Tyramine Functions independently of octopamine in the Caenorhabditis elegans nervous system

Neuron. 2005 Apr 21;46(2):247-60. doi: 10.1016/j.neuron.2005.02.024.


Octopamine biosynthesis requires tyrosine decarboxylase to convert tyrosine into tyramine and tyramine beta-hydroxylase to convert tyramine into octopamine. We identified and characterized a Caenorhabditis elegans tyrosine decarboxylase gene, tdc-1, and a tyramine beta-hydroxylase gene, tbh-1. The TBH-1 protein is expressed in a subset of TDC-1-expressing cells, indicating that C. elegans has tyraminergic cells that are distinct from its octopaminergic cells. tdc-1 mutants have behavioral defects not shared by tbh-1 mutants. We show that tyramine plays a specific role in the inhibition of egg laying, the modulation of reversal behavior, and the suppression of head oscillations in response to anterior touch. We propose a model for the neural circuit that coordinates locomotion and head oscillations in response to anterior touch. Our findings establish tyramine as a neurotransmitter in C. elegans, and we suggest that tyramine is a genuine neurotransmitter in other invertebrates and possibly in vertebrates as well.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Blotting, Western
  • Caenorhabditis elegans
  • Caenorhabditis elegans Proteins / genetics
  • Caenorhabditis elegans Proteins / metabolism
  • Chromatography, High Pressure Liquid
  • Humans
  • Immunohistochemistry
  • Models, Neurological*
  • Molecular Sequence Data
  • Nervous System Physiological Phenomena*
  • Neurotransmitter Agents / genetics
  • Neurotransmitter Agents / metabolism*
  • Octopamine / genetics
  • Octopamine / metabolism*
  • Polymerase Chain Reaction
  • Sequence Homology, Amino Acid
  • Tyramine / metabolism*
  • Tyrosine 3-Monooxygenase / genetics
  • Tyrosine 3-Monooxygenase / metabolism
  • Tyrosine Decarboxylase / genetics
  • Tyrosine Decarboxylase / metabolism


  • Caenorhabditis elegans Proteins
  • Neurotransmitter Agents
  • Octopamine
  • Tyrosine 3-Monooxygenase
  • Tyrosine Decarboxylase
  • Tyramine