Fast Scan Cyclic Voltammetry As a Novel Method for Detection of Real-time Gonadotropin-releasing Hormone Release in Mouse Brain Slices

Pulsatile gonadotropin-releasing hormone (GnRH) release is critical for the central regulation of fertility. There is no method allowing real-time GnRH detection in brain slices. We developed fast-scan cyclic voltammetry (FSCV) using carbon-fiber microelectrodes (CFME) to detect GnRH release and validated it using a biologically relevant system. FSCV parameters (holding potential, switching potential, and scan rate) were determined for stable GnRH detection in vitro, then optimized for GnRH detection in mouse brain slices. Placement of CFMEs in the median eminence (ME) near GnRH terminals allowed detection of both KCl-evoked and spontaneous GnRH release. GnRH release was also detected from GnRH fibers passing near GnRH soma and near fiber-fiber appositions in the preoptic area. No GnRH signal was detected from CFMEs in the ME of hpg mice, which lack GnRH, or in regions not containing GnRH neurons in wild-type mice; application of exogenous GnRH produced a signal similar to that observed for spontaneous/evoked endogenous GnRH release. Using an established mouse model that produces diurnal variations in GnRH neuron activity, we demonstrated corresponding changes in spontaneous GnRH release in the median eminence. These results validate FSCV to detect GnRH in brain slices and provide new information on the sites and amounts of GnRH release, providing insight into its neuromodulatory functions.