Date of Award


Degree Type


Degree Name

Master of Science




Dr. Michael Lehman

Second Advisor

Dr. David Sherry

Third Advisor

Dr. Susan Meakin


Seasonal reproduction in sheep is determined by changes in the responsiveness of GnRH neurons to the negative feedback action of estradiol, mediated by dopaminergic afferents and dopamine D2 receptors (D2R). It is not known whether this influence acts directly onto GnRH neurons or indirectly via interneurons such as KNDy cells. In anestrous ewes, immunocytochemistry revealed D2R expression in ~50% of GnRH neurons independent of region. In contrast, using dynorphin as a marker, D2R colocalized >80% of KNDy cells and <10% of dynorphin cells of the POA. No seasonal variation was found in D2R expression in GnRH cells; however colocalization significantly increased in KNDY cells ¡h anestrous vs. breeding season. Immunochemistry found that kisspeptin fibres contact GnRH neurons synaptically. Results suggest that seasonal changes in this circuit are mediated by dopaminergic afferents contacting D2R-containing KNDy neurons, which in turn decreases expression of the stimulatory neuropeptide kisspeptin, inhibiting GnRH in seasonal anestrous.



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