The authors have devised an apparatus for monitoring the spontaneous locomotor activity of rats, with which the patterns of locomotor activity under the condition of light-dark cycle (light period: twelve hours from 6 a.m., dark period: the other half of the day) were analysed. In addition, changes in locomotor activities due to forced exercise (swimming) were recorded. The results obtained were as follows: 1. The patterns of locomotor activities in rats recorded by the monitor showed the same patterns as reported already by other researchers. The authors believe that this new apparatus can be used practically as a locomotor activity monitor. 2. Due to exhaustive exercise by swimming, changes of the ultradian rhythm in rats were observed. 3. By loading of swimming, locomotor activities in rats decreased significantly, especially in the dark period. These results suggest that this newly devised apparatus is useful as a locomotor activity monitor, and that the fatigue in rats caused by physical load can be shown as the change in locomotor activities.

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n-Hexane is widely used in industry as a solvent and is one of the main ingredients of many petroleum solvents. It is well known as a neurotoxic agent causing polyneuropathy. Methyl n-butyl ketone (MBK) is one of the new so vents but is not widely used in industry today, because it was found to be severely neurotoxic in the U.S.A. 2, 5-Hexanedione is not used as an organic solvent but is known to be neurotoxic. Their neurotoxicity and metabolism have been studied by some reseachers, because they may have similar metabolites. However, comparative toxicity of these three chemicals had not yet been studied enough. Comparative toxicity of them to the peripheral nerve was electrophysiologically studied in the present experiment. Conduction velocity and residual latency were measured in the rat's tail without anesthesia and operation in order to observe the changes of peripheral nerve function for a long time (Fig. 1). n-Hexane, MBK and 2, 5-hexanedione were orally administered to Wistar strain male rats everyday for 4 weeks (Table 1). Motor conduction velocity (MCV), mixed nerve conduction velocity (MNCV) and residual latency (RL) were repeatedly measured for 8 weeks. Nerve conduction velocity increased lineally in the rate of about 1 m/sec/°C within the temperature range from 21 to 38°C in the liquid paraffin bath (Fig. 3), and increased lineally with age from 42 to 110 days after rat's birth (Fig. 4). In n-hexane 0.1 ml/day group, MNCV (CA, i.e. for the span of tail between the points as indicated in Fig. 1) was significantly slower than the control on and after 4 weeks, and MCV and MNCV (CB, Fig. 1) were significantly slower than the control after 8 weeks, and the residual latency was significantly longer than the control after 8 weeks. In n-hexane 0.2 ml/day group, MCV and MNCV (CA, CB) were significantly slower than the control on and after 4 weeks. In MBK 0.1 ml/day group and MBK 0.2 ml/day group, MCV and MNCV (CA, CB) were significantly slower than the control on and after 4 weeks, and the residual latency in MBK 0.2 ml/day group was significantly longer than the control after 8 weeks. In 2, 5-hexanedione 0.05 ml/day group, MCV and MNCV (CA, CB) were significantly slower than the control on and after 2 weeks. In 2, 5-hexanedione 0.1 ml/day group, MCV was significantly slower than the control on and after 1 week, and MNCV (CB) on and after 2 weeks and MNCV (CA) on and after 4 weeks. And the residual latency was significantly longer than the control on and after 4 weeks (Figs. 5-9). Changes of nerve conduction velocities were correlative to body weights in the control and body weights of all groups administered with chemicals were significantly smaller than the control. Therefore, the increase ratio of conduction velocity per body weight gain (ΔCV/ΔBW) of rats was calcurated and compared with the control (Fig. 10). The calcurated values (ΔCV/ΔBW) in MBK and 2, 5-hexanedione groups were significantly smaller than the control. ΔCV/ΔBW in n-hexane group also tended to be smaller than the control, but the differences were statistically not significant. The experiment demonstrated that these chemicals could cause neuropathy in rats by oral administration as well as by inhalation and injection, and they were toxic to the peripheral nerve in the order of 2, 5-hexanedione>MBK>n-hexane. It also showed that the present method was relatively simple and useful to detect the early impairment of the peripheral nerve.

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1, 215 male workers using bush cleaners in Hokkaido were examined by the method based on the notification of the Labor Standard Bureau. The results obtained from clinically normal 548 workers among them were analysed especially on the finger skin temperature, vibratory sense threshold, maximum grip strength and endurable grip strength. 1) Data of the vibratory sense threshold, maximum grip strength and endurable grip strength showed normal distributions. Data of the finger skin temperature, however, showed a skewed distribution. 2) In parallel with aging, the vibratory sense threshold increased, in other words, lowered in function, and the maximum grip strength lowered. 3) The endurable grip strength measured by the five-time repetition method decreased along with aging. 4) Values of one-tail limit of the finger skin temperature were calculated in all 548 workers, and those of the vibratory sense threshold, maximum grip strength and endurable grip strength were done in each age group. The values were compared with the already proposed criteria and discussed.

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