Perisympathetic Organs Research Articles

Zoological terms in the human histological nomenclature Terminologia Histologica. What we think, what we know, and what we think we know

Terminology in morphological and zoological sciences is enormously important. Proper denomination of individual structures of the animal / human body from the microscopic point of view has an irreplaceable role in unambiguous understanding and communication among scientists regardless of their field of expertise. The year 2008 can be considered a crucial year in the developing of internationally accepted histological terminology, because it was the year when the first internationally renowned human histology nomenclature Terminologia Histologica was published. The current version of the Terminologia Histologica contains also the description of many microscopic organs and structures whose presence in different animal species is widely accepted, however their presence in humans is disputable. Typical examples are the haemal lymph nodes and haemal nodes, mentioned in the chapter Lymphoid organs which are secondary lymphoid organs found in many different mammalian species, but also in some birds. They are capable of performing haematopoietic and immunological functions but in the absence of lymphatic system pathology, no structures resembling haemal nodes / haemal lymph nodes have been detected in humans. Neurohaemal organs are mentioned within the chapter Endocrine system. Neurohaemal organs are known by different names, depending on the animal species studied, e.g. corpora allata or abdominal perisympathetic organs. To this date, these structures have been described in many different invertebrate species, but neurohaemal organs are also found in some lower vertebrates, in which the neurohaemal organ is referred to as “urophysis”. According to our opinion, structures called neurohaemal organs in invertebrates are counterparts to circumventricular organs found in vertebrates, but cannot be named as such. Another somewhat controversial term mentioned in human histological nomenclature is the vomeronasal organ mentioned in the chapter Respiratory system. It is a specialized organ, which forms an integral supportive part of the olfaction of many mammalian species and reptiles. It is believed that the main function of vomeronasal organ is to regulate various behavioral aspects of intraspecies interaction by facilitating the detection of pheromones. The function and even existence of the vomeronasal organ in humans is a source of significant dispute among researchers. Some of them stated that vomeronasal organ disappears during fetal development, with except the vomeronasal duct. On the other hand, there are also authors who concluded that the vomeronasal organ is definitely present in adult humans. Similarly disputable question is the presence of multinucleated plasmodia in human body. This opinion article aims to open a wide scientific discussion concerning the importance and aptness of the inclusion of these terms in the human histological nomenclature despite they are probably exclusively zoological.

Identification of mature peptides from pban and capa genes of the moths Heliothis peltigera and Spodoptera littoralis

By transcriptome analysis, we identified PBAN and CAPA precursors in the moths Spodoptera littoralis and Heliothis peltigera which are among the most damaging pests of agriculture in tropical and subtropical Africa as well as in Mediterranean countries. A combination of mass spectrometry and immunocytochemistry was used to identify mature peptides processed from these precursors and to reveal their spatial distribution in the CNS. We found that the sites of expression of pban genes, the structure of PBAN precursors and the processed neuropeptides are very similar in noctuid moths. The sequence of the diapause hormone (DH; tryptopyrokinin following the signal peptide), however, contains two N-terminal amino acids more than expected from comparison with already published sequences of related species. Capa genes of S. littoralis and H. peltigera encode, in addition to periviscerokinins, a tryptopyrokinin showing sequence similarity with DH, which is the tryptopyrokinin of the pban gene. CAPA peptides, which were not known from any noctuid moth so far, are produced in cells of abdominal ganglia. The shape of the release sites of these hormones in H. peltigera represents an exceptionally derived trait state and does not resemble the well-structured abdominal perisympathetic organs which are known from many other insects. Instead, axons of CAPA cells extensively ramify within the ventral diaphragm. The novel information regarding the sequences of all mature peptides derived from pban and capa genes of H. peltigera and S. littoralis now enables a detailed analysis of the bioactivity and species-specificity of the native peptides, especially those from the hitherto unknown capa genes, and to explore their interactions with PBAN/DH receptors.

Identification and Expression of Capa Gene in the Fire Ant, Solenopsis invicta

Recent genome analyses suggested the absence of a number of neuropeptide genes in ants. One of the apparently missing genes was the capa gene. Capa gene expression in insects is typically associated with the neuroendocrine system of abdominal ganglia; mature CAPA peptides are known to regulate diuresis and visceral muscle contraction. The apparent absence of the capa gene raised questions about possible compensation of these functions. In this study, we re-examined this controversial issue and searched for a potentially unrecognized capa gene in the fire ant, Solenopsis invicta. We employed a combination of data mining and a traditional PCR-based strategy using degenerate primers designed from conserved amino acid sequences of insect capa genes. Our findings demonstrate that ants possess and express a capa gene. As shown by MALDI-TOF mass spectrometry, processed products of the S. invicta capa gene include three CAPA periviscerokinins and low amounts of a pyrokinin which does not have the C-terminal WFGPRLa motif typical of CAPA pyrokinins in other insects. The capa gene was found with two alternative transcripts in the CNS. Within the ventral nerve cord, two capa neurons were immunostained in abdominal neuromeres 2–5, respectively, and projected into ventrally located abdominal perisympathetic organs (PSOs), which are the major hormone release sites of abdominal ganglia. The ventral location of these PSOs is a characteristic feature and was also found in another ant, Atta sexdens.

Identification of two capa cDNA transcripts and detailed peptidomic characterization of their peptide products in Periplaneta americana

The first CAPA peptides of insects were identified from Periplaneta americana using extracts of 8000 abdominal perisympathetic organs. The corresponding gene of cockroaches and other basal insects, however, remained undiscovered. Here we identified two capa cDNA transcripts of P. americana. Single cell mass spectrometry of capa neurons in abdominal ganglia yielded a complete coverage of the precursor sequences of both transcripts; with intermediates of precursor processing more prominent in somata than in perisympathetic organs. The processing of the CAPA precursor in P. americana is compared with that in the beetle Tribolium castaneum which was re-evaluated in this study.

Deficiency of prohormone convertase dPC2 (AMONTILLADO) results in impaired production of bioactive neuropeptide hormones in Drosophila

Peptide hormones synthesized by secretory neurons in the CNS are important regulators of physiology, behavior, and development. Like other neuropeptides, they are synthesized from larger precursor molecules by a specific set of enzymes. Using a combination of neurogenetics, immunostainings, and direct mass spectrometric profiling, we show that the presence of Drosophila prohormone convertase 2 encoded by the gene amontillado (amon) is a prerequisite for the proper processing of neuropeptide hormones from the major neurohemal organs of the CNS. A loss of amon correlates with a loss of neuropeptide hormone signals from the larval ring gland and perisympathetic organs. Neuropeptide hormone signals were still detectable in the adult corpora cardiaca of older amon-deficient flies which were amon heat-shock-rescued until eclosion. A semiquantification by direct peptide profiling using stable isotopic standards showed, however, that their neuropeptide hormone levels are strongly reduced. Targeted expression of GFP under the control of amon regulatory regions revealed a co-localization with the investigated peptide hormones in secretory neurons of the brain and ventral nerve cord. The lack of AMON activity resulted in a deficiency of L3 larva to enter the wandering phase. In conclusion, our findings provide the first direct evidence that AMON is a key enzyme in the production of neuropeptides in the fruitfly.

A proteomic approach for studying insect phylogeny: CAPA peptides of ancient insect taxa (Dictyoptera, Blattoptera) as a test case

BackgroundNeuropeptide ligands have to fit exactly into their respective receptors and thus the evolution of the coding regions of their genes is constrained and may be strongly conserved. As such, they may be suitable for the reconstruction of phylogenetic relationships within higher taxa. CAPA peptides of major lineages of cockroaches (Blaberidae, Blattellidae, Blattidae, Polyphagidae, Cryptocercidae) and of the termite Mastotermes darwiniensis were chosen to test the above hypothesis. The phylogenetic relationships within various groups of the taxon Dictyoptera (praying mantids, termites and cockroaches) are still highly disputed.ResultsTandem mass spectrometry of neuropeptides from perisympathetic organs was used to obtain sequence data of CAPA peptides from single specimens; the data were analysed by Maximum Parsimony and Bayesian Interference. The resulting cladograms, taking 61 species into account, show a topology which is in general agreement with recent molecular and morphological phylogenetic analyses, including the recent phylogenetic arrangement placing termites within the cockroaches. When sequence data sets from other neuropeptides, viz. adipokinetic hormones and sulfakinins, were included, the general topology of the cladogram did not change but bootstrap values increased considerably.ConclusionThis study represents the first comprehensive survey of neuropeptides of insects for solely phylogenetic purposes and concludes that sequences of short neuropeptides are suitable to complement molecular biological and morphological data for the reconstruction of phylogenetic relationships.

Neuropeptides in Heteroptera: Identification of allatotropin-related peptide and tachykinin-related peptides using MALDI-TOF mass spectrometry

Recently, the peptidomic analysis of neuropeptides from the retrocerebral complex and abdominal perisympathetic organs of polyphagous stinkbugs (Pentatomidae) revealed the group-specific sequences of pyrokinins, CAPA peptides (CAPA-periviscerokinins/PVKs and CAPA-pyrokinin), myosuppressin, corazonin, adipokinetic hormone, and short neuropeptide F. In this study, we used mass spectrometric profiling of nervous tissue from the species-rich taxon Hemiptera to identify products of two previously unobserved neuropeptide genes from these species, namely allatotropin-related peptide (ATRP) and tachykinin-related peptides (TKRPs). Since neither TKRPs nor allatotropin are accumulated in neurohemal organs, immunocytochemical data were analyzed to find potential accumulation sites within the central nervous system. By mass spectrometry, TKRPs were found to be accumulated in the antennal lobes, and ATRP was identified in the most posterior region of the abdominal ventral nerve cord and fourth abdominal nerves. In addition to neuropeptides from stink bugs, TKRPs and ATRP were also identified from the distantly related bugs Oncopeltus fasciatus (Lygaeidae) and Pyrrhocoris apterus (Pyrrhocoridae). In total, six TKRPs and one ATRP from each species could be elucidated by tandem mass spectrometry. The ATRP of all species is sequence-identical with Locusta migratoria accessory gland myotropin-1 (Lom-AG-MT-1), a member of the highly conserved insect allatotropin family.

PBAN/pyrokinin peptides in the central nervous system of the fire ant, Solenopsis invicta

The pyrokinin/pheromone-biosynthesis-activating neuropeptide (PBAN) family of peptides found in insects is characterized by a 5-amino-acid C-terminal sequence, FXPRLamide. The pentapeptide is the active core required for diverse physiological functions, including the stimulation of pheromone biosynthesis in female moths, muscle contraction, induction of embryonic diapause, melanization, acceleration of puparium formation, and termination of pupal diapause. We have used immunocytochemical techniques to demonstrate the presence of pyrokinin/PBAN-like peptides in the central nervous system of the fire ant, Solenopsis invicta. Polyclonal antisera against the C-terminal end of PBAN have revealed the location of the peptide-producing cell bodies and axons in the central nervous system. Immunoreactive material is detectable in at least three groups of neurons in the subesophageal ganglion and corpora cardiaca of all adult sexual forms. The ventral nerve cord of adults consists of two segmented thoracic ganglia and four segmented abdominal ganglia. Two immunoreactive pairs of neurons are present in the thoracic ganglia, and three neuron pairs in each of the first three abdominal ganglia. The terminal abdominal ganglion has no immunoreactive neurons. PBAN immunoreactive material found in abdominal neurons appears to be projected to perisympathetic organs connected to the abdominal ganglia. These results indicate that the fire ant nervous system contains pyrokinin/PBAN-like peptides, and that these peptides are released into the hemolymph. In support of our immunocytochemical results, significant pheromonotropic activity is found in fire ant brain-subesophageal ganglion extracts from all adult fire ant forms (queens, female and male alates, and workers) when extracts are injected into decapitated females of Helicoverpa zea. This is the first demonstration of the presence of pyrokinin/PBAN-like peptides and pheromonotropic activity in an ant species.

Examination of the role of FMRFamide-related peptides in the circadian clock of the cockroach Leucophaea maderae

The accessory medulla, the circadian clock of the cockroach Leucophaea maderae, is abundant in neuropeptides. Among these neuropeptides are the FMRFamide-related peptides (FaRPs), which generally share the C-terminal RFamide. As a first step toward understanding the functional role of FaRPs in the circadian clock of the cockroach, immunocytochemistry with antisera against various FaRPs, MALDI-TOF mass spectrometry, and injections of two FaRPs combined with running-wheel assays were performed. Prominent FMRFamide-like immunoreactivity was found in maximally four soma clusters associated with the accessory medulla and in most neuropils of the protocerebrum. By MALDI-TOF mass spectrometry, various extended FMRFamides of the cockroach L. maderae were partially identified in thoracic perisympathetic organs, structures known to accumulate extended FMRFamides in insects. By mass match, several of these peptides were also detected in the accessory medulla. Injections of FMRFamide and Pea-FMRFa-7 (DRSDNFIRF-NH(2)) into the vicinity of the accessory medulla caused time-dependent phase-shifts of locomotor activity rhythms at circadian times 8, 18, and 4. Thus, our data suggest a role for the different FaRPs in the control of circadian locomotor activity rhythms in L. maderae.

Comparative peptidomics of four related hemipteran species: Pyrokinins, myosuppressin, corazonin, adipokinetic hormone, sNPF, and periviscerokinins

We performed the first comprehensive peptidomic analysis of neurohormones from hemipteran insects by analyzing the neuropeptides of two major neurohemal organs, namely the corpora cardiaca and abdominal perisympathetic organs. For the experiments we selected four related species of polyphagous stinkbugs (Pentatomidae), three of which are known to attack several important food crops. Peptide sequences were identified by MALDI-TOF mass spectrometry; tandem fragmentation of myosuppressin, sNPF, CAPA-periviscerokinins and pyrokinins revealed novel sequences not known from other insects so far. Most Leu/Ile and Glu/Lys ambiguities could be solved by either specific side-chain fragmentations or on-plate acetylation experiments. The identification of the specific sequences provides a solid basis for forthcoming pharmacological tests to study the neuroendocrine system of these pest insects. However, it should be mentioned in this context that the sequences of the peptides from different stinkbugs are likely not representative of Hemiptera in general. The forthcoming release of the genome from the reduviid Rhodnius prolixus will provide sufficient data to clear this point.

Identification of the first neuropeptides from the CNS of Hemiptera: CAPA peptides of the southern green stinkbug Nezara viridula (L.)

A direct mass spectrometric investigation of nerve homologs of the abdominal perisympathetic organs was employed to reveal the first and complete sequences of CAPA peptides from a hemipteran species, the southern green stinkbug Nezara viridula. Side-chain fragmentations allowed the assignment of internal Leu/Ile; on-plate acetylation was used to distinguish between the mass-related Lys and Gln. The following sequences were obtained: DQLFPFPRV-NH 2 (CAPA-PVK-1), EQLIPFPRV-NH 2 (CAPA-PVK-2), and NGSAGNGGLWFGPRL/I-NH 2 (CAPA-PK). CAPA-PVKs are associated with the regulation of diuresis in insects, and identification of those native to a hemipteran will provide the experimental basis to better understand regulation of water balance in this family of insects.

Morphology and metamorphosis of the peptidergic Va neurons and the median nerve system of the fruit fly, Drosophila melanogaster

Metamorphosis is a fundamental developmental process and has been intensively studied for various neuron types of Drosophila melanogaster. However, detailed accounts of the fate of identified peptidergic neurons are rare. We have performed a detailed study of the larval morphology and pupal remodelling of identified peptidergic neurons, the CAPA-expressing Va neurons of D. melanogaster. In the larva, Va neurons innervate abdominal median and transverse nerves that are typically associated with perisympathetic organs (PSOs), major neurohaemal release sites in insects. Since median and transverse nerves are lacking in the adult, Va neurites have to undergo substantial remodelling during metamorphosis. We have examined the hitherto uncharacterised gross morphology of the thoracic PSOs and the abdominal median and transverse nerves by scanning electron microscopy and found that the complete reduction of these structures during metamorphosis starts around pupal stage P7 and is completed at P9. Concomitantly, neurite pruning of the Va neurons begins at P6 and is preceded by the high expression of the ecdysone receptor (EcR) subtype B1 in late L3 larvae and the first pupal stages. New neuritic outgrowth mainly occurs from P7-P9 and coincides with the expression of EcR-A, indicating that the remodelling of the Va neurons is under ecdysteroid control. Immunogold-labelling has located the CAPA peptides to large translucent vesicles, which are released from the transverse nerves, as suggested by fusion profiles. Hence, the transverse nerves may serve a neurohaemal function in D. melanogaster.

Allatostatin-like immunoreactivity in the abdomen of the locust Schistocerca gregaria

A polyclonal antibody against allatostatin 1 (AST-1) of cockroach Diploptera punctata was used to investigate the distribution of AST-like immunoreactivity within the abdomen of the locust, Schistocerca gregaria. In the abdominal ganglia, AST-like immunoreactivity was found in both cell bodies and neuropile. In ganglia 6 and 7, staining was found in serial homologous cell bodies in anterior dorsolateral and dorsomedial, and posterior ventrolateral and ventromedial locations. In the terminal ganglion, the numerous immunoreactive somata were smaller in size than those in the unfused ganglia. The combination of backfill experiments with immunocytochemistry showed that, in abdominal ganglion 7, one neuron of the ventromedian cell body cluster and two of the ventrolateral cluster innervated the oviduct, which itself was covered with a dense mesh of AST-immunoreactive varicosities. Combining electron microscopy with immunohistochemistry revealed AST-like immunoreactivity in dense-core vesicles located in neurohaemal-like terminals lacking structures normally found in synapses. A mesh of AST-immunoreactive varicosities was also found on the muscles of the spermatheca and the spermathecal duct. In addition, a mesh of strongly stained varicosities was present in the distal perisympathetic organs (neurohaemal organs in the abdomen) and on the lateral heart nerves (a putative neurohaemal release zone). These data indicate that AST is an important neuroactive substance that is probably involved in multiple tasks in the control of the locust abdomen.

Effects of Manduca allatotropin and localization of Manduca allatotropin-immunoreactive cells in earwigs

Manduca sexta allatotropin (Manse-AT) was first isolated on the basis of its ability to stimulate production of juvenile hormone in that insect. We examined whether this neuropeptide affects corpus allatum activity and visceral muscle contraction in adult females of the earwig, Euborellia annulipes. We also assessed the presence of allatotropin-like material in tissues using immunocytochemistry. Manse-AT at 1 nM to 10 μM stimulated juvenile hormone production in vitro by glands of low activity from 2-day virgin females. In glands of high activity from 12-day mated females, 1 and 100 nM allatotropin were effective, but 10 μM was not. Similarly, hindguts of 2-day and 12-day females significantly increased in motility in vitro in response to Manse-AT. A monoclonal antibody to Manse-AT was used to demonstrate allatotropin-like material throughout the nervous system of 2-day, virgin females. Immunoreactivity was most pronounced within varicosities of the corpora cardiaca and perisympathetic organs. No immunofluorescence was observed in gut tissue. Lastly, we showed that extract of retrocerebral complexes also enhanced in vitro hindgut motility from 2-day virgin females, in a dose-dependent manner. These results indicate material similar to M. sexta allatotropin in female earwigs and that such peptides may modulate juvenile hormone biosynthesis and visceral muscle contractions. Sensitivity to the peptides may change with physiological stage.

Mass spectrometric analysis of single identified neurons of an insect

The combination of retrograde labelling with dextran-tetramethylrhodamine and MALDI-TOF mass spectrometry was used to analyse for the first time the peptidome of a series of morphologically identified single neurosecretory cells of an insect. Eight postero-lateral cells of the metathoracic ganglion of the American cockroach, Periplaneta americana, were used to demonstrate that: (1) the complete dissection procedure can be documented and (2) the mass spectrometric analysis of the dissected somata results in highly reproducible mass spectra. In total, 21 FMRFamide-related peptides were detected in each of the postero-lateral cells which release their neurosecretions via thoracic perisympathetic organs. Direct analysis of these neurohemal organs confirmed the co-storage of FMRFamide-related peptides. Two additional abundant peptides from thoracic perisympathetic organs which were not detectable in the postero-lateral cells were characterized using ESI-Q-TOF MS/MS. De novo sequencing yielded two related peptides (FERL/IEamides) without any similarity with known peptide families of insects.

Peptidomics of neurohemal organs from species of the cockroach family Blattidae: how do neuropeptides of closely related species differ?

The primary structures and molecular mass data of neuropeptides that are released from major neuroendocrine sites of the American cockroach, Periplaneta americana, are well known. In the current study we extensively surveyed neuropeptides of the corpora cardiaca, the corpora allata and the abdominal perisympathetic organs, from 14 related cockroach species belonging to the family Blattidae. Mainly, this survey was executed by using mass spectrometric methods (MALDI-TOF MS). Peptides which appeared to be modified, as judged from their mass data and comparison with known data from P. americana, were fragmented by means of the post-source decay technique to determine their amino acid sequence. Single organ preparations sufficed to reveal the peptide pattern in neurohemal organs and to identify species-specific modifications, making it possible to glean information also from tissues of less abundant species that were caught during field trips. The peptide inventory described in this study is very typical of cockroaches of the family Blattidae and clearly separates this taxon from other taxa of cockroaches. The majority of neuropeptides was identical in all investigated species. Some peptides, however, displayed remarkable variations in their sequence which hint to a differential rate of modification among peptides of the same neuropeptide family. These modifications serve to distinguish further relatedness of taxa within the Blattidae.

Differential sorting and packaging of capa-gene related products in an insect

A unique costorage of neuropeptides was recently found in the abdominal perisympathetic organs (PSOs) of the American cockroach, Periplaneta americana. Having specific antisera directed against all peptides belonging to this neurosecretory system, we examined the sorting of PSO-peptides in the soma of the median neurosecretory cells of abdominal ganglia by using immunoelectron microscopic double stainings. The data indicate that all six abundant neuropeptides of this neurohormonal system, which includes three capa-gene related products, are primarily incorporated into separate vesicles. These vesicles fuse with each other in the cytoplasm and become translucent on their way to the axon hillock. By means of light microscopy and MALDI-TOF mass spectrometry, an identical population of neuropeptides was found in interneurons of the brain. As revealed by subsequent immunoelectron microscopic analysis, the peptides of these cells are separately packed into dense core vesicles but do not fuse with each other. Thus, hitherto unknown cell-type-specific sorting mechanisms occur in neurosecretory cells and interneurons, respectively.

Neuropeptides in perisympathetic organs of Manduca sexta: specific composition and changes during the development

We used a combination of matrix-assisted laser desorption-ionization time-of-flight mass spectrometry and immunocytochemistry to investigate the peptides from abdominal perisympathetic organs of Manduca sexta. Altogether three mass peaks, detected in mass spectra from single abdominal perisympathetic organs were identical with already known neuropeptides, namely CAP 2b, CCAP, and Manduca-allatotropin. Only CAP 2b was found throughout the postembryonic development. In larvae, perisympathetic organs of the abdominal ganglia 1 and 7 do not accumulate neuropeptides. During the metamorphosis, the number of putative hormones stored in the abdominal perisympathetic organs, increases dramatically. Not a single substance, however, obtained in mass spectra of larval perisympathetic organs disappeared in the respective adult neurohemal organs. Peptides from abdominal perisympathetic organs are different from those of thoracic perisympathetic organs and the retrocerebral complex. Manduca-FLRFa-2 and -3 are enriched in thoracic perisympathetic organs; FLRFa-1, corazonin and adipokinetic hormone are abundant peptides of the retrocerebral complex. The majority of ion signals, however, represent unknown substances. An antiserum which recognized CAP 2b allowed the morphological characterization of a median neurosecretory system in the abdominal ventral nerve cord of M. sexta, which resembles that of cockroach embryos. Double stainings confirmed that crustacean cardioactive peptide (CCAP) becomes colocalized with CAP 2b in median neurosecretory cells during the last larval instar. This colocalization continues in adult insects.

Mass spectrometric analysis of the perisympathetic organs in locusts: identification of novel periviscerokinins

A mass spectrometric analysis carried out to determine the peptidome of the abdominal perisympathetic organs in the locust species Locusta migratoria and Schistocerca gregaria yielded a number of predominant ion peaks, among which are Lom-PVK (AAGLFQFPRVamide) and Scg-MT-2 (TSSLFPHPRLamide). In addition, three novel peptides were identified: Lom-PVK-2 (identical in Schistocerca): GLLAFPRVamide, Lom-PVK-3: DGGEPAAPLWFGPRVamide, and Scg-PVK-3: DGAETPGAAASLWFGPRVamide. An extensive mass spectrometric study of the central nervous system showed that the periviscerokinins (-PRVamides) and Scg-MT-2 (-FXXPRLamide) are restricted to the abdominal ganglia and their perisympathetic organs, while the pyrokinins (-FXPRLamides) are present only in the brain–retrocerebral complex. Sequence comparison with the Drosophila genes supports a conserved gene structure whereby a capability-like gene encodes the periviscerokinins that are expressed in the abdominal ganglia and stored in the perisympathetic organs, while a hugin-like gene encodes the pyrokinins that are expressed in the head ganglia and stored in the retrocerebral complex.

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.