Research in my laboratory concerns the neural and hormonal regulation of reproductive function, particularly male and female sexual behavior. Its primary goal is to understand how this regulatory system is affected by the seasonal change in day length that is experienced by species inhabiting temporate latitudes. Such species time their reproductive activities so that the birth of young occurs when environmental conditions are optimal for their survival. Our work utilizes the Syrian hamster, a species that exhibits profound alterations in reproductive competence throughout a full seasonal cycle. In summer-like conditions, in which the days are long, males and females are fertile and will readily mate. However, after approximately six weeks exposure to winter-like conditions, in which the days are short, both sexes become infertile and do not mate.
J. Bradley Powers
J. Bradley Powers
Reproductive Behavior and
Seasonality
Two features of this seasonal modulation of reproductive function are of particular interest to my laboratory. One is that it requires an intact pineal gland. The pineal is the primary source of the hormone melatonin which is secreted only at night; the duration of its secretion is proportional to night length. If hamsters are pinealectomized, thus removing the source of melatonin, they are incapable of responding appropriately to the seasonal change in day length. There is a great deal of interest in determining where in the brain melatonin acts to convey this day length information. A number of neural sites contain membrane receptors for melatonin but what functions they serve is unknown. One facet of our research involves direct exposure of specific brain sites to melatonin to evaluate whether or not they are necessary or sufficient to convey seasonal information.
A second feature of interest concerns the change in behavioral responsiveness to hormonal stimulation that hamsters exhibit when placed in winter-like conditions. If males or females are gonadectomized and later given appropriate steroid hormones for facilitating sexual behavior, they respond significantly more poorly if they have been exposed to winter-like, compared to summer-like conditions. We are investigating a number of mechanisms that might account for this altered behaviorial responsiveness. Our approaches include immunocytochemical analyses of steroid receptors and immediate early gene products in relevant sites of the central nervous system, comparing animals that have experienced either summer-like or winter-like day length conditions.
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