17β-Estradiol Increases Persistent Na+ Current and Excitability of AVPV/PeN Kiss1 Neurons in Female Mice

Abstract

In vitro slice studies have revealed that there are significant differences in the spontaneous firing activity between anteroventral periventricular/periventricular preoptic nucleus (AVPV/PeN) and arcuate nucleus (ARC) kisspeptin (Kiss1) neurons in females. Although both populations express similar endogenous conductances, we have discovered that AVPV/PeN Kiss1 neurons express a subthreshold, persistent sodium current (INaP) that dramatically alters their firing activity. Based on whole-cell recording of Kiss1-Cre-green fluorescent protein (GFP) neurons, INaP was 4-fold greater in AVPV/PeN vs ARC Kiss1 neurons. An LH surge-producing dose of 17β-estradiol (E2) that increased Kiss1 mRNA expression in the AVPV/PeN, also augmented INaP in AVPV/PeN neurons by 2-fold. Because the activation threshold for INaP was close to the resting membrane potential (RMP) of AVPV/PeN Kiss1 neurons (-54 mV), it rendered them much more excitable and spontaneously active vs ARC Kiss1 neurons (RMP = -66 mV). Single-cell RT-PCR revealed that AVPV/PeN Kiss1 neurons expressed the requisite sodium channel α-subunit transcripts, NaV1.1, NaV1.2, and NaV1.6 and β subunits, β2 and β4. Importantly, NaV1.1α and -β2 transcripts in AVPV/PeN, but not ARC, were up-regulated 2- to 3-fold by a surge-producing dose of E2, similar to the transient calcium current channel subunit Cav3.1. The transient calcium current collaborates with INaP to generate burst firing, and selective blockade of INaP by riluzole significantly attenuated rebound burst firing and spontaneous activity. Therefore, INaP appears to play a prominent role in AVPV/PeN Kiss1 neurons to generate spontaneous, repetitive burst firing, which is required for the high-frequency-stimulated release of kisspeptin for exciting GnRH neurons and potentially generating the GnRH surge.

Changes in Both Neuron Intrinsic Properties and Neurotransmission Are Needed to Drive the Increase in GnRH Neuron Firing Rate during Estradiol-Positive Feedback

“…The neuromodulator kisspeptin acts directly on GnRH neurons to modulate multiple ionic currents, enhance GnRH neuron excitability, and stimulate AP firing (Pielecka-Fortuna et al, 2008Zhang et al, 2008Zhang et al, , 2013Adams et al, 2018b). AVPV kisspeptin expression is increased by estradiol treatment (Smith et al, 2005) and on the afternoon of proestrus (positive feedback during the cycle) (Smith et al, 2006), and these cells fire higher frequency APs and more bursts under these conditions (Zhang et al, 2015;Wang et al, 2016). We postulate that kisspeptin release during positive feedback enhances GnRH neuron responsiveness to the concurrent increase in GABAergic fast-synaptic inputs.…”

Regulation of persistent sodium currents by glycogen synthase kinase 3 encodes daily rhythms of neuronal excitability

“…29) before and after treatment with the selective persistent sodium channel blocker riluzole (20 μM, 3 min). The voltage ramp elicited an inward current in vehicle-treated cells at the range of I NaP activation, starting at −52.4±1.1 mV and peaking at −26.8±0.7 mV (as in refs 30, 31, 32; means±s.e.m. ; n =20 cells).…”

Arcuate Kisspeptin Neurons Coordinate Reproductive Activities with Metabolism

“…[36][37][38] Kisspeptin is the most potent and efficacious neuropeptide/neurotransmitter to excite GnRH neurons, 22,39,40 and Kiss1 neurons may be the presynaptic pacemaker neurons that drive GnRH neurons. 8,9,28,41 Although single action potential-generated calcium influx is sufficient to spark the release of classical neurotransmitters, burst firing or tetanic stimulation is required for the release of neuropeptides. Indeed, high-frequency electrical stimulation is required to evoke peptide release as originally demonstrated in the frog ganglion by Jan et al 42 (see the study by Arrigoni and Saper 43 for review).…”