Mechanoreceptors innervating soft cuticle in the abdomen of the hermit crab, <Emphasis Type="Italic">Pagurus pollicarus</Emphasis>

Mechanoreceptors in the soft cuticle of the 4th abdominal segment of the hermit crab, Pagurus pollicarus, that are associated with reflex activation of abdominal postural motoneuron, were studied to determine whether their properties are consistent with a feedback control of abdominal stiffness. Three classes of receptors were identified: (1) setal dome receptors, (2) hypodermal receptors, and (3) funnel-canal receptors. The hypodermal receptors, which have the largest extracellular action potentials, were selected for further study. Their axons innervate the entire ipsilateral half of a segment; receptive fields of receptors with different amplitudes show extensive overlap. They are phasic and show significant adaptation; at higher frequencies they signal displacement rather than velocity. Although they are activated by changing muscle tension, their threshold for cuticular displacement is much lower than for forces generated by postural muscles. These features suggest that they are primarily involved in signaling cuticular displacement and shearing forces as they contact the columella of the shell in which the hermit crab lives.     

Mechanosensory afferents innervating the swimmerets of the lobster

Feathered hair sensilla fringe both rami of the lobster (Homarus americanus) swimmeret. The sensory response to hair displacement was characterized by recording afferent impulses extracellularly from the swimmeret sensory nerve while deflecting sensilla with a rigidly-coupled probe or controlled water movements. Two populations of hairs were observed: "distal" hairs localized to the distal 1/3 of each ramus and "proximal" hairs near its base. Distal hairs are not innervated by a mechanosensory neuron but instead act as levers producing strain within adjacent cuticle capable of activating a nearby hypodermal mechanoreceptor. Hair deflections of 25 degrees or more are required to evoke an afferent response and this response is dependent on hair deflection direction. The frequency and duration of the afferent discharge evoked are determined by the velocity of hair displacement. Each proximal hair is innervated by a single mechanosensory neuron responding phasically to hair deflections as small as 0.2 degrees in amplitude. Deflection at frequencies up to 5 Hz elicits a single action potential for each hair movement; at higher frequencies many deflections fail to evoke an afferent response. These sensilla, which are mechanically coupled, may be activated by the turbulent flow of water produced by the swimmerets during their characteristic beating movements.     

Structure of the Cuticle of Metadasynemoides cristatus (Chromadorida: Ceramonematidae)

Structure of the cuticle of Metadasynemoides cristatus (Chromadorida: Ceramonematidae) is examined by light, scanning, and transmission electron microscopy. The nematode has more than 600 annuli, and each annulus has eight cuticular plates. Eight longitudinal ridges, beginning on the cephalic capsule, extend the whole length of the body. Where a ridge traverses an annulus, it forms a complicated articulating structure of overlapping vanes. Within the electron-dense cortical layer, from which the cuticular plates are formed, there are spaces crossed by fine fibrillae, forming what have been termed "vacuoles" by light microscopists. There is an epicuticle and a continuous lucent basal layer. There appears to be no median layer. The cuticle lining of the esophagus and that forming the circum-oral ridge is of much simpler construction.     

Ascaris suum: partial isolation and characterization of hypodermis from the adult female

A method was developed to remove the muscle from body wall strips of adult female Ascaris suum resulting in a hypodermis cuticle preparation. Optimum treatment for obtaining the hypodermis cuticle was a 15 min incubation with trypsin (2.0 mg/ml) at room temperature, followed by mechanical removal of the muscle. The hypodermis cuticle prepared in this manner incorporated radiolabeled amino acids into cuticular and hypodermal proteins; incorporation was inhibited by protein synthesis inhibitors. Characterization of the hypodermal proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the hypodermis apparently contains proteins that differ from those of the cuticle and that the hypodermis of adult A. suum appears to lack cuticle protein precursors. This result will now allow detailed biochemical and physiological investigations of the hypodermis, a tissue which is critical for cuticle synthesis.     

The infrared receptor of Melanophila acuminata De Geer (Coleoptera: Buprestidae): ultrastructural study of a unique insect thermoreceptor and its possible descent from a hair mechanoreceptor

The paired infrared organs of Melanophila acuminata consist of 50-100 sensilla situated at the bottom of a pit next to the coxae of the mesothoracic legs, where no exocuticle is developed. Each sensillum is accompanied by a wax gland and has a cuticular lens-like spherule (diameter 12-15 mum) bulging out with its upper hemisphere above the surface, covered only by a thin cuticle of about 1 mum. Distal processes of two enveloping cells surround the entire spherule in the form of a flattened protoplasmatic layer with the exception of a small apical stalk connecting the spherule to the outer cuticle. The spherule is innervated by a single sensory neuron of the ciliary type which is anchored ventrally with the distal tip of its cylindrical and unbranched DOS in the spherule. The insertion of the dendrite, which contains a well-developed tubular body, is always eccentric like in a hair mechanoreceptor (sensillum trichodeum) and there is no evidence of any optical function of the spherule. Three enveloping cells exist, but only one - probably the trichogen cell - forms a relatively small outer receptor lymph cavity. In the posterior wall of the pit - where exocuticle is developed - so-called suppressed systems can be found which remain completely below the cuticle with their otherwise well-developed spherules. Additionally, there is a tendency towards basally flattening and longitudinally stretching of spherules which are situated more peripherally. They strongly resemble the basal regions of hair mechanoreceptors (sensilla trichodea) in their immediate neighbourhood which are also accompanied by wax glands. Because of the existence of these transitional stages and the great ultrastructural resemblance between infrared receptors and hair mechanoreceptors concerning the bauplan of the sensory neurons and their mode of innervating the cuticular apparatus, we conclude that the infrared sensilla are probably derived from hair mechanoreceptors. Based on these results and transmission measurements of infrared radiation through the cuticular components of the organ, a model of the possible function of the infrared receptor is presented.     

Intersegmental modulation of abdominal postural responses initiated by mechanostimulation of the swimmeret in lobster

In a multiganglionic preparation of the lobster abdominal nerve cord, composed of the first through fifth ganglia (A1-A5) and attached second swimmeret, tactile stimulation of the cuticular surface of the swimmeret initiates a postural motor program in A2 for abdominal extension, whereas deflection of feathered hair sensilla that fringe the swimmeret rami does not affect postural motor activity recorded from A2 (Kotak and Page, 1986a). This report demonstrates that partial isolation of A2 from adjacent abdominal ganglia by sectioning the A1-A2 or the A2-A3 connectives both increases the strength of the extension response evoked by cuticular stimulation and disinhibits a postural flexion inhibition response initiated by feathered hair stimulation. Complete isolation of A2, by cutting the A1-A2 and the A2-A3 connectives, further increases the strength of these postural responses. Intersegmental inhibition of these responses originates in the ganglia adjacent to A2, since mechanoresponsiveness of A2 is not affected by resection of a more distant connective (A3-A4). These results provide evidence for the presence in adjacent abdominal ganglia of intersegmental interneurons that regulate the access of swimmeret sensory activity to the postural motor neurons in A2.     

Tyrosine cross-linking of extracellular matrix is catalyzed by Duox, a multidomain oxidase/peroxidase with homology to the phagocyte oxidase subunit gp91phox

High molecular weight homologues of gp91phox, the superoxide-generating subunit of phagocyte nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, have been identified in human (h) and Caenorhabditis elegans (Ce), and are termed Duox for "dual oxidase" because they have both a peroxidase homology domain and a gp91phox domain. A topology model predicts that the enzyme will utilize cytosolic NADPH to generate reactive oxygen, but the function of the ecto peroxidase domain was unknown. Ce-Duox1 is expressed in hypodermal cells underlying the cuticle of larval animals. To investigate function, RNA interference (RNAi) was carried out in C. elegans. RNAi animals showed complex phenotypes similar to those described previously in mutations in collagen biosynthesis that are known to affect the cuticle, an extracellular matrix. Electron micrographs showed gross abnormalities in the cuticle of RNAi animals. In cuticle, collagen and other proteins are cross-linked via di- and trityrosine linkages, and these linkages were absent in RNAi animals. The expressed peroxidase domains of both Ce-Duox1 and h-Duox showed peroxidase activity and catalyzed cross-linking of free tyrosine ethyl ester. Thus, Ce-Duox catalyzes the cross-linking of tyrosine residues involved in the stabilization of cuticular extracellular matrix.     

Synaptic responses produced in lobster abdominal postural motor neurons by mechanical stimulation of the swimmeret

1. Intracellular recordings were obtained from the somata of identified abdominal postural motor neurons in lobster to examine their subthreshold and suprathreshold responses to tactile stimulation of the swimmeret. 2. Pressure stimulation of the swimmeret surface evoked abdominal extension by producing tonic spiking in the extensor excitors and the synergistic flexor inhibitor (f5) and hyperpolarizing responses in the extensor inhibitor and antagonistic flexor excitors. These responses often continued for several seconds following the termination of the stimulus. The receptive fields of these motor responses extended over most of the swimmeret surface. 3. More localized tactile stimulation of the swimmeret surface elicited EPSPs in f5 and the extensor excitors, and IPSPs in the flexor excitors. The amplitude of these synaptic potentials decreased as the stimulus intensity was reduced. 4. Stimulation of feathered hair (both sexes) and smooth hair (female only) sensilla produced responses characteristic of extension whereas bristly spines on the male accessory lobe excited only two flexor excitors without affecting any of the other postural motor neurons. 5. Summed synaptic responses recorded from the motor neurons differed in their amplitudes and latencies according to the type of mechanoreceptor stimulated-cuticular receptors, feathered hairs or smooth hairs. Stimulation of the swimmeret cuticle produced the strongest responses (shortest latency, largest amplitude), while feathered hair stimulation initiated the weakest responses (longest latency, smallest amplitude). 6. The relatively long latencies (greater than 35 ms) and the complex form of the EPSPs and IPSPs indicate the involvement of multisynaptic interneuronal pathways in the reflex arcs.     

The lipid composition of hypodermal membranes from the blue crab (Callinectes sapidus) changes during the molt cycle and alters hypodermal calcium permeability

Crustaceans are covered by a cuticle that does not grow. In order for an individual to grow, the cuticle must periodically be shed (ecdysis). Replacement of the old cuticle with a new one depends on processes that require precise timing and control, yet the nature and location of these controls remain unclear. A candidate site for them is within the hypodermal microvilli. These cellular structures extend through pore canals deep into the acellular cuticular matrix. Changes in the lipid composition of hypodermal microvilli could modulate water and ion fluxes and enzyme activities during critical stages of the molt cycle; however, the lipid composition of these structures has not been assessed during the molt cycle. Data presented here show that phospholipids isolated from hypodermal microvilli of Callinectes sapidus initially have elevated levels of n-6 fatty acids that decline steadily beginning just after ecdysis. Experiments with liposomes reveal that n-6 fatty acids decrease the calcium permeability of membranes, suggesting that the initially elevated levels in the cuticle may function to reduce calcium flux from the cuticle into the hypodermis. In addition, the ratio of cholesterol to phospholipid and the proportion of oleic acid in membrane phospholipids are maximal at 6 h post-ecdysis. It is known that changes in cholesterol and oleic acid content alter membrane permeability to water. It is, therefore possible that water flux through hypodermal membranes is also modulated in the early post-molt cuticle. Changes in microvillar lipid composition might serve importantly to control biomineralization in the post-ecdysal cuticle.     

Development of the crystalliferous cuticle of Chamaecyparis lawsoniana (A. Murr.) Pari. (Gupressaceae)

A developmental study of the cuticle has shown that it consists of a homogeneous cuticle proper apposed on the wall and a heterogeneous cuticular layer generated by intussusception of cutin into the wall. At an early stage, the adcrusted cuticle proper is underlain by a ruthenium red-positive layer in which the cuticular layer originates. The origin of the anticlinal flange is referable to an electron-dense, ruthenium red-positive ridge which arises above the anticlinal wall and which also becomes cutinized. At leaf maturity, the inner surface of the cuticular layer, including that of the flange, forms interdigitating protuberances with the cell wall.
Development of the cuticle coincides with deposition of crystals of calcium oxalate in the epidermal cell wall. Initiation of large, early-formed crystals is associated with electron-opaque membranous structures formed close and parallel to the plasmalemma in the young cell wall. Crystals undergo periclinal and anticlinal growth and subsequently become engulfed within the cuticle by development of the cuticular layer. Cutin/polysaccharide interaction during development and the significance of crystal deposition are discussed.     

Synaptic interactions among neurons that coordinate swimmeret and abdominal movements in the crayfish

1. Many interneurons in the crayfish (Procambarus clarkii) abdominal nervous system influence two behaviors, abdominal positioning and swimmeret movements. Such neurons are referred to as dual output cells. Other neurons which influence either one behavior or the other are single output cells. 2. Extensive synaptic interactions were observed between both dual and single output neurons involved in the control of abdominal positioning and swimmeret movements. Over 60% of all neuron pairs examined displayed interactions. Pairs of agonist neurons displayed excitatory interactions, while pairs of antagonists had inhibitory interactions. This pattern of interaction was observed in about 75% of interactive neuron pairs whether abdominal positioning or swimmeret outputs were considered. 3. Evidence for both serial and parallel connectivity, as well as, reciprocal or looping connections was observed. Looping connections can be found both between the abdominal positioning and swimmeret systems and within each system. 4. Most (28/34) single output neurons were not presynaptic to dual output neurons. No single output neurons were found to excite dual output neurons to spiking, although inhibitory interactions and weak excitations were observed. 5. Abdominal positioning inhibitors displayed properties consistent with a role in mediating some of the coordination between the swimmeret and abdominal positioning systems. 6. None of the dual output neurons examined influenced the swimmeret motoneurons directly.     

External sensilla of the locust abdomen provide the central nervous system with an interganglionic network

External mechanoreceptors and contact chemoreceptors on the cuticle of the sixth abdominal segment of locusts have divergent primary projections of their sensory neurons that form arbours in the segmental and anterior abdominal ganglia. Homologous interganglionic projections from adjacent segments converge in the neuropile of each abdominal ganglion. Of the contributing types of sensilla, three were previously unknown for locust pregenital segments: tactile mechanosensory hairs with dual innervation, external proprioceptors of the hairplate type covered by intersegmental membranes and single campaniform sensilla that monitor cuticular strain in sternites and tergites. In general, interdependence of motor coordination in the abdominal segments is based on a neural network that relies heavily on intersegmental primary afferents that cooperate to identify the location, parameters and strength of external stimuli.     

The structure of the cuticle and sheath of the infective juvenile of Trichostrongylus colubriformis

The infective third-stage juvenile of Trichostrongylus colubriformis is surrounded by its own cuticle as well as the incompletely moulted cuticle of the second-stage juvenile, which is referred to as the sheath. The sheath comprises an outer epicuticle, an amorphous cortical zone, a fibrous basal zone and an inner electron-dense layer. The basal zone of the sheath consists of three layers of fibres; the fibres are parallel within each layer, but the fibre direction of the middle layer is at an angle to that of the inner and outer layers. The cuticle comprises a complex outer epicuticle, an amorphous cortical zone and a striated basal zone. The lateral alae of the cuticle and the sheath are aligned and overlie the lateral hypodermal cords. The lateral alae of the sheath consist of two wing-like expansions of the cortical zone with associated specializations of the inner electron-dense layer which form a groove. The cuticular lateral alae consist of two tube-like expansions of the cortical zone. The lateral alar complex of the cuticle and the sheath may maximise locomotory efficiency and prevent rotation of the juvenile within the sheath.     

Structure of the integument in Paranthessius anemoniae claus,a copepod associate of the snakelocks anemone Anemonia sulcata (Pennant)

The integument of Paranthessius anemoniae has been studied with light and electron microscopy. A cuticle with clearly defined epicuticular, exocuticular and endocuticular regions overlies a cellular hypodermal layer. The distribution of carbohydrate, lipid and protein components of the cuticle were demonstrated histochemically. Parabolic striations in oblique sections of cuticle suggest that its molecular architecture fits a “twisted sheet” theory proposed for other species. Arthrodial membranes at body and limb joints have a homogeneous structure, lacking exocuticle and endocuticle. Subcuticular glands appear to secrete substances thought to be responsible for the immunity which Paranthessius seems to have to the nematocysts of its host. Small hairs, situated in cuticular cups which occur over the dorsal body surface are considered to function as rheoreceptors.     

A new mechanosensory organ on the anterior spinnerets of the spiderCupiennius salei (Araneae,Ctenidae)

We describe hitherto unknown mechanoreceptors on the anterior spinnerets of the spiderCupiennius salei. These receptors are found at the base of the spigots of the major ampullate glands which produce the dragline used by the spider as a safety thread in various behavioral situations. There are 40–60 mechanoreceptors associated with two spigots of each anterior spinneret. They are likely to provide information on the forces pulling on the dragline and also on its orientation in space. A single sensillum consists of a hole in the cuticle covered by a thin cuticular membrane. It much resembles spider slit sensilla, which are known to detect strains in the exoskeleton. Each sensillum is supplied by two dendrites most likely belonging to two bipolar sensory cells. One of the dendrites ends at the covering membrane and the other more proximally. The sensilla are arranged with their long axes roughly parallel to the circumference of the spigots. External forces, transmitted by the dragline, result in deformation of the central part of the cuticular plate at the base of the spigots and thus in stimulation of the sensilla. This is shown electrophysiologicallly. Considering their morphology, topography, and electrophysiology, these mechanoreceptors are suggested to be important in the sensory control of dragline release by the spider.     

The Ultrastructure of the Presumed Chemoreceptor Aesthetasc "Y" of a Cypridid Ostracode

The aesthetasc "Y" of cypridid ostracodes is divided into three parts: distal, intermediate, and proximal. Distally, it is equipped with five pores containing electron-dense plugs. The distal part shows a peculiar striated pattern formed by two types of cuticle. The intermediate and proximal parts are smooth with no pores or other substructures. 14 cilia run in the large receptor-cavity of the distal part. They originate from 14 bipolar sensory cell bodies within the antenna. From the intermediate part, the cilia are grouped in five cuticular sheaths, surrounded by five sheath cells arranged mesaxonally. At the level of the ciliary junctions, the sheath cells form cavities in which the cilia join the dendrites. Before molting, a new aesthetasc is formed in the antenna by hypodermal cells. The cuticle is secreted in a fold around the sheath cells, which in a way act as moulds. The cilia of the old aesthetasc run through the five pores of the new aesthetasc. The main function of the pores is apparently to enable the animal to obtain information from the surroundings also during the molting period. On morphological grounds, the aesthetasc "Y" is believed to be a chemoreceptor.     

Fine structure of the spermatheca of the mealworm beetle (Tenebrio molitor L.)

The spermatheca of the female mealworm beetle is an inflorescence of branching cuticular ducts which is connected to the bursa copulatrix via a cuticular neck surrounded by a muscular coat. The infolded bursal cuticle consists of a distinct outer epicuticle, inner epicuticle, procuticle, and a subcuticular zone; the latter is rich in mucopolysaccharides. The cuticle of the neck lacks a distinct procuticle. The cuticle of the spermatheca itself is mostly inner epicuticle with two thin underlying lamellae of procuticle. The cells of the bursa are loosely coupled to the procuticle, whereas cuticular projections bind the epithelia of the "neck" and the spermatheca proper to the underlying epithelia. The apical plasma membranes of the spermathecal epithelium are sinuous and much infolded; we believe that this epithelium controls the micro-environment within the cuticular ducts.     

A freeze-fracture study of the body wall of adult, in utero larvae and infective-stage larvae of Trichinella (Nematoda)

The surface layers of the cuticle, the hypodermal membranes and the muscle membranes of the adult, the in utero larvae and the infective-stage larvae of the nematode Trichinella spiralis have been studied by means of the freeze-fracturing technique. The surface of the cuticle of both adults and larvae fractures in ways different from membranes of internal cells. The surface coat on top of the epicuticle is probably the layer that changes antigenically. Reticulate ridges, with associated particles, on the E face of the outer hypodermal membrane of the adult are probably sites of attachment of the hypodermis to the cuticle. Longitudinally arranged ridges, with associated particles, of the outer hypodermal membrane are probably points of attachment to the cuticle in the in utero and infective larvae. Rectilinear arrays of particles are present on the P face of the inner hypodermal membrane and the P face of the muscle membrane adjacent to the hypodermis of adults and larvae and probably play a role in adhesion of the muscle membrane to the hypodermis. Particle-free areas of membrane lie external to the Z bundles of the muscle cell and are similar to the sites of attachment of Z lines in insect muscles.     

Visualization of Caenorhabditis elegans cuticular structures using the lipophilic vital dye DiI

The cuticle of C. elegans is a highly resistant structure that surrounds the exterior of the animal(1-4). The cuticle not only protects the animal from the environment, but also determines body shape and plays a role in motility(4-6). Several layers secreted by epidermal cells comprise the cuticle, including an outermost lipid layer(7). Circumferential ridges in the cuticle called annuli pattern the length of the animal and are present during all stages of development(8). Alae are longitudinal ridges that are present during specific stages of development, including L1, dauer, and adult stages(2,9). Mutations in genes that affect cuticular collagen organization can alter cuticular structure and animal body morphology(5,6,10,11). While cuticular imaging using compound microscopy with DIC optics is possible, current methods that highlight cuticular structures include fluorescent transgene expression(12), antibody staining(13), and electron microscopy(1). Labeled wheat germ agglutinin (WGA) has also been used to visualize cuticular glycoproteins, but is limited in resolving finer cuticular structures(14). Staining of cuticular surface using fluorescent dye has been observed, but never characterized in detail(15). We present a method to visualize cuticle in live C. elegans using the red fluorescent lipophilic dye DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), which is commonly used in C. elegans to visualize environmentally exposed neurons. This optimized protocol for DiI staining is a simple, robust method for high resolution fluorescent visualization of annuli, alae, vulva, male tail, and hermaphrodite tail spike in C. elegans.