Synaptic distribution of individually labeled mitral cells in the external plexiform layer of the mouse olfactory bulb |
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Authors: | Takeshi Matsuno Emi Kiyokage Kazunori Toida |
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Affiliation: | 1. Department of Anatomy, Kawasaki Medical School, Okayama, Japan;2. Research Center for Ultra‐High Voltage Electron Microscopy, Osaka University, Osaka, Japan |
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Abstract: | Mitral cells are the major projection neurons of the olfactory bulb. They receive olfactory inputs, regulate information, and project their axons to the olfactory cortex. To understand output regulation of mitral cells better, we established a method to visualize individual projection neurons and quantitatively examined their synaptic distribution. Individual mitral cells were labeled by viral injection, reconstructed three dimensionally with light microscopy, and serial sectioned for electron microscopy. Synaptic distributions were analyzed in electron microscopically reconstructed cell bodies, two regions of secondary dendrites (near the somata and ~200 μm from the somata), and primary dendrites. The ratio of presynaptic sites (60%) and reciprocal synapses (60% presynaptic and 80% postsynaptic sites) were similar in each region. Characteristically, primary dendrite synapses were distributed mainly within the inner half of the external plexiform layer (EPL). For comparison, tufted cells were also examined, and the synaptic distribution in two secondary dendrite regions, which corresponded with mitral cells, was analyzed. The results showed that the ratio of reciprocal synapses (80% presynaptic and 90% postsynaptic sites) was greater than in mitral cells. The distribution of symmetrical synapses was also analyzed with synaptic and neuronal markers, such as parvalbumin, vesicular gamma‐aminobutyric acid transporter, and gephyrin. Parvalbumin‐expressing neurons tended to form synapses on secondary dendrites near the somata and were more uniformly distributed on primary dendrites of mitral cells. These results indicate that local mitral cell synaptic circuits are formed in accordance with their functional roles and restricted to the inner half of the EPL. J. Comp. Neurol. 525:1633–1648, 2017. © 2016 Wiley Periodicals, Inc. |
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Keywords: | synapse dendrites parvalbumin gephyrin electron microscopy Sindbis viral vector RRID:SCR_001775 RRID:SCR_007370 RRID:SCR_013672 RRID:AB_2534023 RRID:AB_2336890 RRID:AB_887880 RRID:AB_2301998 RRID:AB_10000345 RRID:AB_887717 |
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