High Quality Content by WIKIPEDIA articles! Proctolin is a neuropeptide present in insects and crustaceans. It was first found in Periplaneta americana, a species of cockroach in 1975. Proctolin was extracted from 125,000 cockroaches and the Edman degradation was carried out on the sample to determine the amino acid sequence, which is Arg-Tyr-Leu-Pro-Thr.