Identification and Characterization of a Novel Population of GABAergic Hypothalamic Neurons

Background: The arcuate nucleus of the hypothalamus (ARC) is a major site for the regulation of energy balance. In the ARC, pro-opiomelanocortin (POMC) and agouti-related peptide (AgRP)-expressing neurons are considered as key populations on which signals of the energy state converge to regulate energy homeostasis. However, recent work suggests that unidentified GABAergic neurons of the ARC play a more critical role in the control of the energy balance. Based on RNAseq studies, we identified an uncharacterized GABAergic population of the ARC that robustly express the New arcuate transcript (Nat). We hypothesize that Nat-expressing neurons are critical for the control of energy homeostasis. Here, we aim to characterize the molecular signature of Nat-expressing neurons of the ARC and determine whether this novel GABAergic population is sensitive to metabolic signals. Methods: We first used RNAscope® in situ hybridization technology on mouse coronal brain slices to determine the proportion of Nat-expressing neurons expressing the leptin, glucagon-like peptide 1 (GLP-1) and melanocortin 3 and 4 receptors (Lepr, Glplr, Mc3r and Mc4r respectively). We then administered leptin, liraglutide, and melanotan II to mice and evaluated C-FOS immunoreactivity in Nat-expressing neurons of the ARC. Results: We found that Nat-expressing neurons are a GABAergic population highly enriched in the ARC, and distinct from POMC and AgRP neurons. Subsets of Nat-expressing neurons co-express Lepr (18.3%), while others co-express Glplr (35.3%), Mc3r (37.1%) or Mc4r (7.2%). C-FOS immunoreactivity will allow us to determine whether the activity of Nat neurons can be modulated in response to key metabolic signals. Conclusions: Together, our results suggest that Nat-expressing neurons are a potential new GABAergic "hub" of the ARC, towards which leptin, GLP-1 and melanocortins may converge to mediate some of their metabolic effects. The recent development of a novel Nat-IRES-Cre mouse model will allow us to further investigate the physiological functions of Nat-expressing neurons.