Arcuate kisspeptin neurons display two types of calcium events: Regulation by sex, gonads, and senktide

The pattern of gonadotropin-releasing hormone (GnRH) release controls reproduction in vertebrates and is regulated by feedback from the gonads. Evidence is accumulating that steroid-sensitive hypothalamic arcuate kisspeptin-neurokinin B-dynorphin (KNDy) neurons drive GnRH pulses. KNDy neurons exhibit coordinated, large amplitude calcium signals in vivo that precede LH pulses; coordinated events persist in brain slice recordings of these cells. We used cre-lox to target GCaMP6f expression to KNDy neurons. Brain slice calcium imaging was done to identify putative unitary calcium events. Newly devised analyses identified two types of calcium events (fast and slow) in intact and gonadectomized male and female adult mice. Neurokinin B and the neurokinin-3 receptor agonist senktide are strong activators of action potential firing in KNDy neurons. The effect of senktide on calcium events over 5-min baseline and treatment periods was determined. Gonadectomy unexpectedly increased GCaMP6f fluorescence; illumination levels were adjusted to standardize initial levels. Senktide increased the frequency of fast and slow events; this effect was enhanced in gonadectomized mice for fast events. Senktide increased fast event amplitude only in gonadectomized mice. For slow events, in contrast, senktide increased amplitude in all groups, with the increase being larger in gonadectomized than intact mice. Differential regulation by gonadectomy and senktide modulation of fast and slow events suggests two separate mechanisms for these events, which likely also differ from the large amplitude events observed in vivo in KNDy neurons.