Seasonal Changes in GnRH Neurons and Effects of Dietary Monoamine Precursors on the Hypothalamic-Gonadal Axis in House Sparrows (Passer Domesticus).
Date of Award
Doctor of Philosophy (PhD)
Patricia A. Melrose
Albert H. Meier
Mechanisms modulating avian seasonal reproduction involve a complex interaction between exogenous environmental information and internal physiologic systems, such as functional changes in the hypothalamic-gonadal axis and changes in the influence of monoaminergic neurotransmitters on hypothalamic neuroendocrine cells. This project was undertaken to describe seasonal changes of the testes and immunoreactive-(ir)-gonadotropin-releasing hormone (GnRH) neurons in House Sparrows in southeastern Louisiana, and to examine the role of monoaminergic neurotransmitters in modulating seasonal reproduction through the use of dietary monoamine precursors. Testicular weights rapidly increased from February to March, peaked from April to July, when the seminiferous tubules were spermatagenically active and filled with stratified germinal epithelium and prominent Leydig cells. There was a decrease in stratified epithelium in August, and by September, testicular weights had decreased to weights similar to those of testes previously collected in January. Histologically, September tissues showed little stratified epithelium and an increase in fibroblastic interstitial tissue. More ir-perikarya were identified in brains collected in June (mean $\pm$ SEM = 214.00 $\pm$ 7.50) compared to January (37.66 $\pm$ 14.57) (F = 65.97, DF = 1,5, P $<$ 0.001). During January, significantly more bipolar neurons (58.81 $\pm$ 1.38%) were observed than either multipolar (20.82 $\pm$ 1.61%) or unipolar (20.43 $\pm$ 1.93%) cells (F = 5.36, DF = 1,20, P $<$ 0.005), whereas in June, there were more (P $<$ 0.05) multipolar perikarya than bipolar (58.93 $\pm$ 0.57% and 41.14 $\pm$ 0.68%, respectively) cells; unipolar cells were not found. In September, no ir-perikarya were detected. In April and September, L-tryptophan and L-DOPA were individually added to the sparrows' diets. Compared to control birds (above), tryptophan-fed birds sacrificed in April showed a decrease in testicular weights and numbers of ir-GnRH perikarya. Tryptophan-fed birds sacrificed in September did not differ from controls. Although no effect was observed in April, birds fed L-DOPA and sacrificed in September had testicular histologies and numbers of ir-GnRH perikarya (46.25 $\pm$ 5.76), similar to the control January birds (F = 0.760, DF = 1,68, p $>$ 0.05). It was hypothesized that both monoamine precursors effectively reset the timing of seasonal shifts in the avian reproductive cycle.
Meseke, Christopher Andrew, "Seasonal Changes in GnRH Neurons and Effects of Dietary Monoamine Precursors on the Hypothalamic-Gonadal Axis in House Sparrows (Passer Domesticus)." (1997). LSU Historical Dissertations and Theses. 6507.