High Intensity Microwave Irradiation Research Articles

The low density lipoprotein receptor is not necessary for maintaining mouse brain polyunsaturated fatty acid concentrations

The brain cannot synthesize n-6 or n-3 PUFAs de novo and requires their transport from the blood. Two models of brain fatty acid uptake have been proposed. One requires the passive diffusion of unesterified fatty acids through endothelial cells of the blood-brain barrier, and the other requires the uptake of lipoproteins via a lipoprotein receptor on the luminal membrane of endothelial cells. This study tested whether the low density lipoprotein receptor (LDLr) is necessary for maintaining brain PUFA concentrations. Because the cortex has a low basal expression of LDLr and the anterior brain stem has a relatively high expression, we analyzed these regions separately. LDLr knockout (LDLr(-/-)) and wild-type mice consumed an AIN-93G diet ad libitum until 7 weeks of age. After microwaving, the cortex and anterior brain stem (pons and medulla) were isolated for phospholipid fatty acid analyses. There were no differences in phosphatidylserine, phosphatidylinositol, ethanolamine, or choline glycerophospholipid esterified PUFA or saturated or monounsaturated fatty acid concentrations in the cortex or brain stem between LDLr(-/-) and wild-type mice. These findings demonstrate that the LDLr is not necessary for maintaining brain PUFA concentrations and suggest that other mechanisms to transport PUFAs into the brain must exist.

Estimation of the convulsive effect of cyanide in rats.

Convulsions are frequently observed in severe, acute cyanide intoxication. The mechanisms involved are not well known. In the present study, the convulsive effect of cyanide was examined in the rat by means of a dose threshold determination after infusion of cyanide. An optimal dose rate of 1.80 mg/min./kg was determined. By infusing this optimal dose rate it was possible to divide another cyanide-treated group of rats into two groups: one without and another with convulsions. After the experiment all animals were killed by exposure to high intensity microwave irradiation. Regional dopamine, noradrenaline and main dopamine metabolites were isolated and analyzed using high pressure liquid chromatography and electrochemical detection. Striatal noradrenaline was decreased but dopamine and its metabolites were increased in rats infused with cyanide at the optimal dose rate until the convulsions started. Animals infused with the threshold dose at the optimal dose rate did not show any significant changes in noradrenaline or in dopamine metabolites, but all animals showing convulsions also had increased striatal dopamine levels. Thus changes in dopamine appear to be dependent on convulsions.

In-Office Microwave Disinfection of Soft Contact Lenses

We evaluated the effectiveness of an in-office microwave disinfection procedure which allowed for the disinfection of up to 40 soft contact lenses at one time. Ciba AOSept cases filled with sterile unpreserved saline were contaminated with one of six FDA test challenge microorganisms at a concentration of approximately 10(3) colony forming units per milliliter (CFU/ml). Twenty cases were placed on the rotating plate of a standard 2450 MHz 650 W microwave oven in a 10-cm diameter circle. The cases were exposed to high intensity microwave irradiation for periods of 0 to 15 min. None of the 6 microorganisms evaluated survived 2 min or longer of microwave exposure. Our findings indicated that microwave irradiation can be a convenient, rapid, and effective method of disinfecting a number of soft contact lenses at one time and thus adaptable as an in-office soft contact lens disinfection procedure.

Dielectric loss microwave degradation of polymers: Cellulose

AbstractThe pyrolysis of organic waste polymers to produce fuels and chemicals is of interest to augment petroleum‐based processes. The wide variety of pyrolysis products of low yield and the uncertain role that heat transfer rate plays in determining these have been deterrents to utilization in the past. A possible approach to increased selectivity for products is to heat them rapidly and homogeneously with the aim of narrowing the product distribution. A very rapid means of homogeneous heat transfer throughout the substrate is microwave heating. A laboratory study has been done to determine what effect high‐intensity microwave energy has on the thermal degradative pathways of cellulose. The product distribution found when cellulose is pyrolyzed in the absence of a microwave discharge is similar to that found in conventional furnace pyrolysis. The major products are levoglucosan (27%), carbon dioxide (2–5%), water, and charred residue. However, the total heat‐up and reaction times for even large pellets are reduced to less than 2–3 min when high‐intensity microwave irradiation is employed. Effects of pressure and microwave power are reported. Low external gas temperature also prevents secondary reactions.

Effect of microwave irradiation on brain tissue structure and catecholamine distribution.

Recently we reported regional levels of norepinephrine and dopamine in rat brain following microwave irradiation. In our report, we also compared these levels with those of norepinephrine and dopamine following decapitation. Catecholamine levels following exposure to microwave irradiation significantly increased in several areas. However, whether these increases resulted from compound transfer associated with tissue disruption due to high intensity microwave irradiation was not determined. Sections of corpus striatum and locus coeruleus were examined with a light microscope and the interface of the striatum and the cortex showed no trace of tissue breakdown. Transformed cells, vacuolation, and indications of pyknotic degeneration in the nucleus were found in locus coeruleus after irradiation, but the shapes of these cells were well-defined. Electron microscopic photographs of synapses in the same area showed membrane damage after exposure for 5 s at 1.3 kW, but synaptic vesicles were clearly defined. It was concluded that the increased catecholamine levels were not the result of tissue disruption following rapid heating of the brain by irradiation.

The inactivation of rodent brain enzymes in vivo using high-intensity microwave irradiation

Exposure to high-intensity microwave irradiation is being widely used in neurobiology as a technique for simultaneously sacrificing animals and inactivating brain enzymes, thereby eliminating postmortem artifacts in many heat-stable substrates such as acetylcholine, L-DOPA, gamma aminobutyric acid, cyclic AMP, cyclic GMP, and certain components of the glycolytic pathway. This technique permits dissection of the brain into specific regions-a distinct advantage over quickfreezing methods of sacrifice. One disadvantage of using 2450 MHz is the requirement to immobilize the subject during sacrifice; this requirement might be eliminated at a lower frequency such as 986 MHz. To use the technique reliably the experimenter must monitor and control power source output and frequency, impedance matching with the load, and incident and reflected power. The experimenter must demonstrate the heat stability of the substrate to be measured and study the heat lability characteristics of the enzyme to be inactivated, demonstrating adequacy of inactivation. When the above requirements are met, the microwave enzyme inactivation technique has broad applicability in the neurosciences.

Comparison of Microwave Irradiation at 986 Versus 2450 MHz for In Vivo Inactivation of Brain Enzymes in Rats

The pattern of enzyme inactivation in the brains of rats sacrificed by exposure to high-intensity microwave irradiation at 2450 MHz in a closed-waveguide structure is markedly altered by rotation of the rat. At 986 MHz, the pattern is relatively insensitive to rotation. These data suggest that use of lower frequencies may reduce regional variability of enzyme inactivation and lessen the requirement for immobilization during sacrifice.

Brain temperature and enzyme histochemistry after high intensity microwave irradiation

Rats were subjected to different amounts of microwave irradiation generated by a commercially available apparatus especially designed for biological application. Brain temperature increased with increasing intensities of irradiation. Histochemically assessed telencephalic and mesencephalic acetylcholinesterase (AChE, EC 3.1.1.7) was inactivated for a considerable distance pericentrally by a microwave power level of 5.0 Kw applied for 0.5 second. With these parameters core brain temperature was 56° C, and neuronal somata in the red nucleus and other neural regions displayed pyknotic nuclei or compacted nucleolei, an inflated appearance, and decreased Nissl staining. AChE was completely inactivated by 1-second application of 5.0 Kw microwave power. At the same time brain temperature was 78° C, and, as after lower intensities of microwave irradiation, neuronal somata were hypochromic and inflated. NADH-diaphorase was less thermolabile than AChE. Because it more rapidly inactivates thermolabile brain enzymes, compared to freezing by immersion and chemical fixation protocols, microwave irradiation of neural tissue should become an increasingly important procedure in neurochemical studies.