The Luteinizing Hormone Releasing Hormone System

Neurological Disorders And Stroke

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Abstract

LHRH (also known as GnRH-1) neurons, critical for reproduction, are derived from the nasal placode and migrate into the brain where they become integral members of the hypothalamic-pituitary-gonadal axis. We study mechanism(s) underlying LHRH neuronal differentiation, migration and axonal targeting in normal/transgenic animals, and nasal explants. Using these same models, our work also addresses the mechanisms regulating (intrinsic and trans-synaptic) LHRH gene expression, peptide synthesis and secretion in LHRH neurons. Multiple approaches are used to identify and understand the multitude of molecules and factors which play a role in directing the LHRH neurons to their final location in the CNS. These include differential screening of libraries obtained from migrating versus non-migrating cells, examination of molecules differentially expressed at key locations along the migratory route, morphological examination of the development of the LHRH system in knockout mice, and perturbation of molecules in vitro and subsequent monitoring of LHRH neuronal movement. As LHRH neurons migrate they also mature and the two processes may in fact be linked. To investigate the maturation of LHRH neurons we use calcium imaging, electrophysiology and biochemical measures to examine LHRH neuronal activity and peptide secretion. Continuing on work from the past years, further investigations into the role of GABA in LHRH neuronal migration was examined by mapping the development of LHRH cells in GAD67 knockout mice using immunocytochemistry. As in many of the animal models examined to date, the LHRH system although altered, is able to compensate for the loss of GABA. In addition we are continuing to characterize, using molecular and morphological approaches, LHRH expression in the developing incisor and are determining the lineage relation between these LHRH cells and neuroendocrine LHRH cells derived from the nasal placode as well as common transcription factors that might be important for initiating LHRH gene expression. Studies in progress center on the role of NELF (a ?migrational? molecule), cytokines, and growth factors in LHRH development as well as in situ characterization of the migration of LHRH neurons (real time microscopy). In addition, we continue to study the role of estrogen on LHRH neuronal activity and have recently finished a differential screen (constructed from single LHRH cells) between LHRH neurons ? estrodiol treatment. Currently, the genes identified are being examined at the cellular level (using either immunocytochemistry and/or in situ hybridization histochemistry). These studies will identify the best candidate genes to continue to characterize. Studies in progress examine the electrical properties associated with LHRH neuronal activity (combining electrical recording and calcium imaging). Future studies are designed to expand upon our present results and are directed at the molecules and cues important for development of the olfactory and LHRH neuronal systems as well as the mechanisms regulating LHRH neuronal activity. Specific studies in progress focus on: 1) isolation of midline cues which influence olfactory axon outgrowth; 2) the role of NELF and other molecules in LHRH migration, 3) identifying pacemaker molecules in LHRH neurons that participate in establishment/maintenance of rhythmic activity, 4) genes differentially expressed in LHRH neurons as a function of GABAergic signals and 5) the mechanisms by which estrogen alters LHRH neuronal activity.