Effects Of Multiple Exposures Research Articles

Miotic Tolerance to Sarin Vapor Exposure: Role of the Sympathetic and Parasympathetic Nervous Systems

O-isopropyl methylphosphonofluoridate, also known as sarin or GB, is a highly toxic organophosphorous compound that exerts its effect by inhibiting the enzyme acetylcholinesterase. While the effects of a single exposure to GB vapor are well characterized, the effects of multiple exposures to GB vapor are less clear. Previous studies in the rat and guinea pig have demonstrated that multiple exposures result in tolerance to the miotic effect of nerve agents. The aim of the present study was to examine potential mechanisms responsible for tolerance to the miotic effect of GB vapor that has been observed in the rat after multiple exposures. Multiple whole-body inhalation exposures to GB vapor were conducted in a dynamic airflow chamber. Exposures lasted 60 min and each of the three exposures occurred at 24-h intervals. The results of the present study demonstrate that the alpha-adrenergic antagonist phentolamine and the beta-adrenergic receptor antagonist propranolol did not affect the development of tolerance to the miotic effect of GB vapor, suggesting that enhanced sympathetic tone to the eye is not responsible for the observed tolerance. Administration of atropine before the first exposure prevented the tolerance to the miotic effect of GB vapor after the third exposure, suggesting that the tolerance is the result of muscarinic receptor desensitization secondary to receptor stimulation. The present study extends the findings of previous studies to strengthen the hypothesis that the miotic tolerance observed in the rat upon repeated exposure to nerve agents is due to desensitization of muscarinic acetylcholine receptors located on the pupillary sphincter.

Effects of multiple exposures to d-cycloserine on extinction of conditioned fear in rats

Previous research has shown that an acute, post-training injection of d-cycloserine (DCS) facilitates extinction of conditioned fear in rats; however, the effects of multiple exposures to DCS in this situation are not known. In Experiment 1, rats were conditioned (light-shock pairings) and 24 h later given six extinction (light-alone) trials followed by an injection of DCS (15 mg/kg) or saline. The next day, all rats were tested for light-elicited freezing. In Experiment 2, the effect of DCS on extinction was tested in the same manner, except that rats were pre-exposed to DCS (0, 1, or 5 injections) just prior to conditioning. In Experiment 3, rats received five pre-exposures of DCS but conditioning occurred either 2 or 28 days after the last pre-exposure. The results showed that DCS facilitated extinction of conditioned freezing to the light CS when no drug pre-exposure had occurred, but pre-exposure to DCS just prior to conditioning disrupted the facilitation of extinction effect. When 28 days were interposed between pre-exposure and conditioning, the facilitatory effects of DCS on extinction were restored. These findings suggest that DCS has significant clinical value but that behavioral desensitization may occur with multiple exposures; however, desensitization is not permanent and is reduced by the passage of time.

Vitality analysis of Scots pines using a multivariate approach

Multivariate statistical methods were used to analyse the vitality of Scots pines ( Pinus sylvestris L.) by means of various biochemical, physiological, and nutritional characteristics, irrespective of tree age and without site-specific information. The vitality model was developed in three steps. First, artificial neural networks were used to select a minimal set of biomarkers as input variables with respect to the output variable circular surface increment (regression problem). In the second step, vitality states were classified by using the selected biomarkers (cluster analysis). Finally, discriminant analysis was applied to assign Scots pines to one of four classified vitality states. Sulfate sulfur (SO 4 2−-S), non-protein-nitrogen (NPN), arginine (Arg), and chlorophyll a (Chl a) proved to be the best dynamic input variables to reliably determine the vitality of Scots pines. As the results of regression problem solutions showed, the optimized neural network found growth responses to the driving variables that are valid for both young and mature pine stands. However, the sensitivity analysis of the neural network also indicated that of the four variables, sulfate is the least sensitive. Nevertheless, the sulfate response of the network can be successfully used to analyze the specific effects of multiple exposure on the vitality of Scots pines. To summarize final vitality model enables the vitality of Scots pines to be evaluated without reference to tree age or knowing the specific forest conditions.

Consensus report

Consensus report

Effects of multiple exposures of small doses of Pembina Cardium crude oil and diesel in rats.

In lands used for agricultural purposes, petroleum- or diesel-contaminated wastes and accidental spills of crude oil at some drilling sites pose exposure risks for occupational public, livestock, and wildlife. This study has assessed the effects of an Alberta crude oil, Pembina Cardium crude oil (PCCO), and a commercial diesel fuel #2 (CDF-2) in Sprague-Dawley rats after repeated exposures at small dose levels. Rats were given by gavage on day 1, 3, 5, and 8 specified dosages of either the control vehicle, methylcellulose (MC) (1.25 ml/kg), or PCCO (0.25-1.25 ml/kg), or CDF-2 (1.25 ml/kg). Exposure of rats to these dose levels of the test substances caused no overt symptoms of intoxication. A small but statistically significant increase in liver somatic index was observed in rats exposed to 1.25 ml/kg doses of PCCO and CDF-2; however, kidney somatic index was not significantly affected by these treatments. Blood analyses for hematological and clinical indicators of systemic impairments did not show any significant changes (p > 0.05) between the control and PCCO- or CDF-2-exposed rats. Biochemical assessment of liver and kidney tissues showed that compared to the control group, the PCCO- and CDF-2-exposed groups had a marked and significant increase (p < 0.05) in the hepatic activity of ethoxyresorufin-O-deethylase (EROD, a cytochrome P-450 [CYP] 1A1/A2-linked enzyme). In PCCO-exposed rats, the induction of EROD was dose-dependent. Exposure of rats with PCCO and CDF-2 also caused dose-related increases from the unexposed (control) or MC dosed rats in (1) hepatic activities of aryl hydrocarbon hydroxylase (AHH, a CYP 1A1-linked enzyme), ethoxycoumarin-O-deethylase (ECOD, a CYP 2B/1A-linked enzyme), glutathione transferase (GT), and NADPH-catalyzed microsomal lipid peroxidation; and (ii) ECOD activity in kidneys. The induction of hepatic CYP-linked enzymatic activities by PCCO and CDF-2 could be due to de novo synthesis of selected isoforms, as evidenced by the relative differences in the inhibition of EROD activity with 7,8-benzoflavone or metyrapone.

Acute exposure to the abused inhalant, isobutyl nitrite, reduced T cell responsiveness and spleen cellularity

Isobutyl nitrite is an inhalant abused principally by male homosexuals. We have reported that subchronic inhalation exposure (45 min/day for 14 days) to 900 ppm isobutyl nitrite was immunosuppressive. In the present study, the effects of acute exposure to the inhalant were examined. Mice were exposed in an inhalation chamber to 900 ppm isobutyl nitrite for 45 min. One day later, spleen cellularity was reduced by 39% without selectively depleting CD4 + or CD8 + cells. The numbers of peripheral blood leukocytes and peritoneal cells were also reduced. Following acute inhalation exposure, T cell proliferative responses stimulated with allogeneic cells or anti-CD3 and anti-CD28 antibodies were inhibited, while mitogen-induced responses were not affected. Purified T cells exposed to the inhalant also had compromised responses, suggesting a direct effect on T cells. However, the cumulative effects of multiple exposures were necessary to inhibit T-dependent antibody responses or T cell or macrophage cytotoxicity.

Individual causal models and population system models in epidemiology.

A group of individuals behaves as a population system when patterns of connections among individuals influence population health outcomes. Epidemiology usually treats populations as collections of independent individuals rather than as systems of interacting individuals. An appropriate theoretical structure, which includes the determinants of connections among individuals, is needed to develop a "population system epidemiology." Infection transmission models and sufficient-component cause models provide contrasting templates for the needed theoretical structure. Sufficient-component cause models focus on joint effects of multiple exposures in individuals. They handle time and interactions between individuals in the definition of variables and assume that populations are the sum of their individuals. Transmission models, in contrast, model interactions among individuals over time. Their nonlinear structure means that population risks are not simply the sum of individual risks. The theoretical base for "population system epidemiology" should integrate both approaches. It should model joint effects of multiple exposures in individuals as time related processes while incorporating the determinants and effects of interactions among individuals. Recent advances in G-estimation and discrete individual transmission model formulation provide opportunities for such integration.

The efficacy of clove oil as an anaesthetic for rainbow trout, Oncorhynchus mykiss (Walbaum)

The anaesthetic effects of clove-oil-derived eugenol were studied in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum). Acute lethality and the effects of multiple exposures to eugenol were measured. The estimated 8-96 h LC50 for eugenol was found to be approximately 9 p.p.m. Times to induction and recovery from anaesthesia were measured and compared with MS-222 under similar conditions. Eugenol generally induced anaesthesia faster and at lower concentrations than MS-222. The recovery times for fish exposed to eugenol were six to 10 times longer than in those exposed to similar concentrations of MS-222. Clove oil eugenol was determined to be an acceptable anaesthetic with potential for use in aquaculture and aquatic research. Doses of 40-60 p.p.m. eugenol were found to induce rapid anaesthesia with a relatively short time for recovery in juvenile trout.

Provocative appeals in anti-smoking mass media campaigns targeting adolescents--the accumulated effect of multiple exposures.

This paper reports findings from a longitudinal study that evaluated the accumulated effect of three consecutive mass media campaigns using provocative and dissonance arousing appeals to prevent cigarette smoking by adolescents. In the spring of 1992, all eligible adolescents aged 14 and 15 in one intervention county (N = 4898) and one control county (N = 5439) in Norway were included in the study, and were followed until they were 17 and 18 years of age in 1995. Only students who completed questionnaires both in 1992 and 1995 were included in the analyses. Among the non-smokers at baseline, a significantly lower proportion of adolescents of both genders had started to smoke in the intervention county compared to the proportion in the control county. Among those who were smokers at baseline, significantly more girls in the intervention county had stopped smoking than in the control county, while no significant difference between the counties was detected among boys. Our findings suggest that provocative and dissonance arousing appeals that create affective reactions and lead to interpersonal communication should be given more attention in campaigns designed to influence adolescent smoking. However, such appeals may easily produce negative reactions and the normative context should be thoroughly considered when using such appeals in future interventions.

In-plane displacement measurement using objective speckles in photorefractive two-beam coupling: effect of multiple exposures

A technique is proposed for the real-time measurement of in-plane displacement utilizing objective speckles and two-beam coupling in a photorefractive BaTiO 3 crystal. Speckles generated by a diffuse object in free-space geometry are used as the signal in two-beam coupling. The set-up is such that the phase shift between the refractive index grating and the interference grating is + π 2 (amplification mode). Due to the in-plane displacement, Young's fringes are obtained with a bright speckle background as a result of the signal amplification and beam fanning. The slow process of two-beam coupling amplification in a BaTiO 3 crystal is exploited for recording multiple exposures. This method of recording multiple exposures provides a simple and convenient way of analyzing the rigid body motions with enhanced accuracy by sharpening the fringes and with acceptable contrast. Theory has been developed to obtain the intensity distribution in the fringes formed in real time at the observation plane. Experiments have been conducted to show the validity of the theoretical results. Good agreement is established between the theory and the experiments.

Measurement of out-of-plane displacement in presence of in-plane component of motion; multiple-exposure speckle photography using converging beam illumination in free-space geometry

A theoretical and experimental analysis of the out-of-plane displacement measurement is carried out, showing the effect of multiple exposures on the circular fringes by recording fully correlated speckle patterns. Free-space geometry used for recording the motion is such that the measurement of the out-of-plane displacement can be made in presence of the in-plane displacement component of the motion without any decorrelation. This virtue of the recording geometry makes the setup capable of measuring the out-of-plane displacement component in a case of complex rigid body motion, without any shift in the point of null speckle displacement i.e. fringe centre. A good agreement is demonstrated between the theory and the experiments.

The effects of multiple UV exposures on HIV-LTR expression.

Previous studies have shown that cellular stress agents such as UV radiation induce transcription from the long terminal repeat (LTR) of the human immunodeficiency virus (HIV). Using HeLa cells stably transfected with the HIV-LTR sequence, which transcriptionally drives the chloramphenicol acetyl transferase (CAT) reporter gene, we examined the effects of multiple exposures to UVC (254 nm) on HIV-LTR-CAT expression. Low doses (< or = 5 J m-2) had no effect on CAT expression, but up to 29-fold induction was observed with 10 J m-2 when cells were harvested 48 h after completion of the exposure. Little difference was noted in induction levels when cells were exposed to one 25 J m-2 dose, viable cells were harvested at 24 h, 48 h or 72 h, and cell lysates were assayed for CAT expression. Two sequential 12.5 J m-2 exposures, given 24 h apart, resulted in an additive effect on CAT expression; these two exposures produced CAT activity equivalent to that induced following a single 25 J m-2 dose. This additive effect was not evident at the lower doses (< or = 5 J m-2) or at the higher doses. Maximal induction was observed using doses from 25 to 37.5 J m-2. Multiple exposures with either the low (< or = 5 J m-2) or high doses (> 25 J m-2) did not result in an additive effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental determination of the effective lithographic contrast for x-ray masks

A new technique for measuring effective lithographic contrast based on its definition is presented. Results obtained at the IBM Advanced Lithography Facility using the Helios storage ring are compared with conventional ways of determining mask contrast. In addition, a method to decrease the effects of multiple exposures in adjacent fields during the step and repeat operation of an x-ray lithography stepper is presented.

Evaluating effects of multiple exposure by means of palaeolimnological techniques

The acidification chronology of Gr. Arbersee (Bavarian Forest, Germany) was studied by means of subrecent diatom, and chrysophyte as well as metal (Al, Cu, Cd, Mg, Ca) stratigraphies. pH was inferred by diatom assemblages so that the simultaneous effects of acid and accompanying metals on chrysophytes could be evaluated. The occurrence of seven dominant Mallomonadacean taxa was related to the environmental variables by applying Spearman rank correlation and factor analysis. During the post-glacial period of natural acidification, increases in organic carbon and declining pH favor Mallomonas crassisquama and disfavor M. heterospina and M. caudata. Potentially toxic metals (Al, Cu, Cd) and the two alkaline earth metals (Ca, Mg) impact the occurrence as well. Although acidity appears to be also the major driving force during the recent acidification period, the occurring Mallomonadacean species may be differentiated by their tolerance toward Al and heavy metals.

Measurement of three-dimensional rigid body motion by multiple exposure speckle photography: use of uncollimated beam illumination in free space geometry

A theoretical and experimental analysis is carried out showing the effect of multiple exposures on fringes in the case of three-dimensional motion of a diffuse object illuminated by a diverging beam from a laser point source. Experimental conditions are such that the speckle patterns remain fully correlated in spite of the object moving in three-dimensional space in a direction that makes an angle with the optical axis. Owing to the in-plane component of the three-dimensional displacement the point of null-speckle displacement shifts either in the direction of the in-plane component of the motion or in the opposite direction depending upon the direction of the out-of-plane displacement component. This modifies the fringe profile as compared with the case of pure out-of-plane motion. The intensity distribution at the Fresnel plane of a specklegram is investigated after filtering by a converging beam for double exposure and multiple exposures. Good agreement is found between the theoretical and experimental results.

Multiple-exposure Speckle Photography of the Out-of-plane Motion: Comparative Performance of Filtering by Collimated and Converging Beams

Abstract A theoretical and experimental analysis is carried out, showing the effect of multiple exposures in speckle photography of the out-of-plane motion. The intensity distribution at the Fresnel plane is investigated in the case of filtering by a converging beam for double exposure and multiple exposures and the results compared with those of filtering by a collimated beam. Filtering by a converging beam provides fringes of good contrast. The plane of localization of the fringes shifts when an uncollimated beam is used for filtering and due to this shift the fringe profile is modified. The condition is investigated for complete matching of the theoretical and experimental fringe profiles without consideration of the plane of localization.

Measurement of axial motion by multiple exposure speckle photography: use of uncollimated beam illumination in free space geometry

A theory has been developed showing the effect of multiple exposures on the fringes formed in the case of axial motion of a diffuser illuminated by a diverging beam from a laser point source. Experimental conditions are such that the speckle patterns remain fully correlated. Filtering has been done by the converging beam. Fringe profiles, in the case of multiple exposures, have been investigated for unequal and equal exposure times, and good agreement was found between theoretical and experimental results.

Heating effect of microwave radiation in broilers

Abstract 1. Two experiments are reported in which a total of 1020 broiler chicks was used to examine the heating effect of microwave radiation. 2. In experiment 1, the effects of exposure time and age of birds were studied. In experiment 2, the influence of body mass and the effect of multiple exposures were explored. 3. In the first experiment, microwave treatment caused the birds’ body temperature to rise significantly only at 0, 1 and 2 weeks of age. Body temperature increased linearly with exposure time. 4. Signs of thermal stress were evident during exposure for 80 or 100s up to the age of two weeks. 5. The heating effect of microwaves in the second experiment decreased as the total irradiated body mass increased. For the same body mass, however, the heating effect was greater at the younger age. 6. The effect of using multiple exposures in experiment 2 was additive and varied with the age and body mass of the birds. 7. A model for the heating effect of microwave radiation is discussed which takes in...

Representational guidance of action production in observational learning: a causal analysis.

This experiment tested the hypothesis that the number of model presentations and verbal coding of modeled actions affect reproduction accuracy through their effect on cognitive representation. Subjects viewed a complex action pattern either two or eight times with or without verbal coding to highlight the dynamic structure of the component actions and their temporal sequencing. They then received, in order, a recognition test and a pictorial-arrangement test to assess the accuracy of their cognitive representations of the modeled actions. Subsequently, all subjects were tested for their ability to reproduce the action pattern from memory. Results showed that increased exposure to modeled actions enhanced the accuracy of both the cognitive representation and the behavioral reproduction. Verbal coding also increased cognitive and reproduction accuracy, but only when combined with multiple opportunities to observe the modeled actions. A causal analysis confirmed that the effects of multiple exposures and verbal coding were entirely mediated by changes produced in the accuracy of cognitive representation.

Speckle photography of out-of-plane motion: effect of multiple-exposures in free space geometry of recording

A theoretical and experimental analysis is carried out of the fringe formation in speckle photography of the out-of-plane motion of a diffuse object. Multiple exposure technique has been used to sharpen the fringes. Intensity distribution at the fringe plane is investigated in case of filtering by collimated beam of light for double and multiple exposures. A good agreement is found between the theoretical and experimental results.