Mechanism of kisspeptin neuron synchronization for pulsatile hormone secretion in male mice.

The mechanism by which arcuate nucleus kisspeptin (ARN) neurons co-expressing glutamate, neurokinin B, and dynorphin intermittently synchronize their activity to generate pulsatile hormone secretion remains unknown. An acute brain slice preparation maintaining synchronized ARN neuron burst firing was used alongside in vivo GCaMP GRIN lens microendoscope and fiber photometry imaging coupled with intra-ARN microinfusion. Studies in intact and gonadectomized male mice revealed that ARN neuron synchronizations result from near-random emergent network activity within the population and that this was critically dependent on local glutamate-AMPA signaling. Whereas neurokinin B operated to potentiate glutamate-generated synchronizations, dynorphin-kappa opioid tone within the network served as a gate for synchronization initiation. These observations force a departure from the existing "KNDy hypothesis" for ARN neuron synchronization. A "glutamate two-transition" mechanism is proposed to underlie synchronizations in this key hypothalamic central pattern generator driving mammalian fertility.