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Gonadal hormone regulation of behaviour in the Mongolian gerbil

University of British Columbia

Gonadal steroids have been found to influence a variety of behaviours in mammals. However, many of the models and hypotheses concerning the organizational and activational effects of gonadal steroids are based on data obtained primarily from the rat. Examination of the effects of gonadal steroids on behaviour in rodent species which differ from the rat in their ecological niche would aid in determining the generality of such hypotheses and models. The Mongolian gerbil, a relatively new laboratory animal, inhabits an environment quite different from that of the rat and could provide useful comparative data. The general purpose of the present study was to examine the effects of gonadal steroids on feeding and sexual behaviour in the female gerbil. In addition, the hypothesis that the extent of perinatal androgen-induced defeminization can be used to predict whether androgens or estrogens will be the primary regulator food intake and body weight in adulthood (and vice versa) was tested. In the first series of experiments, it was found that, in the female gerbil, as in other female rodents, ovarian steroids are primary regulators of sexual receptivity. When compared to other female rodents, the system regulating receptivity in the gerbil appeared to be less sensitive to estrogen as well as more dependent on the synergistic action of progesterone with estrogen for the induction of receptivity. The second series of experiments indicated that adrenalectomy significantly decreased sexual receptivity in the female gerbil, an effect not observed in other rodents. Further examination of this effect suggested that adrenal steroids, in addition to ovarian steroids, were essential for the elicitation of high levels of receptivity. However, although particular combinations of adrenal steroids did restore normal responding in animals tested with estrogen alone, they failed to eliminate the decreased receptivity observed when estrogen and progesterone were administered. Thus, in the gerbil, unlike other rodents, adrenalectomy appears to decrease the sensitivity of the system regulating receptivity to progesterone. The effects of ovarian steroids on food intake and body weight in male and female gerbils were examined in the third set of experiments. It was found that, in the gerbil, as in most other rodents, ovarian steroids appeared to be the primary hormonal regulators of food intake and body weight. However, unlike effects observed in other rodents, ovarian steroids were not found to be responsible for the sex difference in food intake and body weight, indicating the involvement of a non-hormonal factor. It was also suggested that interspecific differences in hormone-neurotransmitter interactions might be responsible for the differences in the hormonal effects on food intake and body weight. The findings that ovarian steroids were the prime hormonal regulators of food intake and body weight in the gerbil led to the prediction that perinatal androgens would defeminize the gerbil. At present, only rodents in which ovarian steroids exert the primary hormonal influence on food intake and body weight are defeminized by perinatal androgens. The final set of experiments indicated that, like other such rodents, the gerbil was also defeminized by perinatal androgens. In contrast to effects in the rat, none of the experimental treatments resulted in behavioural masculinization although significant physiological masculinization was observed. The ability of present models of the differentiation process to account for these results was examined and a more general concept proposed. The concept proposed also provides a possible link between interspecific differences in the differentiation of sexual behaviour and the differentiation of other hormonally mediated behaviours. The results of the present study indicate that the organization and activational effects of sex steroids in the Mongolian gerbil are unique in several respects and that further investigation should aid in developing and refining present models of the hormonal regulation of development and behaviour.

Text

2010-03-29

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http://hdl.handle.net/2429/22922

Psychology

University of British Columbia

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