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The effects of chloral hydrate (CH), an in vivo metabolite of trichloroethylene, have been evaluated by cytogenetic observations of mouse secondary spermatocytes after ip treatment with 82.7, 165.4, or 413.5 mg/kg bw. Hyper-haploid metaphases have been scored to determine whether previous observations in various nonmammalian organisms about an effect of this drug on the mitotic spindle could be confirmed in mice. At each dose, the frequencies of hyper-haploid cells have been estimated to assess the response of pachytene, preleptotene, premeiotic, and staminal gonial cells. Significant increases above the control value have been observed particularly after treatment of actively dividing gonial cells, confirming the results obtained with the same batch of the drug in a parallel collaborative investigation with Aspergillus nidulans. Thus: a) chloral hydrate has been shown to be effective in inducing nondisjunction in a mammalian system; b) a prevalent action on the mitotic spindle has been confirmed and quantified; and c) the usefulness of parallel investigations with different methods is stressed, particularly to collect information about the mechanisms of induction of nondisjunction events.

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