Does nitric oxide act in the ventromedial preoptic area to mediate oestrogen negative feedback in the seasonally anoestrous ewe?

Evidence that the mediobasal hypothalamus is the primary site of action of estradiol in inducing the preovulatory gonadotropin releasing hormone surge in the ewe.

Although a neural site of action for estradiol in inducing a LH surge via a surge of GnRH is now well established in sheep, the precise target(s) for estrogen within the brain is unknown. To address this issue, two experiments were conducted during the breeding season using an artificial model of the follicular phase. In the first experiment, bilateral 17beta-estradiol microimplants were positi...

Expression of gonadotropin inhibitory hormone in the preoptic area and its relation with phases of estrous cycle of ewe

Introduction: Gonadotropin inhibitory hormone (GnIH) has been known as a key inhibitor of the secretion of gonadotropin releasing hormone (GnRH). Ewe has estrous cycles comprising of follicular and luteal phases. Follicular phase is in turn divided into proestrous and estrous phases. Blood level of LH increases in follicular and decreases in luteal phases. The aim of the present study was to...

Oestrogen-induced LH surges in the anoestrous and cyclic ewe.

Unmasking the progesterone receptor in the preoptic area and hypothalamus of the ewe: no colocalization with gonadotropin-releasing neurons.

Progesterone powerfully inhibits GnRH secretion in ewes, as in other species, but the neural mechanisms underlying this effect remain poorly understood. Visualization of the neural ovine progesterone receptor has proved elusive but, using a high temperature antigen unmasking technique, the progesterone receptor was revealed in the ewe brain. Progesterone receptors were located in the preoptic-h...

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...