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. Author manuscript; available in PMC: 2017 Dec 1.
Published in final edited form as: Curr Opin Neurobiol. 2016 Sep 23;41:136–148. doi: 10.1016/j.conb.2016.09.002

Figure 1. Models of microcircuit motifs present in the C. elegans olfactory system.

Figure 1

A. A feedback inhibition motif promotes odor adaptation and possibly gain control [23]. The AWC olfactory neurons release NLP-1, which binds NPR-11 on AIA interneurons to inhibit their activity. In the presence of an odor, AWC activity is suppressed. The resulting decrease in NLP-1 signaling permits AIA to release INS-1, which inhibits AWC through an unknown receptor [23]. B. Odor environment modulates feeding through a reciprocal inhibition motif [39]. The presence of attractive odors increases feeding, while the presence of repulsive odors decreases feeding. The attractive odorant diacetyl is sensed by the AWA neurons and causes serotonin (5-HT) release from the NSM neurons. 5-HT binds the serotonin-gated chloride channel MOD-1 on the RIM and RIC interneurons, which inhibits them and increases feeding. Repellents such as quinine or high concentrations of isoamyl alcohol (IAA) are sensed by the ASH neurons and promote release of octopamine (OA) and tyramine (TA) from RIM and RIC. OA and TA bind the SER-2 receptor on the NSM neurons and inhibit serotonin release [39].