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Background: Cosmic radiation exposures have been found to elicit cognitive impairments involving a wide-range of underlying neuropathology including elevated oxidative stress, neural stem cell loss, and compromised neuronal architecture. Cognitive impairments have also been associated with sustained microglia activation following low dose exposure to helium ions. Space-relevant charged particles elicit neuroinflammation that persists long-term post-irradiation. Here, we investigated the potential neurocognitive benefits of microglia depletion following low dose whole body exposure to helium ions., Methods: Adult mice were administered a dietary inhibitor (PLX5622) of colony stimulating factor-1 receptor (CSF1R) to deplete microglia 2 weeks after whole body helium irradiation ( 4 He, 30 cGy, 400 MeV/n). Cohorts of mice maintained on a normal and PLX5622 diet were tested for cognitive function using seven independent behavioral tasks, microglial activation, hippocampal neuronal morphology, spine density, and electrophysiology properties 4-6 weeks later., Results: PLX5622 treatment caused a rapid and near complete elimination of microglia in the brain within 3 days of treatment. Irradiated animals on normal diet exhibited a range of behavioral deficits involving the medial pre-frontal cortex and hippocampus and increased microglial activation. Animals on PLX5622 diet exhibited no radiation-induced cognitive deficits, and expression of resting and activated microglia were almost completely abolished, without any effects on the oligodendrocyte progenitors, throughout the brain. While PLX5622 treatment was found to attenuate radiation-induced increases in post-synaptic density protein 95 (PSD-95) puncta and to preserve mushroom type spine densities, other morphologic features of neurons and electrophysiologic measures of intrinsic excitability were relatively unaffected., Conclusions: Our data suggest that microglia play a critical role in cosmic radiation-induced cognitive deficits in mice and, that approaches targeting microglial function are poised to provide considerable benefit to the brain exposed to charged particles.

A study was undertaken of autopsy cases of suicide where either helium or nitrogen gas had been used (taken from Forensic Science SA files, 2003-2017). 33 deaths involved helium (age range 19-94yrs, average 47yrs; M:F-2.7:1), compared to 23 cases of nitrogen inhalation (age range 29-93yrs, average 66yrs; M:F-2.3:1). The combined numbers of deaths due to both helium and nitrogen inhalation showed a steady increase (5: 2003-2007; 31: 2013-2017); however, while helium deaths plateaued (14: 2008-2012, 15: 2013-2017) nitrogen-related deaths increased 16-fold. Specifically, the percentage of cases due to nitrogen inhalation increased from 20 to 52%, compared to helium which fell from 80 to 48%. Continued observation of the study population is required with evaluation of other communities and larger populations to monitor this potential trend, and to determine whether nitrogen may be superseding helium as the gas of choice in plastic bag and other asphyxial suicides., (Copyright © 2018 Elsevier Ltd and Faculty of Forensic and Legal Medicine. All rights reserved.)

Background: The use of the helium suicide method has been increasing in popularity in Hong Kong since 2012. We have learned a valuable lesson in curbing the spread of charcoal burning (CB) suicide in the past 15 years and hope to prevent the helium suicide method from taking off in the community., Aims: To document what actions have been taken to contain the spread of the helium suicide method and review the preliminary impact of these actions., Method: We adopted a public health approach by engaging stakeholders from multiple sectors, including the police force, the fire services department, coroners, pathologists, mass media, and online media outlets., Results: A monitoring system was established by compiling data extracted from news reports, coroners' reports, and police investigations. Risk and protective factors were identified. Intervention strategies were developed to strengthen protective factors and minimize risk factors. This novel suicide method has not spread as rapidly as the CB suicide method. The preliminary outcomes suggest our actions to be effective., Limitations: The count of helium suicides in 2015 might be low. The impacts of the interventions are only estimated and require additional empirical verifications., Conclusion: The public health approach of engaging multiple partners in the early phase of a potential epidemic can be a good guide to meeting the challenges posed by any new suicide methods that emerge in the future.

Introduction: Annually about 28% of the 5800 death of unnatural cause in the Netherlands are a result of suicide. In 2012 and 2013 a movie and a book were published about a "dignified end of life" which also described the suicide using the exit bag to establish asphyxia using helium. The purpose of this study is to investigate if the suicide methods changed since the publicity in 2013 about suicidal asphyxiation by using helium gas. This study especially focuses on suicide using the 'exit bag' with or without helium gas., Material and Methods: In the period 2005 to 2014 all suicides in the region of Amsterdam-Amstelland and Zaanstreek-Waterland were analyzed and from these suicides cases using the exit bag were selected., Results: The study shows a rising trend with the use of the helium (P > 0.01) and a decreasing trend for suicide by asphyxia using an exit bag (P < 0.05). The data does not show a sudden difference, but there seems to be a gradually change., Discussion: The number of suicides using the helium method is rising in Amsterdam-Amstelland and Zaanstreek-Waterland, while suicides by asphyxiation without helium are decreasing. The specific publicity of books about suicides using helium may have influenced this transition., (Copyright © 2016 Elsevier Ltd and Faculty of Forensic and Legal Medicine. All rights reserved.)

Atmospheric-pressure N2, He, air, and O2 microplasma arrays have been used to inactivate Escherichia coli cells suspended in aqueous solution. Measurements show that the efficiency of inactivation of E. coli cells is strongly dependent on the feed gases used, the plasma treatment time, and the discharge power. Compared to atmospheric-pressure N2 and He microplasma arrays, air and O2 microplasma arrays may be utilized to more efficiently kill E. coli cells in aqueous solution. The efficiencies of inactivation of E. coli cells in water can be well described by using the chemical reaction rate model, where reactive oxygen species play a crucial role in the inactivation process. Analysis indicates that plasma-generated reactive species can react with E. coli cells in water by direct or indirect interactions., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Bacterial spores are the most resistant form of life and have been a major threat to public health and food safety. Nonthermal atmospheric gas discharge plasma is a novel sterilization method that leaves no chemical residue. In our study, a helium radio-frequency cold plasma jet was used to examine its sporicidal effect on selected strains of Bacillus and Clostridium. The species tested included Bacillus subtilis, Bacillus stearothermophilus, Clostridium sporogenes, Clostridium perfringens, Clostridium difficile, and Clostridium botulinum type A and type E. The plasmas were effective in inactivating selected Bacillus and Clostridia spores with D values (decimal reduction time) ranging from 2 to 8 min. Among all spores tested, C. botulinum type A and C. sporogenes were significantly more resistant to plasma inactivation than other species. Observations by phase contrast microscopy showed that B. subtilis spores were severely damaged by plasmas and the majority of the treated spores were unable to initiate the germination process. There was no detectable fragmentation of the DNA when the spores were treated for up to 20 min. The release of dipicolinic acid was observed almost immediately after the plasma treatment, indicating the spore envelope damage could occur quickly resulting in dipicolinic acid release and the reduction of spore resistance.

This article researches a relatively new suicide method advanced by right-to-die organizations: oxygen deprivation by breathing helium inside a plastic hood. The article begins with a review of the role of the coroner and the history of oxygen deprivation with helium; it then examines 20 Judgements of Inquiry (JOI) by British Columbia coroners into this form of suicide. The JOI were obtained through the Freedom of Information and Protection of Privacy Act and cover the period of 1999 to 2007. Findings raise concerns about the coding system used by coroners as well as adherence to internal documentation guidelines. The British Columbia Coroners Service (BCCS) has a public safety mandate to investigate all unnatural deaths and to make recommendations to prevent deaths in similar circumstances. It is a concern that BCCS has no recommendations to prevent suicides by oxygen deprivation with helium. More in-depth, systematic research is recommended to determine the prevalence of suicide by oxygen deprivation and to develop strategies to benefit public health and safety.

Experiments with small test animals have been carried out to study the survival rate of spermatogenic cells in the acute period after exposure to protons with the energy 9 GeV, helium ions with the energy 4 GeV/nucleon, and 60Co gamma radiation in doses of 0.5-7.5 Gy and the reciprocal translocation frequency in spermatocytes under meiosis at the diakinesis-metaphase-1 stage six months after the exposure of the animals to protons with the energy 50 MeV and 9 GeV, helium ions with the energy 4 GeV/nucleon, and 60Co gamma-radiation in doses of 0.5-4.0 Gy. It is shown that the dependence of the effect on the dose is linear or near to linear for all kinds of radiation used. Relative biological effectiveness coefficients of the accelerated nuclei obtained by correlating equally effective doses of the standard and investigated radiations turned out to be higher in survival rate of type B spermatogonium and amounted to 2.0 and 1.3 for 9 GeV protons and helium ions respectively. At the same time, the use of the nonparametric method to determine the RBE coefficients in the course of finding out the reciprocal translocation frequency in spermatocytes points to an increase in the RBE coefficients of charged particles from 1.0 to 2.0.

Nervous disorders may occur after an organism is saturated with inert gases, which may alter the lipid bilayer structure, according to their liposolubility coefficient. Increase in the nitrogen partial pressure induces a neurological syndrome called 'nitrogen narcosis'. By contrast, high pressures of helium induce epilepsy, an high-pressure nervous syndrome symptom. On the basis of an analogy with anaesthetic mechanisms, we used TREK-1 knockout mice, earlier described to volatile the anaesthetics resistance. These mice had a higher threshold of resistance to the narcotic effects of nitrogen and to the death after recurrent epileptic seizure induced by high pressure. TREK-1 channels seem to play a key role in modulating the anaesthetic potential of inert gases and in neuroprotection.

Asphyxial suicide by placing a plastic bag over the head, especially in combination with inhalation of gases, is a rarely described method of committing suicide. This article reports a case of suicidal asphyxiation by inhaling the inert gas helium inside a plastic bag. A 64-year-old man probably followed the instructions described in an article about committing suicide written by a medical practitioner from Zürich. This form of suicide is recommended by right-to-die groups and in the internet as a certain, fast, and painless suicide method. Additionally, it leaves only seldom externally visible marks or pathomorphological findings on the body. If the plastic bag and other auxiliary means are removed by another person, the forensic death investigation of cause and manner of death may be very difficult. Therefore, the death scene investigation and the inquiry ordered in the environment of the deceased are very important.

Introduction: The mechanism of potential tumor cell spread and growth during laparoscopy is poorly understood. Nevertheless, different experimental studies reported a stimulation of tumor cell growth and an increased metastatic potential of carcinoma cells using carbon dioxide as an insufflation medium. Adhesion molecules do play an important and regulatory function in the process of metastatic spread and invasion of cancer cells. Therefore we investigated the influence of CO2 and Helium insufflation on the in-vitro expression of E-Cadherin, CD44v6 and CD54 (ICAM-1) on HT-29 colon carcinoma cells., Methods: HT-29 carcinoma cells were exposed to either CO2 or helium insufflation. Expression of E-Cadherin, CD44v6 and CD54 (ICAM-1) on HT-29 colon carcinoma cells were measured 1, 12, 24, 48 and 96 h after CO2 and helium insufflation using flowcytometry (FACScan). Data were analyzed by Friedman-test., Results: HT-29 cell line showed a short decrease in E-Cadherin expression after CO2 exposure while helium insufflation had no influence. In contrasts to these findings the expression of CD44v6 and CD54 on HT-29 cells were not influenced significantly by either CO2 or helium., Conclusion: CO2 seems only to have a minor influence on the expression of E-Cadherin while expression of other adhesion molecules did not change after CO2 incubation. The alternative gas helium did not cause any significant changes of the expression of either E-Cadherin, CD44v6 and CD54. Further investigations are needed to elucidate the changes of the metastatic potential of tumor cells after laparoscopic and open procedures.

Accelerated helium ions with mean energies at the target location of 3-7 MeV were used to simulate alpha-particle radiation from radon daughters. The experimental setup and calibration procedure allowed determination of the helium-ion energy distribution and dose in the nuclei of irradiated cells. Using this system, the induction of DNA double-strand breaks and their spatial distributions along DNA were studied in irradiated human fibroblasts. It was found that the apparent number of double-strand breaks as measured by a standard pulsed-field gel assay (FAR assay) decreased with increasing LET in the range 67-120 keV/microm (corresponding to the energy of 7-3 MeV). On the other hand, the generation of small and intermediate-size DNA fragments (0.1-100 kbp) increased with LET, indicating an increased intratrack long-range clustering of breaks. The fragment size distribution was measured in several size classes down to the smallest class of 0.1-2 kbp. When the clustering was taken into account, the actual number of DNA double-strand breaks (separated by at least 0.1 kbp) could be calculated and was found to be in the range 0.010-0.012 breaks/Mbp Gy(-1). This is two- to threefold higher than the apparent yield obtained by the FAR assay. The measured yield of double-strand breaks as a function of LET is compared with theoretical Monte Carlo calculations that simulate the track structure of energy depositions from helium ions as they interact with the 30-nm chromatin fiber. When the calculation is performed to include fragments larger than 0.1 kbp (to correspond to the experimental measurements), there is good agreement between experiment and theory.

The effects of long-term hyperbaric exposure on endocrine organ weight and histology and on epiphyseal-plate width were studied in growing male rats. Six groups of rats were exposed to 21 ATA He-O2 (200 mmHg O2), and six groups were maintained at 1 ATA as room-air controls. Each group contained eight rats. At intervals of of 2, 3, 5, 8, 10, and 12 weeks, one group was decompressed and studied along with a paired control group. Results indicated no changes in pituitary and adrenal gland weights. Testis weights were variable but histology and sperm content were normal. Only the accessory sex organs decreased significantly in weight; however, prostate and seminal vesicle histology were normal. Tibial epiphyseal-plate width was reduced in 21-ATA groups. These results suggest that long-term hyperbaric exposure has little effect on endocrine organs of the rat and observed weight changes are probably related to the reduced body weights.

In a previous study, it was shown that helium pressure depressed excitatory synaptic transmission mediated by the Schaffer-commissural afferents and increased the intrinsic excitability of pyramidal cells, in the CA1 region of hippocampal slices in the rat. In the present study, the neurochemical bases of these changes was investigated. Various excitatory amino acids were studied under normal and up to 80 atm of helium. At normal pressure, the amino acids tested induced a decrease in the field excitatory postsynaptic potential (EPSP) and antidromic field potential of CA1 pyramidal cells. These changes probably resulted from the well known depolarizing effect of the compounds. Quisqualate is supposed to activate the synaptic receptors of the pathway tested. Since the effect of this amino acid and other agonists were not significantly affected by helium pressure, it is suggested that the depressed hippocampal synaptic potentials under pressure did not result from reduced sensitivity of synaptic receptors. On the other hand, helium pressure enhanced the action of N-methyl-D-aspartate (NMDA) and depressed the GABA-mediated inhibition of CA1 pyramidal cells. Given that the excitability of these neurones is modulated by NMDA-related events and GABA inhibition, these results indicate that both neurochemical systems were probably involved in the helium pressure-induced hyperexcitability of the cells studied.

A 3-day exposure of mice to a 20%--80% He-O2 environment at 28--30 degrees C led to an earlier decrease of gas exchange, a faster development of pulmonary inflammatory changes, and an earlier death of the animals as compared with an exposure to similar N2-O2 and He-O2 atmospheres at room temperature. The possible role of the indifferent gas in the toxic effect of oxygen on the animal body is discussed.

The mutagenic and toxic effect of high helium and hydrostatic pressure were assessed in an in vitro microbial assay using two histidine-dependent strains of Salmonella typhimurium. TA98 and TA100. Bacteria in the presence or absence of mammalian enzyme system were subjected to either 50 or 100 atmospheres absolute (ATA) helium or 300 ATA hydrostatic pressure. The number of revertant colonies, colony forming units and cell growth rates were measured. There was no mutagenic effect of decrease in number of colony forming units at any of the pressures tested. However, a statistically significant decrease in growth rate of exponentially dividing cells was seen at 300 ATA hydrostatic pressure and 100 ATA helium, but not at 50 ATA helium.

To compare sodium channel block by hyperbaric nitrogen with that induced by other anesthetics and to examine the basis for pressure antagonism to anesthetic condition block, voltage clamped nodes of Ranvier were exposed to nitrogen at pressures at 1-14 atm alone and in combination with helium to a total pressure of up to 100 atm. At 7 and 14 atm nitrogen, sodium currents were reversibly depressed without accompanying changes in the current-voltage relation. The curve relating steady-state inactivation (h infinity) to voltage was shifted in the hyperpolarizing direction, as is the case with other general anesthetic agents. The time constant of inactivation (tau h) was slightly decreased at depolarized potentials. The preceding companion paper demonstrated an opposite effect of hyperbaric helium on the properties of sodium inactivation. Addition of helium pressure in the presence of nitrogen at 14 atm did not increase peak sodium current with inactivation maximally removed, but it did shift the h infinity curve back toward control levels, thus increasing sodium current at points on the slope of the curve. It is proposed that these opposing shifts in steady-state inactivation levels are the basis for pressure antagonism to anesthetic conduction block. In the case of inert gases and volatile anesthetic agents, the antagonism may be direct but has not been shown to be so. In the case of the local anesthetic benzocaine, differences in the voltage dependence of anesthetic and pressure-induced changes in tau h indicate the antagonism is indirect.

Three generations of mice were exposed to an atmosphere of 80% helium and 20% oxygen. The parent generation, born and raised in air until the experiment began, was sacrificed in two groups--one after 160 d and the other after 350 d of exposure. The F1 generation, conceived in air, born and raised in an He/O2 environment, was sacrificed after 160 d. The F2 generation, conceived, born, and raised in the He/O2 atmosphere, was sacrificed also in two groups--one after 85 d and the other after 280 d. Lung tissue from these animals was prepared by conventional methods for ultrastructural study. The most obvious alteration observed was the extensive blebbing, possibly indicative of cellular edema, seen in both the capillary endothlium and the alveolar epithelium. In addition, a highly convoluted basement membrane was observed in many areas. There was debris in some of the alveoli and an increase in platelets in the capillaries.

The resolution rates of gas bubbles in perfused tissue are examined using a mathematical model which is consistent with transient-state and steady-state data from large gas pocket experiments. The tissue surrounding the bubble is assumed to have an infinite number of infinitesimally small capillaries (distributed sink). The time for complete disappearance of a bubble depends on initial bubble size. blood perfusion rate of the tissue, physical characteristics of the inert gas and the fraction (1-Pa/Pg), where Pa and Pg are inert gas partial pressures in the surrounding tissue and inside the bubble, respectively. Calculated time for disappearance of a nitrogen bubble of 1 mm radius in an O2-breathing man is 100-250 min, depending on blood perfusion. Breathing of air increases the time of persistence of the bubble about 10-fold. The "transient state", when gas is dissolving in the immediate surroundings of the bubble, is most influential when there is no perfusion and the partial pressure gradient gas volume is the largest. However, our major conclusion is that the initial transient state has little effect on total lifetime of the bubble in any case.

An anesthetized rat preparation has been used for breathing studies in hyperbaric Ar-O2-CO2 atmospheres in which total saturation pressure was varied in the range 1-19.1 ATA and PCO2 was set at levels of 0.0, 0.05 or 0.10 ATA. The variables monitored were respiration rate and an isotonic measure of diaphragm-twitch amplitude during contracture/relaxation (twitch index). The results indicate that: (1) hyperbaric Ar-O2 atmospheres are able to maintain the animal in stable condition for several hours; (2) elevation in PCO2 level produces enhancements in respiration rate and twitch index that are markedly dependent on the PAr level; (3) successive increases in PAr are able to lower progressively the effects on both breathing parameters produced by either 0.05 or 0.10 ATA of CO2, with full abolition of both effects of inhaled CO2 in the PAr range 14-19 ATA; and (4) the intrinsic ability of hyperbaric argon to abolish respiratory enhancement by CO2 is greater than that of hyperbaric helium. These results have been discussed in terms of possible CNS loci at which hyperbaric argon (or helium) is able to antagonize centrally induced effects from dissolved molecular species derived from inspired CO2, and in relation to the broader task of control of excitatory/inhibitory centers of the CNS during diving by manipulation of the partial pressures of diluent components of breathing-gas mixtures.

The arrhythmogenicity of epinephrine was examined in 34 male mongrel dogs awake and during 1.1 MAC steady state halothane-O2 anesthesia with the addition of 50% N2O, nitrogen, or helium. All anesthetized dogs required more epinephrine than did awake dogs to produce ventricular extrasystoles. Dogs given halothane-N2O were more sensitive to the epinephrine infusion than those given halothane-nitrogen or halothane-helium. The dogs given halothane-N2O also showed a small, but statistically significant difference from dogs given halothane-O2. These results suggest that the addition of N2O to halothane increases the cardiac arrhythmic potential of epinephrine in the dog.

At pressures up to 125 atmospheres, helium failed to anesthetize mice; at slightly higher pressures (135 to 145 atmospheres) it proved lethal. With Italian newts (Triturus italicus), whose sensitivity to anesthesia by nitrogen is similar to that of mice, responsiveness was lost at pressures between 165 and 245 atmospheres, whether the pressure was achieved with helium or neon, or hydrostatically. It was concluded that the anesthetic pressures of helium and neon, for mice and newts, are higher than the tolerable mechanical pressures.