The abdominal perisympathetic neurohemal organs of the cockroach Periplaneta americana: innervation revealed by cobalt chloride diffusion

Identical cellular distribution of all abundant neuropeptides in the major abdominal neurohemal system of an insect (Periplaneta americana)

The median neurosecretory cells in abdominal ganglia of insects synthesize a number of putative hormones, which are abundant in the abdominal perisympathetic organs (PSOs). The peptide inventory of these prominent neurohemal release sites is best investigated in the American cockroach and strongly differs from that of head/thoracic neurohemal organs. In this study, we found a complete colocalization of all abundant neuropeptides in this hormonal system, including periviscerokinin-1 and -2, pyrokinin-5, YLSamide, VEAacid, and SKNacid. The first immunoreactive cells were detected on day 18 of embryonic development and already contained the complete set of peptides. By using antisera against the above-mentioned peptides, the development of this neurohormonal system could be studied and is described in detail. Subsequent electron microscopic immunogold stainings in PSO preparations revealed the costorage of PSO peptides in a single vesicle species. Surprisingly, all these peptides were found in axons containing clear vesicles, whereas all axons with dense core vesicles were totally devoid of immunoreactivity. Unlike the axons with dense core vesicles, immunostained axons ramify in the center of the PSO but exhibit only rare morphological signs of exocytosis. Instead, putative release sites of the clear vesicle-containing axons were detected peripherally to the PSOs, namely, on the hyperneural muscle.

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

The periviscerokinins of Periplaneta americana (Pea-PVKs) were the first neuropeptides directly isolated from perisympathetic organs (PSOs), neurohemal swellings of the transverse and median nerves of insects. It has been demonstrated that Pea-PVK-1 release can be induced from the abdominal PSOs of P. americana by in vitro depolarization. A myotropic effect of Pea-PVK-1 on the hyperneural muscle is restricted to blattid cockroaches, whereas proctolin induces contractions of this muscle in all cockroach species investigated. The location and morphology of Pea-PVK-1-like immunoreactive neurons in species of different cockroach taxa are very similar to those previously described for P. americana. Pea-PVK-1-like immunoreactivity is restricted to cells of the abdominal ganglia which constitute a neurohemal system and project via the median nerve to the abdominal PSOs. Despite interspecific differences in the topography of the transverse nerves of the terminal ganglion, Pea-PVK-1-like immunoreactive fibers always innervate transversal nerves VII and VIII of the terminal ganglion. The results suggest that PVKs act as neurohormones throughout the cockroaches, although they may have different effect(s) depending on the species.

Tagma-specific distribution of FXPRLamides in the nervous system of the American cockroach

FXPRLamide (pyrokinin) distribution in the central nervous system and major neurohaemal organs of the American cockroach and related cockroach species was investigated using immunocytochemistry and MALDI-TOF mass spectrometry. Six isoforms (Pea-PK-1 through -6) were found in different neurohaemal release sites. Pea-PK-1-4 and Pea-PK-6 are all stored in the retrocerebral complex and are all produced in cells located in both the suboesophageal ganglion (SOG) and the tritocerebrum. These pyrokinins were found to be concentrated in and around the corpora allata. No other known peptides were detectable in such high concentrations in this neurohaemal organ. They reach the corpora cardiaca/allata via the nervi corporis cardiaci-1 (NCC-1), NCC-3, and nervi corporis allati-2 (NCA-2). Abdominal perisympathetic organs contained only Pea-PK-5 and low quantities of the sequence-related Pea-PK-6. Neither Pea-PK-5 nor -PK-6 was detected in thoracic perisympathetic organs. It is likely that the expression of pyrokinins in the central nervous system is tagma (body region)-specific. Pea-PK-6 was identified during this study as follows: Ser-Glu-Ser-Glu-Val-Pro-Gly-Met-Trp-Phe-Gly-Pro-Arg-Leu-NH(2).

Periviscerokinin (Pea-PVK): a novel myotropic neuropeptide from the perisympathetic organs of the American cockroach

A myotropic neuropeptide was isolated from extracts of 1000 abdominal perisympathetic organs of males of the cockroach, Periplaneta americana. This peptide, termed periviscerokinin, has excitatory actions on the hyperneural muscle of Periplaneta americana. After peptide sequence analysis and mass spectrometry, the structure of this peptide was confirmed by chemical synthesis and bioassay to be Gly-Ala-Ser-Gly-Leu-Ile-Pro-Val-Met-Arg-Asn-NH2. This sequence is different from the other known myotropic peptides in insects. The threshold concentration for stimulatory effects of the synthetic peptide on the isolated hyperneural muscle was about 10(-9) M, suggesting a physiological role as a neurohormone.

Vasopressin-immunoreactive neurons and neurohemal systems in cockroaches and mantids

Vasopressin-like neuropeptides of insects are of special interest because of their possible function as hormones and neuromodulators. Therefore, this study was undertaken by using whole-mount immunofluorescent staining by two antisera that recognize different types of vasopressin-like immunoreactive groups of neurons in the cockroaches Periplaneta americana, Leucophaea maderae, Nauphoeta cinerea, Diploptera punctata, and Blaberus discoidalis and in the mantids Litaneuria minor and Tenodera aridifolia sinensis. Using an antiserum to Arg/vasopressin, only two cells, the paired ventral paramedian (PVP) neurons, were immunostained in the central nervous system (CNS) of the cockroaches. These cells are located in the subesophageal ganglion, project throughout the CNS, and appear to be neurosecretory. Their varicose collaterals extend into the dorsal (motor) neuropil of the segmental ganglia, and this neuropil may be the principal site of the release of their neurosecretion. The PVP neurons were also stained by an antiserum to Lys/vasopressin; in addition, this antiserum stained several other groups of neurons, most of which appeared to be neurosecretory. Two pairs of Lys/vasopressin-immunoreactive cells are similar to the PVP neurons in that they are located in the subesophageal ganglion, extend through the ventral nerve cord, have collaterals in the dorsal neuropil of the segmental ganglia, and appear to be neurosecretory within the CNS. In addition, midventral and anteroventral clusters of Lys/vasopressin-immunoreactive neurosecretory neurons in the subesophageal ganglion project neurohemal release sites on the corpora allata. Other types of Lys/vasopressin-immunoreactive neurons include median and lateral neurosecretory cells of the protocerebrum and neurosecretory cells in the tritocerebrum, all of which project to the corpora cardiaca. In the abdominal ganglia there are posterolateral clusters of Lys/vasopressin neurosecretory neurons, and these cells extend to neurohemal release sites on the transverse and lateral cardiac nerves. In mantids the anti-Arg/vasopressin and anti-Lys/vasopressin antisera stained most of the same groups of neurons that these antisera recognized in cockroaches. The results of this study suggest that there are two or more vasopressin-like peptides in cockroaches and mantids and that these peptides may be released either as hormones in the blood or as neurosecretions within the CNS. Their function(s) in these insects remains to be determined.

Central and peripheral neurosecretory pathways to an insect flight motor nerve

Ultrastructural examination of the IIN1b nerve to the dorsal longitudinal flight muscle of Manduca sexta L. verified the presence of neurosecretory processes. Subspherical and irregular vesicles were found where the nerve enters the muscle, while spherical vesicles were found in the proximal region only. A dorsal unpaired median (DUM) cell, the median nervous system, and two or more peripheral cells are the sources of these neurosecretory inclusions. Light the electron microscopy CoCl2 backfills of the transverse nerve produced intensification of a peripheral neuron (#1) and processes in nerves IIN1a and IIN1b. Similar backfills of nerve IIN1b produced intensification of a DUM cell, a second peripheral neuron (#2), and processes in the transverse nerve and nerve IIN1a. Neuron #1 contained large spherical electron-dense vesicles while neuron #2 contained smaller subspherical vesicles. These cells were situated upon the link and/or transverse nerves. Based on these results, we suspect central and peripheral neurosecretory processes reach nerve IIN1b as follows: the link nerve projects prothoracic median nervous system and neuron #2 processes, nerve IIN1a projects neuron #1 processes, and nerve IIN1 projects mesothoracic DUM cell processes, although this latter pathway was less clear.