title: Serotonin regulates repolarization of the C. elegans pharyngeal muscle.
abstract: Caenorhabditis elegans feeds by rhythmically contracting its pharynx to ingest bacteria. The rate of pharyngeal contraction is increased by serotonin and suppressed by octopamine. Using an electrophysiological assay, we show that serotonin and octopamine regulate two additional aspects of pharyngeal behavior. Serotonin decreases the duration of the pharyngeal action potential and enhances activity of the pharyngeal M3 motor neurons. Gramine, a competitive serotonin antagonist, and octopamine have effects opposite to those of serotonin: gramine and octopamine increase action potential duration and suppress M3 activity. The effects of serotonin, gramine and octopamine on action potential duration are dependent on the pharyngeal motor neurons MC and M3. When the MC and M3 motor neurons are functionally defective, serotonin and octopamine do not regulate the action potential. Our data suggest that serotonin alters pharyngeal physiology to allow for rapid contraction-relaxation cycles. Reciprocal regulation of pharyngeal behavior by serotonin and octopamine provides a mechanism for adapting to the presence and absence of food, respectively.
authors.affiliation: Department of Molecular Biology, The University of Texas Southwestern Medical Center, 6000 Harry Hines, Dallas TX 75390-9148, USA. tim.niacaris@utsouthwestern.edu
authors.forename: Timothy
authors.initials: T
authors.lastname: Niacaris
authors.forename: Leon
authors.initials: L
authors.lastname: Avery
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D017173:Caenorhabditis elegans / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D026121:Indole Alkaloids; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology; D009154:Mutation; D009655:Octopamine / Q000494:pharmacology; D010609:Pharyngeal Muscles / Q000187:drug effects* / Q000294:innervation / Q000502:physiology*; D012701:Serotonin / Q000172:deficiency / Q000494:pharmacology* / Q000502:physiology
chemical_list: D000470:Alkaloids; D026121:Indole Alkaloids; D009655:Octopamine; D012701:Serotonin; C007884:gramine