Abstract
Odor identification and discrimination is often impaired in elderly adults. The underlying mechanism responsible for this change has yet to be uncovered. Discrimination and identification of odorants by the olfactory system is dependent upon the spatial mapping of different odorant receptors onto specific glomeruli in fixed locations within the olfactory bulb. To determine if the precision of the P2 odorant receptor map changes in old mice, we examined the olfactory bulbs of P2-IRES-tau-lacZ transgenic mice (ages 2 weeks-2.5 years) using X-gal staining to visualize the projections of P2 odorant receptor nerve fibers. For each glomerulus containing P2 axons, the amount of P2 labeling was classified as either full: > 90%; partial: 10-90% or trace: < 10%. Although there was no significant change in the number of "full" P2 glomeruli observed in old mice, there was a significant increase in the number of glomeruli with "trace" amounts of P2 labeling with the highest number observed in the oldest, 2.5 year old mice. Results from this study suggest that axon targeting and the precision of P2 mapping is altered in older adult mice. Alterations in odorant mapping could explain odorant identification impairment frequently observed in elderly adults. [J Physiol Sci. 2007;57 Suppl:S105]
