We previously reported that tyramine inhibits glutamatergic excitatory junction potentials (EJPs) and that tyramine-immunoreactive neurons are present and innervate the muscles in Drosophila larvae, supporting the function of tyramine as a neuromediator (Komatsu et al., 2000, SFN Abstracts). To determine whether tyraminergic neurons are present in animals other than Drosophila, anti-tyramine antibody was used to stain the tyramine-containing neurons in the CNS of the crayfish, Procambarus clarkii. In the supraesophageal ganglion there are two groups of large somata, one in the anterior and the other in the posterior regions. Axons of both neuron groups run the entire ventral nerve cord, reaching to the terminal abdominal ganglion. The subesophageal and thoracic ganglia have many ventral unpaired median (VUM) neurons which send axons to the periphery. Of six abdominal ganglia only the third ganglion has a pair of ventral somata located in the anterior lateral region which send axons in the anterior ipsilate...