Starvation activates MAP kinase through the muscarinic acetylcholine pathway in Caenorhabditis elegans pharynx

Starvation activates MAPK in the pharyngeal muscles of C. elegans through a muscarinic acetylcholine receptor, G_qα, and nPKC as shown by the following results: (1) Starvation causes phosphorylation of MAPK in pharyngeal muscle. (2) In a sensitized genetic background in which G_qα signaling cannot be downregulated, activation of the pathway by a muscarinic agonist causes lethal changes in pharyngeal muscle function. Starvation has identical effects. (3) A muscarinic antagonist blocks the effects of starvation on sensitized muscle. (4) Mutations and drugs that block any step of signaling from the muscarinic receptor to MAPK also block the effects of starvation on sensitized muscle. (5) Overexpression of MAPK in wild-type pharyngeal muscle mimics the effects of muscarinic agonist and of starvation on sensitized muscle. We suggest that, during starvation, the muscarinic pathway to MAPK is activated to change the pharyngeal muscle physiology to enhance ingestion of food when food becomes available.