trp-4 has been reported to be expressed in the CEP and ADE dopamine neurons and in two interneurons, DVA and DVC. TRP-4 expression was also observed in the PDE dopamine neurons, probably owing to the use of a longer promoter region (approx7.5 kb) of the
trp-4 gene. TRP-4 was highly enriched in the cilia of the dopamine neurons, and was localized throughout the whole axon in DVA and DVC.