Neuron
Volume 76, Issue 6, 20 December 2012, Pages 1161-1174
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Article
Cortical Feedback Control of Olfactory Bulb Circuits

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Summary

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.

Highlights

► Cortical feedback projections target diverse olfactory bulb interneurons ► Cortical feedback excites granule cells that inhibit mitral cells ► Cortical feedback modulates mitral cell activity in vivo ► Cortical feedback amplifies odor-evoked inhibition in the olfactory bulb

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These authors contributed equally to this work