Periviscerokinins in cockroaches: Release, localization, and taxon-specific action on the hyperneural muscle

The periviscerokinins of Periplaneta americana (Pea-PVKs) were the first ne uropeptides directly isolated from perisympathetic organs (PSOs), neurohema l swellings of the transverse and median nerves of insects. It has been dem onstrated that Pea-PVK-l release can be induced from the abdominal PSOs of P. americana by in vitro depolarization. A myotropic effect of Pea-PVK-l on the hyperneural muscle is restricted to blattid cockroaches, whereas proct olin induces contractions of this muscle in all cockroach species investiga ted. The location and morphology of Pea-PVK-l-like immunoreactive neurons i n species of different cockroach taxa are very similar to those previously described for P. americana. Pea-PVK-l-like immunoreactivity is restricted t o cells of the abdominal ganglia which constitute a neurohemal system and p roject via the median nerve to the abdominal PSOs. Despite interspecific di fferences in the topography of the transverse nerves of the terminal gangli on, Pea-PVK-l-like immunoreactive fibers always innervate transversal nerve s VII and VIII of the terminal ganglion. The results suggest that PVKs act as neurohormones throughout the cockroaches, although they may have differe nt effect(s) depending on the species. (C) 2001 Academic Press.