Dr. Godwin's Abstracts i, j, & k from his
Bibliographic Publications from 1989-1998

Abstract i. Godwin, J., V. Hartman, M. Grammer, and D. Crews (1996). Progesterone inhibits female-typical receptive behavior and decreases hypothalamic estrogen and progesterone receptor messenger ribonucleic acid levels in female whiptail lizards. Hormones and Behavior 30: 138-144.

Female-typical sexual behavior in tetrapods is mediated primarily by estrogen and progesterone acting through intracellular receptors at specific sites in the mediobasal hypothalamus. Progesterone exerts both faciliatory and inhibitory actions on female sexual behavior and in well-studied rodent models, the inhibitory actions are exerted through downregulation of progesterone and estrogen receptors. This study examined progesterone effects on both female-typical sexual behavior and hypothalamic estrogen and progesterone receptor mRNA expression (ER- and PR-mRNA) in a sexual and parthenogenetic species of whiptail lizard. Progesterone capsules administered to ovariectomized female Cnemidophorus inornatus and Cnemidophorus uniparens following a receptivity-inducing dosage of estradiol benzoate (EB) strongly inhibited receptive behavior as compared to blank implanted controls. Progesterone capsules administered either before or after an EB injection also strongly downregulated ER- and PR-mRNA abundance in the ventromedial nucleus of the hypothalamus relative to blank implanted controls. The correlated decrease in both EB-induced receptive behavior and ER- and PR-mRNAs following progesterone administration are similar to findings in rats and guinea pigs, suggesting this is an evolutionarily conserved mechanism in the regulation of female sexual behavior.
Abstract j. Crews, D., J. Godwin, V. Hartman, M. Grammer, E. Prediger, R. Shepperd. (1996). Intrasexual variation in behavioral sensitivity to progesterone in male whiptail lizards and correlations with brain steroid hormone receptor mRNA expression. J. Neuroscience 16(22): 7347-7352.

A primary tenet of behavioral neuroendocrinology is that gonadal steroid hormones act on limbic nuclei to activate mating behavior in vertebrates. Traditionally, research has focused on the regulation of male-typical sexual behavior by testicular androgens and female-typical sexual behavior by ovarian estrogen and progesterone. Indeed, progesterone generally is regarded as an antiandrogen, acting centrally to inhibit sexual behavior in males. However, experiments with lizards, and more recently with rats, have challenged this paradigm. For example, exogenous progesterone induces mating behavior in some, but not all, castrated male whiptail lizards. The present study determined that implantation of progesterone into the anterior hypothalamus preoptic area of castrated, progesterone-sensitive males completely restored sexual behavior but failed to elicit sexual activity in castrated, progesterone-insensitive males. Further, androgen receptor -and progesterone receptor-mRNA expression in specific brain regions was significantly different in progesterone-sensitive versus progesterone-insensitive animals. Progesterone-sensitive males showed significantly higher relative abundance of androgen receptor-mRNA in the preoptic area, amygdala, and lateral septum, as compared with progesterone-insensitive animals receiving the same treatment. In contrast, progesterone receptor-mRNA abundance was lower in preoptic area of progesterone-sensitive males than in progesterone-insensitive males. No differences were found in the baseline abundance of androgen receptor-or progesterone receptor-mRNA in these nuclei between control groups of progesterone-sensitive and progesterone-insensitive males who were castrated but not implanted. This suggests that progesterone differentially regulates its own receptor as well as androgen receptor in areas of the brain involved in the control of sexual behavior of males and that the nature of this regulation shows individual variability.
Abstract k. Godwin, J., D. Crews, R.R. Warner. (1996) Behavioral sex change in the absence of gonads in a coral reef fish. Proceedings of the Royal Society, Series B 263 (1377): 1683-1688.

It is an axiom of vertebrate behavioural endocrinology that full expression of a male behavioural phenotype depends on testicular influences during development, in adulthood, or both. Sex change in fishes challenges this necessity: behavioural changes are often rapid and greatly precede gonadal changes. However, steroid hormones can have fast actions on the nervous system, so gonadal influences on behavioural sex change cannot be excluded based solely on the speed of these changes. We report that surgical gonad removal does not prevent or discernibly alter female-to-male behavioural sex change in a protogynous coral reef fish. Male behaviour assumption is instead purely dependent on attaining social dominance. This is the first example of a vertebrate fully expressing a male behavioural phenotype without current or prior exposure to a functioning testis.
End of subsite "jrgabs.i-k.html" for Dr. Godwin's Bibliographic Subsite, which you'll want to return to. Abstract subsite created for him 4-7-97 by J.Kemper. (http://www4.ncsu.edu/unity/users/g/godwin/www/jrgabs.i-k.html)