The distribution of cell types and synapses is well characterized in the rodent olfactory bulb (OB), and from that plausible models of odor processing have been constructed. Individual olfactory sensory neurons (OSNs) express only 1 of ~1000 odorant receptors (ORs) and send their axons to specific synaptic targets in the OB glomerular neuropil. Each glomerulus is innervated exclusively by OSN axons expressing the same OR. The distribution of these glomeruli is conserved across animals, as is the numerical relationship between number of expressed ORs and number of glomeruli in the OB. Our objective is to extend such results to the level of the human OB to determine how its cellular and synaptic organization, and more specifically how the number and distribution of its glomeruli, compare to what has been elucidated in mice. As there are ~2,000 glomeruli for ~1,000 ORs in mice, we predicted ~700 glomeruli in humans based on the ~350 intact OR genes identified in the human through genomic studies. Using immunohistochemistry, the organization of cells and synapses in human OBs was evaluated and quantified. While the laminar structure of the OB is broadly conserved between species, in the human OB the laminar organization as well as additional structural features suggest a less rigorously organized OB than in rodents, perhaps suggesting that odor processing in the human OB may be less efficient than in mice. Of particular note, the total number of glomeruli in the human OB differs significantly from predicted and demonstrates a high degree of variability amongst specimens, thus far ranging from approximately 3000 - 9000/OB. These results indicate that the principles of OR-homotypic axon convergence developed from mouse studies may not be readily applicable to the human, and that central processing of odor signals in the human may differ from those characterized in the mouse.
| Identifer | oai:union.ndltd.org:YALE_med/oai:ymtdl.med.yale.edu:etd-08212007-112805 |
| Date | 04 March 2008 |
| Creators | Maresh, Alison |
| Contributors | Charles Greer |
| Publisher | Yale University |
| Source Sets | Yale Medical student MD Thesis |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://ymtdl.med.yale.edu/theses/available/etd-08212007-112805/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Yale School of Medicine or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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