The Journal of Neuroscience, February 18, 2009, 29(7):2043-2052; doi:10.1523/JNEUROSCI.5317-08.2009
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Cellular/Molecular
External Tufted Cells Drive the Output of Olfactory Bulb Glomeruli
Didier De Saint Jan,1,2,3
Daniela Hirnet,1,2,3
Gary L. Westbrook,4 and
Serge Charpak1,2,3
1Institut National de la Santé et de la Recherche Médicale (INSERM) U603, 2Laboratory of Neurophysiology and New Microscopies, Université Paris Descartes, and 3Centre National de la Recherche Scientifique (CNRS), UMR 8154, 75006 Paris, France, and 4Vollum Institute, Oregon Health and Science University, Portland, Oregon 97239
Correspondence should be addressed to Didier De Saint Jan or Serge Charpak, Institut National de la Santé et de la Recherche Médicale U603, Université Paris Descartes, Centre National de la Recherche Scientifique UMR 8154, 45 rue des Saints-Pères, 75006 Paris, France. Email: didier.desaintjan{at}univ-paris5.fr, Email: serge.charpak{at}univ-paris5.fr
Odors synchronize the activity of olfactory bulb mitral cells that project to the same glomerulus. In vitro, a slow rhythmic excitation intrinsic to the glomerular network persists, even in the absence of afferent input. We show here that a subpopulation of juxtaglomerular cells, external tufted (ET) cells, may trigger this rhythmic activity. We used paired whole-cell recording and Ca2+ imaging in bulb slices from wild-type and transgenic mice expressing the fluorescent Ca2+ indicator protein GCaMP-2. Slow, periodic population bursts in mitral cells were synchronized with spontaneous discharges in ET cells. Moreover, activation of a single ET cell was sufficient to evoke population bursts in mitral cells within the same glomerulus. Stimulation of the olfactory nerve induced similar population bursts and activated ET cells at a lower threshold than mitral cells, suggesting that ET cells mediate feedforward excitation of mitral cells. We propose that ET cells act as essential drivers of glomerular output to the olfactory cortex.
Key words: olfactory bulb; glomerulus; external tufted cells; mitral cells; population synchrony; feedforward excitation
Received Nov. 5, 2008;
revised Jan. 5, 2009;
accepted Jan. 9, 2009.
Correspondence should be addressed to Didier De Saint Jan or Serge Charpak, Institut National de la Santé et de la Recherche Médicale U603, Université Paris Descartes, Centre National de la Recherche Scientifique UMR 8154, 45 rue des Saints-Pères, 75006 Paris, France. Email: didier.desaintjan{at}univ-paris5.fr, Email: serge.charpak{at}univ-paris5.fr
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