43. The Trial Study for Establishment of New Mutant Rat Strains Using the Chemical Mutagen

Yoshi-nobu Harada, Aya Sugyo, Atsushi Tsuji and Takashi Imai

Keywords: rat, mutagenesis, chlorambucil

The rat is an experimental animal which has been widely studied in medicine, pharmaceutical sciences, and biology. A method, however, is not available to establish model animals which have lost a specific gene function in rats. Mutagenesis is a good way to produce gene deletion model animals. The aim of our study is to establish a method for making gene deletion models of rats by chemical mutagenesis. It has been reported that chlorambucil could induce deletion mutation in mouse spermatid DNA. The same effect for chlorambucil can be expected it in rats.

A mating experiment was carried out by the following method. Male 12-week-old Brown Norway rats were given 1.0 mg/Kg, 2.5 mg/Kg, 5.0 mg/Kg, 10.0 mg/Kg or 15.0 mg/Kg of chlorambucil intracelially. Each male rat, after injection in with chiorambucil was mated with two normal F344 females at an interval of one week. Then the number of offspring born from F344 female was counted. The litter size observed in 1.0mg/Kg and 2.5mg/Kg injected groups was not different from the control group. However, in 5.0 mg/Kg, 10.0 mg/Kg and 15.0 mg/Kg injected groups, the litter size got from matings 3-4 and 4-5 weeks post-injection significantly decreased. The decrease of the litter size may be caused by dominant lethal mutation induced in the spermatid of the male rats. These results suggested that 5.0 mg/Kg or more chlorambucil could cause some mutations in the spermatid of male rats.