Abstracts from the Thirty-first Annual Meeting of the Association for Chemoreception Sciences

Abstract

Mice and rats use 1,000 olfactory receptor types to probe chemical space. Each glomerulus in the olfactory bulb receives input from a single receptor type, whose ligand binding properties determine the spectrum of odor responses. In this way, the layout of glomeruli on the bulb forms a two-dimensional map of odors. We recorded the odor responses of dorsal glomeruli in mice expressing synaptopHluorin in sensory nerve terminals. By using a chemically diverse battery of several hundred odors, we could assign unique functional identities to several dozen glomeruli. This allowed us to determine that the position of a given glomerulus varies across individuals by only 1 glomerular spacing, corresponding to a precision of 1 part in 1000. We also asked whether the layout of glomeruli is systematically related to their odor sensitivities. The odor response spectra of two neighboring glomeruli were as dissimilar as those of distant glomeruli. This local diversity of odor responses will have important consequences for how mitral cells sample odor space. We have begun to examine this next stage of processing in the bulb by imaging postsynaptic signals in the dendrites of mitral cells in mice expressing the calcium indicator GCaMP2 and multiphoton microscopy. Initial results indicate that the population responses of AChemS Abstracts A13 mitral cell apical tufts are similar to the presynaptic maps constructed from synaptopHluorin mice. We were also able to record robust odor-evoked responses from a large population of individual lateral dendrites, and are currently analyzing their odor tuning.