Serotonin and Octopamine in the Nematode Caenorhabditis elegans

The biogenic amines serotonin and octopamine are present in the nematode Caenorhabditis elegans . Serotonin, detected histochemically in whole mounts, is localized in two pharyngeal neurons that appear to be neurosecretory. Octopamine, identified radioenzymatically in crude extracts, probably is also localized in a few neurons. Exogenous serotonin and octopamine elicit specific and opposite behavioral responses in Caenorhabditis elegans , suggesting that these compounds function physiologically as antagonists.