Meeting Abstract

29.3  Monday, Jan. 5  Photic and non-photic regulation of GnRH-I in male European Starlings (Sturnus vulgaris). STEVENSON, T/J*; BERNARD, D/J; BALL, G/F; Johns Hopkins University; McGill University; Johns Hopkins University tsteve13@jhu.edu

In many temperate zone avian species, the vernal increase in photoperiod is the initial predictive cue that triggers a cascade of events leading to a shift in neuroendocrine state. In several photoperiodic species, changes in gonadotropin releasing-hormone-I (GnRH-I) secretion are primarily responsible for the seasonal variation in gonadotropin release from the pituitary gland and sex steroid synthesis. We recently cloned and characterized the GnRH-I cDNAs in two songbird species. This breakthrough permitted, for the first time, an analysis of GnRH-I mRNA expression in the brains of seasonally breeding European starlings (Sturnus vulgaris). We observed that GnRH-I mRNA exhibits marked variation across reproductive states with greatest expression observed in photostimulated males. GnRH-I mRNA levels gradually decrease to lower levels in photorefractory males, paralleling the observed pattern of testicular involution. These findings contrast data demonstrating that the decrease in GnRH-I protein occurs after testis regression. In addition to photoperiodic cues, social cues fine-tune the timing of reproduction. We recently found that male starlings paired with females have a greater number of GnRH-I immunoreactive (-ir) cells compared to males housed alone. Furthermore, the increase in GnRH-I-ir cells was localized in the rostral-intermediate region of the preoptic area. These data show for the first time that photoperiod-induced changes in reproductive physiology in starlings are associated with alterations in GnRH-I mRNA expression. Moreover, the GnRH-I system is directly regulated by social cues. Future studies will determine whether the latter similarly reflects a change in GnRH-I gene expression.