Abstract
Molecular and cellular studies have begun to unravel a neurobiological basis of olfactory processing, which appears conserved among vertebrate and invertebrate species. Studies have shown clearly that experience-dependent coding of odor identity occurs in “associative” olfactory centers (the piriform cortex in mammals and the mushroom body [MB] in insects). What remains unclear, however, is whether associative centers also mediate innate (spontaneous) odor discrimination and how ongoing experience modifies odor discrimination. Here we show in naïve flies that Gαq-mediated signaling in MB modulates spontaneous discrimination of odor identity but not odor intensity (concentration). In contrast, experience-dependent modification (conditioning) of both odor identity and intensity occurs in MB exclusively via Gαs-mediated signaling. Our data suggest that spontaneous responses to odor identity and odor intensity discrimination are segregated at the MB level, and neural activity from MB further modulates olfactory processing by experience-independent Gαq-dependent encoding of odor identity and by experience-induced Gαs-dependent encoding of odor intensity and identity.
Highlights
Most odors are experienced as complex mixtures in the environment
Experience-dependent changes in odor discrimination have been shown to occur in the piriform cortex of vertebrates [1,5,15,16,17,18] and in the mushroom body (MB) of Drosophila [19,20,21,22], both of which are activated by odor stimulation in naıve animals [23,24,25,26,27,28]
Olfactory processing in higher brain centers, where neuronal activity is assembled into the perception of odor quality, is poorly understood
Summary
Most odors are experienced as complex mixtures in the environment. an animal’s ability to discriminate between two odor cues reflects the interplay between spontaneous and experience-dependent processes [1,2,3]. The cAMP signaling pathway, for instance, has been shown to be involved in both olfactory processing and associative learning in mammals and in Drosophila [10,11,12,13,14]. Experience-dependent changes in odor discrimination have been shown to occur in the piriform cortex of vertebrates [1,5,15,16,17,18] and in the mushroom body (MB) of Drosophila [19,20,21,22], both of which are activated by odor stimulation in naıve animals [23,24,25,26,27,28]
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