An evolutionary treatment of the morphology and physiology of circulatory organs in insects

The complex neurochemistry of the cockroach antennal heart

The innervation of the antennal heart of the cockroach Periplaneta americana was studied with immunocytochemical techniques on both the light and electron microscopic levels. The antennal heart is innervated by two efferent systems, both using one biogenic amine in combination with neuropeptides. In one, we found co-localization of serotonin with proctolin and allatostatin. These fibers most likely originate from paired neurons located in the suboesophageal ganglion. In the second system, we found octopamine co-localized with the short neuropeptide F. The source of this second system is dorsal unpaired median (DUM) neurons, also located in the suboesophageal ganglion. The possible effects of these neuromediators on different targets are discussed.

Evolutionary morphology of the antennal heart in stick and leaf insects (Phasmatodea) and webspinners (Embioptera) (Insecta: Eukinolabia)

The morphology of the antennal hearts in the head of Phasmatodea and Embioptera was investigated with particular reference to phylogenetically relevant key taxa. The antennal circulatory organs of all examined species have the same basic construction: they consist of antennal vessels that are connected to ampullae located in the head near the antenna base. The ampullae are pulsatile due to associated muscles, but the points of attachment differ between the species studied. All examined Phasmatodea species have a Musculus (M.) interampullaris which extends between the two ampullae plus a M. ampulloaorticus that runs from the ampullae to the anterior end of the aorta; upon contraction, all these muscles dilate the lumina of both ampullae at the same time. In Embioptera, only the australembiid Metoligotoma has an M. interampullaris. All other studied webspinners instead have a M. ampullofrontalis which extends between the ampullae and the frontal region of the head capsule; these species do not have M. ampulloaorticus. Outgroup comparison indicates that an antennal heart with a M. interampullaris is the plesiomorphic character state among Embioptera and the likely ground pattern of the taxon Eukinolabia. Antennal hearts with a M. ampullofrontalis represent a derived condition that occurs among insects only in some embiopterans. These findings help to further clarify the controversially discussed internal phylogeny of webspinners by supporting the view that Australembiidae are the sister group of the remaining Embioptera.

Chemical and functional analyses of Rhinella icterica (Spix, 1824) toad secretion screened on contractions of the heart and oviduct in Locusta migratoria

Rhinella icterica is a Brazilian toad with a parotoid secretion that is toxic to insects. In this work, we examined the entomotoxicity of this secretion in locust (Locusta migratoria) semi-isolated heart and oviduct preparations in vitro. The parotoid secretion caused negative chronotropism in semi-isolated heart preparations (at the highest dose tested: 500 μg) and markedly enhanced the amplitude of spontaneous contractions and tonus of oviduct muscle (0.001-100 μg). In addition, the secretion enhanced neurally-evoked contractions of oviduct muscle, which was more sensitive to low concentrations of secretion than the semi-isolated heart. The highest dose of secretion (100 μg) caused neuromuscular blockade. In zero calcium-high magnesium saline, the secretion still enhanced muscle tonus, suggesting the release of intracellular calcium to stimulate contraction. Reverse-phase HPLC of the secretion yielded eight fractions, of which only fractions 4 and 5 affected oviduct muscle tonus and neurally-evoked contractions. No phospholipase A₂ activity was detected in the secretion or its chromatographic fractions. The analysis of fractions 4 and 5 by LC-DAD-MS/MS revealed the following chemical compounds: suberoyl arginine, hellebrigenin, hellebrigenin 3-suberoyl arginine ester, marinobufagin 3-pimeloyl arginine ester, telocinobufagin 3-suberoyl arginine ester, marinobufagin 3-suberoyl arginine ester, bufalin 3-adipoyl arginine, marinobufagin, bufotalinin, and bufalitoxin. These findings indicate that R. icterica parotoid secretion is active in both of the preparations examined, with the activity in oviduct possibly being mediated by bufadienolides.

Trehalose metabolism confers developmental robustness and stability in Drosophila by regulating glucose homeostasis

Organisms have evolved molecular mechanisms to ensure consistent and invariant phenotypes in the face of environmental fluctuations. Developmental homeostasis is determined by two factors: robustness, which buffers against environmental variations; and developmental stability, which buffers against intrinsic random variations. However, our understanding of these noise-buffering mechanisms remains incomplete. Here, we showed that appropriate glycemic control confers developmental homeostasis in the fruit fly Drosophila. We found that circulating glucose levels are buffered by trehalose metabolism, which acts as a glucose sink in circulation. Furthermore, mutations in trehalose synthesis enzyme (Tps1) increased the among-individual and within-individual variations in wing size. Whereas wild-type flies were largely resistant to changes in dietary carbohydrate and protein levels, Tps1 mutants experienced significant disruptions in developmental homeostasis in response to dietary stress. These results demonstrate that glucose homeostasis against dietary stress is crucial for developmental homeostasis.

Sources of Ca2+ for contraction of the heart tube of Tenebrio molitor (Coleoptera: Tenebrionidae)

Insect and vertebrate hearts share the ability to generate spontaneously their rhythmic electrical activity, which triggers the fluid-propelling mechanical activity. Although insects have been used as models in studies on the impact of genetic alterations on cardiac function, there is surprisingly little information on the generation of the inotropic activity in their hearts. The main goal of this study was to investigate the sources of Ca²⁺ for contraction in Tenebrio molitor hearts perfused in situ, in which inotropic activity was assessed by the systolic variation of the cardiac luminal diameter. Increasing the pacing rate from 1.0 to 2.5 Hz depressed contraction amplitude and accelerated relaxation. To avoid inotropic interference of variations in spontaneous rate, which have been shown to occur in insect heart during maneuvers that affect Ca²⁺ cycling, experiments were performed under electrical pacing at near-physiological rates. Raising the extracellular Ca²⁺ concentration from 0.5 to 8 mM increased contraction amplitude in a manner sensitive to L-type Ca²⁺ channel blockade by D600. Inotropic depression was observed after treatment with caffeine or thapsigargin, which impair Ca²⁺ accumulation by the sarcoplasmic reticulum (SR). D600, but not inhibition of the sarcolemmal Na⁺/Ca²⁺ exchanger by KB-R7943, further depressed inotropic activity in thapsigargin-treated hearts. From these results, it is possible to conclude that in T. molitor heart, as in vertebrates: (a) inotropic and lusitropic activities are modulated by the heart rate; and (b) Ca²⁺ availability for contraction depends on both Ca²⁺ influx via L-type channels and Ca²⁺ release from the SR.

Structural and functional characterization of the contractile aorta and associated hemocytes of the mosquito Anopheles gambiae

The primary pump of the circulatory system of insects is a dorsal vessel that traverses the length of the insect. The anterior portion, located in the head, neck and thorax, is the aorta, and the posterior portion, located in the abdomen, is the heart. Here, we characterize the structure and function of the aorta and conical chamber of the mosquito, Anopheles gambiae. The aorta begins in the head with an excurrent opening located above the dorsal pharyngeal plate and ends at the thoraco-abdominal junction where it joins the conical chamber of the heart. The aorta lacks ostia, and based on the diameter of the vessel as well as the density and helical orientation of muscle, is comprised of three regions: the anterior aorta, the bulbous chamber, and the posterior aorta. The aorta contracts in the anterograde direction, but these contractions are independent of heart contractions and do not play a major role in hemolymph propulsion. Intravital imaging of the venous channels, the first abdominal segment and the neck revealed that hemolymph only travels through the aorta in the anterograde direction, and does so only during periods of anterograde heart flow. Furthermore, hemolymph only enters the thoraco-abdominal ostia of the conical chamber when the heart contracts in the retrograde direction, propelling this hemolymph to the posterior of the body. Finally, very few hemocytes associate with the aorta, and unlike what is seen in the periostial regions of the heart, infection does not induce the aggregation of hemocytes on the aorta.

On the Evolution of the Cardiac Pacemaker

The rhythmic contraction of the heart is initiated and controlled by an intrinsic pacemaker system. Cardiac contractions commence at very early embryonic stages and coordination remains crucial for survival. The underlying molecular mechanisms of pacemaker cell development and function are still not fully understood. Heart form and function show high evolutionary conservation. Even in simple contractile cardiac tubes in primitive invertebrates, cardiac function is controlled by intrinsic, autonomous pacemaker cells. Understanding the evolutionary origin and development of cardiac pacemaker cells will help us outline the important pathways and factors involved. Key patterning factors, such as the homeodomain transcription factors Nkx2.5 and Shox2, and the LIM-homeodomain transcription factor Islet-1, components of the T-box (Tbx), and bone morphogenic protein (Bmp) families are well conserved. Here we compare the dominant pacemaking systems in various organisms with respect to the underlying molecular regulation. Comparative analysis of the pathways involved in patterning the pacemaker domain in an evolutionary context might help us outline a common fundamental pacemaker cell gene programme. Special focus is given to pacemaker development in zebrafish, an extensively used model for vertebrate development. Finally, we conclude with a summary of highly conserved key factors in pacemaker cell development and function.

Mass Transport: Circulatory System with Emphasis on Nonendothermic Species

Mass transport can be generally defined as movement of material matter. The circulatory system then is a biological example given its role in the movement in transporting gases, nutrients, wastes, and chemical signals. Comparative physiology has a long history of providing new insights and advancing our understanding of circulatory mass transport across a wide array of circulatory systems. Here we focus on circulatory function of nonmodel species. Invertebrates possess diverse convection systems; that at the most complex generate pressures and perform at a level comparable to vertebrates. Many invertebrates actively modulate cardiovascular function using neuronal, neurohormonal, and skeletal muscle activity. In vertebrates, our understanding of cardiac morphology, cardiomyocyte function, and contractile protein regulation by Ca2+ highlights a high degree of conservation, but differences between species exist and are coupled to variable environments and body temperatures. Key regulators of vertebrate cardiac function and systemic blood pressure include the autonomic nervous system, hormones, and ventricular filling. Further chemical factors regulating cardiovascular function include adenosine, natriuretic peptides, arginine vasotocin, endothelin 1, bradykinin, histamine, nitric oxide, and hydrogen sulfide, to name but a few. Diverse vascular morphologies and the regulation of blood flow in the coronary and cerebral circulations are also apparent in nonmammalian species. Dynamic adjustments of cardiovascular function are associated with exercise on land, flying at high altitude, prolonged dives by marine mammals, and unique morphology, such as the giraffe. Future studies should address limits of gas exchange and convective transport, the evolution of high arterial pressure across diverse taxa, and the importance of the cardiovascular system adaptations to extreme environments. © 2017 American Physiological Society. Compr Physiol 7:17-66, 2017.

Insect immunology and hematopoiesis

Insects combat infection by mounting powerful immune responses that are mediated by hemocytes, the fat body, the midgut, the salivary glands and other tissues. Foreign organisms that have entered the body of an insect are recognized by the immune system when pathogen-associated molecular patterns bind host-derived pattern recognition receptors. This, in turn, activates immune signaling pathways that amplify the immune response, induce the production of factors with antimicrobial activity, and activate effector pathways. Among the immune signaling pathways are the Toll, Imd, Jak/Stat, JNK, and insulin pathways. Activation of these and other pathways leads to pathogen killing via phagocytosis, melanization, cellular encapsulation, nodulation, lysis, RNAi-mediated virus destruction, autophagy and apoptosis. This review details these and other aspects of immunity in insects, and discusses how the immune and circulatory systems have co-adapted to combat infection, how hemocyte replication and differentiation takes place (hematopoiesis), how an infection prepares an insect for a subsequent infection (immune priming), how environmental factors such as temperature and the age of the insect impact the immune response, and how social immunity protects entire groups. Finally, this review highlights some underexplored areas in the field of insect immunobiology.

Nano-architecture of gustatory chemosensory bristles and trachea in Drosophila wings

In the Drosophila wing anterior margin, the dendrites of gustatory neurons occupy the interior of thin and long bristles that present tiny pores at their extremities. Many attempts to measure ligand-evoked currents in insect wing gustatory neurons have been unsuccessful for technical reasons. The functions of this gustatory activity therefore remain elusive and controversial. To advance our knowledge on this understudied tissue, we investigated the architecture of the wing chemosensory bristles and wing trachea using Raman spectroscopy and fluorescence microscopy. We hypothesized that the wing gustatory hair, an open-ended capillary tube, and the wing trachea constitute biological systems similar to nano-porous materials. We present evidence that argues in favour of the existence of a layer or a bubble of air beneath the pore inside the gustatory hair. We demonstrate that these hollow hairs and wing tracheal tubes fulfil conditions for which the physics of fluids applied to open-ended capillaries and porous materials are relevant. We also document that the wing gustatory hair and tracheal architectures are capable of trapping volatile molecules from the environment, which might increase the efficiency of their spatial detection by way of wing vibrations or during flight.

A new kind of auxiliary heart in insects: functional morphology and neuronal control of the accessory pulsatile organs of the cricket ovipositor

Introduction

In insects, the pumping of the dorsal heart causes circulation of hemolymph throughout the central body cavity, but not within the interior of long body appendages. Hemolymph exchange in these dead-end structures is accomplished by special flow-guiding structures and/or autonomous pulsatile organs (“auxiliary hearts”). In this paper accessory pulsatile organs for an insect ovipositor are described for the first time. We studied these organs in females of the cricket Acheta domesticus by analyzing their functional morphology, neuroanatomy and physiological control.

Results

The lumen of the four long ovipositor valves is subdivided by longitudinal septa of connective tissue into efferent and afferent hemolymph sinuses which are confluent distally. The countercurrent flow in these sinuses is effected by pulsatile organs which are located at the bases of the ovipositor valves. Each of the four organs consists of a pumping chamber which is compressed by rhythmically contracting muscles. The morphology of the paired organs is laterally mirrored, and there are differences in some details between the dorsal and ventral organs. The compression of the pumping chambers of each valve pair occurs with a left-right alternating rhythm with a frequency of 0.2 to 0.5 Hz and is synchronized between the dorsal and ventral organs. The more anteriorly located genital chamber shows rhythmical lateral movements simultaneous to those of the ovipositor pulsatile organs and probably supports the hemolymph exchange in the abdominal apex region. The left-right alternating rhythm is produced by a central pattern generator located in the terminal ganglion. It requires no sensory feedback for its output since it persists in the completely isolated ganglion. Rhythm-modulating and rhythm-resetting interneurons are identified in the terminal ganglion.

Conclusion

The circulatory organs of the cricket ovipositor have a unique functional morphology. The pumping apparatus at the base of each ovipositor valve operates like a bellow. It forces hemolymph via sinuses delimited by thin septa of connective tissue in a countercurrent flow through the valve lumen. The pumping activity is based on neurogenic control by a central pattern generator in the terminal ganglion.

Pacemaker activity in the insect (T. molitor) heart: role of the sarcoplasmic reticulum

The electrophysiological properties of the myogenic cardiac cells of insects have been analyzed, but the mechanisms that regulate the pacemaker activity have not been elucidated yet. In mammalian pacemaker cells, different types of membrane ion channels seem to be sequentially activated, perhaps in a cooperative fashion with the current generated by Ca(2+) extrusion mediated by the electrogenic Na(+)/Ca(2+) exchanger, which is sustained by the diastolic sarcoplasmic reticulum (SR) Ca(2+) release. The objective of the present work was to investigate the role of the SR function on the basal beating rate (BR), and BR modulation by extracellular Ca(2+) concentration ([Ca(2+)](o)) and neurotransmitters in the in situ dorsal vessel (heart) of the mealworm beetle Tenebrio molitor. The main observations were as follows: 1) basal BR was reduced by 50% by inhibition of SR function, but not affected by perfusion with CsCl or ZD7288; 2) spontaneous activity was abolished by Cd(2+); 3) a robust positive chronotropic response could be elicited to serotonin (5-HT), but not to norepinephrine or carbamylcholine; 4) SR inhibition abolished the sustained chronotropic stimulation by [Ca(2+)](o) elevation and by 5-HT, while the latter was unaffected by CsCl. It is concluded that, in T. molitor heart, BR is markedly, but not exclusively, dependent on the SR function, and that BR control and modulation by both [Ca(2+)](o) and 5-HT requires a functional SR.

Octopamine--a single modulator with double action on the heart of two insect species (Apis mellifera macedonica and Bactrocera oleae): Acceleration vs. inhibition

The effects of octopamine, the main cardioacceleratory transmitter in insects, were investigated, in the isolated hearts of the honeybee, Apis mellifera macedonica, and the olive fruit fly, Bactrocera oleae. Octopamine induced a biphasic effect on the frequency and force of cardiac contractions acting as an agonist, with a strong acceleratory effect, at concentrations higher than 10(-12)M for the honeybee and higher than 50×10(-9)M for the olive fruit fly. The heart of the honeybee is far more sensitive than the heart of olive fruit fly. This unusual sensitivity is extended to the blockers of octopaminergic receptors, where phentolamine at 10(-5)M stopped the spontaneous contractions of the honeybee heart completely and permanently, while the same blocker at the same concentration caused only 50% inhibition in the heart of the olive fruit fly. Phentolamine and mianserin at low concentrations of 10(-7)M also blocked the heart octopaminergic receptors, but for a short period of time, of less than 15.0 min, while a partial recovery in heart contraction started in spite of the presence of the antagonist. The unusual response of the honeybee heart in the presence of phentolamine and/or mianserin suggests excitatory effects of octopamine via two different receptor subtypes. At lower concentrations, 10(-14)M, the agonist octopamine was converted to an antagonist, inducing a hyperpolarization in the membrane potential of the honeybee cardiac pacemaker cells and inhibiting the firing rate of the heart. The inhibitory effects of octopamine on certain parameters of the rhythmic bursts of the heart of the honeybee, were similar to those of mianserin and phentolamine, typical blockers of octopaminergic receptors. The heart of the olive fruit fly was 10(5) times less sensitive to octopamine, since a persistent inhibition of heart contractions occurred at 10(-9)M. In conclusion, the acceleration of the insect heart is achieved by increasing the levels of octopamine, while there is a passive but also an active decrease in heart activity due to the minimization of octopamine.

Structural mechanics of the mosquito heart and its function in bidirectional hemolymph transport

The insect circulatory system transports nutrients, signaling molecules, wastes and immune factors to all areas of the body. The primary organ driving circulation is the dorsal vessel, which consists of an abdominal heart and a thoracic aorta. Here, we present qualitative and quantitative data characterizing the heart of the mosquito, Anopheles gambiae. Visual observation showed that the heart of resting mosquitoes contracts at a rate of 1.37 Hz (82 beats per minute) and switches contraction direction, with 72% of contractions occurring in the anterograde direction (toward the head) and 28% of contractions occurring in the retrograde direction (toward the tip of the abdomen). The heart is tethered to the midline of the abdominal tergum by six complete and three incomplete pairs of alary muscles, and propels hemolymph at an average velocity of 8 mm s−1 by sequentially contracting muscle fibers oriented in a helical twist with respect to the lumen of the vessel. Hemolymph enters the heart through six pairs of incurrent abdominal ostia and one pair of ostia located at the thoraco-abdominal junction that receive hemolymph from the abdominal hemocoel and thoracic venous channels, respectively. The vessel expels hemolymph through distal excurrent openings located at the anterior end of the aorta and the posterior end of the heart. In conclusion, this study presents a comprehensive revision and expansion of our knowledge of the mosquito heart and for the first time quantifies hemolymph flow in an insect while observing dorsal vessel contractions.

Head capsule, chephalic central nervous system and head circulatory system of an aberrant orthopteran, Prosarthria teretrirostris (Caelifera, Hexapoda)

The head capsule, the circulatory system and the central nervous system of the head of Prosarthria teretrirostris (Proscopiidae) is described in detail, with special consideration of modifications resulting from the aberrant head shape. The transformations of the head are completely different from those found in phasmatodeans, which are also characterised by twig mimesis. The circulatory system is distinctly modified. A hitherto undescribed additional structure in the posterior head region very likely functions as a pulsatile organ. The cephalic central nervous system is strongly elongated, with changes in the position of the suboesophageal ganglion, the corpora cardiaca and the course of the nervus mandibularis. Three-dimensional reconstructions of these two organ systems in combination with the pharynx were made using Alias Maya 6.0 software. Comparisons with other representatives of Caelifera suggest a clade comprising Proscopiidae and Morabinae. The presence of a transverse muscle connecting the antennal ampullae in Prosarthria shows that this structure likely belongs to the groundplan of Orthoptera, even though it is missing in different representatives of this group. The transverse ampullary muscle is a potential synapomorphy of Orthoptera, Phasmatodea and Dictyoptera.

Neuromuscular organization and aminergic modulation of contractions in the Drosophila ovary

Background

The processes by which eggs develop in the insect ovary are well characterized. Despite a large number of Drosophila mutants that cannot lay eggs, the way that the egg is moved along the reproductive tract from ovary to uterus is less well understood. We remedy this with an integrative study on the reproductive tract muscles (anatomy, innervation, contractions, aminergic modulation) in female flies.

Results

Each ovary, consisting of 15–20 ovarioles, is surrounded by a contractile meshwork, the peritoneal sheath. Individual ovarioles are contained within a contractile epithelial sheath. Both sheaths contain striated muscle fibres. The oviduct and uterine walls contain a circular striated muscle layer. No longitudinal muscle fibres are seen.

Neurons that innervate the peritoneal sheath and lateral oviduct have many varicosities and terminate in swellings just outside the muscles of the peritoneal sheath. They all express tyrosine decarboxylase (required for tyramine and octopamine synthesis) and Drosophila vesicular monoamine transporter (DVMAT). No fibres innervate the ovarioles. The common oviduct and uterus are innervated by two classes of neurons, one with similar morphology to those of the peritoneal sheath and another with repeated branches and axon endings similar to type I neuromuscular junctions.

In isolated genital tracts from 3- and 7-day old flies, each ovariole contracts irregularly (12.5 ± 6.4 contractions/minute; mean ± 95% confidence interval). Peritoneal sheath contractions (5.7 ± 1.6 contractions/minute) move over the ovary, from tip to base or vice versa, propagating down the oviduct. Rhythmical spermathecal rotations (1.5 ± 0.29 contractions/minute) also occur. Each genital tract organ exhibits its own endogenous myogenic rhythm.

The amplitude of contractions of the peritoneal sheath increase in octopamine (100 nM, 81% P < 0.02) but 1 μM tyramine has no effect. Neither affects the frequency of peritoneal sheath contractions.

Conclusion

The muscle fibres of the reproductive tract are circular and have complex bursting myogenic rhythms under octopaminergic neuromodulation. We propose a new model of tissue-specific actions of octopamine, in which strengthening of peritoneal sheath contractions, coupled with relaxation of the oviduct, eases ovulation. This model accounts for reduced ovulation in flies with mutations in the octopaminergic system.

Nitric oxide: a co-modulator of efferent peptidergic neurosecretory cells including a unique octopaminergic neurone innervating locust heart

Our findings suggest that nitric oxide (NO) acts as peripheral neuromodulator in locusts, in which it is commonly co-localized with RF-like peptide in neurosecretory cells. We also present the first evidence for NO as a cardio-regulator in insects. Putative NO-producing neurones were detected in locust pre-genital free abdominal ganglia by NADPH-diaphorase histochemistry and with an antibody against NO synthase (NOS). With both methods, we identified the same 14 somata in each examined ganglion: two dorsal posterior midline somata; six ventral posterior midline somata; and three pairs of lateral somata. A combination of NOS-detection methods with nerve tracing and transmitter immunocytochemistry revealed that at least 12 of these cells were efferent, of which four were identified as peptidergic neurosecretory cells with an antiserum detecting RFamide-like peptides. One of the latter was unequivocally identified as an octopaminergic dorsal unpaired median (DUM) neurone, which specifically projected to the heart ("DUM-heart"). Its peripheral projections revealed by axon tracing appeared as a meshwork of varicose endings encapsulating the heart. NOS-like immunoreactive profiles were found in the heart nerve. NO donors caused a dose-dependent increase in heart rate. This cardio-excitatory effect was negatively correlated to resting heart rate and seemed to be dependent on the physiological state of the animal. Hence, NO released from neurones such as the rhythmically active DUM-heart might exert continuous control over the heart. Possible mechanisms for the actions of NO on the heart and interactions with other neuromodulators co-localized in the DUM-heart neurone (octopamine, taurine, RF-amide-like peptide) are discussed.

From variable to constant cell numbers: cellular characteristics of the arthropod nervous system argue against a sister-group relationship of Chelicerata and "Myriapoda" but favour the Mandibulata concept

In the new debate on arthropod phylogeny, structure and development of the nervous system provide important arguments. The architecture of the brain of Hexapoda, Crustacea and Chelicerata in recent years has been thoroughly compared against an evolutionary background. However, comparative aspects of the nervous systems in these taxa at the cellular level have been examined in only a few studies. This review sets out to summarize these aspects and to analyse the existing data with respect to the concept of individually identifiable neurons. In particular, mechanisms of neurogenesis, the morphology of serotonergic interneurons, the number of motoneurons, and cellular features and development of the lateral eyes are discussed. We conclude that in comparison to the Mandibulata, in Chelicerata the numbers of neurons in the different classes examined are much higher and in many cases are not fixed but variable. The cell numbers in Mandibulata are lower and the majority of neurons are individually identifiable. The characters explored in this review are mapped onto an existing phylogram, as derived from brain architecture in which the Hexapoda are an in-group of the Crustacea, and there is not any conflict of the current data with such a phylogenetic position of the Hexapoda. Nevertheless, these characters argue against a sister-group relationship of "Myriapoda" and Chelicerata as has been recently suggested in several molecular studies, but instead provide strong evidence in favour of the Mandibulata concept.

Unique accumulation of neuropeptides in an insect: FMRFamide-related peptides in the cockroach, Periplaneta americana

FMRFamides belong to the most extensively studied neuropeptides in invertebrates and exhibit diverse physiological effects on different target organs, such as muscles, intestine and the nervous system. This study on the American cockroach confirms for the first time that extended FMRFamides occur in non-dipteran insects. By means of tandem mass spectrometry, these neuropeptides were structurally elucidated, and sequence information was used for subsequent cloning of the cockroach FMRFamide gene. This precursor gene encodes for 24 putative peptides and shows sufficient similarity with the Drosophila FMRFamide gene. Of the 24 peptides, 23 were detected by mass spectrometric methods; it is the highest number of neuropeptide forms shown to be expressed from a single precursor in any insect. The expression was traced back to single neurons in the thoracic ganglia. The unique accumulation of these FMRFamide-related peptides in thoracic perisympathetic organs provides the definite evidence for a tagma-specific distribution of peptidergic neurohormones in neurohaemal release sites of the insect CNS. Excitatory effects of the cockroach FMRFamides were observed on antenna-heart preparations. In addition, the newly described FMRFamides reduce the spike frequency of dorsal-unpaired median neurons and reduce the intracellular calcium concentration, which may affect the peripheral release of the biogenic amine octopamine.