title: The Interglomerular Circuit Potently Inhibits Olfactory Bulb Output Neurons by Both Direct and Indirect Pathways.
abstract: Sensory processing shapes our perception. In mammals, odor information is encoded by combinatorial activity patterns of olfactory bulb (OB) glomeruli. Glomeruli are richly interconnected by short axon cells (SACs), which form the interglomerular circuit (IGC). It is unclear how the IGC impacts OB output to downstream neural circuits. We combined in vitro and in vivo electrophysiology with optogenetics in mice and found the following: (1) the IGC potently and monosynaptically inhibits the OB output neurons mitral/tufted cells (MTCs) by GABA release from SACs: (2) gap junction-mediated electrical coupling is strong for the SAC→MTC synapse, but negligible for the SAC→ETC synapse; (3) brief IGC-mediated inhibition is temporally prolonged by the intrinsic properties of MTCs; and (4) sniff frequency IGC activation in vivo generates persistent MTC inhibition. These findings suggest that the temporal sequence of glomerular activation by sensory input determines which stimulus features are transmitted to downstream olfactory networks and those filtered by lateral inhibition.
  
  
  
  Odor identity is encoded by combinatorial patterns of activated glomeruli, the initial signal transformation site of the olfactory system. Lateral circuit processing among activated glomeruli modulates olfactory signal transformation before transmission to higher brain centers. Using a combination of in vitro and in vivo optogenetics, this work demonstrates that interglomerular circuitry produces potent inhibition of olfactory bulb output neurons via direct chemical and electrical synapses as well as by indirect pathways. The direct inhibitory synaptic input engages mitral cell intrinsic membrane properties to generate inhibition that outlasts the initial synaptic action.
authors.affiliation: Department of Anatomy and Neurobiology, Program in Neurosciences, University of Maryland School of Medicine, Baltimore, Maryland 21042 sliu@som.umaryland.edu.
authors.forename: Shaolin
authors.identifier: 0000-0003-3351-8642
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Anatomy and Neurobiology, Program in Neurosciences, University of Maryland School of Medicine, Baltimore, Maryland 21042.
authors.forename: Adam C
authors.initials: AC
authors.lastname: Puche
authors.affiliation: Department of Anatomy and Neurobiology, Program in Neurosciences, University of Maryland School of Medicine, Baltimore, Maryland 21042.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Shipley
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D000075402:Channelrhodopsins; D005260:Female; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000494:pharmacology; D009830:Olfactory Bulb / Q000166:cytology*; D009833:Olfactory Pathways / Q000502:physiology*; D062308:Optogenetics; D018408:Patch-Clamp Techniques; D012903:Smell / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics / Q000378:metabolism; D000097573:Red Fluorescent Protein
chemical_list: D000075402:Channelrhodopsins; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D018377:Neurotransmitter Agents; D014446:Tyrosine 3-Monooxygenase; D000097573:Red Fluorescent Protein; C485184:enhanced green fluorescent protein
keywords: GABA; electrical coupling; interglomerular circuit; intrinsic properties; monosynaptic inhibition; olfactory bulb