NOVEL MECHANISMS UNDERLYING THE TRANSSYNAPTIC CONTROL OF LHRH RELEASE

Oregon Health & Science University, Portland OR

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Luteinizing hormone-releasing hormone (LHRH) secretion is controlled by transsynaptic inputs of both excitatory and inhibitory nature, in addition to glia-to-neuron signaling pathways. Neurons that utilize gamma aminobutyric acid (GABA) for synaptic communication provide the major inhibitory input to the LHRH neuronal network. We have demonstrated that, contrary to the prevailing dogma, the direct GABAA receptor (R)-mediated input to LHRH neurons is excitatory and not inhibitory. Using gene transfer-cell grafting techniques and transgenic approaches we demonstrated that a GABAergic tone is required for the normalcy of both LHRH neuronal migration and adult female reproductive capacity. We also identified the cellular mechanisms underlying the GABAAR-mediated excitation of LHRH neurons and identified genes that appear to be upstream components of the dual inhibitory/excitatory transsynaptic control of LHRH secretion. Studies are now being conducted to define the impact that each of these regulatory components may exert on the functional competence of LHRH neurons during female adulthood. The hypotheses being tested include: 1) that excitatory GABAAR-mediated inputs exerted directly on LHRH neurons are required for normal reproductive cyclicity, 2) that members of the novel FXYD family of ion transport-controlling proteins play in the regulation of LHRH secretion, 3) that Nell2, a novel gene specifically expressed in glutamatergic neurons, is an upstream regulatory element required for the glutamatergic control of reproduction, and 4) that a novel gene known as C14ORF4 plays a role in coordinating the dual excitatory/inhibitory transsynaptic control of reproductive cyclicity. The concepts derived from these studies are expected to increase our understanding of the cellular mechanisms underlying the loss of reproductive competence in human syndromes such as hypothalamic amenorrhea and idiopathic hypothalamic hypogonadism.