98.電磁環境特にマイクロ波のショウジョウバエの生体におよぼす影響 : 続報

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In recent years human life has been altered by the remarkable progress in the electromagnetic environment, suggesting the advent of a society with access to advanced microelectronics. It is, however, feared that electromagnetic waves may have adverse effects on human bodies. Since 1985, we have conducted irradiation tests as part of a basic study of the effects of electromagnetic waves on humans, using Drosophila, an eukaryote, and microwaves (2.45 GHz, with output powers of 550 W, 500 W, and 200 W) emitted by home-use microwave cookers (Tonomura and Shima 1986; Ono, Shima and Tonomura 1988; Tonomura, Shima, Suzuki and Kishi 1990). The current study proposes to establish the chromosomal aberration of somatic division, using preparations of salivary gland cells and ganglion cells which are somatic cells. (I) Additional test for somatic mutagenesis using wing-hair-spot tester stock. This is an irradiation test using third instar larvae and microwaves with output powers of 200 W and 500 W (Table 1). Flies irradiated with 200 W microwaves for five seconds developed wing-hair-spots at a high frequency; these results are considered to be positive in comparison with these for the controls. This is consistent with the results of the irradiation test with low-power microwaves for a short period (10 seconds or less) conducted by Suzuki (1990) in order to observe only the nonthermal effects of microwaves. (II) Observation of chromosomes of the somatic cells of larvae in the late period irradiated with microwaves of 2.45 GHz, with output powers of 200 W and 500 W, using a homeuse microwave cooker. (1) Chromosome samples were taken from third-instar larvae. For each output and irradiation, third-instar larvae were placed in styrofoam cages at the center of a microwave cooker. The salivary gland chromosomes are shown in photomicrographs in Fig. 1, a to j, and the ganglion chromosomes, in Fig. 2, a to j. The effects of the microwaves could be higher on third-instar larvae since they were in the process of pupation. An asynapsis of the chromosomal arms, an abnormal swelling of the euchromatin, and the collapse of the chromosomes were observed in 90-second sections at 200 W and in 5-second sections and 30-second sections at 500 W. In ganglion chromosomes, somatic nuclear division was notably reduced; no nuclear division was seen in the 90-second sections at either 200 W or 500 W. Moreover, the samples used in this test were not well prepared. We have also observed the rate of the emergence of adult flies from siblings used in this test. As may be seen in Fig. 3, the rate was 96 at 200 W in a 5-second section, the same as for the controls; 91 percent in 10-second section and 80 percent in 30-second sections, 72 percent in 60-second sections, and as low as 51 percent in 90-second sections. At an output power of 500 W, the rate was 95 percent in 5-second sections, 60 percent in 10-second sections, 49 percent in 30-second sections, 16 percent in 60-second sections, and 7 percent in 90-second sections. This suggests that these results were parallel with such damages as the changes in the salivary chromosomal arms and the somatic nuclear division of ganglion chromosomes. (2) We also irradiated larvae 72 hours after hatching (late second instar) with microwaves, waited until they reached third instar, and then observed the salivary-gland chromosomes and ganglion chromosomes with an eye to planning an experiment to determine the effects of irradiation on young larvae. Fig. 4 shows photomicrographs showing the salivary-gland chromosomes from each section using an output power of 200 W; these chromosomes were little different from the controls up to 60-second sections. However, significant puffs were seen on chromosomal arms in 90-second sections. It is not clear whether the puffs are a dynamic change in gene resulting from chromosomal bands on the chromosome arms of larvae between the third instar and the prepupa period, or simply an effect of microwaves. Fig. 5, a shows salivary-gland chromosomes in a 5-second section at 500 W, while b shows the chromosomes in a 10-second section at 500 W. Fig. 6 shows photomicrographs of the salivary gland in 30-, 60-, and 90-second sections. Ganglion chromosomes are shown in Fig. 7 for 200 W, and Fig. 8 shows the nuclear division of metaphase in each section at 500 W. Unlike the test (1), the results of this test were similar to those for the control. The samples were good, and there were a large number of nuclear divisions of salivary and ganglion chromosomes. One extremely interesting datum was obtained. At 200 W, 30-second section polyploidy cells are found among ganglion cells in one individual. The rate of occurrence was as high as three percent in 230 divided cells. This phenomenon may be attributable to the fact that the function of the spindle body deteriorated during the nuclear division of larvae in the process of development due to microwave irradiation (Fig. 7f). Another notable fact was found. Normally, Drosophila take 10 or 14 days from first-generation fertilization to adulthood. However irradiated with microwaves 72 hours after hatching needed at least one extra day for development. The rate of emergence was monitored as in the previous test. The rate was 79 percent at 200 W in 5-second sections, 95 percent at 10 seconds, 97 percent (the rate may have something to do with polyploidy aberration) at 30 seconds, 87 percent at 60 seconds and 86 percent at 90 seconds. At 500 W, the rate was 96 percent at 5 seconds (the same as in the control), 94 percent at 10 seconds, 93 percent at 30 seconds, 85 percent at 60 seconds and 72 percent at 90 seconds. In every section, 50 percent or more survived (Fig. 9). From the above tests, the following conclusions may be drawn: 1) Seventy-nine percent of the emergence at 5-seconds in the 200 W section could be the non-thermal effect of microwaves; 2) yound larvae irradiated with microwaves needed extra time before reaching the late third-instar period because their cells were weakened by microwaves and produced less energy per unit hour, resulting in a decreasein power and requiring time to recover the normol metabolic rate. (III) A plan was made to compare biologically the protein synthesis of the siblings used in Test (1) of (II) and those used in Test (2) of (II). According to the results of the one-dimensional electrophoresis method (Fig. 10), (1) sibling adult flies of the irradiation test using third-instar larvae (200 W, 5-second and 10-second only) revealed a decrease in over-all proteins in comparison to the control, rather than the disappearance of particular protein bands. This finding is important because it suggests that there remain effects on the stability or other similar elements of synthesized protein in addition to damage to third-instar larvae. A question remains as to the relation concerning the pupation hormone (ecdysone) that exists in the prepupa period prior to the metaphase from the late third-instar larvae. (2) No significant differences were observed in the electrophoresis patterns on sibling adult flies of the irradiation test using 72 hour larvae with 200 W and 500 W. We expected some changes in the electrophoresis patterns since there was a high rate of polyploidy in 200 W, 30-second sections. However, no changes were observed. One of the more important results obtained from the above experiments is the induction of polyploidy. This suggests the possibility of the induction of abnormal chromosomes in germ cells. We propose to perform an experiment next year with an emphasis on the effects on microwaves on the germ cells of Drosophila.
東京女子大学の論文
1992-03-16

98.電磁環境特にマイクロ波のショウジョウバエの生体におよぼす影響 : 続報

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