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Effects of Dietary Phytoestrogens on Paternal Responsiveness and Maturation in the Biparental California Mouse Aaron T. Stamp, Trey Amador studies; however, the method by which Nelson et. al (27) quantified sperm counts was not described. We considered the possibility that the differences in soy content between the diets used in our study were too small to affect our measures. This seems unlikely, as Wisniewski et al. (28) studied the effect of a high-Genistein diet of 300 ppm (almost 3 times as low as our HS diet) on C57BL/6 mice and found a significant decrease in testis size compared to mice not exposed to Genistein, with mice being of approximately equal age as those in our study (28). Another possibility is that the testes and fat pads are not as responsive to estrogens in California mice as in some other species; however, no data are available with which to evaluate this hypothesis. Analysis of body mass over time revealed that the LS group was initially heavier than the HS and MS groups but gained body mass more slowly over the next few months than the HS mice. This result is consistent with previous findings in which male C57BL/6 mice that were exposed to dietary Genistein weighed less than controls at the age of puberty (40-45 days of age) (28). Importantly, though, the only time point at which body mass differed significantly among our groups was at weaning and from week 1 through week 3 after weaning; at the time of sacrifice, no significant differences were observed. Therefore, it is unclear whether the increased body-mass gain in the HS group resulted from their diet or was simply an artifact of their lower body mass at the time of weaning. CONCLUSION AND FUTURE OBJECTIVES This is one of the first studies to determine if soy has an effect on parental behavior in any species. The results may be of interest to animal researchers, zoo administrators, and farmers, as soy is common in many animal feeds and bedding. This study also has implications for the human population, as soy consumption has been increasing steadily in the United States since the 1950’s (29). In the near future, we hope to assay the blood samples from our animals for plasma testosterone and Daidzein or Genistein concentrations, and to quantify ER-α expression in the collected brains, to further characterize possible effects of dietary phytoestrogens in male California mice. Eventually, a similar study examining organizational effects could be employed. References 1. Woodroffe R. & Vincent A. (1994). Mother’s little helpers: Patterns of male care in mammals. Trends in Ecology and Evolution. 9: 294–29. 2. Kleiman D.G. (1977). Monogamy in mammals. Quarterly Review of Biology. 52: 39–69. 3. Ribble, D. O. (1991). The monogamous mating system of Peromyscus californicus as revealed by DNA fingerprinting. Behavioral Ecology and Sociobiology. 29: 161–166. 4. Gubernick D., Schneider K.A., and Jeannotte L.A. (1994). Individual differences in the mechanisms underlying the onset and maintenance of paternal behavior and the inhibition of infanticide in the monogamous biparental California mouse, Peromyscus californicus. Behavioral Ecology and Sociobiology. 34: 225–231. 5. de Jong, T.R., Chauke, M., Harris, B.N., Saltzman, W. (2009). From here to paternity: neural correlates of the onset of paternal behavior in California mice (Peromyscus californicus). Hormones and Behavior. 56: 220-231. 6. Trainor B.C., Bird I.M., Alday N.A., Schlinger B.A., and Marler C.A. (2003). Variation in aromatase activity in the medial preoptic area and plasma progesterone is associated with the onset of paternal behavior. Neuroendocrinology. 78: 36-44. 7. Trainor B. C., Marler C. A. (2002). Testosterone promotes paternal behaviour in a monogamous mammal via conversion to oestrogen. Proceedings of the Royal Society of London Series B. 269: 823-829. 8. Verdeal K., Ryan D.S. (1979). Naturally-occurring oestrogens in plant foodstuffs – a review. Journal of Food Protection. 7: 577-83. 9. Liggins J., Bluck L.J., Runswick S., Atkinson C., Coward W.A., and Bingham S.A. (2000). Daidzein and Genistein content of fruits and nuts. Journal of Nutritional Biochemistry. 11: 326-331. 4 8 U C R U n d e r g r a d u a t e R e s e a r c h J o u r n a l
Effects of Dietary Phytoestrogens on Paternal Responsiveness and Maturation in the Biparental California Mouse Aaron T. Stamp, Trey Amador 10. Yildiz F. (2005). Phytoestrogens in Functional Foods. CRC Press, Boca Raton, pp. 3-5. 11. Dalsenter P. R., Santana G. M., Grande S. W., Andrade A. J., and Araujo S. L. (2006). Phthalate affect the reproductive function and sexual behavior of male Wistar rats. Human and Experimental Toxicology. 25: 297–303. 12. Naaz A., Yellayi S., Zakroczymski A., Bunick D., Doerge D., Lubahn D., Helferich W., Cookie P. (2003). The soy isoflavone Genistein decreases adipose deposition in mice. Endocrinology. 144: 3315-3320. 13. Sharpe R. M., Skakkebaek N. (1993). Are oestrogens involved in falling sperm counts and disorders of the male reproductive tract? The Lancet. 341: 1392−1395. 14. Levine S., Mullins Jr. R. (1964). Estrogen administered neonatally affects adult sexual behavior in male and female rats. Science. 144: 185-187. 15. Adams N.R. (1995). Organizational and activational effects of phytoestrogens on the reproductive tract of the ewe. Proceedings of the Society of Experimental Biology and Medicine. 208: 87–91. 16. Moyes C., Schulte P. (2006). Chapter 15: Reproduction. Principles of Animal Physiology. Pp. 634-665. 17. Gubernick D.J., Nordby J.C. (1992). Parental influences on female puberty in the monogamous California mouse, Peromyscus californicus. Animal Behavior. 44: 259–267. 18. de Jong T.R., Measor K.R., Chauke M., Harris B.N., Saltzman W. (2010). Brief pup exposure induces Fos expression in the lateral habenula and serotonergic caudal dorsal raphe nucleus of paternally experienced male California mice (Peromyscus californicus). Neuroscience. 169: 1094-1104. 19. Blumstein D.T., Daniel J.C. (2007). Quantifying behavior the J Watcher way. Sunderland, MA: Sinauer Associates, Inc. 20. Trainor B., Bird I., Marler C. (2004). Opposing hormonal mechanisms of aggression revealed through short-lived testosterone manipulations and multiple winning experiences. Hormones and Behavior. 45: 115-121 21. Hansen P.J. (2000). Use of a Hemocytometer. Dept of Animal Sciences, University of Florida. 22. Trainor B.C., Rowland M.R., Nelson R.J. (2007). Photoperiod affects estrogen receptor alpha, estrogen receptor beta, and aggressive behavior. European Journal of Neuroscience. 26: 207–218. 23. Kirkpatrick B., Kim J.W., Insel T.R. (1994). Limbic system fos expression associated with paternal behavior. Brain Research. 658: 112–118. 24. Brown R.E., Lee A.W. (2002). Medial preoptic lesions disrupt parental behavior in both male and female California mice (Peromyscus californicus). Behavioral Neuroscience. 116: 968–975. 25. Ehret G., Jurgens A., Koch M. (1993). Oestrogen receptor occurrence in the male mouse brain: modulation by paternal experience. NeuroReport. 4: 1247-1250. 26. Richeter C., Birnbaum L., Farabollini F., Newbold, R., Rubin B., Talsness C., Vandenbergh J.G., Walser- Kuntz D.R., vom Saal F. (2007). In vivo effects of Bisphenol A in laboratory rodent studies. Reproductive Toxicology. 24: 199-224. 27. Nelson R., Gubernick D., Blom J. (1995). Influence of photoperiod, green food, and water availability on reproduction in male California mice (Peromyscus californicus). Physiology and Behavior. 57: 1175-1180. 28. Wisniewski A., Klein S., Lakshmanan Y., Gearhart J. (2003). Exposure to Genistein during gestation and lactation demasculinizes the reproductive system in rats. Journal of Urology. 169: 1582-1586. 29. Messina M.J., Messina V. (1991). Increasing use of soyfoods and their potential role in cancer prevention. Journal of the American Diet Association. 91: 836-840. U C R U n d e r g r a d u a t e R e s e a r c h J o u r n a l 4 9
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