Localization and neurohemal release of FMRFamide-related peptides in the stick insect Carausius morosus.

FMRFamide-like immunoreactivity was localized immunohistochemically in the central stomatogastric nervous systems, visceral tissues, and the neurohemal corpora cardiaca, transverse, and segmental nerves. Each of these neurohemal areas contains one morphologically distinct type of immunoreactive neurosecretory granule. The hemolymph level of FMRFamide-like peptides, quantified by RIA, is higher in animals sampled 2 h into the dark cycle, relative to those sampled at mid-light cycle or 9 h into the dark cycle. High potassium depolarization evokes the calcium-dependent release of FMRFamide-like peptides from neurohemal areas in vitro and HPLC fractionation of hemolymph, corpora cardiaca, and their bathing medium suggests that these organs contribute a single peptide to the FMRFamide-related peptides circulating in the hemolymph of active animals.