The molecular machinery that mediates odor adaptation in the olfactory neurons is well documented in various animal species. However, types of adaptation that depend on neural circuits are mostly unexplored.We report here that the Ras-MAPK pathway is essential for such a type of odor adaptation, called early adaptation, in C. elegans. Early adaptation requires a pair of AIY interneurons, which receive synaptic inputs from olfactory neurons. Mutants of the Ras-MAPK pathway show defects in early adaptation. Continued exposure to an odorant causes activation of MAP kinase not only in the olfactory neurons, but also in the AIY interneurons. While activity of the Ras-MAPK pathway in the olfactory neurons is important for odor perception, its activity in the AIY interneurons is important for odor adaptation. Our results thus reveal a dual role of the Ras-MAPK pathway in sensory processing in the nervous system of C. elegans.
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