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. 2017 May 31;8:357. doi: 10.3389/fphys.2017.00357

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Copyright © 2017 Chieffi, Carotenuto, Monda, Valenzano, Villano, Precenzano, Tafuri, Salerno, Filippi, Nuccio, Ruberto, De Luca, Cipolloni, Cibelli, Mollica, Iacono, Nigro, Monda, Messina and Messina.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Schematic representation of orexin system. Orexin A and orexin B are derived from a common precursor peptide, prepro-orexin. The actions of orexins are mediated via two G protein-coupled receptors named orexin-1 (OX₁R) and orexin-2 (OX₂R) receptors. OX₁R is selective for orexin A, whereas OX₂R is a non-selective receptor for both orexin A and orexin B. OX₁R is coupled exclusively to the Gqsubclass of heterotrimeric G proteins, whereas OX₂R couples to Gi/oand/or Gq.