Chemical Senses Advance Access originally published online on July 17, 2008
Chemical Senses 2008 33(9):793-802; doi:10.1093/chemse/bjn040
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Comparison of Identified Mitral and Tufted Cells in Freely Breathing Rats: II. Odor-Evoked Responses
1 Department of Biological Sciences, University of Cincinnati, ML 0006, Cincinnati, OH 45221-0006, USA 2 Laboratoire de Neurosciences et Systèmes Sensoriels, CNRS, UMR 5020, Université Claude Bernard Lyon 1, 50 Avenue Tony Garnier, 69366, Lyon, France 3 Institut Camille Jordan, Equipe Probabilités et Statistiques, UMR 5208, Université Claude Bernard Lyon 1, 43 Bd du 11 Novembre 1918, Lyon-Villeurbanne, France
Correspondence to be sent to: Edwin R. Griff, Department of Biological Sciences, University of Cincinnati, ML 0006, Cincinnati, OH 45221-0006, USA. e-mail: edwin.griff{at}uc.edu
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Abstract |
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Mitral and tufted cells are the 2 types of output neurons of the main olfactory bulb. They are located in distinct layers, have distinct projection patterns of their dendrites and axons, and likely have distinct relationships with the intrabulbar inhibitory circuits. They could thus be functionally distinct and process different aspects of olfactory information. To examine this possibility, we compared the odor-evoked responses of identified single units recorded in the mitral cell layer (MCL units), in the core of the external plexiform layer (not at the glomerular border tufted cells), or at the glomerular border of this layer (GB tufted cells) of the entire olfactory bulb. Differences between mitral and tufted cells were observed only when subtle aspects of the responses were explored, such as the firing rate per respiratory cycle or the distribution of firing activity along the respiratory cycle. By contrast, more clear differences were found when the 2 subtypes of tufted cells were examined separately. GB units were significantly more responsive, had significantly higher firing activity, and showed greater activity at the transition between inspiration and expiration. The projection-type tufted cells situated closer to the entrance of the olfactory bulb may thus form a distinct physiological class of output neurons and differ from mitral cells and other tufted cells in the manner of processing olfactory information.
Key words: main olfactory bulb, mitral cells, odor-evoked responses, olfaction, respiration cycle, tufted cells
Accepted 17 June 2008