Symmetry, stereotypy, and topography of odorant representations in mouse olfactory bulbs

The molecular basis of vertebrate odorant representations has been derived extensively from mice. The functional correlates of these molecular feature s were visualized using optical imaging of intrinsic signals in mouse olfac tory bulbs. Single odorants activated clusters of glomeruli in consistent, restricted portions of the bulb. Patterns of activated glomeruli were clear ly bilaterally symmetric and consistent in different individual mice, but t he precise number, position, and intensity of activated glomeruli in the tw o bulbs of the same individual and between individuals varied considerably. Representations of aliphatic aldehydes of different carbon chain length sh ifted systematically along a rostral-caudal strip of the dorsal bulb, indic ating a functional topography of odorant representations. Binary mixtures o f individual aldehydes elicited patterns of glomerular activation that were topographic combinations of the maps for each individual odor. Thus the pr inciples derived from the molecular organization of a small subset of murin e olfactory receptor neuron projection patterns-bilateral symmetry, local c lustering, and local variability-are reliable guides to the initial functio nal representation of odorant molecules.