The stomatogastric nervous system (STNS) of crustaceans offers several circuits that serve as models for central pattern generation. Many fundamental questions regarding monoaminergic neuromodulation have been addressed with this system. Though physiological responses to these modulators are well understood, their molecular mechanisms are only beginning to be revealed. Monoamines communicate with target neurons through highly conserved G protein coupled receptors (GPCRs). Database mining expeditions suggest that arthropods possess 18 monoamine receptors. Based on previous research manuscripts, these 18 receptors can be divided into 5 types: dopamine receptors (3), serotonin receptors (5), octopamine receptors (1), tyramine receptors (1), and unknown receptors (8). Preliminary characterizations for 3 of these unknown proteins were presented at the 2004 SFN meeting revealing a 4th dopamine receptor and 2nd and 3rd octopamine receptor. The remaining 5 unknown receptors have never been cloned or characterized ...