Peptidergic neurohemal system of an insect: mass spectrometric morphology.

Neuropeptides are by far the most diverse group of messenger molecules in insects. To understand cell signaling and function, it is essential to reveal the complete neuropeptide profile of a single neuron/nerve/neurohemal organ first. In this study, matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry was used to analyze the peptidergic system of an insect, focussing on the neurohemal structures. Major neurohemal organs were investigated, including the retrocerebral complex, perisympathetic organs, and all nerves supplying these organs with neurosecretions. Additionally, peripheral neurohemal release sites such as the dilator muscle of the antennal circulatory organ and lateral heart nerves were studied, as well as parts of the stomatogastric nervous system. The following neuropeptide families were analyzed: kinins, allatostatins, leucomyosuppressin, corazonin, adipokinetic hormones, myoinhibitory peptide, sulfakinins, periviscerokinins, YLSamide, VEAacid, SKNacid, proctolin, the head peptide, and pyrokinins. Beyond a contribution to a map of the distribution of neuropeptides in a neurohemal system, the following conclusions can be drawn from these experiments. (1) Nearly all abundant peaks in the different mass spectra represent peptides that have already been identified. (2) Although only adult males were used in this study, variations in the peptide abundances were observed that are possibly correlated with different physiological/developmental conditions. (3) Peptides have a body-region-specific distribution in the neurohemal system. (4) A clear compartmentalisation of the retrocerebral complex could be observed.