FMRFamide-expressing efferent neurons in eighth abdominal ganglion innervate hindgut in the silkworm, Bombyx mori

The tetrapeptide FMRFamide is known to affect both neural function and gut contraction in a wide variety of invertebrates and vertebrates, including insect species. This study aimed to find a pattern of innervation of specific FMRFamide-labeled neurons from the abdominal ganglia to the hindgut of the silkworm Bombyx mori using the immunocytochemical method. In the 1st to the 7th abdominal ganglia, labeled efferent neurons that would innervate the hindgut could not be found. However, in the 8th abdominal ganglion, three pairs of labeled specific efferent neurons projected axons into the central neuropil to eventually innervate the hindgut. Both axons of two pairs of labeled cell bodies in the lateral rind and axons of one pair of labeled cell bodies in the posterior rind extended to the central neuropil and formed contralateral tracts of a labeled neural tract with a semi-circular shape. These labeled axons ran out to one pair of bilateral cercal nerves that extended out from the posterior end of the 8th abdominal ganglion and finally to the innervated hindgut. These results provide valuable information for detecting the novel function of FMRFamide-related peptides in metamorphic insect species.     

FMRFamide-related peptides in the gut of Locusta migratoria L.: a comprehensive map and developmental profile

The gut tissues and associated nervous system of the African migratory locust, Locusta migratoria, were found to contain FMRFamide-like immunoreactive (FLI) material throughout the five larval instars and 2 weeks into the adult stage in both males and females. FMRFamide-like immunoreactivity associated with the locust gut was described using camera lucida techniques. FMRFamide-like immunoreactivity is observed in the frontal connectives, recurrent nerve, and oesophageal nerves; projections from the ingluvial ganglion onto the anterior midgut, and from the proctodeal nerve onto the hindgut and posterior midgut; in the neuropils of the frontal ganglion, hypocerebral ganglion and ingluvial ganglia; 30 cell bodies in the frontal ganglion; multipolar sensory cells on the foregut; and endocrine-like cells in the gastric caecae and midgut. Radioimmunoassay (RIA) was used to determine the quantities of FLI material in foreguts, gastric caecae, anterior and posterior midguts, and hindgut of first-fifth instar larvae, 1-3- and 14-17-day male and female adult locusts. As expected, as the tissue size (assessed by total protein content) increases, so does the amount of FLI material in each tissue. Normalizing for tissue size reveals significant differences in FLI content among the stages for each tissue tested. Reversed phase-high pressure liquid chromatography (RP-HPLC) followed by RIA has identified four groups of FLI fractions present in the gut, and different members of these groups are present in the various gut tissues.     

小地老虎成虫直肠的发生和直肠乳突细胞功能性分化

本研究观察了小地老虎Agrotis ypsilon末龄幼虫、预蛹、蛹和成虫的直肠结构及成虫直肠乳突的细胞结构特点。结果表明：(1)成虫直肠是由幼虫的隐肾复合体解体后,原有幼虫直肠细胞经过分裂、重组和分化形成的,关键时期是预蛹至化蛹5d;(2)成虫直肠乳突呈圆盘形,自内向外包括内膜、乳突细胞、底膜、肌肉和围膜5层。乳突细胞按结构和功能特点分为帽状细胞、微气管细胞、网状细胞和盘底细胞4种;(3)试验发现成虫直肠膨大是由乳突体积扩增引起的。细胞结构剖析,直肠乳突有一整套完整而精细的结构,能扩增乳突体积和供应足够氧气及营养。文中还讨论了直肠的多种生理功能。     

An osmoregulatory syncytium and associated cells in a freshwater mosquito

In embryological terms the anal papillae are the product of eversion of the hindgut tissues. The rectum and the anal papillae have the same origin and have a marked structural similarity. The insect hindgut is very labile being able to produce salt transporting or ‘chloride cells’ from any of the tissues of which it is composed.The hindgut consists of four distinct regions: the ileum and part of the anal canal have a mechanical function, the rectum and the posterior anal canal contain transporting cells. Two new cell types, ‘interstitial’ and ‘tertiary’ are reported in the rectum.The structure of the anal papillae changes with increased salinity. Changes in the plasma membranes alter the surface area for transport. Changes in the number of mitochondria are not accompanied by changes in oxygen consumption. If mitochondria are the site of oxidative metabolism then their number docs not control the level of oxygen consumption.In Aedes aegypti the papillary epithelium appears to be a syncytium. Across the lumen of the papillae there are cellular sheets supporting the tracheoles. At the base of the papillae there is a cellular transition zone; circular muscles in this region may be used to occlude the papillae. The control of salt transport may be hormonal.     

Segmental peptidergic innervation of abdominal targets in larval and adult dipteran insects revealed with an antiserum against leucokinin I

Summary An antiserum against the cockroach neuropeptide leucokinin I (LKI) was used to study peptidergic neurons and their innervation patterns in larvae and adults of three species of higher dipteran insects, the flies Drosophila melanogaster, Calliphora vomitoria, and Phormia terraenovae, as well as larvae of a primitive dipteran insect, the crane fly Phalacrocera replicata. In the larvae of the higher dipteran flies, the antiserum revealed three pairs of cells in the brain, three pairs of ventro-medial cells in the subesophageal ganglion, and seven pairs of ventro-lateral cells in the abdominal ganglia. Each of these 14 abdominal leucokinin-immunoreactive (LKIR) neurons innervates a single muscle of the abdominal body wall (muscle 8), which is known to degenerate shortly after adult emergence. Conventional electron microscopy demonstrates that this muscle is innervated by at least one axon containing clear vesicles and two axons containing dense-cored vesicles. Electronmicroscopical immunocytochemistry shows that the LKIR axon is one of these two axons with dense-cored vesicles and that it forms terminals on the sarcolemma of its target muscle. The abdominal LKIR neurons appear to survive metamorphosis. In the adult fly, the efferent abdominal LKIR neurons innervate the spiracles, the heart, and neurohemal regions of the abdominal wall. In the crane fly larva, dorso-medial and ventrolateral LKIR cell bodies are located in both thoracic and abdominal ganglia of the ventral nerve cord. As in the larvae of the other flies, the abdominal ventrolateral LKIR neurons form efferent axons. However, in the crane fly larva there are two pairs of efferent LKIR neurons in each of the abdominal ganglia and their peripheral targets include neurohemal regions of the dorsal transverse nerves. An additional difference is that in the crane fly, a caudal pair of LKIR axons originating from the penultimate pair of dorso-median LKIR cells in the terminal ganglion innervate the hindgut.     

Ultrastructure of the midgut and hindgut of Derocheilocaris remanei (Crustacea, Mystacocarida)

Ultrastructural features and structure of the midgut and hindgut of Derocheilocaris remanei were studied. The large endodermal midgut is differentiated into an anterior midgut and a posterior midgut separated by a conspicuous constriction. Both circular and longitudinal striated muscle bands surround the midgut, while the hindgut only presents longitudinal muscles. The limit between the midgut and the cuticle-lined hindgut is marked by a rectal valve. In cross-section, the short hindgut is triradiate and has a distinct Y-shaped lumen. The hindgut cuticular lining appears interrupted at the tip of every branch of the Y. Three different cell types are found in the midgut epithelium: basally located undifferentiated cells that give rise to the other two specialized cell types; secretory zymogen-like cells responsible for extracellular digestion and located mainly in the anterior midgut; and vacuolated cells, distributed all along the midgut and appearing to have several functions, including absorption, intracellular digestion, and nutrient transport. A single basic cell type forms the hindgut epithelium. The suggested function for the hindgut is the transport and ejection of waste products.     

Ultrastructural characteristics of anterior gut innervation of Gallus gallus

The enteric nervous system of the bird's anterior gut is very well developed. Myelin fibres are seen accompanying the nervous trunks up to the mucous layer. Glial cells duplicate the number of neurons in the myenteric plexuses. Their number decreases at the submucous plexuses, but it is always higher than the neurons. Isolated neurons are widely spread in the circular muscle coat accompanying the nervous trunks which can be inter and intrafascicularly located. Direct synaptic contacts with the soma neuronal membranes are very often seen. We have never observed synaptic specializations. The most prominent varicosities either in the peripheric nervous trunk axons or directly laying on the soma membranes are those containing peptidergic or mixed vesicles of cholinergic and peptidergic types. The neurons show big nuclei of different size and shape. Neighbouring smooth muscle cells show abundant caveolae near the nervous elements. Although we have not observed close contacts with glands, thin axon bundles spread near the glandular cells of the mucous layer.     

Peptidergic regulation of the Limulus midgut

1. The morphology and innervation of the midgut (intestine) in the horseshoe crab, Limulus polyphemus was investigated. The organization of this tissue was examined with routine histology. Radioimmunoassay, immunohistochemistry and high performance liquid chromatography were employed to detect, localize and identify peptidergic innervation of the midgut. The actions of synthetic and native proctolin-like and FMRFamide-like peptides were compared on the isolated midgut preparation. 2. Levels of proctolin and FMRFamide were determined in extracts of Limulus midgut tissue using radioimmunoassay. High levels of proctolin-like immunoreactivity (69.5 +/- 11.3 ng/g) were detected, while levels of FMRFamide-like immunoreactivity (0.8 +/- 0.2 ng/g) were less. Proctolin levels were equally distributed, while the levels of FMRFamide-like immunoreactivity exhibited an anterior bias. 3. Proctolin- and FMRFamide-like immunoreactivities in the Limulus midgut were localized with immunohistochemistry. Proctolin- and FMRFamide-immunoreactive elements were detected in intestinal nerve branches and individual fibers running along the surface of the midgut in whole-mount preparations. In sectioned tissue, staining for these peptides was observed throughout the midgut, typically associated with muscle bands and fibers. Only a few immunoreactive cell bodies were observed. 4. Proctolin, and several FMRFamide-like peptides produced distinct and opposing actions on the isolated Limulus midgut preparation. Proctolin elicited contracture and rhythmic contractions of this tissue, while FMRFamide and N-terminally extended analogs of FLRFamide relaxed gut tension. FMRFamide-like peptides partially reversed the excitatory actions of proctolin. 5. Proctolin- and FMRFamide-like peptides in Limulus midgut extracts were partially characterized with high performance liquid chromatography. One peak of proctolin-like activity was detected on a linear gradient of 18 to 31.5% acetonitrile. The native proctolin-like peptide produced excitatory actions on the isolated midgut preparation which were indistinguishable from those produced by synthetic proctolin. Several peaks of FMRFamide-like bioactivity (Busycon radula protractor muscle assay) were detected with a linear gradient of 5 to 30% acetonitrile. Fractions from two distinct peaks produced FMRFamide-like inhibitory effects on the isolated Limulus midgut preparation. These findings suggest a role for proctolin-like and FMRFamide-like peptides as regulators of intestinal motility in Limulus.     

Collapsin-1/semaphorin D is a repellent for chick ganglion of Remak axons.

Chick collapsin-1/human semaphorin III/mouse semaphorin D is believed to guide the extension of specific axons by a repellent mechanism. Here we examine its role in the guidance of axons of the ganglion of Remak (Remak) in the developing chick intestine. Early in embryogenesis Remak axons extend parallel to, but do not enter, the intestine when collapsin-1 is expressed in the adjacent rectal wall. Remak axons later penetrate the peripheral portions of the rectal wall when collapsin-1 expression retreats from the outer muscle layer to the more internal submucosal and mucosal layers of the rectum. Extension of Remak neurites is repelled in vitro by rectum explants and also by 293T cells expressing collapsin-1. The rectal chemorepellent activity is blocked by anti-collapsin-1 antibodies. Our results suggest that collapsin-1 may help prevent Remak axons from projecting into the intestinal wall at early developmental times and later restricts Remak axon trajectories to the outer part of the intestinal muscle layer.     

Fine Structure of the Midgut and Hindgut in Lepidocampa weberi (Insecta,Diplura)

The fine structure of the alimentary canal, especially the midgut and hindgut of Lepidocampa weberi (Diplura: Campodeidae) is described. The general organization of the canal is similar to that of Campodea. The midgut epithelium is composed of columnar apical microvillated cells. Each nucleus contains a single intranuclear crystal. Close to the pyloric region, the posterior midgut cells are devoid of microvilli and intranuclear crystals. There is no special pyloric chamber as in Protura or pyloric cuticular ring as in Collembola but a morphological transformation from midgut to hindgut cells. Eight globular Malpighian papillae, consisting of distal microvillated cells and flat proximal cells, open into the gut lumen via ducts formed by hindgut cells. The structure of the hindgut is complicated and can be divided into three segments. The anterior hindgut cells have an irregular shape and compact cytoplasm. A striking interdigitation between the large bottle-shaped epithelial cells and longitudinal muscle cells occurs in the middle segment of the hindgut. The thick cuticle gives rise to long spikes projecting into the gut lumen. The posterior hindgut cells possess the morphological features for water reabsorption. Some hypotheses are advanced about the function of the different regions of the gut.     

The rectal organ of Ophelia bicornis Savigny (Polychaeta): a device for efficient defaecation

The rectum of the sand-dwelling polychaete Ophelia bicornis is modified by the presence of a ciliated organ and a series of muscular papillae which serve to increase the rate of evacuation of spent sand from the gut. The structure of the rectal apparatus has been investigated by direct observation, by dissection and by optical- and electron-microscopy.
The rectal organ is discussed as an adaptation to the poor food-levels of the sandy habitat of O. bicornis and the consequent need for the rapid, movement of large masses of sand through the digestive system.     

Morphology of the Midgut–Hindgut Juncture in the Ghost Shrimp Lepidophthalmus louisianensis (Schmitt) (Crustacea: Decapoda: Thalassinidea)

Abstract Unique morphological structures occur near the midgut–hindgut juncture in decapod crustaceans, and neither their fine structure nor function are well understood. In the ghost shrimp Lepidophthalmus louisianensis. structures associated with this juncture include an elongate posterior midgut caecum (PMGC) extending into the abdominal hemocoel, a massive swelling of acinar glands encasing the juncture, and a dorso-lateral valve complex involving cuticularized lumenal surfaces of the anterior hindgut. Vivisection, histological studies (LM, TEM) and paraffin-carving (SEM) have been applied to reconstruct morphology of these components and characterize constituent tissues. The lumen of the PMGC is lined by very elongate columnar cells underlain by a thin layer of circular muscle. The hemocoelic surface of the PMGC is covered by cells richly endowed with unique lamellar bodies. The acinar glands are composed of multiple rosettes of secretory cells, from which products appear to empty into the anterior extreme of the hindgut. The dorso-lateral valve complex of the hindgut consists of anterior and posterior components, differing in strength of lumenal ridging and microdentition of the cuticular lining. Unique features of these structures may relate to behavioral, feeding and metabolic adaptations in this obligate fossorial crustacean.     

Abundance and distribution of the gut flora of the desert locust,Schistocerca gregaria

The abundance of bacteria in the gut of Schistocerca gregaria was determined. A large population of Enterobacteriaceae was found with numbers increasing posteriorly from foregut to rectal sac. In the hindgut, Enterobacter agglomerans was the dominant organism. Streptococci were also present but they were 10- to 100-fold less numerous than the Enterobacteriaceae. The distribution of the microflora was investigated using light microscopy and scanning electron microscopy. Bacteria in the anterior regions of the gut were restricted to the lumen and inside of the peritrophic membrane. However, in the hindgut, bacteria were also associated with the cuticular lining.     

FMRfamide-like immunoreactivity in the ventral nerve cord of the larval eastern spruce budworm,Choristoneura fumiferana (clemens) (Lepidoptera : Tortricidae)

Distribution of FMRFamide-like immunoreactivity was examined in the larval ventral nerve cord of the eastern spruce budworm, Choristoneura fumiferana (Lepidoptera : Tortricidae). Indirect immunofluorescent methods revealed the existence of 3 groups of FLI neurons in each ganglion. The neurons are distributed in a bilaterally symmetrical fashion at the anterodorsal, midlateral and posteroventral regions of the ganglia. There are 4 FMRFamide-like immunoreactive fiber tracts on the dorsal surface of the ganglia to which the anterodorsal FLI neurons project ipsilaterally, while the midlateral pair projects both ipsi-, and contralaterally. The last abdominal ganglion (AG8) has 4 additional pairs of FLI neurons; and axons from some of these extend into the median abdominal nerve, which suggests some role for this neuropeptide in the control of posterior structures of the larva.     

Neuropeptides in the gastrointestinal canal of Necturus maculosus

Summary The presence and distribution of regulatory peptides in nerves and endocrine cells of the stomach, intestine and rectum of a urodele amphibian, the mudpuppy, Necturus maculosus, was studied immunohistochemically in sections or whole-mount preparations of the gut wall. The effect of the occurring peptides on gut motility was studied in isolated strip preparations of circular and longitudinal smooth muscle from different parts of the gut.Bombesin-, neurotensin-, substance P- and VIP-like immunoreactivity was present in abundant nerve fibres in the myenteric plexus of both stomach, intestine and rectum. Single fibres or bundles were present in the circular muscle layer and in a well-developed deep muscular plexus in the intestine and rectum. Immunoreactive nerve cells were found in the myenteric plexus of the stomach, intestine (neurotensin only) and rectum. Gastrin/CCK-like immunoreactivity was observed only in a few fibres in stomach and rectum.Endocrine cells containing bombesin-, met-enkephalin-, gastrin/CCK-, neurotensin-, somatostatin- or substance P- like immunoreactivity were present in the mucosa.The effect of bombesin was an inhibition of the rhythmic activity in circular muscle preparations and in longitudinal muscle from the rectum, while longitudinal muscle from the stomach usually responded with a weak increase in tonus. Neurotensin, like bombesin, was inhibitory on the spontaneous rhythmic activity of circular muscle throughout the gut, while the effect on longitudinal muscle was an increase in tonus. Met-enkephalin and substance P increased the tonus of all types of preparations, and often, in addition, initiated a rhythmic activity superimposed on this maintained tonus. VIP had a general inhibitory effect on the preparations, decreasing tonus and/or abolishing rhythmic activity.It is concluded that bombesin-, neurotensin-, substance P- and VIP-like peptides are present in nerves throughout the urodele gut and may have physiological functions in regulating the motility of the gut. The gastrin/CCK-like peptide present in nerves of the stomach and rectum may affect the function of these parts of the gut. The regulatory peptides present in endocrine cells may, perhaps with the exception of the somatostatin-like peptide, affect the motility humorally.     

Light and electron microscopic study of the hindgut of the ant (Formica nigricans, hymenoptera): II. Structure of the rectum

The rectum of the ant Formica nigricans is composed of six ovoid rectal papillae inserted into a rectal pouch. The wall of the rectal pouch is made up of a flat epithelium of simple rectal cells lined by cuticle, and surrounded by a circular muscle layer. Each rectal papilla is comprised by a simple columnar epithelium of principal cells facing the lumen, and a simple cuboid epithelium of secondary cells towards the hemolymph; a group of 20-25 slender junctional cells lies laterally between both epithelia enclosing an intrapapillar sinus. The muscle layer of the rectal wall also surrounds the base of the papillae. Principal cells do not exhibit extensive infoldings at the apical and basal plasma membranes. Lateral membranes, in contrast, develop highly folded mitochondria-scalariform junction complexes enclosing very narrow intercellular canaliculi between adjacent cells. These canaliculi open to wider intercellular sinuses that ultimately drain into the intrapapillar sinus at the sites of entry of tracheal cells. The lateral plasma membranes do not link to the apical or basal plasma membrane, thus originating a syncytium throughout the principal cells. The apical plasma membrane of secondary cells shows invaginations in relation with an apical tubulovacuolar system, bearing portasomes to the cytoplasmic side of the membrane. Secondary cells unite by convoluted septate junctions, and basolateral infoldings are also developed. These ultrastructural traits, some of them different from those found in other insects, are discussed and examined in relation to their role in water and solute absorption. A route for rectal transport in F. nigricans is proposed.     

The control of hindgut motility in the lobster,Homarus gammarus (L.)

1. The sixth abdominal ganglion (6 A.G.) of the lobster Homarus gammarus (L.) innervates the rectum via the paired posterior intestinal nerves (P.I.N.’s) and the paired anal nerves. The anterior branches of the P.I.N.’s supply the anterior hindgut, the main faecal expulsion region, whilst the posterior branches (P.I.N.p.’s) supply the posterior region and the 5 extrinsic radial muscle groups around the anus.

2. Stimulation of the ventral nerve cord (V.N.C.) or the oesophageal connectives initiates co‐ordinated hindgut movements, the defaecatory response. The nervous activity eliciting these movements passes down the P.I.N.’s. The anal nerves are devoid of motor function with respect to the hindgut.

3. In addition to neurogenic movements the rectum also undergoes non‐coordinated, low amplitude longitudinal and circular muscle contractions. These are thought to be due to independently acting endogenous oscillators within the muscles themselves. The radial muscles of the anus also exhibit rhythmical contractions after an initial maximal contraction following stimulation of the P.I.N.p.’s.

4. Receptors responding to anal dilation and closure have been shown to exist in the anal nerves. They are non‐specific soft cuticle receptors which are, apparently, positionally sensitive. These receptors are not thought to modulate motor output from the 6 A.G. to the rectum at the level of the 6 A.G.

5. Bifurcating motor axons are thought to exist in the P.I.N.’s.

6. It is concluded that the defaecatory response of the lobster is a centrally programmed phenomenon.     

Effects of different regions of the developing gut on the migration of enteric neural crest-derived cells: a role for Sema3A, but not Sema3F

The enteric nervous system arises from vagal (caudal hindbrain) and sacral level neural crest-derived cells that migrate into and along the developing gut. Data from previous studies have suggested that (i) there may be gradients along the gut that induce the caudally directed migration of vagal enteric neural precursors (ENPs), (ii) exposure to the caecum might alter the migratory ability of vagal ENPs and (iii) Sema3A might regulate the entry into the hindgut of ENPs derived from sacral neural crest. Using co-cultures we show that there is no detectable gradient of chemoattractive molecules along the pre-caecal gut that specifically promotes the caudally directed migration of vagal ENPs, although vagal ENPs migrate faster caudally than rostrally along explants of hindgut. Exposure to the caecum did not alter the rate at which ENPs colonized explants of hindgut, but it did alter the ability of ENPs to colonize the midgut. The co-cultures also revealed that there is localized expression of a repulsive cue in the distal hindgut, which might delay the entry of sacral ENPs. We show that Sema3A is expressed by the hindgut mesenchyme and its receptor, neuropilin-1, is expressed by migrating ENPs. Furthermore, there is premature entry of sacral ENPs and extrinsic axons into the distal hindgut of fetal mice lacking Sema3A. These data show that Sema3A expressed by the distal hindgut regulates the entry of sacral ENPs and extrinsic axons into the hindgut. ENPs did not express neuropilin-2 and there was no detectable change in the timetable by which ENPs colonize the gut in mice lacking neuropilin-2.     

The histology and ultrastructure of a nuclear polyhedrosis virus of the webbing clothes moth, Tineola bisselliella

A histological and ultrastructural study of a nuclear polyhedrosis virus in the webbing clothes moth, Tineola bisselliella, was conducted. Polyhedral development was observed in nuclei of cells of the foregut, cardiac valve, midgut, pyloric valve, hindgut, Malpighian tubules, ganglia of the ventral nerve cord, muscle, tracheae, fat, and hypodermis. Observations made with the electron microscope suggest that virions from the gut lumen are transported in vesicles through the cytoplasm into the nuclei of the columnar cells. Here they are released, replicate, take on membrane, and ultimately become multiply occluded in polyhedral protein. Polyhedra observed in nuclei of other tissues appeared identical to those in the gut.     

Immunogold labelling of serotonin-like and FMRFamide-like immunoreactive material in neurohaemal areas on abdominal nerves of Rhodnius prolixus

The ultrastructure of neurohaemal areas on abdominal nerves of the blood-sucking bug Rhodnius prolixus was investigated. Four types of axon terminals were found, distinguished by the morphology of their neurosecretory granules. By use of post-embedding immunogold labelling, granules in Type I axon terminals were shown to contain serotonin-like immunoreactive material, and granules in Type II axon terminals were shown to contain FMRFamide-like immunoreactive material. There was no colocalization of these materials. It is suggested that Type III terminals contain peptidergic diuretic hormone, which has previously been reported to be present in electron-dense neurosecretory granules in this neurohaemal area. The identity of material in Type IV terminals is unknown.