Abstract
Proctolin is a peptide neurotransmitter, discovered in the visceral muscles of the cockroach. The peptide has recently been identified in the nervous systems of many invertebrates. Using reverse phase high pressure liquid chromatography together with a sensitive bioassay, we analyzed the distribution of proctolin in the central nervous system of the grasshopper Schistocerca nitens. We also used immunocytochemistry to identify about 70 diverse proctolin-staining neurons in the postembryonic ventral nerve cord. Proctolin immunoreactivity is rare, being found in only about 0.6% of the ganglionic neurons. Among the cells we stained for proctolin were thoracic skeletal motoneurons, a cluster of efferents to the intrinsic muscles of the hindgut, and both inter- and intraganglionic thoracic interneurons, as well as several interspecies homologues to proctolin-staining neurons in the cockroach. The map of proctolin expression within the central nervous system is not extensively altered during postembryonic life. It is the product of embryonic development, which is the subject of the following paper (Keshishian, H., and M. O'Shea (1985) J. Neurosci. 5: 1005–1015).
