LHRH 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. Previous work in our lab 1) showed GABA was an important factor in the migration of LHRH neurons in nasal regions, 2) identified a novel gene termed NELF which we hypothesize acts via a homophilic interaction to influence LHRH neuronal migration on olfactory axons and 3) demonstrated that biosynthesis and secretion of LHRH in vitro mimics that seen in vivo. Over the past year, we have worked on the role of NELF by examining its expression after olfactory axotomy and establishing a system to produce full length NELF protein for biochemical and functional studies. To further elucidate the influence of GABAergic signals on LHRH neurons we have characterized the expression of GABAA receptor subunits in LHRH neurons and found two subunits, alpha 2 and alpha 6, show inverse changes over development ? alpha 2 increases while alpha 6 decreases. In addition we have performed a differential screen of LHRH neurons after GABAergic treatment and have begun to examine the role of these genes both in vivo and in vitro. One gene that was differentially expressed was the peptide CCK. To date we have shown that CCK is co-expressed in LHRH neurons during development and influences both movement and maturation of LHRH neurons. We also examined the expression pattern of calcium channels in LHRH cells as a function of development and the functional consequences of changes in these expression patterns with respect to LHRH cell migration and/or regulation. We have found that although N and L type channels are present, disruption of only the N type channel alters LHRH movement. Finally, based on work from last year which showed estrogen receptor beta subtypes in LHRH neurons, we have examined LHRH neuronal activity and the effects of estrogen on this parameter. First, we documented that LHRH neurons exhibit synchronized calcium oscillations, independent of CNS cues, which temporally correlate with pulsatile LHRH secretion. Recent experiments have found that estrogen has a direct effect of LHRH neuronal activity and increases the number of LHRH cells which participate in a synchronized calcium pulse. We hypothesize that this phenomenon is related to the positive feedback that occurs in vivo during the preovulatory surge. Future studies 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.
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