Adult Cytogenesis and Reproductive Regulation in the American Bullfrog

The purpose of the present study was to investigate seasonal changes in cell proliferation in the brains of adult American bullfrog. Our main question was whether there are seasonal differences in the proliferation and/or differentiation of newborn brain cells into arginine vasotocin- (AVT) or gonadotropin releasing hormone- (GnRH) producing neurons that might regulate bullfrog reproduction. . Bullfrogs in four distinct seasonal groups received injections of bromodeoxyuridine (BrdU), a thymidine analog that is taken up by dividing cells, and then euthanized six weeks later. Using doubleimmunofluorescence procedures to visualize BrdU and AVT or GnRH, we found no evidence for newborn AVT- or GnRH-ergic cells, but observed newborn cells in close proximity to AVT and GnRH cells. My project was a follow-up study to explore seasonal changes in adult cytogenesis related to AVT and GnRH terminal fields. GnRH fiber density fluctuated seasonally in the rostral pre-optic area (RPOA) and lateral septum (LS), and newborn cell numbers changed seasonally in the amygdala (AM) and RPOA. Seasonal differences in plasma testosterone concentrations were negatively related to GnRH fiber density in the LS. These results reinforce the seasonality of reproductive signaling and adult cytogenesis and support a role for seasonal steroid-peptide hormone interactions in modulating GnRH levels. Our results suggest a relationship between seasonal adult cytogenesis and reproduction, and set the stage for further research into the nature of this relationship.