To clarify the neurochemical basis of methyl bromide toxicity in rats, we measured changes in the sensitivity of cerebral monoamine, dopamine (DA) and norepineph-rine (NE) receptors, using abnormal behavior and locomotor activity as indicators of receptor sensitivity. Apomorphine and clonidine were used as specific agonists of DA (D1 and D2) and NE (α2) receptors, respectively. In the first experiment, rats were exposed to methyl bromide gas at 25-200 ppm for 8hr once or to methyl bromide at 5-50 ppm 8hr a day for 7 days. The intensity of stereotyped oral (STO) behavior produced by an injection of apomorphine, 0.5 mg/kg i.p., was rated over the following 28 days. The STO behavior of rats exposed to methyl bromide (MB rats) was much more intense than in air-exposed (control) rats. This finding strongly suggests that the sensitivity of striatal DA, D1 and D2, receptors to apomorphine was increased by methyl bromide exposure. In the second experiment, rats were exposed to 50 ppm methyl bromide for 8hr once or to 10-50 ppm methyl bromide 8hr a day for 7 days. Seven days after the final exposure, rats were injected with a small dose of apomorphine, 0.3 mg/kg i.p., and the counts of apomorphine-induced locomotor activity (ALA) were recorded. The ALA counts of MB rats were markedly higher than in the control rats. This finding suggests that the DA receptors in the nucleus accumbens of MB rats are more sensitive to apomorphine than those of control rats. In the third experiment, rats were exposed to 50 ppm methyl bromide, 8hr a day for one day or 7 consecutive days, and the degree of attenuation of locomotor activity following clonidine injection (CLA) was rated. CLA counting was performed 7 days after the final exposure. CLA counts in MB rats were not attenuated as much as in the control rats. This indicates that the cerebral NE receptors, i.e., α2-adrenoceptors, of MB rats may be less sensitive to clonidine than those of control rats. Increased behavioral sensitivity to apomorphine was observed in rats even when exposed to 5 ppm (TLV) methyl bromide.
To monitor the exposure to mercury (Hg) vapor among university staff members and students who occasionally handle elemental Hg in laboratory experiments, urine samples were collected at health examinations conducted by the Health Service Center, University of Tokyo, for six years. Geometric mean of urinary Hg concentrations of 343 samples collected from 234 subjects was 1.61, ug Hg/g creatinine (Cr), with the range of 0.30 to 9.31, ug Hg/g Cr. Elevated urinary Hg levels, i.e. 3 fig Hg/g Cr or higher, were found only among the subjects who worked in several laboratories. This urinary Hg level is judged to correspond to 1-2μg/m3 of air Hg concentration in working areas. The contribution of dental amalgam fillings to urinary Hg excretion, though it exists, was concluded to be small from the result of multiple regression analysis.
A cross-sectional analysis on the dose-related change in time domain spirogram indices induced by lifetime cigarette consumption was conducted to examine the ability of those indices to detect early changes in the lung periphery in comparison with conventional spirometric indices. The subjects were asymptomatic healthy male workers from three occupational cohorts including asbestos workers and welders. They were asked to perform the forced expiration maneuver at least three times to obtain reliable results. A total of 893 subjects were enrolled in the study, and 484 of them who were aged 30 years or more and were free from chronic respiratory symptoms and abnormalities in chest radiography and spirometry, were analyzed. Although conventional indices, such as forced expiratory volume in one second and maximal midexpiratory flow, were not significantly different between smokers and nonsmokers, the standard deviation of transit times and of time constant distribution in smokers were significantly elevated compared with nonsmokers. Furthermore a dose-related change accord-ing to lifetime cigarette consumption was observed in those indices. We conclude that time domain spirogram indices, especially the standard deviation of time constant distribution, would be more useful than conventional indices in detecting early changes in the lung periphery.
A reagent consisting of 0.4% of nitrobenzyl pyridine and 0.5% of sodium acetate in ethanol was found to be applicable as a sampling and coloring solution to a sensitive and relatively specific spectrophotometric determination of phosgene. This method is a modifica-tion of the method developed by Noweir et al. An aqueous 0.005% methyl orange pretrap was used to eliminate interference with chlorine and hydrogen chloride which are likely to be encountered in industrial environment. This colour produced by this method was stable for 2 hours, reduced by 3% and 7% after 3 and 4 hours of sampling respectively. The method is so sensitive as to detect phosgene at a concentration of 0.1 geml in the sampling solution with the coefficient of variation (CV) of 4.5%. The collection efficiency of phosgene with the sampling solution was found to be greater than 98% at a sampling rate of 1l/min.
Noise levels were evaluated before and during aerobic sessions in 3 aerobic studios. In addition, hearing threshold levels (HTLs) of 10 female aerobic instructors with the mean (±SD) ages of 25.4 (±12.4) years were measured before and 2 min after an aerobic session. The mean (±SD) of total instruction time of these subjects was 1274.0 (±704.9) h. Before the aerobic session, noise level was 63 dB(A) and increased to 87 dB(A) during a warm-up period. The highest noise levels of 93-96 dB(A) were recorded during a peak exercise period and decreased to 73 dB(A) during a cool-down period. The dominant spectra of sound pressure levels (SPLs) during the aerobic session were in the frequency range of 1-2 kHz at levels of 75-88 dB(C). The mean values of HTL obtained for each ear of these subjects were between 5 and 15 dB in the frequency range of 1-8 kHz. No significant differences in the mean HTLs of pre-and post-aerobic sessions could be obtained. The mean values of HTL of two groups of subjects divided by their total instruction time (n =5 in each group, and p<0.01 in their total instruction time) were quite comparable.