Identification of proctolin-containing neurons

Proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH), a highly bioactive peptide found first in insects, is shown to be localized to specific neurons in the central nervous system (CNS) of the cockroach Periplaneta americana. Application of an antiproctolin serum to whole ganglia in a whole-mount immunohistochemical technique reveals the presence of proctolin immunoreactive neurons throughout the CNS. These neurons can be mapped and appear in consistent positions in different individuals. Some have been uniquely identified by intracellular dye injection combined with immunological localization. The presence of proctolin in individually identified neurons has been determined by high-pressure liquid chromatography combined with proctolin bioassay detection performed on extracts made from single identified cells. Some proctolin-containing neurons contain large vacuolelike inclusions in their cell bodies. These vacuoles appear to be the greatly enlarged lumena of the rough endoplasmic reticulum and may be part of the morphological substrate for the manufacture of proctolin. Electrophysiological studies suggest that some proctolin-containing neurons in different segmental ganglia, although not all, are normally recruited together as a functional unit by shared presynaptic input. This characterization of individual proctolin neurons is a prelude to a cellular study of the physiological role of a neuropeptide.