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PubMed1994

Rhesus monkey behavior during exposure to high-peak-power 5.62-GHz microwave pulses.

Limits on the exposure to high-peak-power, short-duration microwave pulses have only recently been adopted. Additional data, however, are needed to understand the effects that may be produced by exposure to high-peak-power pulsed microwaves. Four male rhesus monkeys (Macaca mulatta) were trained on an operant task for food pellet reward to investigate the behavioral effects of very high-peak-power 5.62 GHz microwaves. The operant task required monkeys to pull one plastic lever on a variable interval schedule (VI-25 s) and then respond to color signals and pull a second lever to obtain food. The monkeys were conditioned to perform a color discrimination task using one of three colors displayed by a fiber-optic cable. A red signal was the discriminative stimulus for responding on the first lever. A response on the second lever when a green signal was presented (1 s duration) delivered a food pellet. If a response on the second lever was made in the presence of a white signal, a 30-s timeout occurred. While performing the behavioral task, the monkeys were exposed to microwave pulses produced by either a military radar (FPS-26A) operating at 5.62 GHz or the same radar coupled to a Stanford linear energy doubler (SLED) pulse-forming device (ITT-2972) that enhanced peak power by a factor of nine by adding a high power pulse to the radar pulse. The effects of both types of pulses were compared to sham exposure. Peak field power densities tested were 518, 1270, and 2520 W/cm2 for SLED pulses and 56, 128, and 277 W/cm2 for the radar pulses. The microwave pulses (radar or SLED) were delivered at 100 pps (2.8 microseconds radar pulse duration; approximately 50 ns SLED pulse duration) for 20 min and produced averaged whole-body SARs of 2, 4, or 6 W/kg. Compared to sham exposures, significant alterations of lever responding, reaction time, and earned food pellets occurred during microwave exposure at 4 and 6 W/kg but not at 2 W/kg. There were no differences between radar or SLED pulses in producing behavioral effects.

Analysis of Variance↗

PubMed1995

Microwave influence on the isolated heart function: II. Combined effect of radiation and some drugs.

The combined effects of microwave radiation and some drugs were studied in an isolated frog auricle preparation. The experiments established that exposure to pulse-modulated 915 MHz microwaves for up to 40 min had no effect on either the rate or the amplitude of spontaneous auricle twitches, unless the average absorbed power was high enough to produce preparation heating. Treatment of the preparation with saline containing (0.6-3.0) 10(-5) M of propranolol or (0.5-1.5) 10(-7) M of atropine altered neither its pacemaker nor its contractile functions; these drugs also had no effect when they were combined with nonthermal microwave irradiation. Caffeine (1 mM) strongly increased the average heart power, which was calculated as the product of twitch rate and amplitude. The caffeine effect appeared to be significantly augmented (by about 15%, P < 0.02) under exposure to burst-type pulsed microwaves (pulse width, 1.5 msec; pause, 2.5 msec; 8 pulses/burst, 16 bursts/s; average SAR, 8-10 W/kg). By itself, this modulation was not effective; the heating of the preparation and saline during exposure was approximately 0.1 degrees C, which could not account for the detected changes. The experimental results demonstrate that caffeine treatment increases the microwave sensitivity of the frog auricle preparation and reveals primarily subthreshold, nonthermal microwave effect.

Animals↗

PubMed1991

Microwave energy fixation of plant tissue: an alternative approach that provides excellent preservation of ultrastructure and antigenicity.

Immunocytochemical techniques are confronted with the problem of obtaining adequate tissue preservation together with retention of protein antigenicity. Various methods, including freeze-drying and freeze-substitution, have been devised to circumvent this problem. In the present study, we report that microwave energy used in combination with low concentrations of glutaraldehyde (0.1%) and paraformaldehyde (2%) preserved the structural integrity of plant tissue and antigenicity of proteins. Tobacco leaf samples fixed in a time as brief as 15-20 s exhibited excellent preservation of fine structures. By contrast, specimens irradiated for shorter (5-10 s) or longer (30-40 s) periods showed poor morphological preservation. Microwave irradiation for 15-20 s was found useful for immobilizing large amounts of soluble antigens. The fast microwave fixation method was successfully used to preserve pathogenesis-related (PR) proteins, which were subsequently localized by a postembedding immunogold procedure. In addition to soluble antigens, cellulose subunits and pectic substances, two major plant cell wall components, were found to be highly preserved in microwave-irradiated tobacco plant tissue. The present study demonstrates that microwave fixation of plant tissue is a simple and inexpensive method that is easy to perform with commercially available microwave ovens. The incubation time for fixation is reduced from 2 h to 15-20 s without loss of fine structural details. This method will undoubtedly acquire increasing applicability and relevance in plant biology.

Antigens↗

PubMed1995

Microwave fixation: understanding the variables to achieve rapid reproducible results.

The use of microwave irradiation for rapid chemical fixation of tissues in electron microscopy is a subject of current interest. The effects of water load size and location, sample placement in the oven cavity (hot or cold spots), and time on tissue preservation were examined. The use of a microwave container (4 dram vial) encased in 60 ml of ice in a 100 ml polyethylene beaker and a 0% power setting between two 100% power settings (time interval) provided reliable control of temperature during microwave irradiation. High brightness neon lights provided a quick and easy method to identify and map hot and cold spots within the oven cavity. Using microwave irradiation for rapid glutaraldehyde and osmium tetroxide fixation of tissues (Pacific yew needle and mouse kidney and liver) for electron microscopy yielded preservation equal or better than routine immersion fixation when a time interval, a cold spot (as the sample location), and an ice-encased vial were used during microwave fixation. These adaptations provided reliable control of fixation conditions in an 800 watt laboratory microwave oven.

Animals↗

PubMed2005

Assessment of microwave-assisted enzymatic digestion by measuring glycated hemoglobin A1c by mass spectrometry.

Enzymatic digestion of proteins and analysis of the resulting peptides by mass spectrometry is an established approach in proteomics and in clinical and environmental chemistry. The long digestion times of several hours prevent the fast turnover of samples and results. Qualitative applications showed that microwave radiation profoundly shortens enzymatic digestion. However, its usefulness for quantitative applications had not been assessed. In this study, the microwave-assisted enzymatic digestion of hemoglobin at different temperatures, buffer concentrations, and digestion times was assessed and compared with conventional digestion for the proteolytic enzymes trypsin and Glu-C. A microwave-assisted enzymatic digestion method optimized for digestion time and temperature was applied for the analysis of glycated hemoglobin HbA1c and compared with a reference method. Using trypsin, complete digestion was obtained at 50 degrees C within 20 min. Under these conditions, the digestion efficiency was 20% higher than with conventional trypsin digestion. These effects were not observed with Glu-C as enzyme, probably because of the decreased stability of Glu-C at elevated temperatures in comparison with the trypsin used. The comparison of the optimized microwave-assisted digestion method using trypsin with the reference method for HbA1c using Glu-C gave a close correlation in the results (R2: 0.996). A significant bias of 0.33% HbA1c was observed, with higher values obtained with the microwave-assisted tryptic digest; this finding might have resulted from the use of a different enzyme. This study showed that microwave-assisted enzymatic digestion can substantially reduce digestion times to minutes and can be used in qualitative as well as quantitative applications.

Catalysis↗

PubMed2002

Microwave-assisted protein staining: mass spectrometry compatible methods for rapid protein visualisation.

The effects of microwave irradiation on the staining of electrophoresed and electroblotted proteins have been assessed using currently available detection methods. Although the absorption of microwave radiation was found to be uneven, band intensity following microwave-assisted protein staining (MAPS) was comparable and in some cases exceeded the intensity of the bands visualised by the original staining methods. It was found that microwave treatment drastically reduced the duration of the staining protocols for visualisation of the proteins separated by both one- and two-dimensional electrophoresis. Application of MAPS methods did not affect peptide mass fingerprinting analysis by mass spectrometry and subsequent identification of the protein by database searching. The peptide mass maps corresponding to the proteins visualised using both the conventional and MAPS methods did not show significant difference in signal/noise ratio. Moreover, it appeared that microwave treatment of the gels resulted in the increased recovery of the peptides following in-gel trypsin digestion. Briefly, microwave-assisted protein staining methods were rapid, compatible with mass spectrometry and were equally effective on thin (0.75-mm) and thick (1.5-mm) gels (such as those used in 2D electrophoresis).

DNA Fingerprinting↗

PubMed1997

Novel microwave technology for cryopreservation of biomaterials by suppression of apparent ice formation.

Ice formation inside or outside cells has been proposed to be a factor causing cryoinjury to cells/tissues during cryopreservation. How to control, reduce, or eliminate the ice formation has been an important research topic in fundamental cryobiology. The objective of this study was to test a hypothesis that the coupled interaction of microwave radiation and cryoprotectant concentration could significantly influence ice formation and enhance potential vitrification in cryopreservation media at a relative slow cooling rate. Test samples consisted of a series of solutions with ethylene glycol (a cryoprotectant) concentration ranging from 3 to 5.5 M. A specific microwave resonant cavity was built and utilized to provide an intense oscillating electric field. Solutions were simultaneously exposed to this electric field and cooled to -196 degrees C by rapid immersion in liquid nitrogen. Control samples were similarly submerged in liquid nitrogen but without the microwave field. The amount of ice formation was determined by analysis of digital images of the samples. The morphology of the solidified samples was observed by cryomicroscopy. It was found that ice formation was greatly influenced by microwave irradiation. For example, ice formation could be reduced by roughly 56% in 3.5 M ethylene glycol solutions. An average reduction of 66% was observed in 4.5 M solutions. Statistical analysis indicated that the main effects of microwave and ethylene glycol concentration as well as the interaction between these two factors significantly (P < 0.01) influenced ice formation amount, confirming the hypothesis. This preliminary study suggests that a combined use of microwave irradiation and cryoprotectant might be a potential approach to control ice formation in cells/tissues during the cooling process and to enhance vitrification of these biomaterials for long-term cryopreservation.

Cryopreservation↗

PubMedDate not supplied

Microwave-stimulated incubation in immunoelectron microscopy: a quantitative study.

Microwave irradiation has been applied to reduce the immunogold staining time of ultrathin sections of Lowicryl embedded specimens. Labelling has been stimulated by microwave irradiation during incubation with 10 nm colloidal gold particles coated with either goat anti-mouse antibodies (GaM-gold) or goat anti-rabbit antibodies (GaR-gold) and has been compared with control incubations. Quantification has been performed on cytoplasmic membranes or lysosomes labelled with a primary antibody. Counting the gold particles over specific and non-specific sites in electron micrographs and electron microscopic images by IBAS 2000 revealed that irradiation of 25 microliters droplets both at 80 W and 150 W resulted in an accelerated immunogold labelling, while the non-specific background levels were not increased. A plateau level in immunogold labelling intensity was reached after 25 min incubation under microwave irradiation at 150 W as compared to 120 min incubation without microwaves. No improvement in localization sharpness of immunogold labelling on membranes was achieved by microwave irradiation. The microwave-mediated acceleration of immunogold staining may be considered as an example of a staining method with a restricted thermal action on microvolumes as indicated by direct temperature measurements using a fibre-optic thermometer.

Antibodies, Monoclonal↗

PubMedDate not supplied

Preservation of structure and cytochemical reactivity at the ultrastructural level, using microwave irradiation.

The application of microwave irradiation at various steps in 'normal' EM procedures has been investigated. 1. The temperatures in various aqueous volumes were measured during microwave irradiation. Increases were small and the final temperature could be controlled by cooling the glass base plate. 2. The influence of microwave irradiation on the various fixation schedules for the electron microscopy of single cell populations was studied and the results favoured the idea that by the application of microwave irradiation a more life-like ultrastructural preservation could be obtained. 3. Peroxidase-like activity in erythrocytes, acid phosphatase activity in resident macrophages and peroxidase activity in monocyte granules was apparently not influenced by microwave irradiation during aldehyde fixation and incubation. 4. The anticipated microwave-induced penetration enhancement of cerium ions in a cytochemical reaction procedure to detect acid phosphatase activity in resident macrophages was not observed.

Acid Phosphatase↗

PubMedDate not supplied

Notes on the application of microwaves in histopathology.

In this article two applications of microwaves in histopathology, microwave-stimulated staining of tissue sections and microwave-stimulated fixation of cryostat sections, are reviewed. For a good understanding of the influence of microwaves on physico-chemical processes like staining and fixation the relevant physics are included. Major advantages of microwave techniques are speed and/or improved quality. The cryostat-microwave technique appears to be well-suited for the demonstration of intermediate filament proteins: the sensitivity of monoclonal antibodies directed against keratins and vimentin can be substantially increased using the ethanol based fixative Kryofix.

Histocytochemistry↗

PubMedDate not supplied

A practical approach to routine immunostaining of paraffin sections in the microwave oven.

The Streptavidin-Biotin Complex (SABC) Immunostaining method can be carried out by performing the rinsing and blocking steps and in addition the incubation with the primary and the secondary antibody sera in the microwave oven. Irradiation of the Streptavidin-Biotin Complex reduces stain activity due to destruction of horseradish peroxidase (HRP) (Boon & Kok, 1988). Therefore, we decided not to perform this step in the microwave oven. The microwave incubations can be performed using antisera dilutions of 1:1000 (instead of 1:50) in tissue fixed with Kryofix, allowing staining in staining racks. This keeps hands-on time low and simplifies the microwave steps. It is very difficult to obtain reproducible results in the microwave oven using droplet incubations due to problems with hot spots and antenna effects. These problems are avoided when cuvettes are used and air is blown through the solutions during microwave incubations. With effective temperature control the method is highly reproducible, and takes at least 100 min less than the conventional SABC method. It is, in particular, attractive when large series of slides must be routinely immunostained and when reproducible results are desired.

Antibodies↗

PubMed1991

Effect of chronic microwave radiation on T cell-mediated immunity in the rabbit.

Experiments were conducted to elucidate the effects of chronic low power-level microwave radiation on the immunological systems of rabbits. Fourteen male Belgian white rabbits were exposed to microwave radiation at 5 mW/cm2, 2.1 GHz, 3 h daily, 6 days/week for 3 months in two batches of 7 each in specially designed miniature anechoic chambers. Seven rabbits were subjected to sham exposure for identical duration. The microwave energy was provided through S band standard gain horns connected to a 4K3SJ2 Klystron power amplifier. The first batch of animals were assessed for T lymphocyte-mediated cellular immune response mechanisms and the second batch of animals for B lymphocyte-mediated humoral immune response mechanisms. The peripheral blood samples collected monthly during microwave/sham exposure and during follow-up (5/14 days after termination of exposures, in the second batch animals only) were analysed for T lymphocyte numbers and their mitogen responsiveness to ConA and PHA. Significant suppression of T lymphocyte numbers was noted in the microwave group at 2 months (P less than 0.01, delta % 21.5%) and during follow-up (P less than 0.01, delta % 30.2%). The first batch animals were initially sensitised with BCG and challenged with tuberculin (0.03 ml) at the termination of microwave irradiation/sham exposure and the increase in foot pad thickness (delta mm), which is a measure of T cell-mediated immunity (delayed type hypersensitivity response, DTH) was noted in both the groups. The microwave group revealed a better response than the control group (delta % +12.4 vs. +7.54). The animals were sacrificed and the tissue T lymphocyte counts (spleen and lymph node) were analysed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1979

The effect of environmental temperature and average dose rate of microwave radiation on the oxygen-consumption rate of mice.

The oxygen consumption rate of CF1 male mice was determined before, during, and after sham- and microwave-irradiation at environmental temperatures of 20 degrees C, 24 degrees C, 30 degrees C, and 35 degrees C, relative humidity of 55%, and air flow rate of 78 ml/min. Five forward power levels ranging from 0.09 to 3.3 W, which resulted in corresponding average dose rates ranging from 1.2 to 45.1 mW/g were used. The values of the oxygen consumption rate were converted to those of the specific metabolic rate (SMR). The result indicates that with high levels of microwave dosing (greater than 10 mW/g) the specific metabolic rate of mice decreased in some cases, in the environmental temperatures of 20 degrees C and 24 degrees C. However, the decreased SMR values were not lower than the SMR values of the sham-irradiated group in 30 degrees C. In the case of 35 degrees C, the high level dosing with microwave radiation caused increases in the SMR value over the sham value. A possible trend towards increased SMR value during and after irradiationwith low level (1.6 mW/g) microwave radiation in the environmental temperatures of 24 degrees C and 30 degrees C suggests further experiments with low level microwave radiation to determine possible effects of low level microwave radiation in stimulating increases in specific metabolic rate.

Animals↗

PubMed1981

Influence of CW microwave radiation on in vitro release of enzymes from retinol- treated hepatic lysosomes.

Hepatic lysosomes were exposed in vitro to microwave radiation (2450 MHz) either prior to or simultaneously with treatment with retinol (vitamin A), and the release of the lysosomal enzymes, beta-glucuronidase, acid phosphatase, and cathepsin D, determined. A 60-min microwave exposure (10 or 100 mW/g) of retinol-treated lysosomes had no effect on the amount of release of beta-glucuronidase, cathepsin D, or acid phosphatase. In addition, 10 and 100 mW/g irradiation of lysosome fractions for 40 min prior to a 20-min retinol and microwave treatment, had no influence on the release of these enzymes. Finally, the effect of microwave radiation on the loss of latency of acid phosphatase and beta-glucuronidase from retinol-treated lysosomes was determined. Microwave radiation had no influence on the rate of appearance of these enzymes in the suspending medium. The results indicate that microwave radiation had no effect on the retinol-induced lysosomal enzyme release.

Acid Phosphatase↗

PubMed2005

Development of heating method by microwave for sterilization of bone allografts.

The purpose of this study was to develop a disinfection method using a microwave apparatus to treat large bone allografts. Heating of a bone allograft is an effective method for the disinfection of bacteria or inactivation of viruses. However, the size of the bone we can treat is limited, and following the popular method of using a bathtub is a lengthy process. The experimental system described here was designed using a microwave oven, an optical-fiber thermometer, and a power regulator. Large and small specimens, a femoral head, and a metatarsal were harvested from a bovine femur. The influence of size and the electrical or thermal characteristics of the specimens were assessed regarding temperature distribution after microwave irradiation. The effects of humidity or hot-air supply were also assessed. The average temperature of the bovine femoral head became 80 degrees C throughout the 15 min of microwave irradiation, although the temperature in the metatarsal did not attain uniformity. Microwave irradiation with a hot-air supply realized a uniform distribution of temperature at 83.0 degrees +/- 0.4 degrees C in the metatarsal within 15 min. Use of microwave irradiation enables quick heating for disinfection of large allograft bones when a hot-air supply was used as well.

Animals↗

PubMed1995

Microwave ablation of canine atrial tachycardia induced by aconitine.

We tested the efficacy of microwave-frequency energy for ablating atrial tachycardia in eight open-chest dogs. Five other dogs served as controls. Atrial tachycardia was induced by direct application of aconitine crystals to the epicardial atrial surface or by injection of aconitine solution (0.15 mg/ml) into the right or left atrial myocardium. Atrial tachycardias (n = 15) developed at a cycle length of 253 +/- 64 msec or within 245 +/- 116 sec after topical application or injection of aconitine. Catheter ablation was attempted on 10 atrial tachycardias in 8 experiment dogs by using continuous, unmodulated microwave energy from a 915 MHz frequency signal generator via a 7F helical or whip antenna catheter. Successful ablation was defined as conversion of atrial tachycardia to sinus rhythm during delivery of microwave energy and maintenance of sinus rhythm for > 5 minutes after termination of energy delivery. All 10 atrial tachycardias were successfully ablated by 2.3 +/- 1.6 applications of microwave energy for each atrial tachycardia induced. Forward microwave power level was 50.5 +/- 8.1 W, and the duration of energy application was 25.0 +/- 27.6 seconds. Sinus rhythm resumed 9.5 +/- 9.2 seconds after the onset of microwave energy application. After a mean follow-up of 10.4 minutes, seven atrial tachycardias recurred, most likely the result of diffusion of aconitine beyond the perimeter of rhe ablation lesions. Atrial tachycardia did not recur in 3 of 3 dogs that had larger ablation lesion. Gross examination revealed 10 demarcated round or oval transmural lesions in the right or left atrium, ranging from 12.6 to 105.6 mm2 in area.(ABSTRACT TRUNCATED AT 250 WORDS)

Aconitine↗

PubMed1993

Design of a microwave system for endoscopy: an experimental study of energy, tissue contact, and hemostatic efficacy.

BACKGROUND: A microwave generator and delivery system for endoscopic use was built. Using a 650-W, 2450-MHz magnetron, 0-160 W were generated from the tip of a 180-cm flexible coaxial cable (2.1 mm diameter). METHODS: Three methods of achieving hemostasis with microwaves were identified studying standard bleeding canine ulcers: (1) interstitial method: inserting the coaxial tip into the tissue and heating slowly until bleeding stopped; (2) contact method: tip held in contact, light pressure applied; (3) noncontact method: microwave-induced sparking (dielectric breakdown) with tip held 1 mm from tissue. RESULTS: Studies of optimal energy levels for hemostasis showed that high power (70 W) noncontact methods required significantly less energy to stop bleeding than contact or interstitial methods. The noncontact method was more effective than the contact method, stopping 20 of 20 bleeding ulcers vs. 10 of 20 (P < 0.001) and was more rapidly effective causing less tissue damage (P < 0.05) than the interstitial method. CONCLUSIONS: In a randomized comparison using a non-contact method, microwave coagulation was superior (P < 0.001) to a polidocanol 1% + adrenaline 1:10,000 injection and control treatment stopping 40 of 40 vs. 0 of 20 and 0 of 20 standard bleeding ulcers. Microwaves stopped bleeding from 10 of 10 severed mesenteric vessels, whereas injection was ineffective (0 of 10, P < 0.001). Microwaves look promising for hemostasis at flexible endoscopy.

Animals↗

PubMed1996

A novel method of microwave treatment for detection of cytoplasmic and nuclear antigens by flow cytometry.

Flow cytometry has recently become a useful technique for the quantitative analysis of cytoplasmic and nuclear antigens. We report here a rapid, simple, reproducible, and sensitive method for the simultaneous detection of cytoplasmic and nuclear antigens by flow cytometry. This technique involves the treatment of cell suspensions with 60 s of microwave oven heating after fixation with 2% paraformaldehyde. Following this treatment a number of cytoplasmic and nuclear antigens were detected on the human myelomonocytic cell line U937 (CD68, PCNA and Ki-67), peripheral blood leukocytes from both normal donors and leukemia patients (CD68, lipocortin-1 and PCNA) and a rat mesangial cell line 1097 (desmin, alpha-smooth muscle actin) using a standard indirect immunofluorescent staining with mouse monoclonal antibodies (mAbs). There are several advantages of this technique over the routinely used methods currently available. Firstly, microwave treatment is a rapid, simple, and reproducible method, which largely reduces both time and cost expenditure, and makes this technique widely available for flow cytometric analysis in many areas of diagnostic and research purposes. Secondly, microwave treatment produces optimal results for simultaneous detection of both cytoplasmic (CD68, lipocortin-1, desmin, alpha-smooth actin) and nuclear (PCNA, Ki67) antigens. Thirdly, microwave treatment also produces a discrete profile for DNA content analysis. Finally, microwaving retains a clear discrimination between cells and debris as measured by light scatter. This study demonstrates that microwave treatment is a powerful technique which will be particularly applicable to flow cytometric analysis in the detection of many cytoplasmic and nuclear antigens.

Animals↗