Abstract
Introduction: Synchronous and pulsatile neural activation of kisspeptin neurons in the arcuate nucleus (ARN) are important components of the gonadotropin-releasing hormone pulse generator, the final common pathway for central regulation of mammalian reproduction. However, whether ARN kisspeptin neurons can intrinsically generate self-sustained synchronous oscillations from the early neonatal period and how they are regulated remain unclear. Objective: This study aimed to examine the endogenous rhythmicity of ARN kisspeptin neurons and its neural regulation using a neonatal organotypic slice culture model. Methods: We monitored calcium (Ca<sup>2+</sup>) dynamics in real-time from individual ARN kisspeptin neurons in neonatal organotypic explant cultures of Kiss1-IRES-Cre mice transduced with genetically encoded Ca<sup>2+</sup> indicators. Pharmacological approaches were employed to determine the regulations of kisspeptin neuron-specific Ca<sup>2+</sup> oscillations. A chemogenetic approach was utilized to assess the contribution of ARN kisspeptin neurons to the population dynamics. Results: ARN kisspeptin neurons in neonatal organotypic cultures exhibited a robust synchronized Ca<sup>2+</sup> oscillation with a period of approximately 3 min. Kisspeptin neuron-specific Ca<sup>2+</sup> oscillations were dependent on voltage-gated sodium channels and regulated by endoplasmic reticulum-dependent Ca<sup>2+</sup> homeostasis. Chemogenetic inhibition of kisspeptin neurons abolished synchronous Ca<sup>2+</sup> oscillations, but the autocrine actions of the neuropeptides were marginally effective. Finally, neonatal ARN kisspeptin neurons were regulated by N-methyl-D-aspartate and gamma-aminobutyric acid receptor-mediated neurotransmission. Conclusion: These data demonstrate that ARN kisspeptin neurons in organotypic cultures can generate synchronized and self-sustained Ca<sup>2+</sup> oscillations. These oscillations controlled by multiple regulators within the ARN are a novel ultradian rhythm generator that is active during the early neonatal period.
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