title: Cortical feedback control of olfactory bulb circuits.
abstract: Olfactory cortex pyramidal cells integrate sensory input from olfactory bulb mitral and tufted (M/T) cells and project axons back to the bulb. However, the impact of cortical feedback projections on olfactory bulb circuits is unclear. Here, we selectively express channelrhodopsin-2 in olfactory cortex pyramidal cells and show that cortical feedback projections excite diverse populations of bulb interneurons. Activation of cortical fibers directly excites GABAergic granule cells, which in turn inhibit M/T cells. However, we show that cortical inputs preferentially target short axon cells that drive feedforward inhibition of granule cells. In vivo, activation of olfactory cortex that only weakly affects spontaneous M/T cell firing strongly gates odor-evoked M/T cell responses: cortical activity suppresses odor-evoked excitation and enhances odor-evoked inhibition. Together, these results indicate that although cortical projections have diverse actions on olfactory bulb microcircuits, the net effect of cortical feedback on M/T cells is an amplification of odor-evoked inhibition.
authors.affiliation: Center for Neural Circuits and Behavior, Department of Neuroscience, University of California, San Diego, School of Medicine, La Jolla, CA 92093, USA.
authors.forename: Alison M
authors.initials: AM
authors.lastname: Boyd
authors.forename: James F
authors.initials: JF
authors.lastname: Sturgill
authors.forename: Cindy
authors.initials: C
authors.lastname: Poo
authors.forename: Jeffry S
authors.initials: JS
authors.lastname: Isaacson
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000166:cytology / Q000502:physiology; D025461:Feedback, Physiological / Q000502:physiology*; D066298:In Vitro Techniques; D007395:Interneurons / Q000166:cytology / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D009830:Olfactory Bulb / Q000166:cytology* / Q000502:physiology; D009833:Olfactory Pathways / Q000166:cytology / Q000502:physiology*; D055696:Olfactory Perception / Q000502:physiology*; D017966:Pyramidal Cells / Q000166:cytology / Q000502:physiology*