Single Exposure Group Research Articles

Apoptotic mechanisms after repeated noise trauma in the mouse medial geniculate body and primary auditory cortex.

A correlation between noise-induced apoptosis and cell loss has previously been shown after a single noise exposure in the cochlear nucleus, inferior colliculus, medial geniculate body (MGB) and primary auditory cortex (AI). However, repeated noise exposure is the most common situation in humans and a major risk factor for the induction of noise-induced hearing loss (NIHL). The present investigation measured cell death pathways using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) in the dorsal, medial and ventral MGB (dMGB, mMGB and vMGB) and six layers of the AI (AI-1 to AI-6) in mice (NMRI strain) after a second noise exposure (double-exposure group). Therefore, a single noise exposure group has been investigated 7 (7-day-group-single) or 14days (14-day-group-single) after noise exposure (3h, 5-20kHz, 115dB SPL peak-to-peak). The double-exposure group received the same noise trauma for a second time 7days after the initial exposure and was either TUNEL-stained immediately (7-day-group-double) or 1week later (14-day-group-double) and data were compared to the corresponding single-trauma group as well as to an unexposed control group. It was shown that TUNEL increased immediately after the second noise exposure in AI-3 and stayed upregulated in the 14-day-group-double. A significant increase in TUNEL was also seen in the 14-day-group-double in vMGB, mMGB and AI-1. The present results show for the first time the influence of a repeated noise trauma on cell death mechanisms in thalamic and cortical structures and might contribute to the understanding of pathophysiological findings and psychoacoustic phenomena accompanying NIHL.

Study on dose-dependent, frequency-dependent, and accumulative effects of 1.5\u2009GHz and 2.856\u2009GHz microwave on cognitive functions in Wistar rats

Many studies have revealed the cognitive decline induced by microwave radiation. However, the systematic study on dose-dependent, frequency-dependent and accumulative effects of microwave exposure at different frequencies was lacking. Here, we studied the relationship between the effects and the power and frequency of microwave and analyzed the accumulative effects of two different frequency microwaves with the same average power density. After microwave radiation, declines in spatial learning and memory and fluctuations of brain electric activities were found in the 10 mW/cm2 single frequency exposure groups and accumulative exposure groups. Meanwhile, morphological evidences in hippocampus also supported the cognitive dysfunction. Moreover, the decrease of Nissl contents in neurons indicated protein-based metabolic disorders in neurons. By detecting the key functional proteins of cholinergic transmitter metabolism, cytokines, energy metabolism and oxidative stress in the hippocampus, we found that microwave could lead to multiple metabolic disorders. Our results showed that microwave-induced cognitive decline was largely determined by its power rather than frequency. Injury effects were also found in accumulative exposure groups. We particularly concerned about the safety dose, injury effects and accumulative effects of microwaves, which might be very valuable in the future.

The protective study about alleviation of simvastatin on the damages of PEG-BNs in mice

Boron nitride nanoparticles have been proved to cause various toxicities, damages or inflammations after entering into in vivo in previous reports. However, up to now, there are rare investigations about the alleviation of damages caused by nanoparticles in vivo through natural small molecule drugs. Therefore, in this work, PEG-BNs with high solubility was successfully synthesized, and then their biodistribution in mice were studied using radiolabeling technique. And the heart, lung, liver, spleen, kidney tissues and blood samples were done for histology and biochemical analysis. The results showed that PEG-BNs were mainly distributed in lung, liver, kidney and spleen with an obviouse decreasing distribution as the experimental time was increasing. Besides, significantly serum biochemical and tissue pathological changes induced by PEG-BNs were confirmed. Moreover, after simvastatin (SST) exposure to the PEG-BNs model mice, the damages and biochemical indexes were recovered significantly as compared to the single exposure group mice in serum, which indicates a good treatment effect on the toxicity of PEG-BNs in vivo in mice. This study provides some basic data and useful information for the treatment of damages caused by the nanoparticles in mice in the future.

Bioconcentration and multi-biomarkers of organic UV filters (BM-DBM and OD-PABA) in crucian carp

Organic UV filters (OUV-Fs) are increasingly used in sunscreens and personal care products. In the present work, the bioconcentration and multi-biomarker effects of butyl methoxydibenzoylmethane (BM-DBM) and ethylhexyl dimethyl p-aminobenzoate (OD-PABA) were investigated in crucian carp (Carassius auratus). The fish were exposed to various concentrations of BM-DBM (3.88, 35.61, 181.85 and 337.15μg/L), OD-PABA (4.66, 53.83, 264.22 and 459.32μg/L) and their mixture (2.31+2.79, 23.69+26.18, 97.37+134.81 and 193.93+246.08μg/L) for 28 days. The maximal concentrations of two OUV-Fs were detected in the fish liver, followed by the brain, kidney, gill and muscle in most cases. The maximal BCF values of OD-PABA calculated in various exposure concentrations were 0.37 – 101.21 in single exposure groups and 0.11 – 31.09 in mixed exposure groups. Acetylcholinesterase (AChE) activity was significantly inhibited by BM-DBM as well as the mixtures at all of the exposure concentrations and by OD-PABA at higher concentrations (≥264.22μg/L) during 28 days of exposure. The maximal inhibition rates of AChE activity reached 64.04% for BM-DBM, 41.05% for OD-PABA and 61.50% for the mixtures at the highest concentration, which indicated that these two OUV-Fs might damage the central nervous system. Concerning oxidative stress status, BM-DBM and the mixtures significantly increased superoxide dismutase (SOD) and glutathione reductase (GR) activities and inhibited catalase (CAT) activity, while OD-PABA caused a significant increase of GR and CAT activities. AChE and GR activities seemed to be more sensitive biomarkers for BM-DBM and OD-PABA.

The toxic effect and bioaccumulation in aquatic oligochaete Limnodrilus hoffmeisteri after combined exposure to cadmium and perfluorooctane sulfonate at different pH values

Cadmium (Cd) and Perfluorooctane sulfonate (PFOS) have been detected in aquatic environment. In this study, we investigated the acute effect, bioaccumulation and oxidative stress status in the aquatic oligocheate Limnodrilus hoffmeisteri after exposure to Cd and PFOS at different pH values. In the studied pH range, acute Cd toxicity was significantly enhanced with pH increasing from 6.2 to 8.0, and the 48h-EC50 of Cd was (significantly) decreased in the presence of PFOS. Bioaccumulation analysis results show that the accumulated Cd/PFOS in single exposure group increased with increasing exposure concentrations, and co-exposure makes internal Cd concentration significantly lowered for Cd(0.1) group at pH 8.0. Significant changes in superoxide dismutase activity, glutathione level and malondialdehyde content were observed in single and combined treatments. Based on IBR value, single Cd and PFOS exposure caused largest damage to the antioxidant defense system at pH 8.0 and pH 6.2, respectively, while the harmful effects of joint exposure were always the “compromise” between single Cd and PFOS exposure. This work could provide useful information for the risk assessment of co-exposure to perfluorinated compounds and heavy metals in natural environment.

Combined toxicity of amorphous silica nanoparticles and methylmercury to human lung epithelial cells

Exposure to the ambient particulate matters (PM) has been associated with the morbidity and mortality of cardiopulmonary diseases. Compared with coarse particles, ultrafine particles (UFP) absorb or condense higher concentration of toxic air pollutants and are easily inhaled into the lung. However, the combined effects of UFP and air pollutants on human health are still poorly understood. In this study, a co-exposure in vitro model of amorphous silica nanoparticles (nano-SiO2) and methyl mercury (MeHg) was established to investigate their combined effects and the potential joint action type. Lung adenocarcinoma cells (A549) were exposed to either nano-SiO2 or MeHg alone, or a combination of both. Factorial design was applied to analyze their potential joint action type. Higher interfacial energy was observed in the mixed solution of nano-SiO2 and MeHg. The intracellular content of both silicon and mercury in combination group were much higher than those in single exposure groups. In addition, the co-exposure of nano-SiO2 and MeHg enhanced the reactive oxygen species (ROS) generation, lipid peroxidation and reduced the activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-px). The excessive oxidative stress led to oxidative DNA damage as well as cellular apoptosis. Factorial design analysis demonstrated that additive and synergistic interactions were responsible for the combined toxicity of nano-SiO2 and MeHg.

Biodistribution and toxicity of pegylated single wall carbon nanotubes in pregnant mice

BackgroundSingle wall carbon nanotubes (SWCNTs) are considered promising nanoparticles for industrial and biomedical applications; however their potential toxicity in several biological systems, including the feto-placental unit, has been demonstrated. Functionalization of SWCNTs with polyethylene glycol chains (PEG-SWCNTs) dramatically reduces their toxicity, and for this reason PEG-SWCNTs are candidates for biomedical applications. However, no data are available on their safety for the developing embryo, in spite of the clinical and social relevance of this topic. The purpose of this study is therefore to investigate the safety of PEG-SWCNTs for their use as biomedical carriers in pregnancy.MethodsFor toxicological studies, amino-functionalized PEG-SWCNT were intravenously injected in CD1 pregnant mice at different doses (range 0.1-30 μg/mouse), in single or multiple administrations. For biodistribution studies, fluorescently labeled PEG-SWCNTs were obtained by acylation of terminal PEG amino groups with near infrared emitting fluorochromes (PEG-SWCNT-750) and injected at the dosage of 10 μg/mouse, at either day 5.5 (when the placenta is still developing) or day 14.5 of gestation (when the maturation of the placenta is complete).ResultsWe found no adverse effects both on embryos and dams up to the dose of 10 μg/mouse. At the dose of 30 μg/mouse, occasional teratogenic effects, associated with placental damage, were detected both when administered as a single bolus (1 out of 10 dams; 1 malformed embryo) or as multiple doses (2 out of 10 dams; 5 malformed embryos). The difference in the prevalence of dams with malformed embryos between the 30 μg exposed group and controls approached the statistical significance (p = 0.06). Hepatic damage in dams was seen only in the multiple exposure group (4 out of 10; p = 0.04 when compared with the single exposure group or controls). PEG-SWCNT-750 reached the conceptus when administered early in pregnancy. At later stages, PEG-SWCNT-750 were detected in the placenta and the yolk sac, but not in the embryo.ConclusionsPEG-SWCNTs may cause occasional teratogenic effects in mice beyond a threshold dose. Such effect might depend on their ability to reach the feto-placenta unit. Although not automatically transferable to humans, these data should be considered if exposing women during pregnancy.

Histological and micrometric effects of diazinon exposure on adrenal medulla and cortex in mice

Histopathological effects of Diazinon (DZ) were studied on adrenal gland in virgin young female mice divided into five groups (10 animals each): (1) Control (untreated); (2) and (3) 9 and 18 mg kg−1 single exposure groups (given distilled water on day 1 and 2 and DZ on day 3); (4) and (5) 9 and 18 mg kg−1 multiple exposure groups (given respective DZ doses on days 1–3). All doses were applied by gavage. Animals were euthanized by cervical dislocation on day 6. Adrenals were removed surgically for histological and micrometric assessments of medulla and cortex. Histological examination of adrenal medulla revealed apoptotic changes and granular depletion in chromaffin cells while cortex gave impression of increased thickness of Zona Fasciculata following multiple DZ exposures. Mean cell sizes in cortical and medullary regions showed dose and exposure dependent significant decline. In conclusion, DZ exposure caused granular depletion in chromaffin cells indicating a rapid release of adrenaline and increased fascicular thickness indicating an anticipated shift from adrenal sex steroids to glucocorticoids biosynthesis and release. Apoptotic changes and significant decline in mean cell sizes of cortical and medullary regions were considered as the outcomes of oxidative and biosynthetic stresses of DZ exposure.

Repeated exposure to fruit results in increased fruit intakes in older low consumers of fruit

Recent reports suggest low fruit and vegetable intakes in older people. This study investigated the impact of two community-based repeated exposure interventions on fruit intakes in older people. Ninety-five participants (aged 65 years and over) were randomized to receive either one (E1), five (E5) or five plus (E5+) exposures to fruit over a 5 week period. Fruit exposures occurred during fruit tasting sessions (E1, E5, E5+), and through fruit provision (E5+), in community-based social group meetings. Intakes of fruit and vegetables were assessed before and after interventions. In low consumers of fruit (1 portion/day or less), fruit intakes increased significantly in the repeated exposure groups (E5, E5+), but no differences were found between E5 and E5+ groups and no change was found in the single exposure group. Similar effects were also found in fruit and vegetable intakes. Compared to single exposure, repeated exposure to fruit via fruit tasting sessions once per week for five weeks in a community setting significantly improved fruit intakes, and fruit and vegetable intakes in older low consumers of fruit, although no benefits of additional fruit provision were found. Repeated exposure was also easy to implement, low cost and enjoyable.

Comparison between three detective methods of sun protection factor for sunscreen in vivo

Objective To investigate the three methods for sun protection factor determination in vivo in Chinese under the same condition, and to evaluate the feasibility and reliability of the three methods. Methods There were 45 healthy volunteers in Guangzhou area were involved in the study. All of them were randomly divided into three groups. Among them 15 volunteers were in the current method group, 5 volunteers in the simplified method group, and 25 volunteers were in the single-exposure method group. Two standard sunscreens of SPF 4 and SPF 15 and one sunscreen labeled as SPF 20 were tested by all the three methods in the study. Two experienced observers read results, respectively, under the same conditions. Results The volunteers in the current method group received the largest dose of UV light.The simple method was next to it and the single-exposure reduced 4-5 folds of UV dose received. The results of the two observers in the current method group and the single-exposure group were very close. But the test results of P3 were not completely coincident between the two observers in the simplified method group. SPFs value of the three sunscreens were 4. 12, 16.09, and 22.60 obtained by the observer 1 and 4. 18, 15.92, and 21.97 obtained by the observer 2, respectively. In the simplified method group, SPFs values of ＜4, ＞15, ＞20 and ＜4, ＜15, ＞20 were obtained by the two observers. In the single-exposure method group, SPFs values of the three sunscreens were 4.04, 15.34, 21.33 by the observer 1 and 3. 96, 15.82, 21.33 by the observer 2, respectively. Conclusion The single-exposure method is convenient and easily to operate and may replace the current method some day. The simple method is not valuable in determination of SPF labeled on the packages of sunscreens, but may be useful in supervision of the market sunscreen products. Key words: Sun protection faction value; Sunscreens; Determination in vivo

NMR-based metabolomic studies on the toxicological effects of cadmium and copper on green mussels Perna viridis

Traditional toxicology studies have focused on selected biomarkers to characterize the biological stress induced by metals in marine organisms. In this study, a system biology tool, metabolomics, was applied to the marine mussel Perna viridis to investigate changes in the metabolic profiles of soft tissue as a response to copper (Cu) and cadmium (Cd), both as single metal and as a mixture. The major metabolite changes corresponding to metal exposure are related to amino acids, osmolytes, and energy metabolites. Following metal exposure for 1 week, there was a significant increase in the levels of branched chain amino acids, histidine, glutamate, glutamine, hypotaurine, dimethylglycine, arginine and ATP/ADP. For the Cu + Cd co-exposed mussels, the levels of lactate, branched chain amino acid, succinate, and NAD increased, whereas the levels of glucose, glycogen, and ATP/ADP decreased, indicating a different metabolic profile for the single metal exposure groups. After 2 weeks of exposure, the mussels showed acclimatization to Cd exposure based on the recovery of some metabolites. However, the metabolic profile induced by the metal mixture was very similar to that from Cu exposure, suggesting that Cu dominantly induced the metabolic disturbances. Both Cu and Cd may lead to neurotoxicity, disturbances in energy metabolism, and osmoregulation changes. These results demonstrate the high applicability and reliability of NMR-based metabolomics in interpreting the toxicological mechanisms of metals using global metabolic biomarkers.

Combined exposure to cyanobacterial biomass, lead and the Newcastle virus enhances avian toxicity

Under environmental conditions, wild birds can be exposed to multiple stressors including natural toxins, anthropogenic pollutants and infectious agents at the same time. This experimental study was successful in testing the hypothesis that adverse effects of cyanotoxins, heavy metals and a non-pathogenic immunological challenge combine to enhance avian toxicity. Mortality occurred in combined exposures to naturally occurring cyanobacterial biomass and lead shots, lead shots and Newcastle vaccination as well as in single lead shot exposure. Mostly acute effects around day 10 were observed. On day 30 of exposure, there were no differences in the liver accumulation of lead in single and combined exposure groups. Interestingly, liver microcystin levels were elevated in birds co-exposed to cyanobacterial biomass together with lead or lead and the Newcastle virus. Significant differences in body weights between all Pb-exposed and Pb-non-exposed birds were found on days 10 and 20. Single exposure to cyanobacterial biomass resulted in hepatic vacuolar dystrophy, whereas co-exposure with lead led to more severe granular dystrophy. Haematological changes were associated with lead exposure, in particular. Biochemical analysis revealed a decrease in glucose and an increase in lactate dehydrogenase in single and combined cyanobacterial and lead exposures, which also showed a decreased antibody response to vaccination. The combined exposure of experimental birds to sub-lethal doses of individual stressors is ecologically realistic. It brings together new pieces of knowledge on avian health. In light of this study, investigators of wild bird die-offs should be circumspect when evaluating findings of low concentrations of contaminants that would not result in mortality on a separate basis. As such it has implications for wildlife biologists, veterinarians and conservationists of avian biodiversity.

Usefulness of Monitoring Platelet Function by Multiple Electrode Aggregometry in Primary Coronary Artery Bypass Surgery

Antiplatelet therapy commonly is used for the prevention of cardiovascular complications but increases the risk of perioperative bleeding. Multiple-electrode aggregometry (MEA) was investigated for monitoring platelet inhibition by acetylsalicylic acid (ASA) and clopidogrel in patients undergoing elective coronary artery bypass graft (CABG) surgery with regard to clinical outcome as measured by postoperative blood loss and transfusion requirements. A prospective observational study. A teaching hospital. One hundred fifty patients scheduled for elective CABG surgery were included: without antiplatelet therapy (group A, n = 50), single ASA exposure (group B, n = 50), and combined therapy with ASA and clopidogrel (group C, n = 50). MEA was assessed preoperatively using either collagen (COL-MEA) or ADP (ADP-MEA). Postoperative blood loss and transfusion requirements were recorded for 24 hours after surgery. Postoperative blood loss significantly increased only from combined antiplatelet therapy (group A: 572 ± 297 mL, group B: 721 ± 356 mL, group C: 865 ± 346, p < 0.01) and correlated with ADP (r(p) = -0.35, p < 0.01) and COL-MEA (r(p) = -0.23, p > 0.01). COL-MEA and ADP-MEA discriminated between preoperative ASA and clopidogrel intake (ASA: sensitivity = 86.3%, and specificity = 89.3%; clopidogrel: sensitivity = 87.5%, and specificity = 95.1%). The postoperative transfusion risk was increased in patients diagnosed for clopidogrel treatment by ADP-MEA (odds ratio = 2.92; confidence interval: 1.44-5.92; p = 0.005). MEA is a suitable method for the detection of platelet inhibition by ASA and clopidogrel in patients undergoing CABG surgery. In these patients, preoperative ADP MEA seems to indicate patients at risk for postoperative transfusion requirements.

The mechanism of elevated toxicity in HepG2 cells due to combined exposure to ethanol and ionizing radiation

Ethanol and ionizing radiation exposure are independently known to cause tissue damage through various mechanisms. The non-enzymatic and enzymatic metabolism of ethanol, the latter via the cytochrome P(450) 2E1-dependent pathway produces free radicals, which deplete cellular glutathione (GSH). Ionizing radiation exposure has been shown to induce lipid peroxidation, DNA damage, protein oxidation and GSH depletion. It was postulated that cells sensitized by ethanol will be susceptible to additional insult, such as by radiation through increased oxidative stress. In this investigation, cultured liver cells (HepG2, human hepatocellular liver carcinoma) were exposed to ethanol, followed by ionizing radiation. The antioxidant status of the cells was evaluated by an array of techniques. Levels of glutathione, cysteine (CYS), and malondialdehyde (MDA) were measured by HPLC. Activities of antioxidant enzymes, catalase and glutathione reductase (GR) were determined enzymatically. Apoptosis was evaluated by the caspases-3 assay and fluorescence microscopy. The data showed that combined treatment with ethanol and radiation resulted in the lowest levels of GSH, and highest MDA level compared with the control. The catalase activity was lower in the combined exposure groups, when compared with the single agent exposure groups, and the glutathione reductase activity was the highest in the combined exposure groups and lowest in the control. These findings suggest that a combination of ethanol and ionizing radiation results in greater toxicity in vitro through elevated oxidative stress.

Cold tolerance: Behavioral differences following single or multiple cold exposures

Previous research has demonstrated that repeated exposure to cold water results in cold tolerance. The present set of experiments examined whether spontaneous behavioral activity and the rate of rewarming differed between cold tolerant and nontolerant rats. Animals receiving six cold exposures (one per day) were compared to subjects receiving a single cold exposure but cooled to match the final day temperature of the six-exposure group. Immediately following the final or only cold exposure, activity was measured by an activity monitor (Exp. 1) or was videotaped and scored by an independent observer (Exp. 2). Furthermore, rats' temperatures were monitored for 90 min (Exp. 2) and 60 min (Exp. 3) following the activity measurement. The results indicated that cold-tolerant rats exhibited activity similar to normal, noncooled subjects, whereas the activity in the single exposure group was impeded. Moreover, rats in the multiple exposure groups rewarmed more quickly than subjects in the single exposure condition. The third experiment also examined if the procedures of Experiments 1 and 2 resulted in associative cold tolerance. Experiment 3 replicated earlier findings, which have shown that exposure to the same cold stimulus in an altered context resulted in a loss of tolerance. These findings suggest that the processing of contextual stimuli is necessary for the acquisition of cold tolerance and that behavioral activity and rewarming rates can be used as alternative measures of cold tolerance.

Effect of Simultaneous Exposure to Methanol and Toluene Vapor on Their Metabolites in Rats

Effect of Simultaneous Exposure to Methanol and Toluene Vapor on Their Metabolites in Rats: Hajime Horn, et al. Department of Environmental Management I, School of Health Sciences, University of Occupational and Environmental Health, Japan—Wistar male rats were exposed to methanol and toluene vapors by inhalation individually and simultaneously. Blood was sampled from the tail of the rats at 0, 1.5 and 3 h after a 6‐h exposure and the methanol and/or toluene concentrations were measured by the headspace‐gas chromatography‐mass spectrometry (GC/MS). Major metabolites of methanol and toluene, that is, formic acid and hippuric acid in urine were measured at 0,18 and 42 h after the end of the exposure. The toluene concentration in blood in the simultaneous exposure group was lower than that in the toluene exposure one. The biological half time of toluene in blood in the simultaneous exposure group was shorter than that in the single exposure one. The excretion rate of hippuric acid in urine in the simultaneous exposure group was significantly lower than that in the toluene exposure one when both the methanol and toluene concentrations were 300 ppm. These results suggest that the metabolic rate of toluene was enhanced by methanol. On the other hand, the biological half time of methanol in blood and the formic acid concentration in urine were not significantly different in the single and simultaneous exposure groups, although the methanol concentration in blood in the simultaneous exposure group was lower than that in the methanol exposure one.

Working memory deficits induced by single but not repeated exposures to domoic acid

Single injections of domoic acid, given either intraperitoneally to mice or directly into the hippocampal formation of rats, have been shown to impair learning on the place version of the Morris water maze task and the eight arm radial maze task. The present study was designed to test whether both single and repeated exposures of intraperitoneally administered domoic acid (1.0 or 2.0 mg/kg) impair spatial working memory in mice on a delayed matching-to-sample task. DBA strain mice were given a series of four injections over a 7-day period consisting of either saline or one of two doses of domoic acid. During the 18 days of testing, each subject was given one trial per day consisting of one information run, followed by three test runs. On non-alternation days (days in which the correct response was the same as the preceding day) the saline injected group significantly outperformed the single injection 2.0 mg/kg domoic acid group. This indicates that domoic acid-treated animals were incapable of forming a memory that persisted for 24 h and hence were less able to utilize the prior day's experience. However, the repeated exposure groups did not perform as poorly on non-alternation days than the single exposure groups, indicating that domoic acid may affect multiple mechanisms involved in memory consolidation.

Inhalation Carcinogenesis of Repeated Exposures to High-fired 244CmO2 in Rats

Rats were given single or multiple (10 exposures at about 21-d intervals) inhalation exposures to 244CmO2 starting at 70 d of age. Mean lung and bone doses (+/- standard deviation) were 1.4 +/- 1.3 and 0.74 +/- 1.1 Gy, respectively, in the single exposure group, and 1.8 +/- 2.9 and 0.53 +/- 0.74 Gy, respectively, in the multiple exposure group. After cessation of exposure in the multiple exposure group, mean cumulative lifetime radiation doses to lung and skeleton were not significantly different in the two groups. The percentages of rats with lung and bone tumors were 9.1 and 12%, respectively, in the single exposure group, and 20 and 24%, respectively, in the multiple exposure group. However, the multiple exposure regimen did not significantly alter survival times or tumor incidences in lung or bone from a single inhalation exposure to 244CmO2 when survival patterns were taken into account.

Long Term Effects of Intense Sound on Endocochlear DC Potential

Changes in endocochlear DC potential (EP) after single and repeated intense sound exposure and negative EP induced by anoxia were observed in guinea pigs with passage of time. The intense sound used was a pure tone of 2 kHz at 145 dB SPL for 4 h. The single exposure group was divided into 8 groups of 1, 2, 5, 10, 20, 30, 45, and 60 days after sound exposure. The EP level dropped remarkably in the 1 and 2 day groups and recovered almost completely in the remaining groups. In the 60 day group, EP was significantly higher than that of the control group. The double exposure group consisted of 1, 2, 5, 10, 20, and 30 day groups after the second exposure at an interval of 30 to 40 days. EP in the 1, 2, 5, and 10 day groups was significantly lower than the control level and in the 20 and 30 day groups was almost the same as that of the controls. In all groups after single and double sound exposure, disappearance of negative EP during anoxia was observed. The EP decrease after sound exposure was apparently caused by a mechanical but reversible lesion at the stria vascularis. The disappearance of negative EP after sound exposure was thought to be induced by an irreversible lesion of Corti's organ.

Effects of Sublethal Exposure to Diazinon on Longevity and Temporal Division of Labor in the Honey Bee (Hymenoptera: Apidae)

When worker honey bees, Apis mellifera L., were exposed to sublethal pesticide concentrations, the majority of tests revealed no significant differences between control and treatment groups in the ages when tasks were conducted. Longevity was the most consistently affected category studied, with division-of-labor tasks not consistently affected. Single exposures to various concentrations of diazinon reduced longevity in one case and altered task performance in three cases—“clean,” “entrance,” and “forage.” In experiments that exposed workers once, twice, or three times to acetone or a dose of diazinon causing approximately 10% mortality, a number of adverse effects were seen; the majority were in the single-exposure groups. Longevity was reduced in two cases, and certain temporal division- of-labor tasks were adversely affected, especially nectar handling and foraging. Treatment age had a significant effect on the results, with workers treated at emergence being more sensitive to pesticide exposure than older workers (14 of the 20 significant results reported). Stress in the form of pesticide exposure and handling appears to be more harmful to newly emerged bees than any other age group. Longevity and foraging measures hold promise as potential methods of evaluating sublethal pesticide stress on the honey bee worker.