The effects of hyperthermia and hyperthermia plus microwaves on rat brain energy metabolism

The effects of hyperthermia, alone and in conjunction with microwave exposure, on brain energetics were studied in anesthetized male Sprague-Dawley rats. The effect of temperature on adenosine triphosphate concentration [ATP] and creatine phosphate concentration [CP] was determined in the brains of rats that were maintained at 35.6, 37.0, 39.0, and 41.0 degrees C. At 37, 39, and 41 degrees C brain [ATP] and [CP] were down 6.0, 10.8, and 29.2%, and 19.6, 28.7, and 44%, respectively, from the 35.6 degrees C control concentrations. Exposure of the brain to 591-MHz radiation at 13.8 mW/cm2 for 0.5, 1.0, 3.0, and 5.0 min caused further decreases (below those observed for 30 degrees C hyperthermia only) of 16.0, 29.8, 22.5, and 12.3% in brain [ATP], and of 15.6, 25.1, 21.4, and 25.9% in brain [CP] after 0.5, 1.0, 3.0, and 5.0 min, respectively. Recording of brain reduced nicotinamide adenine dinucleotide (NADH) fluorescence before, during, and after microwave exposure showed an increase in NADH fluorescence during microwave exposure that returned to preexposure levels within 1 min postexposure. Continuous recording of brain temperatures during microwave exposures showed that brain temperature varied between -0.1 and +0.05 degrees C. Since the microwave exposures did not induce tissue hyperthermia, it is concluded that direct microwave interaction at the subcellular level is responsible for the observed decrease in [ATP] and [CP].     

Antibody responses of mice exposed to low-power microwaves under combined, pulse-and-amplitude modulation

Irradiation by pulsed microwaves (9.4 GHz, 1 microsecond pulses at 1,000/s), both with and without concurrent amplitude modulation (AM) by a sinusoid at discrete frequencies between 14 and 41 MHz, was assessed for effects on the immune system of Balb/C mice. The mice were immunized either by sheep red blood cells (SRBC) or by glutaric-anhydride conjugated bovine serum albumin (GA-BSA), then exposed to the microwaves at a low rms power density (30 microW/cm2; whole-body-averaged SAR approximately 0.015 W/kg). Sham exposure or microwave irradiation took place during each of five contiguous days, 10 h/day. The antibody response was evaluated by the plaque-forming cell assay (SRBC experiment) or by the titration of IgM and IgG antibodies (GA-BSA experiment). In the absence of AM, the pulsed field did not greatly alter immune responsiveness. In contrast, exposure to the field under the combined-modulation condition resulted in significant, AM-frequency-dependent augmentation or weakening of immune responses.     

Hematologic and immunologic effects of pulsed microwaves in mice

Mice were exposed in the far field in an anechoic chamber to 2,880-MHz pulsed microwaves 3 to 7.5 h daily, 5 days/week for 60 to 360 h. Three experiments were performed at average power densities of 5 mW/cm2 and six at 10 mW/cm2, corresponding to averaged specific absorption rates (SARs) of 2.25 and 4.50 mW/g, respectively. Each experiment consisted of eight mice, with a concurrently sham-exposed group of eight. In two of three studies at 5 mW/cm2, there was a significant increase in bone marrow cellularity in the microwave-exposed groups compared to the sham-exposed groups. Significant differences were occasionally seen in erythrocyte, leukocyte, and platelet values from microwave-exposed groups, but were not consistently observed. In one of six groups exposed at 10 mW/cm2, mean bone marrow cellularity was reduced significantly in the microwave-exposed mice; in another group, the lymphocyte count was increased. In only one exposure (10 mW/cm2 for 360 h) was any significant effect noted on serum proteins: a reduction to 5.1 +/- 0.3 g/dl in the exposed versus 5.6 +/- 0.4 g/dl in the sham-exposed mice. This was due to a decrease in alpha and beta globulins, with no effect on albumin or gamma globulin concentrations. No effect on bone marrow granulocyte/macrophage colony-forming units (CFU) was revealed following exposure of mice to pulsed microwaves at 5 mW/cm2. In one of four exposures at 10 mW/cm2, there was a significant increase in CFU-agar colonies. No significant effects of exposures at 10 mW/cm2 were observed on in vivo and in vitro assays of cell-mediated immune functions. No exposure-related histopathologic lesions were found from examination of several tissues and organs. Results of these series of exposures of mice at SARs of 2.25 and 4.50 mW/g indicated no consistent effects on the hematologic, immunologic, or histopathologic variables examined.     

Comparative effects of pulsed and continuous-wave 2.8-GHz microwaves on temporally defined behavior

The effects of pulsed-(PW) and continuous-wave (CW) 2.8-GHz microwaves were compared on the performance of rodents maintained by a temporally defined schedule of positive reinforcement. The schedule involved food-pellet reinforcement of behavior according to a differential-reinforcement-of-low-rate (DRL) contingency. The rats were independently exposed to PW and to CW fields at power densities ranging from 1 to 15 mW/cm². Alterations of normal performance were more pronounced after a 30-minute exposure to the PW field than to the CW field. The rate of emission of appropriately timed responses declined after exposure to PW at 10 and 15 mW/cm², whereas exposure at the same power levels to the CW field did not consistently affect the rate of responding. Change in performance associated with microwave exposure was not necessarily related to a general decline in responding: in some instances, increases in overall rates of responding were observed.     

Investigation of the effects of continuous-wave,pulse- and amplitude-modulated microwaves on single excitable cells of chara corallina

Single internodal excitable cells of Chara corallina were exposed to CW, pulse-modulated and sinusoidally modulated S-band microwave fields in a temperature-controled waveguide exposure chamber. All electrical measurements were made external to the waveguide (ie, under no impressed microwave field). The dependent variables measured before, during, and after exposure to the S-band microwave fields included: resting potential, amplitude of the action potential, rise and decay time of the action potential, conduction velocity, and excitability. Cells maintained at 22 ± 0.1 °C during exposure showed no consistent or statistically significant microwave-dependent alterations in any of the dependent variables.     

Alteration of life span of mice chronically exposed to 2.45 GHz CW microwaves

Female CD 1 mice were exposed from the thirty-fifth day of age for the remainder of their lives to 2.45 GHz, CW-microwave radiation at a power density of 3 or 10 m W/cm² (SAR = 2.0 or 6.8 W/kg). Exposures took place 1 h/day, 5 day/week in an anechoic chamber at an ambient temperature of 22 °C and a relative humidity of 50%. There were 25 animals in each exposure group, and an equal number of controls were concurrently sham exposed. The average life span of animals exposed at 10 mW/cm² was significantly shorter than that of sham-exposed controls (572 days vs. 706 days; P = .049; truncation >20%). In contrast, the average lifespan of the animals exposed at 3 mW/cm² was slightly, but not significantly, longer (738 days) than that of controls (706 days). © 1994 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Microwave effects on energy metabolism of rat brain

Rat brain was exposed to 591-MHz, continuous-wave (CW) microwaves at 13.8 or 5.0 mW/cm² to determine the effect on nicotinamide adenine dinucleotide, reduced (NADH), adenosine triphosphate (ATP) and creatine phosphate (CP) levels. On initiation of the in vivo microwave exposures, fluorimetrically determined NADH rapidly increased to a maximum of 4.0%–12.5% above pre-exposure control levels at one-half minute, then decreased slowly to 2% above control at three minutes, finally increasing slowly to 5% above control level at five minutes. ATP and CP assays were performed on sham- and microwave-exposed brain at each exposure time. At 13.8 mW/cm², brain CP level was decreased an average of 39.4%, 41.1%, 18.2%, 13.1%, and 36.4% of control at exposure points one-half, one, two three, and five minutes, respectively, and brain ATP concentration was decreased an average of 25.2%, 15.2%, 17.8%, 7.4%, and 11.2% of control at the corresponding exposure periods. ATP and CP levels of rat brain exposed to 591-MHz cw microwaves at 5 mW/cm² for one-half and one minute were decreased significantly below control levels at these exposure times, but were not significantly different from the 13.8 mW/cm² exposures. For all exposures, rectal temperature remained constant. Heat loss through the skull aperture caused brain temperature to decrease during the five-minute exposures. This decrease was the same in magnitude for experimental and control subjects. Changes in NADH, ATP, and CP levels during microwave exposure cannot be attributed to general tissue hyperthermia. The data support the hypothesis that microwave exposure inhibits mitochondrial electron transport chain function, which results in decreased ATP and CP levels in brain.     

Alteration of circulating antibody response of mice exposed to 9-GHz pulsed microwaves

A significant increase was observed in the circulating antibody titers of mice exposed to 9-GHz pulsed microwaves at an average power density of 10 mW/ cm², two hours per day for five days compared with sham-irradiated animals. The mice were previously immunized with type III pneumococcal polysaccharide. Following irradiation, a portion of the immunized animals were challenged with virulent ^{Streptococcus pneumoniae}, type III. Ten days after challenge, mortality was essentially the same in the two groups, but during the ten day period, there was a noticeable increase in the survival time of the irradiated animals compared with the sham-irradiated animals, suggesting that the increased circulating antibody response afforded some degree of temporary protection to the animals.     

Effect of 9.6-GHz pulsed microwaves on the orb web spinning ability of the cross spider (Araneus diadematus)

Eight cross spiders (Araneus diadematus) were exposed overnight (16 h) during web-building activity to pulsed 9.6-GHz microwaves at average power densities of 10, 1, and 0.1 mW/cm2 (estimated SARs 40, 4, and 0.4 mW/g). Under these conditions, 9.6-GHz pulsed microwaves did not affect the web-spinning ability of the cross spider.     

The differential effects of 200, 591, and 2,450 MHz radiation on rat brain energy metabolism

Three key compounds in brain energy metabolism have been measured during and after exposure to continuous wave radiofrequency radiation at 200, 591, and 2,450 MHz. Frequency-dependent changes have been found for all three compounds. Changes in NADH fluorescence have been measured on the surface of a surgically uncovered rat brain during exposure. At 200 and 591 MHz, NADH fluorescence increased in a dose-dependent manner between approximately 1 and 10 mW/cm2, then became constant at higher exposures. There was no effect at 2,450 MHz. Levels of ATP and CP were measured in whole brain after exposure. The ATP levels were decreased at 200 and 591 MHz but not at 2,450 MHz. The CP levels decreased only at 591 MHz. The effect of duration of exposure (up to 5 min) was investigated for all compounds at 200 MHz and 2,450 MHz, and exposures to 20 minutes were examined at 591 MHz. Temperature in the rat brain was essentially constant for all exposures. A general mechanism for inhibition of the mitochondrial electron transport chain and the CP-kinase reaction pathway by radiofrequency radiation has been proposed.     

Effects of continuous and pulsed 2450-MHz radiation on spontaneous lymphoblastoid transformation of human lymphocytes in vitro.

Normal human lymphocytes were isolated from the peripheral blood of healthy donors. One-ml samples containing (10(6)) cells in chromosome medium 1A were exposed for 5 days to conventional heating or to continuous wave (CW) or pulsed wave (PW) 2450-MHz radiation at non-heating (37 degrees C) and various heating levels (temperature increases of 0.5, 1.0, 1.5, and 2 degrees C). The pulsed exposures involved 1-microsecond pulses at pulse repetition frequencies from 100 to 1,000 pulses per second at the same average SAR levels as the CW exposures. Actual average SARs ranged to 12.3 W/kg. Following termination of the incubation period, spontaneous lymphoblastoid transformation was determined with an image analysis system. The results were compared among each of the experimental conditions and with sham-exposed cultures. At non-heating levels, CW exposure did not affect transformation. At heating levels both conventional and CW heating enhanced transformation to the same extent and correlate with the increases in incubation temperature. PW exposure enhanced transformation at non-heating levels. This finding is significant (P less than .002). At heating levels PW exposure enhanced transformation to a greater extent than did conventional or CW heating. This finding is significant at the .02 level. We conclude that PW 2450-MHz radiation acts differently on the process of lymphoblastoid transformation in vitro compared with CW 2450-MHz radiation at the same average SARs.     

In vitro study of microwave effects on calcium efflux in rat brain tissue

In this study we investigated the prospect of microwave-induced alteration of ⁴⁵Ca²⁺ efflux from rat neural tissue at low pulse repetition frequencies and low power densities under in vitro conditions. Rat cerebral tissue, preloaded with ⁴⁵Ca²⁺, was exposed to pulsed-microwave radiation (1-GHz carrier frequency) according to one of several PRF-power density exposure schemes: 16 Hz at 0.5, 1.0, 2.0, or 15 mW/cm², or 32 Hz at 1.0 or 2.0 mW/cm² average power density. Measurements of radioactivity in the efflux medium and in the tissue sample were used to calculate an efflux value for each sample. The results indicate that the radiation conditions used did not alter calcium efflux in rat brain tissue.     

Tests of mutagenesis and reproduction in male rats exposed to 2,450-MHz (CW) microwaves

Tests of mutagenesis and reproduction were conducted in male rats which were irradiated by 2,450-MHz, continuous-wave (CW) microwaves, 4 hr/day from day 6 of gestation to 90 days of age at 5 mW/cm²; or 5 hr/day for five days beginning on the 90th day of age at 10 mW/cm²; or 4 hr/day, 5 days/ wk for four weeks, beginning on the 90th day of age. During selected weekly periods after treatment, the rats were bred to pairs of untreated, normal female rats that were examined in late pregnancy by means of the dominant lethal assay. The reproductive efficiency of these males, as reflected in their breeding, was also examined for changes relating to their microwave experience. No significant evidence of germ-cell mutagenesis was detected when data of microwave-exposed males were compared with those of sham-exposed males, even though there were significant increases in rectal and intra-testicular temperatures at a power density of 28 mW/cm². Temporary sterility, as indexed by fewer pregnancies, was seen at the highest power density.     

Effects of acute low-level microwaves on pentobarbital-induced hypothermia depend on exposure orientation

Two series of experiments were performed to study the effects of acute exposure (45 min) to 2,450-MHz circularly polarized, pulsed microwaves [1 mW/cm², 2-μs pulses, 500 pps, specific absorption rate (SAR) 0.6 W/kg] on the actions of pentobarbital in the rat. In the first experiment, rats were irradiated with microwaves and then immediately injected with pentobarbital. Microwave exposure did not significantly affect the extent of the pentobarbital-induced fall in colonic temperature. However, the rate of recovery from the hypothermia was significantly slower in the microwave-irradiated rats and they also took a significantly longer time to regain their righting reflex. In a second experiment, rats were first anesthetized with pentobarbital and then exposed to microwaves with their heads either pointing toward the source of microwaves (anterior exposure) or pointing away (posterior exposure). Microwave radiation significantly retarded the pentobarbital-induced fall in colonic temperature regardless of the orientation of exposure. However, the recovery from hypothermia was significantly faster in posterior-exposed animals compared to those of the anterior-exposed and sham-irradiated animals. Furthermore, the posterior-exposed rats took a significantly shorter time to regain their righting reflex than both the anterior-exposed and sham-irradiated animals.     

Inter-beat intervals of cardiac-cell aggregates during exposure to 2.45 GHz CW,pulsed, and square-wave-modulated microwaves

Inter-beat intervals of aggregated cardiac cells from chicken embryos were studied during 190 s exposures to 2.45 GHz microwaves in an open-ended coaxial device. Averaged specific-absorption rates (SARs) and modulation conditions were 1.2–86.9 W/kg continuous-wave (CW). 1.2–12.2 W/kg pulse modulation (PW, duty cycle ∽ 11%). and 12.0–43.5 W/kg square-wave modulation (duty cycle = 50%). The inter-beat interval decreased during microwave exposures at 42.0 W/kg and higher when CW or square-wave modulation was used, which is consistent with established effects of elevated temperatures. However, increases in the inter-beat interval during CW exposures at 1.2–12.2 W/kg, and decreases in the inter-beat interval after PW exposures at 8.4–12.2 W/kg. are not consistent with simple thermal effects. Analysis of variance indicated that SAR. modulation, and the modulation-SAR interaction were all significant factors in altering the interbeat interval. The latter two factors indicated that the cardiac cells were affected by athermal as well as thermal effects of microwave exposure. © 1993 Wiley-Liss. Inc.     

Glutamate metabolism in cerebral mitochondria after ischemia and post‐ischemic recovery during aging: relationships with brain energy metabolism

Glutamate is involved in cerebral ischemic injury, but its role has not been completely clarified and studies are required to understand how to minimize its detrimental effects, contemporarily boosting the positive ones. In fact, glutamate is not only a neurotransmitter, but primarily a key metabolite for brain bioenergetics. Thus, we investigated the relationships between glutamate and brain energy metabolism in an in vivo model of complete cerebral ischemia of 15 min and during post‐ischemic recovery after 1, 24, 48, 72, and 96 h in 1‐year‐old adult and 2‐year‐old aged rats. The maximum rates (V _max) of glutamate dehydrogenase (GlDH ), glutamate‐oxaloacetate transaminase, and glutamate‐pyruvate transaminase were assayed in somatic mitochondria (FM ) and in intra‐synaptic ‘Light’ mitochondria and intra‐synaptic ‘Heavy’ mitochondria ones purified from cerebral cortex, distinguishing post‐ and pre‐synaptic compartments. During ischemia, none of the enzymes were modified in adult animals. In aged ones, glutamate‐oxaloacetate transaminase was increased in FM and GlDH in intra‐synaptic ‘Heavy’ mitochondria, stimulating glutamate catabolism. During post‐ischemic recovery, FM did not show modifications at both ages while, in intra‐synaptic mitochondria of adult animals, glutamate catabolism was increased after 1 h of recirculation and decreased after 48 and 72 h, whereas it remained decreased up to 96 h in aged rats. These results, with those previously published about Krebs’ cycle and Electron Transport Chain (Villa et al ., [2013] Neurochem. Int . 63, 765–781), demonstrate that: (i) V _max of energy‐linked enzymes are different in the various cerebral mitochondria, which (ii) respond differently to ischemia and post‐ischemic recovery, also (iii) with respect to aging.

     

Regional cerebral energy metabolism in bicuculline induced seizures

In order to assess the early regional changes in energy metabolism in bicuculline induced seizures, mice were injected and sacrificed before the onset of overt seizure activity, and shortly after clonic-tonic seizures began. The energy metabolites glucose, ATP, and phosphocreatine were measured in layers of the motor cortex and the cerebellar vermis. Results showed minimal metabolite changes in the cerebellum, whereas changes in energy metabolism in the motor cortex were largely localized to the layers containing pyramidal cells. These results are in agreement with previous studies showing a relative sparing of the cerebellum, and suggest early cortical changes occur in pyramidal cells.     

Effect of chronic hypernatremic dehydration and rapid rehydration on brain carbohydrate, energy, and amino acid metabolism in weanling mice

Abstract: This is a study of the effects of chronic hypernatremic dehydration and rehydration on carbohydrate, energy, and amino acid metabolism in the brains of weanling mice. Chronic hypernatremic dehydration induced by 4 days of water deprivation and salt loading was associated with severe weight loss (no other observed clinical effects), increased brain Na⁺ levels, and a decreased brain water content. Changes in the concentrations of brain glucose, glycolytic and citric acid cycle metabolic intermediates, and phosphocreatine were compatible with reduced cerebral metabolic rate. In adaptation to chronic hypernatremia, there was a significant increase in the content of the measured brain amino acids. Rapid rehydration over a 4-h period with 2.5% dextrose in water returned plasma Na⁺ levels and brain Na⁺ and water contents to normal. After rehydration, metabolites were altered in a manner consistent with increased fluxes through the glycolytic pathway and citric acid cycle; the brain glycogen content almost tripled. Brain taurine and glutamine levels were not lowered by rehydration, and the total content of the measured amino acids in brain was still significantly higher than in controls. We speculate that these metabolic perturbations may relate to the development of cerebral edema and seizures or coma following rapid rehydration of humans with chronic hypernatremic dehydration.     

The role of coherence time in the effect of microwaves on ornithine decarboxylase activity

Previously, we demonstrated the requirement for a minimum coherence time of an applied, small amplitude (10 μT) ELF magnetic field if the field were to produce an enhancement of ornithine decarboxylase activity in L929 fibroblasts. Further investigation has revealed a remarkably similar coherence time phenomenon for enhancement of ornithine decarboxylase activity by amplitude-modulated 915 MHz microwaves of large amplitude (SAR 2.5 W/kg). Microwave fields modulated at 55, 60, or 65 Hz approximately doubled ornithine decarboxylase activity after 8 h. Switching modulation frequencies from 55 to 65 Hz at coherence times of 1.0 s or less abolished enhancement, while times of 10 s or longer provided full enhancement. Our results show that the microwave coherence effects are remarkably similar to those observed with ELF fields. © 1993 Wiley-Liss. Inc.     

Simulated biological effects of microgravity on phospholipid and energy metabolism of chicken embryonic brain cells studied by 31P-NMR spectroscopy

Levels of phosphomonoester (PME), phosphodiester (PDE), ATP and pH in brain cells of chicken embryos rotated for 24 h in a clinostat during the period of hatching the 13th day (E13) and 15th day (E15) embryos were investigated by using 31P-NMR spectroscopy. Significant increases in the values of PME, ATP and pH were identified after E13 rotating for 24 h. With the same treatment, differences were obtained in the phospholipid and energy metabolism of E15, but no significant levels have been reached . The calorimetric assay (malachite green method) was used for measuring the activity of total ATPase. A dramatic decrease was evident in the activity of ATPase in brain cells of rotated E13 and E15. The former is more sensitive than the latter. All the levels mentioned above could restore in 24 h after the rotation stopped, except that the level of ATP was still higher than the control.