Neurokinin B Activates Arcuate Kisspeptin Neurons Through Multiple Tachykinin Receptors in the Male Mouse

Kisspeptin neurons located in the arcuate nucleus (ARN) coexpress dynorphin and neurokinin B (NKB) and may interact to influence gonadotropin secretion. Using a kisspeptin-green fluorescent protein mouse model, the present study examined whether the neuropeptides kisspeptin, dynorphin, and NKB modulate the electrical activity of ARN kisspeptin neurons in the adult male mouse. Cell-attached recordings showed that kisspeptin itself had no effect on kisspeptin neuron firing. Dynorphin and the κ-opioid receptor agonist U50-488 evoked a potent suppression of all ARN kisspeptin neuron firing that was blocked completely by the κ-opioid receptor antagonist nor-Binaltorphimine. Both NKB and Senktide, a neurokinin 3 receptor agonist, exerted a potent stimulatory action on ∼95% of ARN kisspeptin neurons. Although the selective neurokinin 3 receptor antagonists SB222200 and SR142801 blocked the effects of Senktide on kisspeptin neurons, they surprisingly had no effect on NKB activation of firing. Studies with selective neurokinin 1 receptor (SDZ-NKT343) and neurokinin 2 receptor (GR94800) antagonists revealed that the activation of kisspeptin neurons by NKB was only blocked completely by a cocktail of antagonists against all 3 tachykinin receptors. Whole-cell recordings revealed that individual kisspeptin neurons were activated directly by all 3 tachykinins substance, P, neurokinin A, and NKB. These experiments show that dynorphin and NKB have opposing actions on the electrical activity of kisspeptin neurons supporting the existence of an interconnected network of kisspeptin neurons in the ARN. However, the effects of NKB result from an unexpected activation of multiple tachykinin receptors.