The mouse olfactory system mediates the sense of odorants and appropriate behavioral responses. The main olfactory epithelium (MOE) expresses the largest number of G-protein coupled receptors (GPCRs). In the MOE, there are over 1000 olfactory receptor (OR) genes and yet each olfactory sensory neuron OSN, selects and expresses only a single OR allele in a stochastic manner. All OSNs expressing a given OR protein converge on typically two spatially invariant neuropil structures in the olfactory bulb (OB), termed glomeruli. The resulting glomerular map comes about from an extraordinary feat of axonal guidance by over 1000 distinct OSN populations, defined by OR expression, to 1800 distinct glomerular locations. In this thesis previous research and models of glomerular map formation in the olfactory bulb are reviewed. We present evidence that the ORs direct the formation glomerular map by using two lines of mice expressing two ORs per OSN. We find that OSNs expressing two receptors form glomeruli, arguing against a strict heterotypic repulsion model in the formation of the glomerular map. In addition, we observe that glomerular position in the OB occurs along a diagonal axis of symmetry in the OB. Furthermore, we conclude that there is a hierarchy amongst ORs in their ability to direct axons in glomerular formation.
Herrick, Scott P.,
"Co-expression of chemoreceptors in the murine olfactory system"
Neuroscience Theses and Dissertations.
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