Estrogenic-dependent glutamatergic neurotransmission from kisspeptin neurons governs feeding circuits in females

The neuropeptides tachykinin2 (Tac2) and kisspeptin (Kiss1) in hypothalamic arcuate nucleus Kiss1 (Kiss1ARH) neurons are essential for pulsatile release of GnRH and reproduction. Since 17β-estradiol (E2) decreases Kiss1 and Tac2 mRNA expression in Kiss1ARH neurons, the role of Kiss1ARH neurons during E2-driven anorexigenic states and their coordination of POMC and NPY/AgRP feeding circuits have been largely ignored. Presently, we show that E2 augmented the excitability of Kiss1ARH neurons by amplifying Cacna1g, Hcn1 and Hcn2 mRNA expression and T-type calcium and h-currents. E2 increased Slc17a6 mRNA expression and glutamatergic synaptic input to arcuate neurons, which excited POMC and inhibited NPY/AgRP neurons via metabotropic receptors. Deleting Slc17a6 in Kiss1 neurons eliminated glutamate release and led to conditioned place preference for sucrose in E2-treated KO female mice. Therefore, the E2-driven increase in Kiss1 neuronal excitability and glutamate neurotransmission may play a key role in governing the motivational drive for palatable food in females.

Regulation of Arcuate Neurons Coexpressing Kisspeptin, Neurokinin B, and Dynorphin by Modulators of Neurokinin 3 and κ-Opioid Receptors in Adult Male Mice

Pulsatile GnRH release is essential to fertility and is modulated by gonadal steroids, most likely via steroid-sensitive afferents. Arcuate neurons coexpressing kisspeptin, neurokinin B (NKB), and dynorphin (KNDy neurons) are steroid-sensitive and have been postulated to both generate GnRH pulses and mediate steroid feedback on pulse frequency. KNDy neurons are proposed to interact with one another via NKB and dynorphin to activate and inhibit the KNDy network, respectively, and thus alter kisspeptin output to GnRH neurons. To test the roles of NKB and dynorphin on KNDy neurons and the steroid sensitivity of these actions, targeted extracellular recordings were made of Tac2(NKB)-GFP-identified neurons from castrate and intact male mice. Single-cell PCR confirmed most of these cells had a KNDy phenotype. The neurokinin 3 receptor (NK3R) agonist senktide increased action potential firing activity of KNDy neurons. Dynorphin reduced spontaneous KNDy neuron activity, but antagonism of κ-opioid receptors (KOR) failed to induce firing activity in quiescent KNDy neurons. Senktide-induced activation was greater in KNDy neurons from castrate mice, whereas dynorphin-induced suppression was greater in KNDy neurons from intact mice. Interactions of dynorphin with senktide-induced activity were more complex; dynorphin treatment after senktide had no consistent inhibitory effect, whereas pretreatment with dynorphin decreased senktide-induced activity only in KNDy neurons from intact but not castrate mice. These data suggest dynorphin-mediated inhibition of senktide-induced activity requires gonadal steroid feedback. Together, these observations support the hypotheses that activation of NK3R and KOR, respectively, excites and inhibits KNDy neurons and that gonadal steroids modulate these effects.