at 24 h after exposure. Sham and normal animals were not significantly different in NK activity, indicating no significant stress‐related immunosuppressive effects due to handling. Differential leukocyte counts taken for each exposure condition showed significant lymphopenia at 4, 8, and 16 h after exposure, near normal levels at 24 h, and complete recovery by 48 h. The number of circulating mononuclear cells at 4 h showed a dose‐related suppression as the exposure intensities were i

ISSN:0197-8462    

DOI:10.1002/bem.2250070305

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

年代:1986

数据来源: WILEY

摘要:

AbstractElectromagnetic fields can interact with biological tissue both electrically and mechanically. This study investigated the mechanical interaction between brain tissue and an extremely‐low‐frequency (ELF) electric field by measuring the resultant vibrational amplitude. The exposure cell is a section of X‐band waveguide that was modified by the addition of a center conductor to form a small TEM cell within the waveguide structure. The ELF signal is applied to the center conductor of the TEM cell. The applied ELF electric field generates an electrostrictive force on the surface of the brain tissue. This force causes the tissue to vibrate at a frequency equal to twice the frequency of the applied sinusoidal signal. An X‐band signal is fed through the waveguide, scattered by the vibrating sample, and detected by a phase‐sensitive receiver. Using a time‐averaging spectrum analyzer, a vibration sensitivity of approximately 0.2 nmp‐pcan be achieved. The amplitude of the brain tissue vibrational response is constant for vibrational frequencies below 50 Hz; between 50 and 200 Hz resonant phenomena were observed; and above 200 Hz the amplitude fall

ISSN:0197-8462    

DOI:10.1002/bem.2250070306

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

年代:1986

数据来源: WILEY

摘要:

AbstractWe have previously reported that exposing the vegetative plasmodia stage ofPhysarum polycephalumto either individual or simultaneously applied electric and magnetic fields (45–75 Hz, 0.14–2.0 G, and 0.035–0.7 V/m) lengthens their mitotic cycle, depresses their rate of reversible shuttle streaming, and lowers their respiration rate. In this article we report the effects of simultaneously applied electromagnetic fields (60 Hz, 1.0 G, 1.0 V/m), electric fields only (60 Hz, 1.0 V/m), magnetic fields only (60 Hz, 1.0 G) on the haploid amoeba ofPhysarumexposed for 120–180 days. Statistically significant depressions (about 8–11%) in ATP levels were observed with all field conditions; however, respiration was significantly decreased only when amoebae were subjected to either combined fields or electric fields alone. Magnetic fields alone failed to induce a significant decrease in re

ISSN:0197-8462    

DOI:10.1002/bem.2250070307

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

年代:1986

数据来源: WILEY

摘要:

AbstractLong‐Evans male adult rats were intermittently exposed for 14 weeks to continuous wave (CW) 2450‐MHz microwaves at an average power density of 2.5 mW/cm2. The mean specific absorption rate was 0.70 W/kg (± 0.02 SEM). The rats were exposed 7 h/day, 7 days/week in a radiation chamber with a monopole above ground, while housed in Plexiglas cages. Weekly measures of body mass and food intake did not indicate statistically significant effects of microwave irradiation. Assessments of threshold for electric‐footshock detection revealed a significant difference between microwave and sham‐exposed animals. Assessments of cholinesterase and sulfhydryl groups in blood and 17‐ketosteriods in urine did not distinguish the two groups of rats. Behavioral measures made at the end of the 14‐week exposure included an open‐field test, shuttlebox avoidance performance, and schedule‐controlled lever‐pressing for food pellets. Statistically significant differences between microwave‐ and sham‐exposed rats were observed for these measures. Examination of adrenal tissue, plasma electrolytes, and organ masses after 14 weeks of exposure revealed no difference between

ISSN:0197-8462    

DOI:10.1002/bem.2250070308

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

年代:1986

数据来源: WILEY

摘要:

AbstractAir ions and direct current (DC) electric fields have been reported to exert subtle behavioral and biological effects on rodents and humans. These effects often appear inconsistent, yet there have been few attempts to resolve these inconsistencies by experimental replication. Rats exposed to negatively or positively charged air ions over a wide range of concentrations and exposure periods have been reported to show alterations in their level of locomotor activity. In this study, locomotor activity of Sprague‐Dawley rats was quantified during exposure to either (1) unipolar air ions and DC fields of the same polarity or (2) DC fields alone. Both polarities were studied. Air ion concentrations were 5.0 × 103, DC fields were 3 kV/m, and exposures lasted 2, 18, or 66 h. In one experiment rats were exposed to DC fields of 12 kV/m. No exposure condition exerted any effect on locomotor activity or rearing behavior. In addition, no behavioral perturbations were observed after the onset of any of the exposure conditions, suggesting that the rats may have failed to detect the altered environme

ISSN:0197-8462    

DOI:10.1002/bem.2250070309

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

年代:1986

数据来源: WILEY

摘要:

AbstractRectal temperatures were recorded in mice and rats during exposure to a stationary 7.55 Tesla (1 T = 104Gauss) homogeneous magnetic field, and to magnetic field gradients ranging from 58.1–58.6 T/m. Contrary to observations reported recently by other investigators, no evidence was found for a change in the body temperature of rodents exposed to strong homogeneous or gradient magnetic field

ISSN:0197-8462    

DOI:10.1002/bem.2250070310

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

年代:1986

数据来源: WILEY

ISSN:0197-8462    

DOI:10.1002/bem.2250070311

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

年代:1986

数据来源: WILEY