Sodium selenite-induced hypothermia in mice: indirect evidence for a neural effect

Cumulative risk: toxicity and interactions of physical and chemical stressors

Recent efforts to update cumulative risk assessment procedures to incorporate nonchemical stressors ranging from physical to psychosocial reflect increased interest in consideration of the totality of variables affecting human health and the growing desire to develop community-based risk assessment methods. A key roadblock is the uncertainty as to how nonchemical stressors behave in relationship to chemical stressors. Physical stressors offer a reasonable starting place for measuring the effects of nonchemical stressors and their modulation of chemical effects (and vice versa), as they clearly differ from chemical stressors; and "doses" of many physical stressors are more easily quantifiable than those of psychosocial stressors. There is a commonly held belief that virtually nothing is known about the impact of nonchemical stressors on chemically mediated toxicity or the joint impact of coexposure to chemical and nonchemical stressors. Although this is generally true, there are several instances where a substantial body of evidence exists. A workshop titled "Cumulative Risk: Toxicity and Interactions of Physical and Chemical Stressors" held at the 2013 Society of Toxicology Annual Meeting provided a forum for discussion of research addressing the toxicity of physical stressors and what is known about their interactions with chemical stressors, both in terms of exposure and effects. Physical stressors including sunlight, heat, radiation, infectious disease, and noise were discussed in reference to identifying pathways of interaction with chemical stressors, data gaps, and suggestions for future incorporation into cumulative risk assessments.

Systemic administration of [6]-gingerol, a pungent constituent of ginger, induces hypothermia in rats via an inhibitory effect on metabolic rate

We investigated the effects of systemic administrations of ginger (Zingiber officinale Roscoe, Zingiberaceae) or its pungent constituent, [6]-gingerol, on resting body temperature in rats. Rats given ginger-containing rat chow for 5 days showed no changes in their day-night cycle of body temperature or physical activity. However, a single intraperitoneal (i.p.) injection of [6]-gingerol (2.5 or 25 mg/kg) induced a rapid, marked drop in body temperature in a dose-related manner, with no change in physical activity. A significant decrease in metabolic rate was observed immediately after an i.p. injection of [6]-gingerol (25 mg/kg), although heat-loss responses underwent no alteration (versus vehicle). These results suggest that in rats: (a) a decrease in metabolic rate is responsible for the [6]-gingerol-induced hypothermia, and (b) [6]-gingerol modulates or interferes with the mechanisms underlying body temperature regulation, while other bioactive constituents of ginger may counteract the hypothermic effect of [6]-gingerol.

Selenium, an antioxidant, attenuates methamphetamine-induced dopaminergic toxicity and peroxynitrite generation

Methamphetamine (METH) has been known to produce neurotoxicity via generation of reactive oxygen and nitrogen species. Selenium, an antioxidant, was reported to protect against METH-induced dopaminergic neurotoxicity in mouse caudate nucleus. In the present study, the in vitro and in vivo efficacy of the supplementation of selenium was studied in METH-induced generation of peroxynitrite. PC12 cell cultures were exposed to 200 microM METH either with or without 10 microM and 20 microM selenium (30 min prior to METH exposure). After 24 h, METH exposure resulted in the significant depletion of dopamine, and its metabolites DOPAC and HVA, as well as the significant formation of 3-nitrotyrosine (3-NT), a marker of peroxynitrite generation, in PC12 cell cultures. Selenium supplementation attenuated the depletion of dopamine and its metabolites, DOPAC and HVA and the formation of 3-NT in PC12 cells. For in vivo studies, adult male mice were supplemented with selenium in drinking water, 1 week before and 1 week after the multiple injections of METH (4x10 mg/kg, i.p. at 2-h interval) or an equivalent volume of saline. The supplementation of Se attenuated the formation of 3-NT in the striatum resulting from METH treatment. These data suggest that METH-induced neurotoxicity is mediated by the production of peroxynitrite, and selenium plays a protective role in METH-induced neurotoxicity.

In utero exposure to methylmercury and Se deficiency converge on the neurobehavioral outcome in mice

Pregnant female ICR mice, maintained on torula-based diets containing various amounts of Se (0.02, 0.05, or 0.4 mg/kg diet), were given methyl-mercury (MeHg; 0, 5, or 9 mg Hg/kg in total) on the 12-14th days of gestation. The neurobehavioral function of the offspring born to these dams was evaluated with respect to reflex and motor development, thermal preference, and open-field activity. Se deficiency per se as well as exposure to MeHg exerted additive or synergistic effects on the neurobehavioral functions examined. The group of mice most affected was the group given the lowest amount of Se and the highest dose of MeHg. Thus, the neurobehavioral outcome of in utero MeHg exposure and Se deficiency converged. Although the dietary level of Se did not affect the Hg concentration in the fetal brain, the Se concentration and the activity of glutathione peroxidase, a selenoenzyme, were severely depressed by MeHg in the neural tissue. The possibility that functional Se deficiency by MeHg exposure partly accounts for the neurobehavioral toxicity of MeHg is discussed.

Brain selenium status and behavioral development in selenium-deficient preweanling mice

The influence of Se deficiency on behavioral development in preweanling mice was evaluated. Female ICR mice were fed either Se-deficient or control diet (containing < 20 or 400 ng Se/g diet, respectively) from 4 weeks before conception to the end of the suckling period. In the offspring of Se-deficient dams, liver and brain Se levels were reduced to < 5% and 60% of those in the control offspring, respectively, from as early as the third postnatal day. At weaning, brain Se content exceeded the hepatic one in Se-deficient offspring, whereas in the control offspring the liver contained 10 times more Se than the brain did. Thus, tissue-specific metabolism of Se was already functioning during the neonatal period. When placed in a thermogradient and allowed to move along the gradient, Se-deficient offspring exhibited a preference for a significantly warmer environment than did the controls. They also showed slightly retarded development of walking ability. These results showed that Se-deficient offspring differed from the controls in behavioral development. Possible mechanisms of these alterations are discussed.

Behavioral thermoregulation in mice inoculated with influenza virus

Mice housed at 30 degrees C and inoculated with a mouse-adapted influenza virus show a fall in body temperature (Tb) and a decrease in food intake to almost 0 grams per day. This study tested whether the fall in Tb could be accounted for by the decreased food intake and whether the fall in Tb was due to a decrease of thermoregulatory set point or to an inability to maintain Tb at set point level. The fall in Tb of influenza-infected mice was greater than that of food-deprived mice. When food deprived, mice given access to a thermal gradient increased their preference for warmer areas in the gradient and, as a result, Tb did not fall as much as Tb of starved mice not given access to a thermal gradient. When infected with influenza virus, mice given a thermal gradient decreased Tb less and at a slower rate than mice not given a gradient. However, this fall in Tb of influenza-infected mice was greater than that of food-deprived mice given a thermal gradient. Mice given a thermal gradient increased their preference for the warmer temperatures after inoculation; this returned to preinoculation preference for cooler temperatures during the later days of infection despite a continuous fall in Tb. Influenza-infected mice given a thermal gradient survived significantly fewer days than infected mice not given a thermal gradient. We conclude that the influenza-induced fall of Tb in mice cannot be explained solely by the decrease in food intake, and is partially due to a decrease in thermoregulatory set point.

Toxic-induced hypothermia and hypometabolism: do they increase uncertainty in the extrapolation of toxicological data from experimental animals to humans?

Commonly used experimental mammals, such as the rat and mouse, exhibit hypothermia and hypometabolism when exposed acutely to many drugs and other chemical substances. This toxic-induced hypothermic/hypometabolic state may be an inherently protective response that can reduce the lethality of a toxic insult. However, as body mass increases, the ability to lower body temperature in response to toxic insult is diminished. Hence, the presence of a protective hypothermic/hypometabolic response in small laboratory mammals and apparent lack thereof in larger species, such as humans, may represent an additional physiological dissimilarity which may underestimate the risk assessment of acute toxicological data. It is proposed that acute toxicological studies in rodents be performed at relatively warm ambient temperatures (ca. 28 to 32 degrees C) to prevent toxic-induced hypothermia. This would assure a more uniform internal thermal environment between species, thus reducing a major physiological variable in species-to-species extrapolation.

Toxicity modification of sodium selenite by a brief exposure to heat or cold in mice

The effect of a brief exposure to heat/cold on the subsequent development of toxicity of sodium selenite (SS) was evaluated in male ICR mice. Mice were exposed to one of three ambient temperatures (Ta; approx. 8 degrees, 22 degrees and 33 degrees C). One and a half hours after the beginning of the exposure, they were injected with 45 mumol/kg of SS subcutaneously. The exposure was terminated 3 h after injection and the mice were returned to Ta of 22 degrees C. Heat-induced enhancement of toxicity was recognized in some plasma enzyme activities 3 days after injection and in the suppression of body weight for up to 3 weeks. On the other hand, cold exposure alleviated SS toxicity in terms of these indices. Thus, the Ta during this short period was recognized to be important in determining subsequent development of SS toxicity. At the end of the thermal exposure, heat increased renal concentration of the injected Se. On the other hand, in the liver and the other organs examined, the highest Se concentration was found in the cold-exposed group, followed by the control (room temperature) and the heat-exposed. The relation between the modification of toxicity and the altered distribution was not clear. Neither glutathione level in the liver nor that in the kidney at the time of SS injection could explain the observed modification of the toxicity.

Transient hypothermia and hyperphagia induced by selenium and tellurium compounds in mice

The effects of sublethal doses of selenite, selenate, selenocystine (Se-Cys) and selenomethionine (Se-Met) as well as of tellurite on body temperature and feeding behavior were examined in male ICR mice. Ten or 30 mumol/kg of chemicals were injected subcutaneously and body temperature was measured up to 4 h. In a separate experiment, the gastric content was weighted 4 h after injection. All chemicals except Se-Met induced both hypothermia and hyperphagia, suggesting that: (a) these two effects are related to each other; (b) among the chemicals tested, Se-Cys appears to be the most potent hypothermia inducer; (c) Se-Met is unique in that it has neither effect.

Temperature regulation in laboratory mammals following acute toxic insult

The purpose of this paper is to provide a concise review of the effects of acute chemical toxicity on thermoregulation in mammals, with particular emphasis on the effects of xenobiotic compounds in laboratory rodents. It has been shown that acute administration of compounds such as nickel, cadmium, lead, and some pesticides causes a reduction in the body temperature of mice when tested at normal room temperatures. When provided with the option of selecting their preferred ambient temperature, the toxic-treated animals generally select cool temperatures which augment the hypothermic effect of the toxic compounds. It would appear that many of the xenobiotic compounds have central as well as peripheral effects on the control of body temperature. That is, the hypothermic animals select cool temperatures, a condition indicative of a centrally mediated decrease in the set-point. This decrease in set-point, or regulated hypothermia, may be beneficial to survival since the lethality of most xenobiotic compounds increases with rising body temperature. The observation that acute doses of various compounds leads to behaviorally and autonomically mediated changes in body temperature may have significant implications for the measurement of other biological effects of these chemical agents (e.g., CNS dysfunction, bradycardia, immunosuppression).

Modification of lethal, hypothermic and hyperphagic effects of sodium selenite by reduced glutathione in mice

The effects of co-administration of reduced glutathione (GSH) on the lethality of sodium selenite (SS) and on SS-induced hypothermia and hyperphagia were examined in adult male ICR mice. Tissue GSH levels after s.c. injection were also determined. In the plasma, GSH concentration was significantly elevated up to 2 h after injection of 2 mmol/kg of GSH. Little change was observed in liver, and erythrocyte levels, the lethality of SS was enhanced by a similar dose of GSH. This enhancement, however, was observed only when SS was injected during the period when plasma GSH was elevated. These results suggest that the interaction between GSH and SS in plasma was the major contributor to the enhancement of SS toxicity. Hypothermia induced by SS was also enhanced by a 60-fold dose of GSH but not by a 6-fold dose of GSH. With respect to hyperphagia, GSH suppressed the effect of SS, probably because of depressing effect of co-administration of SS an GSH.

Metallothionein induction by sodium selenite at two different ambient temperatures in mice

The induction of metallothionein (MT) synthesis by sodium selenite was investigated in mice with regard to the hypothermic response known to be caused by sodium selenite. Mice received a subcutaneous injection of sodium selenite at two doses (20 and 45 mumol/kg) under two ambient temperature (22 and 33 degrees C) conditions. Hepatic MT concentration was significantly increased by an injection of sodium selenite compared to the control, whereas no significant effect of ambient temperature was observed. The distribution of radiolabeled selenium was examined in vivo and in vitro. When sodium selenite was injected into mice, radiolabeled selenium was mostly eluted in a fraction larger in molecular weight than MT and was not found in a fraction corresponding to MT. When sodium selenite was added to the hepatic supernatant of the mice that had been injected with zinc sulfate, zinc in zinc-thionein was not displaced by radiolabeled selenium.