Neurotoxicity of organic solvents is one of the most important emerging issues in the field of occupational health. Psychological testing has been proven useful not only in clinical diagnosis but also in experimental and epidemiological studies. Although various psychobehavioral performance test batteries have been applied in the study of neurotoxicity of organic solvents during these last two decades among European countries and America, only few studies have been made on these in Japan. It is therefore considered very important to review the major papers published to date, clarify the issues being currently discussed, and propose important studies for future.
The present paper provides a review of the results obtained by the application of behavioral performance tests in the study of solvent toxicity. The studies reviewed are classified into the follwoing five parts: 1. psychological test batteries developed to date, 2. human experimental studies and experimental field studies on the acute toxicity of organic solvents, 3. epidemiological studies on industrial workers, 4. characteristics of the central nervous system dysfunction caused by organic solvents, and 5. prognosis of workers diagnosed as chronic organic solvent intoxication. The paper also discusses the applicability of psychobehavioral techniques and addresses issues in data collection in the study of the effects of solvent exposure on the nervous system.

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Prevalence rates of vibration syndrome in two groups of forestry workers who were employed in private enterprises in Fukushima Prefecture and were operating chain saws not less than 25 days a year were evaluated in relation to the vibration acceleration levels of chain saws and the total working hours per year with the tools. The lst group consisted of 261 workers (mean age and SD: 46.2±11.0 yr) who had begun to operate the tools between 1965 and 1976 and were examined at least once in 1976 or 1977 and the 2nd group of 225 workers (46.1±11.0 yr) who were at work between 1976 and 1987 and examined at least once during 1983 to 1988. The following results were obtained:
1. It was estimated that the maximum acceleration levels of the chain saws used between 1965 and 1975, and between 1976 and 1988 ranged approximately from 2.5 G to 8 G (mean: 5.1 G) and from 1 G to 2.5 G (mean: 1.7 G) by the one-third octave band filters, respectively. The average intensity of vibration was thus reduced by 89% after 1976.
2. The number of working days per year and hours per day with the tools were 157±70 d (mean±SD) and 3.7±1.3 h (mean±SD) in the first group and 120±55d and 3.0±1.3 h in the second group, respectively. Therefore, the average total hours per year decreased by 38% after 1976.
3. Prevalence rates of typical symptoms due to vibration syndrome such as Raynaud's phenomenon, coldness of hands, numbness or paresthesia of hands, and pain in hands or arms decreased remarkably among workers of the second group in comparison with those of the first group (p<0.001, respectively). Regarding to Raynaud's phenomenon, prevalence rates according to years of work with the tools in the first group and second groups were 0% and 2.8% within 4 years, 11.1% and 5.0% from 4 to 6 years, 30.2% and 0% from 6 to 8 years and 32.3% and 3.7% from 8 to 12 years, respectively.
4. It is concluded that the remarkable reduction in the prevalence rates of vibration syndrome during the course of some 10 years from 1976 to 1988 was attributable, first of all, to the marked reduction of acceleration levels of chain saws after 1976 and secondarily to the decreased total hours per year during which the tools were used.

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Sex difference of effects of single exposure of carbon monoxide (CO) on operant behavior was studied in adult rats. The animals were obtained by continued selective breeding and have a high level of avoidance ability and small individual differences (THA rat: Tokai high avoider rat).
Experiments were conducted as follows:
Exposure were carried out at the concentrations of 50, 100, 200 and 400 ppm of CO gas for 4h in THA rats, and their operant behavior was studied by Sidman avoidance test conducted 1 h before and after CO exposure. Rats whose carboxyhemoglobin (COHb) in blood was determined after the terminat on of CO exposure were of the same strain and age as those that under went operant behavior test. Exposure of CO 50 ppm did not produce any marked change in operant behavior.
In male rat groups, response counts in the Sidman avoidance test decreased after exposure to CO 100, 200 and 400 ppm when compared to the value before exposure, but increase in shock counts was observed only by exposure to CO 400 ppm.
In female rat groups, response counts decreased after the exposure to CO 200 and 400 ppm, but shock counts did not show any marked change at all the CO exposure concentrations.
COHb concentrations in medialety after the exposure to CO 50, 100, 200 and 400 ppm for 4 h were 9.1±1.2, 13.5±0.5, 24.3±0.7 and 43.6±1.6%, respectively, in males, and 9.2±1.1, 13.7±0.8, 24.0±1.0 and 42.0±1.4%, respectively, in females. Operant behavioral effect of CO exposure on male rats was more apparent than that on female rats. This finding was related to the difference in COHb decrease rate between male and female rats.

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The effects of lead on the drug metabolizing system in liver microsomes and porphyrin metabolism in the bone marrow were studied using male Wistar rats (about 250 g in weight). To study the acute effects of lead, rats were given lead injection intraperitoneally once a day for three consecutive days at a dose of 0 (control), 0.1, 1.0, 10 or 50 mg/kg of lead in the form of lead acetate in a 5% glucose solution. In the 2nd experiment, the chronic effects of lead were studied by administering lead at a dose of 0 (control), 5 and 20 mg/kg once a week for 9 wk for a total of 10 administrations. After the last injection, each rat was fasted for 22 h in a metabolic cage to prevent the animal from eating bed chips or feces and was then sacrificed by decapitation. The rat liver microsome enzymes were used to evaluate the effects of lead on the hepatic functions.
In the acute stage, lead decreased the activities of drug metabolizing enzymes, such as aniline hydroxylase and aminopyrine N-demethylase, and decreased the contents of microsomal cytochrome P-450 and cytochrome b₅. In the chronic stage, lead decreased the cytochrome P-450 and cytochrome b₅ contents and induced hypertrophic liver, but did not affect the activity of aniline hydroxylase. These findings suggest that the rat gradually gained resistance against lead toxicity in the chronic stage.
In a supplementary experiment, lead was found to decrease the contents of heme in the microsome and to increase the activity of hemeoxygenase. The contents of heme-protein, such as cytochrome P-450 and cytochrome b₅, were regulated not only by heme biosynthesis but also by heme degradation in the lead administered rats. Serum GPT and bilirubin showed no evident changes compared to the control in either the acute or the chronic stages in the hematological tests. Lead, however, increased total erythrocyte protoporphyrin (total EP) in rats administered lead for 9 wk in the chronic stage but not in those in the acute stage. The increase of total EP in the circulating blood might affect the life span of erythrocytes in the chronic stage.

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