Ethyl methanesulphonate induced changes in the differentiation, structure and functions of spermatozoa of the house rat, Rattus rattus L.

Intraperitoneal administration of 500 mg/kg and 625 mg/kg doses of the germ cell mutagen, ethyl methanesulphonate (EMS) in 5 consecutive days to the house rat, Rattus rattus caused a dose-dependent reduction in its body weight, cauda epididymides weight, concentration, motility and percentage of live spermatozoa with simultaneous increase in the percentage of their abnormal forms. Compared to 0·65% spermatozoa with abnormal heads in the cauda epididymidis of untreated control rats, 24·86% and 65·72% such spermatozoa were observed in rats on day 14 post treatment with 500 mg/kg and 625 mg/kg doses of EMS respectively. On day 28 post treatment corresponding values for abnormal spermatozoa were 16·21% and 14·32%. Similarly, spermatozoa with abnormal flagella increased from 0·78% in control rats to 9·25% and 5·75% on day 14 post treatment of 500 and 625 mg/kg doses of EMS respectively and declined to 2·91% and 2·40% on day 28 post treatment. Abnormality in the sperm head was mainly due to acrosomelessness and in the flagellum due to bending at proximal region. However, the main effect of EMS was the development of spermatozoa without or deformed acrosomes which may impair the fertility of rats. Analysis of various stages of differentiation of spermatozoa inthe testis revealed that population of preleptotene and pachytene spermatocytes and of round spermatids showed a gradual decline which became significantly less than controls on day 28 of EMS treatment. Occurrence of abnormal heads of testicular spermatids indicated that the sperm head abnormalities originated in the testis during late spermiogenesis.

Conditioned taste aversion in lesser bandicoot rat, Bandicota bengalensis.

The lesser bandicoot rat after ingesting a sublethal dose of 0.025% zinc phosphide, in preferred food millet (Pennisetum typhoides) grains, for 4 days, showed aversion for 5-6 days towards plain millet offered in choice with the less preferred sorghum (Sorghum vulgare) grains. The aversion response to nontoxic bait was stronger (aversion index greater than 0.7) for first 3-4 days in individual and for 1-2 days in paired rats. 100% or more shift in aversion index from pre-treatment to post-treatment periods indicated that the aversive and naive partners of the heterosexual and unisexual female pairs mutually influence the feeding preferences of each other as a result of which they showed aversion for first 2-3 days to the plain food in which poison was given to one of the partner earlier.