Temporal segregation of mitral and tufted cell activity – the role of glomerular and granule layer interneurons
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1
MPI for Medical Research, Max Planck Research Group Behavioural Neurophysiology, Germany
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2
Max Planck Instutute of Neurobiology, Germany
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3
Ruprecht-Karls-University Heidelberg, Institute for Anatomy and Cell Biology, Germany
In olfaction, the sniff rhythm shapes activity across cell populations. We have previously shown that the two major types of output neurons of the mammalian olfactory bulb (OB), mitral and tufted cells (M / TC), lock to different phases of the sniff rhythm, and that this temporal segregation is caused by GABAergic inputs selectively delaying MC activation. Here we assess, using optogenetic manipulations of selective populations of OB interneurons, in combination with whole cell recordings from principal and interneurons in vivo, which inhibitory circuits underlie this separation.
We first tested the contribution from granule cells (GC). AAV carrying flexed ArchT and GFP were injected into the GC layer of mice that express cre under the control of Gad65 promoter. Intracellular recordings from GCs show that 42% (8/19 cells) of GCs were infected, hyperpolarizing by 10-30 mV in response to light presentations, at depth up to 0.8 mm. Despite the efficient silencing of GCs, there was no change in the physiology of MC or TC.
Next we turned to glomerular interneurons. Periglomerular cells (PG) comprise of heterogeneous populations, among others PGo, receiving direct olfactory sensory neuron (OSN) input, and PGe, whose dominant drive is generated by OB excitatory neurons, i.e. MC, TC and other excitatory cells. To functionally dissect the role of PGo and PGe, we expressed ChR2 in Gad65+ neurons in the GC layer. Then, optically driving such GCs resulted in strong hyperpolarisations of MCs and TCs, reducing the excitatory drive in PGe cells, while leaving PGo cells unaltered. Whole cell recordings from such identified PGo cells (n = 8 cells), revealed that their peak depolarization occurs 43 ms before the trough of MC membrane potential, but synchronized to TCs. This is consistent with the notion that TCs and PGo are both directly driven by OSN input, while MCs are selectively delayed by PGo input.
To test if PG cells, indeed, separate MC activation from TC activation, we directly assessed the role of Gad65+ neurons in the glomerular layer by optogenetic silencing with AAV carrying flexed ArchT. Our preliminary results indicate that, unlike with GC silencing, which consistently produced no observable alterations to MC or TC phase, silencing of glomerular layer Gad65+ neurons cause a wide range of effect, most notably changes in sniff-coupling of MCs.
Hence, our work suggests that feed-forward inhibitory circuits consisting of PGo cells delay sniff-coupled activities in MCs. The study also stresses the crucial, but complex nature of glomerular circuitry in OB processing.
Acknowledgements
We are grateful to Max Planck Society, Bauer Foundation, Alexander von Humboldt Foundation and ExcellenzCluster CellNetworks for the generous support.
Keywords:
in vivo,
inhibition,
Olfaction,
optogenetics
Conference:
Bernstein Conference 2012, Munich, Germany, 12 Sep - 14 Sep, 2012.
Presentation Type:
Poster
Topic:
Sensory processing and perception
Citation:
Fukunaga
I,
Berning
M,
Herb
JT,
Köllö
M and
Schaefer
AT
(2012). Temporal segregation of mitral and tufted cell activity – the role of glomerular and granule layer interneurons.
Front. Comput. Neurosci.
Conference Abstract:
Bernstein Conference 2012.
doi: 10.3389/conf.fncom.2012.55.00243
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Received:
10 May 2012;
Published Online:
12 Sep 2012.
*
Correspondence:
Prof. Andreas T Schaefer, MPI for Medical Research, Max Planck Research Group Behavioural Neurophysiology, Heidelberg, 69120, Germany, Andreas.Schaefer@mpimf-heidelberg.mpg.de