SPATIAL SEGREGATION OF ODORANT RECEPTOR EXPRESSION IN THE MAMMALIAN OLFACTORY EPITHELIUM

The signal elicited by the interaction of odorous ligands with recepto rs on olfactory sensory neurons must be decoded by the brain to determ ine which of the numerous receptors have been activated. We have exami ned the-patterns of odorant receptor expression in the rat olfactory e pithelium to determine whether the mammalian olfactory system employs spatial segregation of sensory input to encode the identity of an odor ant stimulus. In situ hybridization experiments with probes for 11 dif ferent odorant receptors demonstrate that sensory neurons expressing d istinct receptors are topologically segregated into a small number of broad, yet circumscribed, zones within the olfactory epithelium. Withi n a given zone, however, olfactory neurons expressing a specific recep tor appear to be randomly distributed, rather than spatially localized . The complex mammalian olfactory system may therefore compartmentaliz e the epithelium into anatomically and functionally discrete units, su ch that each zone expresses only a subset of the entire receptor reper toire.