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GnRH-producing neurons are stimulated into production in response to spontaneous rhythms and by sensory impulses from sensory inputs derived from the external environment. Alterations in the internal conditions of the body can also result in altered GnRH production. For example in some species such as the sheep, there is seasonal sexual activity and the cerebral cortex, hypothalamus, pituitary and testes interact to regulate functions further along the signalling chain.  

GnRH-producing neurons are stimulated into production in response to spontaneous rhythms and by sensory impulses from sensory inputs derived from the external environment. Alterations in the internal conditions of the body can also result in altered GnRH production. For example in some species such as the sheep, there is seasonal sexual activity and the cerebral cortex, hypothalamus, pituitary and testes interact to regulate functions further along the signalling chain.  

====GnRH in Males====

In males there are between 4-12 GnRH peaks per day. Plasma concentrations of LH peak approximately 10mins post GnRH surge.  

====GnRH in Females====

In females when the oestrogen concentration prior to ovulation reaches a certain threshold, large quantities of GnRH are released in the form of a surge. This results in a corresponding peak in LH that stimulates ovulation. In females this surge centre is often called the '''preovulatory centre'''. In males this surge centre becomes inactivated during fetal life due to the brain maturation effects of estradiol (see section below) being able to pass through the blood brain barrier in males, please see the [[Reproductive_System_Development#Sexual_Differentiation_of_the_Brain|reproductive development of the brain]] for more details. In males there are between 4-12 GnRH peaks per day. Plasma concentrations of LH peak approximately 10mins post GnRH surge.  

Although the hypothalamus via GnRH stimulates the secretion of LH and FSH, it cannot regulate LH and FSH independantly. Therefore another hormone produced from the developing ovarian follicle in the female and sertoli cells in the male acts as a negative feedback mechanism for FSH. Sex hormones also alter the level of production of GnRH from the hypothalamus via a negative feedback system. High concentrations of progesterone or testosterone will reduce the secretion of GnRH and also therefore the secretion of LH and FSH.

===Leutinising Hormone (LH)===

===Leutinising Hormone (LH)===