Electrophysiological effects of neuropeptide S on rat ventromedial hypothalamic neurons in vitro

The newly identified neuropeptide S (NPS) is a ligand for a previously orphan G protein-coupled GPR 154 receptor, now named the NPS receptor (NPSR). Previous studies have shown that NPS induces hyperlocomotion, increases arousal and suppresses anxiety-like behaviors via NPSR. Although NPS also inhibits food intake, nothing is known about the neuronal mechanisms underlying this action. Anatomical studies show that NPSRs are expressed abundantly in the dorsomedial part of the ventromedial hypothalamic nucleus (VMH), a satiety center for food intake. Hence, we examined the electrophysiological effects of NPS on rat VMH neurons in vitro. NPS predominantly depolarized the VMH neurons, and the effects were postsynaptic and dose-dependent. Membrane resistance was significantly decreased during the depolarization, suggesting an opening of some ionic channels. The NPS-induced depolarization was significantly attenuated in Ca(2+)-free, NiCl(2)-containing and mibefradil-containing TTX ACSFs, but it did not disappear. The NPS-induced depolarization was also attenuated in low-Na(+) TTX ACSF, and completely abolished in Ca(2+)-free/low-Na(+) TTX ACSF. Pretreatment with 30 microM KB-R7943, an inhibitor of forward-mode Na(+)/Ca(2+) exchanger, did not have any significant effect on the NPS-induced depolarization in Ca(2+)-free TTX ACSF. These results suggest that NPS depolarizes VMH neurons via activations of R- and T-type Ca(2+) channels and nonselective cation channels, and that VMH neurons might be involved in the cellular process through which NPS participates in the regulation of food intake and energy homeostasis.