Further, the methods used in this study are being adapted to study the role of neuropeptides whose functions remain unknown. Prolonged exposure to the attractive odorant benzaldehyde in the absence of food results in a decreased attractiveness dependent on an association with the absence of food [23]. Lin et al. [24•] showed that insulin signaling was key
for this type of associative learning and used a conditional allele of daf-2 to distinguish insulin’s role in different phases of memory. INS-1 and DAF-2 were each shown to be necessary for benzaldehyde-starvation associative plasticity, and rescue experiments showed that INS-1 released from ASI and AIA acted on DAF-2 receptors on the AWC sensory neurons to mediate benzaldehyde-starvation associative plasticity. Taking advantage
of the temperature sensitive daf-2 allele, Lin et al. [24•] disrupted signaling during Stem Cell Compound Library order the training or testing learn more phases of the assay to reveal that DAF-2 signaling is only partially involved in memory acquisition, but absolutely necessary for memory retrieval. Prolonged exposure to a different odorant also detected by AWC, isoamyl alcohol, leads to decremented attractiveness that is not dependent on feeding state 25, 26•• and 27••. Chalasani et al. [27••] found that the decreased attractiveness, as well as decreased responsivity of AWC to isoamyl alcohol was dependent on NLP-1, a buccalin-related peptide expressed in AWC. Based on the expression pattern of orphan neuropeptide receptors they managed to link NLP-1 with NPR-11 using mutant analysis followed by biochemical confirmation. Expressing nlp-1 in AWC and npr-11 in AIA interneuron rescued the behavioral deficits associated with each mutant. They propose a neuropeptide feedback loop, whereby NLP-1 released from the AWC sensory neuron acts on AIA to induce release of INS-1, which acts on AWC to modulate odor sensitivity. When grown at a temperature between 15 and 25 °C, well-fed worms placed on a temperature gradient thermotax to their previous cultivation temperature and then move isothermally 28 and 29. This preferred
cultivation temperature is reset with extended cultivation with food at a new temperature, however, worms will thermotax away from a cultivation temperature if it is associated with starvation 28 and 30•. A forward genetic screen Vorinostat ic50 uncovered the aho-2 mutant (later determined to be an allele of ins-1), which was severely deficient in thermosensory starvation conditioning [31]. Kodama et al. [30•] found that starvation-induced INS-1 release inhibits the core thermotaxis interneurons AIY, AIZ, and RIA via DAF-2. In the current model, thermosensory neurons AFD and AWC store a memory of cultivation temperature, while neuroendocrine and monoamine signals act on the interneurons to modulate the circuit in response to feeding state. This differs from gustatory and olfactory conditioning, where insulin signaling acts on the sensory neurons themselves.