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the yield of chromosome breakage. Similar experi- mental cultures were done for SCE analysis, ad- ding BrdU during the last 48 h.

Our preliminary results show a slight, but not statistically significant, increase in chromosome aberrations (CA) in cultures exposed to EMF at 70 /~T (5.99% CA) and 145 /tT (6% CA) when compared with control cultures (4.9% CA, includ- ing gaps). These results show that a low-frequency EMF of 50 Hz has no clastogenic effect in human lymphocytes in vitro.

Cycloheximide effect on the Drosophila melano- gaster repair system

Guzm~n, J., O. Olivera, M.E. de la Rosa, C. Arceo, E. Pimentel, M. Cruces and C. Cortinas de Nava, Departamente de Radiobiologla I.N.I.N., Km. 36.5 Carret. Mexico-Toluca, Salazar Edo. de Mexico and Instituto de Investigaciones Biomrdi- cas, U.N.A.M., Mexico D.F. (Mexico)

Previous studies suggested that the irradiation of females could reduce the frequency of X-chro- mosome loss induced in mature fertilizing spermatozoa. This could be due to an induced repair system in Drosophila melanogaster. Cyclo- heximide is an antibiotic agent which inhibits the synthesis of proteins, by impeding the transfer of the aminoacyl RNAt to the polypeptidic chain. Due to the fact that an inducible response requires newly synthesized proteins it is possible to use cycloheximide to determine whether or not the phenomenon depends on protein synthesis. Ex- periments were designed in order to test whether or not the maternal repair system would be mod- ified with this treatment~ To determine the frequency of chromosome loss, 6-day-old females of strain Yw/Yw were mated to X c2 y f b b - / B s Y y÷ males. Eight groups were formed: (1) non- treated females with non-treated males; (2) females with cycloheximide treatment with non-treated males; (3) non-treated females with irradiated males; (4) cycloheximide-treated males; (5) irradi- ated females with non-treated males; (6) irradiated and cycloheximide-treated females with non- treated males; (7) irradiated females with irradia-

ted males; (8) irradiated and cycloheximide-treated females with irradiated males. For the cyclohexi- mide treatment, the feeding technique was used after having left them unfed for 6 h. The dose applied was 100/~g/ml in sucrose solution. All the groups that were irradiated received 2.5 Gy. The results showed an increase in the frequency of X-chromosome loss induced in mature sperma- tozoa in all the groups in which the females had been previously treated with cycloheximide as compared with non-treated females, regardless of whether they had been irradiated. This seems to indicate that the repair of DNA damage is less efficient in those cases in which cycloheximide was used.

Suspected spindle poisons analysed by micro- nucleus test using mouse bone marrow and human iymphocytes

Van Hummelen, P., Laboratory of Anthropo- genetics, Vrije Universiteit Brussel, Brussels (Bel- gium)

Eight compounds (econazole, chloral hydrate, hydroquinone, diazepam, tiabendazole, cadmium chloride, thimerosal and pyrimethamine) were selected for their specific action on the spindle. Colchicine and vinblastine were used as positive controls.

All the chemicals were tested by the in vivo micronucleus test (MNT) using mouse bone mar- row. Colchicine, chloral hydrate, hydroquinone and thimerosal were also tested by the in vitro MNT using human lymphocytes. In the in vivo MNT only colchicine, vinblastine and hydro- quinone were positive. The other chemicals did not induce micronuclei. However, econazole, cadmium chloride and thimerosal induced a sig- nificant decrease in the erythropoiesis of the tested animals. In contrast to colchicine and vinblastine, hydroquinone gave a positive result after 24 h but lost its effect after 48 h.

Results of the in vitro MNT indicate a positive effect of chloral hydrate, hydroquinone and col- chicine. Thimerosal was negative.