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J. J. Cowley and R. K. Pewtress

Summary. The daily exposure of newly born female mice to the urine of lactating mice with a small ano-genital distance accelerated the onset of first oestrus while the urine from donors with a large ano-genital distance was without effect in advancing puberty. The rate of growth of the mice exposed to the urine of lactating mothers was greater than that of a control sample but it was only those mice exposed to the urine of lactating females with a small ano-genital distance which continued to grow, after the cessation of treatment at 21 days of age, at a faster rate. There was no difference in the mass of the uterus when the mice were killed when adult but there were significant age-dependent differences in the mass of the ovaries and adrenal glands. The mice exposed to the urine from lactating mothers (with both large and small ano-genital indices) had smaller ovaries than the control mice while the adrenal glands of mice exposed to the urine of lactating mothers with a large ano-genital index were of greater mass than those of the control mice and mice exposed to mothers with a small ano-genital distance. Exposure to the urine of lactating mothers had no effect on the subsequent activity of the mice when tested in an automated activity recorder. The results confirm that urine from lactating mothers accelerates the onset of puberty and suggests that the effects are restricted to the urine from mothers with a small ano-genital index.

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J. J. Cowley, R. Pewtress and S. McDonald

Summary. Newly born TO strain female mice were exposed daily to the urine from male albino mice of the same and CFLP strains, from feral mice carrying Robertsonian translocation chromosomes and to water as a control condition. At 21 days of age, when exposure was discontinued, there were differences in body weight between treatments which were not present when adult. Exposure to urine from mice with Robertsonian translocations did not accelerate puberty and the interval between vaginal opening and first oestrus was longer (4·2 days) than in mice exposed to the urine from the albino strains (1·8 days). Mice exposed to the urine from the Robertsonian stock were in dioestrus more often than those exposed to the urine from laboratory strains. The Robertsonian mice also differed in their behaviour in an open arena in that they passed fewer faecal pellets than those exposed to the urine from the albino mice. The water control mice defecated the least frequently. The mice exposed to the Robertsonian urine were less active than the laboratory strains but the differences did not reach an acceptable level (P < 0·06) of significance.

Keywords: pheromones; mice; translocation chromosomes; sexual development

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D. Pomp, D. E. Cowley, E. J. Eisen, W. R. Atchley and D. Hawkins-Brown

Summary. Reciprocal embryo transfers amongst two inbred strains (C3HeB/FeJ and SWR/J) and their F1 cross (C3SWF1) were used to examine donor and recipient genotype and heterosis effects on survival and prenatal growth of mouse embryos. Among inbred strains, significant recipient genotype effects were detected for both embryo survival (P < 0·01) and prenatal growth (P < 0·05), while no donor genotype effects were observed. The recipient effect on overall embryo survival was due to a higher proportion of C3H recipients maintaining pregnancy to term than SWR recipients (P < 0·01), rather than survival within litters. Irrespective of their own genotype, embryos developing in C3H uteri achieved larger body weights (P < 0·01) and longer tail lengths (P < 0·05) at birth than did embryos developing in SWR uteri. Recipient heterosis was not significant, while donor heterosis was significant for prenatal growth traits (P < 0·001).

Keywords: embryo survival; uterus; maternal effects; genetics; mice