Dell, Leigh-AnneSpocter, Muhammad A.Patzke, NinaKarlson, Karl Æ.Alagaili, Abdulaziz N.Bennett, Nigel CharlesMuhammed, Osama B.Bertelsen, Mads F.Siegel, Jerome M.Manger, Paul R.2016-08-012015-10Dell, L-A, Spocter, MA, Patzke, N, Karlson, KÆ, Alagaili, AN, Bennett, NC, Muhammed, OB, Bertelsen, MF, Siegler, JM & Manger, PR 2015, 'Orexinergic bouton density is lower in the cerebral cortex of cetaceans compared to artiodactyls', Journal of Chemical Neuroanatomy, vol. 68, pp. 61-76.0891-0618 (print)1873-6300 (online)10.1016/j.jchemneu.2015.07.007http://hdl.handle.net/2263/56146The species of the cetacean and artiodactyl suborders, which make up the cetartiodactyl order, have very different arousal thresholds and sleep-wake systems. The aim of this study was to determine whether cetaceans or artiodactyls have differently organized orexinergic arousal systems by examining the density of orexinergic innervation to the cerebral cortex. This study provides a comparison of orexinergic bouton density in the cerebral cortex of twelve cetartiodactyl species by means of immunohistochemical staining and stereological analysis. It was observed that the morphology of the axonal projections of the orexinergic system to the cerebral cortex was similar across all species, as the presence, size and proportion of large and small orexinergic boutons were similar. Despite this, orexinergic bouton density was lower in the cerebral cortex of cetaceans compared to artiodactyls, even when corrected for brain mass, neuron density, glial density and glial: neuron ratio. Glial density was identified as the major determinant for the observed differences. It appears a synergy exists between the orexinergic neurons and their projections, glial cells, and the biochemical correlates of appetitive drive and arousal, but further studies need to be performed to understand the full extent of the orexinergic system and its role in sustained arousal.en© 2015 Elsevier B.V. All rights reserved. Notice : this is the author’s version of a work that was accepted for publication in Journal of Chemical Neuroanatomy. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Chemical Neuroanatomy, vol. 68, pp. 61-76, 2015. doi : 10.1016/j.jchemneu.2015.07.007.CetartiodactylaOrexinHypocretinComparative neuroanatomyEvolutionComparative sleepMammaliaPostprint Article