title: Cannabinoid type 1 receptor-containing axons innervate NPY/AgRP neurons in the mouse arcuate nucleus.
abstract: Phytocannabinoids, such as THC and endocannabinoids, are well known to promote feeding behavior and to control energy metabolism through cannabinoid type 1 receptors (CB1R). However, the underlying mechanisms are not fully understood. Generally, cannabinoid-conducted retrograde dis-inhibition of hunger-promoting neurons has been suggested to promote food intake, but so far it has not been demonstrated due to technical limitations.
  
  
  
  We applied immunohistochemical labeling of CB1R for light microscopy and electron microscopy combined with three-dimensional reconstruction from serial sections in CB1R-expressing and CB1R-null mice, which served as a negative control. Hunger-promoting neurons expressing Agouti-related protein and neuropeptide Y (AgRP/NPY) in the hypothalamic arcuate nucleus were identified in NPY-GFP and NPY-hrGFP mice.
  
  
  
  Using three-dimensional reconstruction from serial sections we demonstrated numerous discontinuous segments of anti-CB1R labeling in the synaptic boutons and axonal shafts in the arcuate nucleus. We observed CB1R in the symmetric, presumed GABAergic, synaptic boutons innervating AgRP/NPY neurons. We also detected CB1R-containing axons producing symmetric and asymmetric synapses onto AgRP/NPY-negative neurons. Furthermore, we identified CB1R in close apposition to the endocannabinoid (2-arachidonoylglycerol)-synthesizing enzyme diacylglycerol lipase-alpha at AgRP/NPY neurons.
  
  
  
  Our immunohistochemical and ultrastructural study demonstrates the morphological substrate for cannabinoid-conducted feeding behavior via retrograde dis-inhibition of hunger-promoting AgRP/NPY neurons.
authors.affiliation: Department of Neuroscience, Yale University School of Medicine, 06520 New Haven, CT, USA; Kavli Institute for Neuroscience, Yale University School of Medicine, 06520 New Haven, CT, USA. Electronic address: yury.morozov@yale.edu.
authors.forename: Yury M
authors.initials: YM
authors.lastname: Morozov
authors.affiliation: Program in Integrative Cell Signaling and Neurobiology of Metabolism, Section of Comparative Medicine, Yale University School of Medicine, 06520 New Haven, CT, USA; Institute of Anatomy, University of Leipzig, 04103 Leipzig, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Koch
authors.affiliation: Department of Neuroscience, Yale University School of Medicine, 06520 New Haven, CT, USA; Kavli Institute for Neuroscience, Yale University School of Medicine, 06520 New Haven, CT, USA.
authors.forename: Pasko
authors.initials: P
authors.lastname: Rakic
authors.affiliation: Program in Integrative Cell Signaling and Neurobiology of Metabolism, Section of Comparative Medicine, Yale University School of Medicine, 06520 New Haven, CT, USA. Electronic address: tamas.horvath@yale.edu.
authors.forename: Tamas L
authors.initials: TL
authors.lastname: Horvath
mesh_terms: D054369:Agouti-Related Protein / Q000378:metabolism; D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D001369:Axons / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009478:Neuropeptide Y / Q000378:metabolism; D043884:Receptor, Cannabinoid, CB1 / Q000378:metabolism*
chemical_list: D054369:Agouti-Related Protein; D009478:Neuropeptide Y; D043884:Receptor, Cannabinoid, CB1
keywords: 3D reconstruction; Agouti-related protein; Arcuate nucleus; Electron microscopy; Hypothalamus; Neuropeptide Y