Demonstration that the neural network for the LHRH surge generator is distinct from that for the pulse generator.

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In the present study, we revealed, by means of electrophysiological, immunohistochemical and molecular biological methods, that two distinct subgroups of LHRH neurons are involved in the control of two different modes of gonadotropin secretion, i.e., one is for preovulatory surge secretion and the other for pulsatile secretion, .1.LHRH surge generating neuronal systemIn the rat, LHRH neurons located in the preoptic area constitutes the LHRH surge generator with GABA neurons as an estrogen-responsive element. The generator receives the clock information from the suprachiasmatic nucleus (SCN) probably through neuronal pathways. Estrogen affects GABA neuronal activity by acting at mRNA transcriptional level and increasing glutamic acid dehydrogenase, and exerts inhibition on LHRH neurons. The inhibition mediated by GABA neurons is disrupted somehow in the afternoon of proestrus to make the surge of LHRH secretion. We are currently studying what is the mechanism for disrupting inhibition by GABA neurons on LHRH neurons and what kind of neurons send clock information from the SCN to the surge generator.2.LHRH pulse generating neuronal systemLHRH neurons located in the mediobasal hypothalamus constitute the LHRH pulse generator with opioid neurons as a mediator of negative feedback effects of estrogen. We are focussing the current study on what is the mechanism of synchronizing firing in LHRH neurons.