Richard A DeFazio

• Excitation-release coupling is a common feature in physiology. Action potentials depolarize the membrane potential near the release site, open voltage-gated calcium channels, and calcium influx triggers release. Pulsatile release of gonadotropin releasing hormone (GnRH) from neurons projecting to the median eminence regulates the release of luteinizing hormone and follicle stimulating hormone, which in turn drive gonadal function. Kisspeptin is a synaptic released peptide originating in two hypothalamic nuclei (arcuate and AVPV) and is a potent activator of GnRH neurons. Previous work in the Moenter lab demonstrated action potential-independent release of GnRH in brain slices. Preliminary evidence in GnRH neurons (and arcuate kisspeptin neurons) suggests large changes in intracellular calcium can occur independently from action potential firing (and action potential firing is not always associated with changes in calcium). We are harnessing the power of transgenic encoded calcium reporters with calcium imaging and electrophysiology to understand these physiologic mechanisms and ultimately their relationship to GnRH and kisspeptin release.
• Dynamic clamp permits direct evaluation of the realtime interaction between simulated conductances (voltage-gated and ligand-gated ion channels) and the electrophysiologic properties of neurons. Dynamic clamp provides a link between computational modeling and the temporal relationship between voltage-gated ion channels and synaptic potentials. Using classic whole cell electrophysiology, dynamic clamp, and in silico modeling, we have previously demonstrated that voltage-gated potassium channels can influence the amplitude of depolarizing GABA postsynaptic potentials in arcuate kisspeptin neurons. A similar role is hypothesized in GnRH neurons which have a stronger depolarizing GABA response. Dynamic clamp and in silico modeling can help elucidate the role of ion channels in the release of kisspeptin and GnRH, and in the response of GnRH neurons and gonadotropes.