Genetic targeting of green fluorescent protein to gonadotropin-releasing hormone neurons: Characterization of whole-cell electrophysiological properties and morphology

GnRH neurons form the final common pathway for central control of reproduct ion, with regulation achieved by changing the pattern of GnRH pulses. To he lp elucidate the neurobiological mechanisms underlying pulsatile GnRH relea se, we generated transgenic mice in which the green fluorescent protein (GF P) reporter was genetically targeted to GnRH neurons. The expression of GFP allowed identification of 84-94% of immunofluorescently-detected GnRH neur ons. Conversely, over 99.5% of GFP-expressing neurons contained immunologic ally detectable GnRH peptide. In hypothalamic slices, GnRH neurons could be visualized with fluorescence, allowing for identification of individual Gn RH neurons for patch-clamp recording and subsequent morphological analysis. Whole-cell current-clamp recordings revealed that all GnRH neurons studied (n = 23) fire spontaneous action potentials. Both spontaneous firing (n = 9) and action potentials induced by injection of depolarizing current (n = 17) were eliminated by tetrodotoxin, indicating that voltage-dependent sodi um channels are involved in generating action potentials in these cells. Di rect intracellular morphological assessment of GnRH dendritic morphology re vealed GnRH neurons have slightly more extensive dendrites than previously reported. GnRH-GFP transgenic mice represent a new model for the study of G nRH neuron structure and function, and their use should greatly increase ou r understanding of this important neuroendocrine system.