Intermediary role of kisspeptin in the stimulation of gonadotropin-releasing hormone neurons by estrogen in the preoptic area of sheep brain

Introduction: The role of estrogen in the stimulation of gonadotropin-releasing hormone (GnRH) neurons is clear. These neurons do not express estrogen alpha receptors, so other mediator neurons should be present to transmit the positive feedback effect of estrogen to the GnRH neurons. Kisspeptin neurons have an important role in the stimulation of GnRH neurons, so they can be the mediator of the effect of estrogen on GnRH neurons in preoptic area of sheep brain. One of the known effects of estrogen is the stimulation of Fos gene in the brain. The aim of the present study was to determine the intermediary role of kisspeptin in the transmission of estrogen effects to the gonadotropin-releasing hormone neurons in the preoptic area of sheep brain. Methods: Six mature ewes in breeding season were selected and ovariectomised. Three ewes in treatment group were injected with 50 mg estradiol benzoate in 1 ml of sunflower oil and three ewes in control group were injected with saline solution intramuscularly. Immediately after estradiol injections, the hypothalamus of the ewes was removed. The count of kisspeptin neurons, Fos genes, and kisspeptin neurons which colocalized with Fos genes were determined by immunohistochemistry. Results: Estradiol injection increased the colocalization of kisspeptin with Fos gene in the preoptic area of the sheep brain (P=0.01). Results of the present study showed that 86.9 percent of kisspeptin neurons colocalized with Fos gene in the preoptic area (P=0.01). Conclusion: Kisspeptin neurons are important mediators in transmission of positive feedback effect of estrogen into GnRH neurons in the preoptic area of sheep brain.