Ambient air pollution alters heart rate regulation in aged mice

Context:?Heart rate alterations associated with exposure to particulate matter (PM) and gaseous pollutants have been observed in epidemiological studies and animal experiments. Nevertheless, the time-lag of these associations is still unclear.

Objective:?Determine the association at different time-lags between the complex mixture of ambient concentrations of PM, carbon monoxide (CO), and nitrogen dioxide (NO₂), and markers of cardiac function in a model of aged mice.

Materials and methods:?AKR/J inbred mice were exposed to ambient air, 6?h daily for 40 weekdays. During this period, the animals’ electrocardiogram (ECG), deep body temperature (Tdb), and body weight (BW) were registered, and concentrations of PM, CO, NO₂, as well as air temperature and relative humidity (RH) were measured. Data analysis included random effects models with lagged covariate methods.

Results:?CO was significantly associated with declines in heart rate (HR) and heart rate variability (HRV), PM was significantly associated with declines in HRV and BW, and NO₂ was significantly associated with declines in HR. Some significant associations occurred in the same day (PM and HRV, PM and BW, CO and HR), whereas others were delayed by 1 to 3 days (CO and HR, CO and HRV, NO₂ and HR, PM and HRV).

Discussion and conclusion:?Finding significant declines in heart function in aged mice associated with the combined effects of air pollutants at ambient concentrations and at different time-lags is of great importance to public health. These results further implicate the potential short term and delayed effects of air pollution on HR alterations.     

An analysis of cocaine effects on locomotor activities and heart rate in four inbred mouse strains

The effects of cocaine on Y-maze activity and heart rate have been examined in four inbred strains of mouse (BALB, C57BL, C3H and DBA). In addition, brain [3H]-cocaine concentrations were measured at the time of maximal response to cocaine. Cocaine produced a dose-related increase in Y-maze cross activity in C3H, DBA and C57BL, with C3H mice being considerably more sensitive than DBA or C57BL. Cocaine was without effect on Y-maze cross activity in BALB mice. Cocaine produced a biphasic effect on rearing activity in C3H mice, a dose related depression in BALB mice, and was without effect on C57BL and DBA mice. At the highest dose studied (15 mg/kg), cocaine produced a small decrease in heart rate in C3H mice. Strain differences in behavior were maximal 15 minutes after a dose of 5 mg/kg, IP. At this dose and time interval, brain [3H]-cocaine concentrations were not significantly different among the four strains of mice. The results suggest a genetically-determined difference in CNS sensitivity to cocaine.     

Stress-induced hyperthermia in mice: effects of flesinoxan on heart rate and body temperature

Stress-induced hyperthermia in mice has predictive validity for anxiolytic properties of drugs. In this paradigm, 60 min after drug administration rectal temperature is measured, which causes hyperthermia of 1-1.5 degrees C (DeltaT) in about 10 min. Flesinoxan, a selective 5-HT(1A) receptor agonist with anxiolytic-like properties, causes hypothermia, which complicates interpretation of stress-induced hyperthermia. Therefore, we combined flesinoxan treatment and the stress paradigm with radiotelemetric measurement of body temperature and heart rate, which is also related to anxiety. Subjects were either undisturbed or injected with flesinoxan (0-0.1-0.3-1.0 and 3.0 mg/kg), with or without the stress paradigm. Flesinoxan (1.0 and 3.0 mg/kg) caused a relatively long-lasting hypothermia, but did not lower heart rate. The rectal temperature procedure caused hyperthermia and tachycardia. Flesinoxan reduced the stress-induced hyperthermia and the tachycardia evoked by the stress procedure. Continuous radiotelemetric measurement of heart rate, apart from body temperature, revealed that flesinoxan has anxiolytic-like properties in mice.     

Beijing ambient particle exposure accelerates atherosclerosis in ApoE knockout mice

Background

Air pollution is associated with significant adverse health effects including increased cardiovascular morbidity and mortality. However research on the cardiovascular effect of “real-world” exposure to ambient particulate matter (PM) in susceptible animal model is very limited. In this study, we aimed to investigate the association between Beijing ambient particle exposure and the atherosclerosis development in the apolipoprotein E knockout mice (ApoE^−/− mice).

Methods

Two parallel exposure chambers were used for whole body exposure among ApoE knockout mice. One of the chambers was supplied with untreated ambient air (PM group) and the other chamber was treated with ambient air filtered by high-efficiency particulate air (HEPA) filter (FA group). Twenty mice were divided into two groups and exposed to ambient PM (n = 10 for PM group) or filtered air (n = 10 for FA group) for two months from January 18th to March 18th, 2010. During the exposure, the mass concentrations of PM_2.5 and PM₁₀ in the two chambers were continuously monitored. Additionally, a receptor source apportionment model of chemical mass balance using 19 organic tracers was applied to determine the contributions of sources on the PM_2.5 in terms of natural gas, diesel vehicle, gasoline vehicle, coal burning, vegetable debris, biomass burning and cooking. At the end of the two-month exposure, biomarkers of oxidative stress, inflammation and lipid metabolism in bronchoalveolar lavage fluid (BAL) and blood samples were determined and the plaque area on the aortic endothelium was quantified.

Results

In the experiment, the concentrations of PM₁₀ and PM_2.5 in PM chamber were 99.45 μg/m³ and 61.0 μg/m³ respectively, while PM_2.5 in FA chamber was 17.6 μg/m³. Source apportionment analysis by organic tracers showed that gasoline vehicle (39.9%) and coal burning (24.3%) emission were the two major sources contributing to the mass concentration of PM_2.5 in Beijing. Among the ApoE knockout mice, the PM group were significantly higher than the FA group in terms of serum total cholesterol, low-density lipoprotein, tumor necrosis factor-alpha (TNF-alpha) and C-reactive protein as well as TNF-alpha and interleukin-6 in BAL. Also the total antioxidant capacity and oxidized low-density lipoprotein were significantly different between the two groups. In addition, pathological analysis of aortic arch reveals that the plaques area in the PM group increased significantly compared to the FA group.

Conclusions

Our results demonstrated that ambient PM exposure could induce considerable oxidative stress and systemic inflammation in ApoE knockout mice and contribute to the progression of atherosclerosis.     

Genetic effects on PCP-induced stimulation in recombinant inbred strains of mice

The stimulation of motor activity by phencyclidine was found to differ significantly in BALB/c and C57B1/6By inbred strains of mice. Phencyclidene-induced stimulation was compared for these strains, their reciprocal F1 hybrids, and their recombinant inbred offspring. There were significant differences in responsitivity among the strains, suggesting a genetic influence on the PCP response; however, the strains did not segregate into two distinct groupings, suggesting that this genetic influence was not carried by a single gene. In addition, there was no relationship between the responsitivity of these strains of mice to PCP and their previously-reported responses to amphetamine or scopolamine, which suggests that PCP-induced stimulation is not a simple cholinergic or amphetamine-like response.     

Pharmacological effects on two inbred substrains of AB mice.

Mice of the two substrains AB/Gat and AB/Hal from the Jena AB inbred strain differ in behavior from each other by their aggressiveness occurring especially in the latter group after maturity. In order to ascertain the neurobiological background of aggressiveness, we injected mice of both substrains with either haloperidol, diazepam, or hexobarbital and measured their response on motor activity. In a second experiment, the reaction to a seizure evoking agent (pentylenetetrazol) was determined. Mice of both substrains were found to differ significantly in their reaction to haloperidol or diazepam injection. In contrast to that no changes in motor activity could be detected following hexobarbital administration. Animals of the aggressive AB/Hal substrain reacted more pronounced to pentylenetetrazol than those of the AB/Gat group. In conclusion, the varying aggressiveness of both AB mice substrains may be due to differences in dopaminergic and GABAergic neurotransmission.     

Combined air pollution particle and ozone exposure increases airway responsiveness in mice

We investigated whether coexposure to inhaled ambient particles and ozone affects airway responsiveness (AR, measured as enhanced pause, Penh) and allergic inflammation (AI) in a murine model of asthma. Ovalbumin-sensitized mice were challenged with either ovalbumin ("asthmatic") or phosphate-buffered saline (PBS) aerosols for 3 successive days. Immediately after daily challenge, mice were exposed for 5 h to concentrated ambient particles (CAPs), or 0.3 ppm ozone, or both, or neither (n > or = 61/group, 12 experiments). Exposure to CAPs alone or coexposure to CAPs + O(3) caused an increase in Penh in both normal and "asthmatic" mice. These responses were transient and small, increasing approximately 0.9% per 100-microg/m(3) increase in CAPs. Analysis of the effects of particle composition on AR revealed an association between the AlSi particle fraction and increased AR in "asthmatic" mice exposed to ozone and particles. No effects of pollutants on AI were noted. We conclude that (1) particle exposure causes an immediate, short-lived (<24 h) increase in AR in mice; (2) these responses are small; and (3) changes in AR may be correlated with specific elements within the particle mixture.     

Dose-dependent effects of heroin on memory in two inbred strains of mice

Heroin was administered to DBA/2 and C57BL/6 mice, trained in the five-choice Yerkes-Thompson-Bryant-Bovet-Nitti apparatus for pattern discrimination, in two sets of experiments. In a first set, pretrial administrations of heroin (0.1, 0.25, or 0.5 mg/kg) improved performance in both strains. In a second set, heroin (0.5 mg/kg) immediately following each training session were followed by performance improvements in both strains, while the performance of C57 mice was improved and that of the DBA mice was impaired by 5 mg/kg of opiate. No effect was evident in this set of experiments when heroin was injected 2 h after each session, suggesting that effects of the pretrial treatments were due to influences of the opiate on the consolidation processes of the strains tested.     

Chromosomal mapping of the psychomotor stimulant effects of cocaine in BXD recombinant inbred mice

To elucidate genes associated with cocaine's locomotor stimulant effects, we used recombinant inbred-quantitative trait loci (RI-QTL) analyses to identify chromosomal loci associated with locomotor activity before (baseline) and after cocaine treatment. RI-QTL analyses seek to identify associations between a quantitative measure of a phenotype and one or more previously mapped marker loci across a panel of RI strains. In the present study, 11 BXD RI strains were used to identify several putative QTLs for each phenotype. Both baseline locomotor activity and cocaine's locomotor stimulant effects are polygenic, with both unique and overlapping genetic influences. The largest associations for baseline activity were observed on chromosomes 5 and 9 and the largest associations for cocaine's psychomotor stimulant effects on chromosomes 3 and 17.     

Variation in effects of chlorpromazine in three strains of mice

Summary Mice of strains C3HeB/J, C57BL/6J and RF/J were trained in nondiscriminated avoidance (Sidman type). Experimental subject could terminate or defer shock by crossing between cage components. Controls received shock but could not control it. Chlorpromazine in doses up to 4 g/g body weight had no effect on the activity of controls. Avoidance activity, defined as the excess activity of experimentals, was reduced by the drug, particularly in C57BL. C3H avoided best at all drug levels. The poorest strain at low dosage was RF, at higher dosage, C57BL. The results suggest need for care in the choice of phenotypes in experimental pharmacogenetics.This investigation was supported in part by Public Health Service Grant MH-01775 from the National Institutes of Health.The author gratefully acknowledges the technical assistance of Jane Harris.     

Differential regulation of cocaine-induced locomotor activity in inbred long-sleep and short-sleep mice by dopamine and serotonin systems

Acute injection of cocaine increases locomotor activity of inbred long-sleep (ILS) mice to a greater extent than inbred short-sleep (ISS) mice. Strain differences in dopamine and/or serotonin (5-HT) neurotransmission could underlie these behavioral differences. Here, we found that dopamine D1, 5-HT(2A) and 5-HT3 receptor antagonists reduced cocaine-stimulated activity selectively in ILS mice. In contrast, 5-HT transporter (SERT) or 5-HT(1A) receptor antagonists potentiated cocaine-stimulated activity in ISS, but not in ILS, mice; this potentiation in ISS mice was abolished by dopamine D1 receptor blockade. Thus, in ILS mice, cocaine-induced activation of D1, 5-HT(2A) or 5-HT3 receptors is sufficient to produce locomotor stimulation. In contrast, ISS mice require pharmacologically increased 5-HT levels, which appear to result in increased dopamine neurotransmission, for cocaine-induced activation. Our results demonstrate strain differences in dopamine/5-HT receptor subtypes and their interactions that contribute to the differential behavioral responsiveness of ILS and ISS mice to cocaine.     

Ultrafine carbon black disturbs heart rate variability in mice

Previous epidemiological and toxicological studies have reported the associations between ambient particulate matter (PM) exposure and changes in heart rate variability (HRV), a marker of cardiac autonomic nervous system (ANS) function. However, both the responsible components in PM and their mechanisms affecting HRV remain uncertain. We propose that carbon black (CB), one of the main components in PM, may affect HRV through mechanisms independent of cardio-pulmonary and systemic inflammation and/or injury. Male C57BL/6 mice were exposed by intra-tracheal instillation to ultrafine CB (once every two days for three times) at doses of 0, 0.05, 0.15 and 0.6 mg/kg. HRV indices, standard deviation of all normal R-R intervals (SDNN) and the square root of mean of sum of squares of differences between adjacent normal R-R intervals (RMSSD), showed significant decreases in 0.15 and 0.6 mg/kg CB exposed groups. Slight pulmonary inflammation and myocardial injury were only observed in 0.6 mg/kg CB exposed group. We conclude that CB can disturb cardiac ANS function in mice, indicated by the withdrawal of parasympathetic modulation, through mechanisms independent of apparent myocardial and pulmonary injury.     

Behavioural effects of (-)naloxone in mice from four inbred strains

To study the role of endogenous opioid peptides in the regulation of behavioural responses to novelty, male mice from the inbred strains SRH, SRL, C57BL/6, and DBA/2 were injected IP with either saline alone, or the opiate antagonist naloxone, dissolved in saline, in dosages of 4 or 8 mg/kg. After 10 min, the animals were placed individually for 20 min in a novel environment and some 12 behavioural components were recorded. Naloxone reduced grooming and incipient rearing in all four strains and it reduced sniffing, leaning against the wall, and locomotor activity in some of them. Object-sniffing, object-leaning, defecation, freezing, and Straub tail elevation remained unaffected. The results for grooming and locomotor activity are largely in agreement with reports from others. Rather unexpectedly, the drug enhanced rearing responses in all strains. Although in several cases, a genotype-treatment interaction became apparent, the observed strain differences usually persisted and the correlations found between the behavioural components did not alter much. The naloxone-induced reductions in sniffing, leaning, locomotion, and grooming suggest endogenous opioid involvement in the control of behavioural activation in a novel situation. The increases in rearing possibly result from an additional agonist action of naloxone.     

Conditioned tolerance to the heart rate effects of smoking

This study extended our findings that behavioral tolerance to nicotine in animals can be influenced by conditioning to cardiovascular tolerance in humans. Subjects smoked one-half a cigarette during each of five trials. In the ten-minute intersmoking interval the contexts that preceded smoking were varied. Smokers in the Changing group attended to a different five-minute segment of a Sherlock Holmes radio mystery before each trial, while those in the Repeated group listened to the same segment of the tape. Presmoking heart rates were stable across the groups from trials 1 to 5. As predicted, heart rate for subjects who smoked in the same context showed tolerance to smoking from trials 1 to 5 (84.5 to 78 bpm), while subjects who smoked in in the same context showed tolerance to 83.9 bpm). COa levels increased equally for both groups over the five trials. The results of this study suggest tolerance to smoking can be influenced by learning.     

d-Amphetamine: disruptive effects on the long-term store of memory and proactive facilitatory effects on learning in inbred mice.

Male, C57BL/6J mice were given two daily trials on an appetitively-motivated successive brightness discrimination maze problem; they then received daily intraperitoneal injections of saline or d-amphetamine for 5 days. When trained again in the maze, mice in all d-amphetamine groups tended to display impaired retention: retention was significantly impaired in the 2.0 mg/kg group. Naive mice were treated exactly as were the pretrained mice except that they received no initial maze training prior to drug treatments. Mice in all naive d-amphetamine groups tended to display enhanced acquisition of the maze problem: acquisition was significantly enhanced in the 1.0 mg/kg groups. These results could not be explained as effects of d-amphetamine on attentional, motivational or other performance factors.     

Systemic effects of acute cigarette smoke exposure in mice

Abstract

Context: Cigarette smoke (CS) causes both pulmonary and extrapulmonary disorders.

Objective: To determine the pulmonary and extrapulmonary effects of acute CS exposure in regard to inflammation, oxidative stress and DNA damage.

Materials and methods: Mice were exposed to CS for 10 days and then their lungs, heart, liver, pancreas, kidneys, gastrocnemius muscle and subcutaneous (inguinal and flank) and visceral (retroperitoneum and periuterus) adipose tissues were excised. Bronchoalveolar lavage fluid samples were obtained for differential cell analysis. Inflammatory cell infiltration of the tissues was assessed by immunohistochemistry for Mac-3⁺ cells, F4/80⁺ cells and CD45⁺ cells. Oxidative stress was determined by immunohistochemistry for thymidine glycol (a marker of DNA peroxidation) and 4-hydroxy hexenal (a marker of lipid peroxidation), by enzyme-linked immunosorbent assay for protein carbonyls (a marker of protein peroxidation) and by measurements of enzyme activities of glutathione peroxidase, superoxide dismutase and catalase. DNA double-strand breaks were assessed by immunohistochemistry for γH2AX.

Results: CS exposure-induced inflammatory cell infiltration, oxidative stress and DNA damage in the lung. Neither inflammatory cell infiltration nor DNA damage was observed in any extrapulmonary organs. However, oxidative stress was increased in the heart and inguinal adipose tissue.

Discussions: Induction of inflammatory cell infiltration and DNA damage by acute CS exposure was confined to the lung. However, an increased oxidative burden occurred in the heart and some adipose tissue, as well as in the lung.

Conclusions: Although extrapulmonary effects of CS are relatively modest compared with the pulmonary effects, some extrapulmonary organs are vulnerable to CS-induced oxidative stress.     

The alteration of immune reactions in inbred BALB/c mice following low-level sarin inhalation exposure

To study the influence of low-level sarin inhalation exposure on immune functions, inbred BALB/c mice were exposed to low concentrations of sarin for 60 min in the inhalation chamber. The evaluation of immune functions was carried out using phenotyping of CD3 (T lymphocytes), CD4 (helper T lymphocytes), CD8 (cytotoxic T lymphocytes), and CD19 cells (B lymphocytes) in the lungs, blood, and spleen, lymphoproliferation of spleen cells stimulated in vitro by various mitogens (concanavalin A, lipopolysaccharides), phagocyte activity of peritoneal and alveolar macrophages, production of N-oxides by peritoneal macrophages, and the measurement of the natural killer cell activity at 1 wk following sarin exposure. The results were compared to the values obtained from control mice exposed to pure air instead of sarin. The results indicate that low doses of sarin are able to alter the reaction of immune system at one week following exposure to sarin. While the numbers of CD3 cells in the lungs, blood, and spleen were slightly decreased, an increase in CD19 cells was observed, especially in the lungs and blood. The reduced proportion of T lymphocytes is caused by decay of CD4-positive T cells. Lymphoproliferation was significantly decreased regardless of the mitogen and sarin concentration used. The production of N-oxides by peritoneal macrophages was stimulated after exposure to the highest dose of sarin, whereas their ability to phagocytize the microbes was increased after exposure to the lowest dose of sarin. The natural killer cell activity was significantly higher in the case of inhalation exposure of mice to the highest level of sarin. Thus, not only organophosphorus insecticides but also nerve agents such as sarin are able to alter immune functions even at a dose that does not cause clinically manifested disruption of cholinergic nervous system in the case of inhalation exposure. Nevertheless, the alteration of immune functions following the inhalation exposure to a symptomatic concentration of sarin seems to be more pronounced.     

Particle effects on heart-rate regulation in senescent mice

Because epidemiology studies consistently identify the elderly at risk for air pollution-related morbidity and mortality, we developed a model of senescent-dependent susceptibility based on indices of physiological aging. In the current study, we hypothesized that heart-rate regulation during particulate matter (PM) exposure differs with senescence-dependent susceptibility owing to variation in autonomic nervous control. Heart rate (HR) and heart-rate variability (HRV) parameters were measured from 162 samples of 2-min electrocardiograph (ECG) recordings in age-matched healthy (n = 5) and terminally senescent (n = 3) AKR mice during 3-h exposures to filtered-air (FA, day 1) and carbon black (CB, day 4; <200 microg/m(3)). On day 1, HR was significantly (p <.01) depressed during FA in terminally senescent mice. By day 4, HR was further slowed significantly (p <.01) due to the effects of CB exposure for 3 days. The combined effects of terminal senescence and CB exposure acted to depress HR to an average (+/-SEM) 445 +/- 40 bpm, or approximately 80 bpm lower compared to healthy HR responses. The change in rMSSD, an HRV parameter corresponding to relative influences of parasympathetic tone on HR, was significantly (p <.01) greater on day 1 and day 4 in terminally senescent mice compared to healthy mice. In contrast, the LF/HF ratio, an HRV parameter derived from spectral analysis indicating relative changes in cardiac sympathetic tone, was significantly (p <.01) depressed in terminally senescent mice on day 1. By day 4, significant increases in LF/HF were evident in healthy mice during CB exposure, suggesting that HR regulation was associated with an increase in sympathetic tone. Alternatively, terminally senescent mice appeared to modulate a lower HR without change in LF/HF ratio during CB exposure, suggesting an absence of sympathetic tone. In conclusion, older healthy mice increase cardiac sympathetic tone during PM exposure while terminally senescent mice show a greater PM-induced parasympathetic tone in regulating HR. The significance of the current results suggest that PM-induced HR regulatory changes may ultimately depend on the degree of physiological aging.     

Neurobehavioral effects of prenatal exposure to the organophosphate Diazinon in mice

Pregnant mice were given to daily dose of 0, 0.18, or 9.0 mg Diazinon per kilogram body weight throughout gestation. Mothers of all dose groups gave birth to viable, overtly normal offspring. However, pups born to mothers receiving the higher dose of the organophosphate grew significantly slower than controls and remained significantly smaller at 1 month of age. Offspring of mothers receiving the lower dose apparently were unaffected, but systematic behavioral testing revealed subtle deviations from normal developmental ontogeny as shown by significant delays in the appearance of the contact placing reflex and of sexual maturity (descent of testes or vaginal opening). Mature offspring of mothers exposed to either dose of the pesticle displayed impaired endurance and coordination on rod cling and inclined plane tests of neuromuscular function. Offspring from the 9.0 mg/kg group, in addition, had slower running speeds in a Lashley III maze and less endurance in a swimming test. Brains obtained after sacrifice at 101 days of age revealed neuropathology in the forebrains of offspring born of mothers exposed to the higher dose. Despite functional impairments in offspring from the lower dose group, no corresponding brain pathology was observed by examination under the light microscope.