Nesfatin-1 inhibits NPY neurons in the arcuate nucleus

Abstract

Although the novel satiety factor nesfatin-1 has been shown to influence feeding behavior through effects on melanocortin signaling, the specific hypothalamic neuronal substrates through which such effects are mediated have yet to be elucidated. To identify neuronal cell types potentially important in mediating nesfatin-1's effects, whole cell current clamp recordings were made from hypothalamic arcuate nucleus neurons and the effects of bath applied nesfatin-1 on membrane excitability determined. Neurons then underwent phenotypic identification post hoc using single cell RT-PCR. Nesfatin-1 (10 nM) had effects on the majority of arcuate nucleus neurons tested, with most responsive cells hyperpolarizing following exposure. Furthermore, 9 of 11 identified NPY neurons hyperpolarized in response to nesfatin-1 exposure. Pharmacological experiments revealed that glibenclamide (500 nM), an ATP-sensitive potassium conductance antagonist, prevented nesfatin-1-induced hyperpolarization. Therefore, nesfatin-1-induced inhibition of feeding may be mediated through the inhibition of orexigenic NPY neurons.

Introduction

The arcuate nucleus of the hypothalamus is an integral component of the central control of feeding behavior. Here signals that indicate the metabolic state of the animal are received and processed following which the activity of either orexigenic NPY neurons or anorexigenic αMSH-containing neurons is increased (Abizaid et al., 2006, Schwartz et al., 2000, Zigman and Elmquist, 2003). Over the last decade several peptides have been identified as satiety signals, including one of the most recently described satiety peptides, nesfatin-1 (Oh-I et al., 2006). This peptide arises from cleavage of the calcium and DNA-binding protein nucleobindin-2 yielding an 82 amino acid product that, when injected intracerebroventricularly, reduces feeding. Moreover, inactivation of endogenous nesfatin-1 with a neutralizing antibody increases feeding, underscoring the potential importance of this peptide in the central control of appetite. Nesfatin-1 is expressed in many hypothalamic nuclei, including the arcuate where levels are affected by fasting/refeeding (Brailoiu et al., 2007). Furthermore, nucleobindin-2 recently was found to belong to the adipocyte proteome presenting the possibility that nesfatin-1 may also be a peripheral satiety signal (Adachi et al., 2007). While there is good information available on the activity and distribution of nesfatin-1 in the rat, so far there has been no receptor identified for this peptide. However, results showing that increases in intracellular calcium in cultured hypothalamic neurons are inhibited by pretreatment with pertussis toxin and by exposure to inhibitors of protein kinase A indicate the receptor is likely to belong to the family of G-protein coupled receptors (Brailoiu et al., 2007).

We previously have demonstrated that nesfatin-1 has effects on the excitability of neurons within the hypothalamic paraventricular nucleus (PVN) (Price et al., 2008b). Nesfatin-1 either excited or inhibited PVN neurons without much discrimination based on electrophysiological or molecular phenotypic criteria, thereby suggesting that nesfatin-1 broadly influences the output of the PVN. Owing to the importance of the arcuate nucleus in the regulation of feeding behavior and that the arcuate nucleus receives inputs from many brain structures, such as the PVN, nucleus of the solitary tract (NTS) and the raphe nuclei, that possess nesfatin-1 expressing neurons (Brailoiu et al., 2007, Ricardo and Koh, 1978) we now have performed electrophysiological recordings on neurons within the arcuate nucleus, examining how nesfatin-1 influences the excitability of these neurons.