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. Author manuscript; available in PMC: 2010 Mar 1.
Published in final edited form as: J Neuroendocrinol. 2009 Mar;21(4):327–333. doi: 10.1111/j.1365-2826.2009.01826.x

Figure 1.

Figure 1

Model depicting possible feedback actions of estradiol upon the GnRH neuronal network. Oestradiol interacts with the circadian clock to produce diurnal changes in the regulatory network afferent of GnRH neurons, including changes in GABA and glutamate transmission and neuromodulation of GnRH neurons, resulting in a net negative afferent signal during negative feedback in the AM and positive feedback as the time of lights-out approaches in the PM. This produces an alteration between a strictly episodic GnRH signal and one that is elevated in surge mode for several hours. Oestradiol may also act directly on GnRH neurons in a positive manner that is independent of the circadian clock to modulate the output of these cells.