Proctolin is a bioactive neuropeptide that modulates interneuronal and neuromuscular synaptic transmission in a wide variety of arthropods.

Proctolin, an insect neuropeptide prevalent in arthropods, plays a significant role as a neuromodulator and potentially a neurohormone, although it doesn't act as a conventional neurotransmitter. It enhances action potential frequency, amplifies muscle contraction, and activates dormant systems. Structurally, Proctolin is a pentapeptide featuring the sequence RYLPT, notable for being the first insect neuropeptide with both sequenced and chemically characterized attributes. Identified first in D. melanogaster through the Proctolin precursor gene CG7105, it was previously undetected in B. mori due to lack of a mature peptide—attributed to missing cleavage sites around the RYLPT sequence. Recent proteomic analyses in B. mori wings have identified this pentapeptide, yet similar genetic characteristics in C. suppressalis suggest the absence of functional Proctolin in both species.