Central afferent pathways of long hair sensilla in the ventral nerve cord of the Indian black scorpion,Heterometrus fulvipes Koch

Histological and electrophysiological studies of identified long hair sensilla (LHS) have provided information on primary afferent fibre pathways in the ventral nerve cord of the Indian black scorpion, Heterometrus fulvipes.Cobalt-filling of single LHS on the metasoma showed that sensory axons enter the respective segmental ganglion, ascend ipsilaterally through the next anterior ganglia and terminate in a 4th ganglion. In each ganglion, these plurisegmental fibres give off collateral branches that terminate in the ganglionic neuropil. Fibres entering heterolateral connectives were not found.Recordings from peripheral nerves after deflections of a hair showed single or multiple spike discharges. A single spike could be recorded from ipsilateral anterior connectives of the ventral nerve cord, indicating a through-conductance of the sensory pathways. Strong deflections of a single hair activated several ipsilateral and fewer contralateral ascending interneurons and some segmentai motor neurons. Behavioral studies demonstrate the mechanoreceptive function of the LHS.The present study provides evidence in support of the notion that sensory afferents of the postabdomen in the scorpion bring about rapid, co-ordinated intersegmental movements of the multisegmented tail of the scorpion.Abbreviations CNS central nervous system - LHS long hair sensillum - TR trichobothria     

Central projections of campaniform sensilla on the cerci of crickets and cockroaches

Summary Campaniform sensilla associated with filiform hairs comprise an important receptor type of the multimodal sensory system of the cerci of crickets and cockroaches. Their axon projections were investigated using iontophoretic cobalt injection into single sensilla.In crickets (Gryllus bimaculatus, Acheta domestica), six different types of cereal campaniform sensilla projections can be distinguished on the basis of their axonal arborizations and terminations. Typically, a proportion of cereal campaniform sensilla, associated with long filiform hairs, give rise to axons that ascend as through fibres from the terminal ganglion to reach the sixth abdominal ganglion. Cereal campaniform sensilla associated with clavate hairs have projections restricted to the terminal ganglion alone.Whereas in crickets axons of cercal campaniform sensilla invade only certain segmental neuropils in the terminal ganglion, in cockroaches (Periplaneta americana) axons from cercal campaniform sensilla branch in every segmental neuropil. A proportion of cereal campaniform sensilla in this species also gives rise to through fibres to the fifth abdominal ganglion.We discuss morphological and functional interpretations of differences between crickets and cockroaches and consider the significance of this type of receptor in the context of previous studies of the cercal system.     

Coxal hair plates in spiders: physiology,fine structure,and specific central projections

Coxal hair-plate sensilla in the spider Cupiennius salei are described with respect to their innervation, central projection pattern, electrical response to mechanical stimulation, and putative behavioral function.

Advanced sub social behaviour in the scorpionHeterometrus fulvipes Brunner (Arachnida)

Scorpions arc generally non-social, solitary animals that interact with conspecifics at birth, courtship or predation only. The present study reports the presence of advanced sub social behaviour inHeterometrus fulvipes Brunner and evaluates the importance of its burrowing as a cause for such social behaviour.Heterometrus fulvipes constructed deep angular burrows at the base of plants. Burrows provided (i) protection against predation, (ii) increased availability of food and (iii) ideal microclimate for year round activity of the scorpions. No cannibalism was observed in laboratory maintained colonies. The risk of predation and the difficult by immatures to dig tunnels during dry soil conditions may have forced the mother and offspring to live together in the burrow for longer durations. The cohabitation of relative offsprings transforms the burrow into a nest. The members of a colony exhibits division of labour for nest expansion and in foraging. The mother communicates with the immatures through “Buzz” sound and may provide premasticated food. There is food sharing also among colony members. All these behaviours indicate the presence of advanced sub social behaviour inHeterometrus fulvipes.     

Fine structure and primary sensory projections of sensilla located in the sacculus of the antenna of Drosophila melanogaster

Sensilla lining the inner walls of the sacculus on the third antennal segment of Drosophila melanogaster were studied by light and transmission electron microscopy. The sacculus consists of three chambers: I, II and III. Inside each chamber morphologically distinct groups of sensilla having inflexible sockets were observed. Chamber I contains no-pore sensilla basiconica (np-SB). The lumen of all np-SB are innervated by two neurons, both resembling hygroreceptors. However, a few np-SB contain one additional neuron, presumed to be thermoreceptive. Chamber II houses no-pore sensilla coeloconica (np-SC). All np-SC are innervated by three neurons. The outer dendritic segments of two of these neurons fit tightly to the wall of the lumen and resemble hygroreceptor neurons. A third, more electron-dense sensory neuron, terminates at the base of the sensillum and resembles a thermoreceptor cell. Chamber III of the sacculus is divided into ventral and dorsal compartments, each housing morphologically distinct grooved sensilla (GS). The ventral compartment contains thick GS₁, and the dorsal compartment has slender sensilla GS₂. Ultrastructurally, both GS₁ and GS₂ are doublewalled sensilla with a longitudinal slit-channel system and are innervated by two neurons. The dendritic outer segment of one ofthe two neurons innervates the lumen of the GS and branches. On morphological criteria, we infer this neuron to be olfactory. The other sensory neuron is probably thermoreceptive. Thus, the sacculus in Drosophila has sensilla that are predominantly involved in hygroreception, thermoreception, and olfaction. We have traced the sensory projections of the neurons innervating the sacculus sensilla of chamber III using cobaltous lysine or ethanolic cobalt (II) chloride. The fibres project to the antennal lobes, and at least four glomeruli (VM₃, DA₃ and DL_2-3) are projection areas of sensory neurons from these sensilla. glomerulus DL₂ is a common target for the afferent fibres of the surface sensilla coeloconica and GS, whereas the VM₃, DA₃ and DL₃ glomeruli receive sensory fibres only from the GS.     

Central projections of the lagena (the third otolith endorgan of the inner ear) in the pigeon

Central projections of the lagena were studied in the pigeon using transport of biotinylated dextran amine (BDA) that was locally applied to the lagenar epithelium through the opened cochlear canal. Descending (dorsocaudal part) and superior (middle part) vestibular nuclei were the main rhombencephalon structures with the maximum density of labeled fibers and terminals. Lesser numbers of labeled fibers were observed in the ventral part of the lateral vestibular nucleus and also in the medial vestibular nucleus; single labeled fibers were found in the cochlear nuclei. In the cases where BDA diffused not only in the lagena but also on the basilar papilla after application of the marker to the cochlear canal, considerable numbers of labeled fibers were observed in the cochlear nuclei; apart from this, the pattern of distribution of labeled fibers in the vestibular nuclei did not differ in general from that described above (in the case of a sufficiently local application of BDA only to the lagena). Efferent lagenar neurons were localized ventrally with respect to the vestibular nuclei, in particular in the nucl. reticularis pontis caudalis. Neirofiziologiya/Neurophysiology, Vol. 40, No. 3, pp. 199–210, May–June, 2008.     

Ultrastructure of the nerve cells and sensilla of Geocentrophora baltica (Platyhelminthes,Lecithoepitheliata) and the surface sensilla in the Geocentrophora group

Two types of nerve cell could be distinguished ultrastructurally in the central nervous system of Geocentrophora baltica (Prorhynchida, Lecithoepitheliata). Both show invaginations in the plasma membrane, but they differ in the character of the cytoplasm (light or densely stained) and the distribution of the neuronal vesicles (evenly or in groups). Different kinds of vesicles and neuronal release sites are observed. Special features of the synapses are pronounced local thickenings of the presynaptic membrane connected to paramembranous densities. In G. baltica and five endemic Geocentrophora spp. from Lake Baikal six types of surface sensillum were observed at the epidermal surface: 1. those with a long thin rootlet; 2. a short, balloon-shaped cilium with an aberrant axoneme and a reduced rootlet; 3. a rootlet branching into many striated bundles; 4. a thick rootlet; 5. a reduced rootlet and numerous neurotubules;and 6. collared sensilla each with one cilium in a deep pit surrounded by a collar of 11 to 12 microvilli. The variable number of microvilli in the collared sensillum is considered plesiomorphic relative to the stable number of eight microvilli known in sensilla of the Prolecithophora, Proseriata, and Rhabdocoela. The ultrastructure of the collar sensillum indicates that the Lecithoepitheliata is only distantly related to the Prolecithophora and higher turbellarians.     

Distribution and specific central projections of mechanoreceptors in the thorax and proximal leg joints of locusts

Summary Tactile hairs on the locust thorax can be divided into two classes by their external morphology and their central projection pattern: Short hairs, 10–100 m in length, which are assembled in distinct plates and rows, and long hairs, 100–800 m in length, which are distributed all over the body and are organized in large fields or aligned along the ridges of the appendages.The sensory fibers of the first class arborize in the lateral dorsal neuropile of thoracic ganglia and then extend further into the ipsilateral half of the corresponding ganglion in three main bundles from which fine rami of fibers end in the intermediate neuropile. In all three thoracic ganglia the projection pattern of homologous hair plates is similar.The sensory fibers of the second class exclusively terminate in special median ventral neuropiles, the ventral association center (VAC) and ventralmost ventral association center (VVAC). In addition fibers from meso- and metathoracic hairs, located close to the longitudinal midline of the animal, may terminate in the contralateral VAC and with one branch project to the next anterior ganglion through the ipsilateral connective. In contrast, fibers from prothoracic hairs were not found to leave their ganglion.With support by the DFG Neurale Mechanismen des VerhaltensSome of the studies were started at Universität Bielefeld, Fakultät für Biologie II (Abtlg. Prof. Dr. P. Görner)     

Fine-structural characteristics of the antennal sensilla of Agrotis segetum (Insecta: Lepidoptera)

Summary The turnip moth Agrotis segetum possesses seven different types of sensilla: four single-walled (SW), one double-walled (DW), one terminal-pore (TP), and one poreless sensilla (NP).The SW 1 and SW 2 sensilla have the same external appearance, being long and slender, but differ in the branching pattern of the sensory processes: unbranched and branched in SW 1 and SW 2, respectively. The SW 3 sensilla are shorter, sickle-shaped, and contain a large number of branches from the sensory processes. These three sensillar types are innervated by 2–3 sensory cells. The SW 4 sensilla are raisin-shaped and possess three profusely branched sensory processes. The DW sensilla are short and have apical slit-like pores. This sensillar type has 5–6 sensory processes. The TP sensilla possess five sensory processes, one of them terminates basally in a tubular body, the others in the apical part of the long cuticular bristle. The NP sensilla are stout and have apical conelike structures. Two of the sensory processes terminate in the apical part, the third proximally. The third sensory process has a lamellar pattern. The fine structure indicates the following functions: SW and DW sensilla: chemoreception; TP sensillum: chemoreception and mechanoreception; NP sensillum: thermoreception and hygroreception.Supported by joint grants from the Swedish Council for Planning and Coordination of Research, the Swedish Natural Science Research Council, and the Swedish Council for Forestry and Agricultural Research     

Retinofugal and retinopetal projections in the teleost Channa micropeltes (Channiformes)

Summary Retinofugal and retinopetal projections were investigated in the teleost fish Channa micropeltes (Channiformes) by means of the cobaltous lysine and horseradish peroxidase (HRP) tracing techniques. Retinofugal fibers cross completely in the optic chiasma. A conspicious lamination is present in those parts of the optic tract that give rise to the marginal branches of the optic tract. This layering of optic fibers continues in the marginal branches to mesencephalic levels. Retinal projections to the preoptic and hypothalamic regions are sparse; they are more pronounced in the area of pretectal nuclei. The medial pretectal complex and the cortical pretectal nucleus are more fully differentiated than in other teleostean species. Further targets include the thalamus and the optic tectum. The course of major optic sub-tracts and smaller fascicles is described. Retinopetal neurons are located contralaterally in a rostral and a caudal part of the nucleus olfactoretinalis, and in a circumscribed nucleus thalamoretinalis. The present findings are compared with reports on other teleost species.     

A hairy business—Periostracal hair formation in two species of helicoid snails (Gastropoda,Stylommatophora, Helicoidea)

In molluscs, the calcareous shell is covered externally by a thin organic layer, the periostracum. The periostracum of some pulmonate species is of special taxonomic interest because it bears distinct microscale architectures. Where and how these structures are formed is as yet unknown. Using histological sections through their shells, gelatin cuts, and live observations I studied the pattern by which the periostracal hair‐like projections in two helicoid land snail species are secreted and evenly arranged on the shell. The results indicate a complex mechanism: a hair is formed in the periostracal groove independently of the periostracum, after which it is attached to the edge of the shell, drawn out of the tissue, and finally swivelled to the upper side of the periostracum. Upon further growth of the periostracum, the hairs are finally fixed upright on the shell. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

小峰熊蜂工蜂触角感器的扫描电镜观察

利用扫描电镜对小峰熊蜂Bombus hypocrita的触角形态和感器进行了观察。结果表明:小峰熊蜂触角呈膝状,由柄节、梗节和鞭节组成。工蜂的柄节约为触角全长的三分之一,其长度约为(2099.40±112.26)μm,梗节呈方圆形,最短,长度为(212.86±12.51)μm。鞭节全长为(3861.43±137.86)μm,共由10节组成。触角上广布11种类型的感受器,即板形感器、坛形感器、钟形感器、锥形感器、腔锥形感器、毛形感器、刺形感器、芽形感器、端指形感器、缘感器和刚毛,不同感器在触角上的分布部位不同。其中,芽形感器和端指形感器在膜翅目昆虫中属首次发现。     

Antennal sensilla of grasshoppers (Orthoptera: Acrididae) in relation to food preferences and habits

The external structure, i.e. number and distribution of sensillae on male and female antennae of 12 species of grasshoppers belonging to Pamphaginae, Catantopinae, Oedipodinae and Gomphocerinae in the grasslands of Inner Mongolia was investigated using scanning electron microscopy. Five major types of antennal sensillae were detected - trichoid, long basiconic, short basiconic, slender and short basiconic, and coeloconic sensillae. Total number of antennal sensillae varied among different sexes, subfamilies, feeding groups, life forms and eco-forms. Males showed significantly more sensillae than females, due to presence of more short basiconic and coeloconic sensillae. Species under Catantopinae showed more long basiconic sensillae than the others. The Oedipodinae had the highest number of slender and short basiconic sensillae and coeloconic sensillae, followed by Catantopinae and Gomphocerinae; while Pamphaginae had the fewest. The total number of sensillae showed the same trend for these two types amongst the subfamilies as well, species which prefer habits on the ground possessed fewer antennal sensillae than species which prefer to stay on plants. The maximal number of antennal sensillae were observed in hygrophytous species,Chorthippus albomarginatus, in the 12 grasshopper species investigated, although the data is not statistically significant. The general trend which emerged was that species feeding on grass possessed more antennal sensillae, particularly coeloconic sensillae, compared to other feeding group species.     

Effect of age on the responsiveness of peripheral chemosensory sensilla of the turnip root fly (Delia floralis)

The effect of insect age on the neural responsiveness of gustatory sensilla was investigated. Electrophysiological recordings were obtained from type A and type D sensilla on the pro- and meso-thoracic tarsi, and from sensilla on the labellum of the turnip root fly,Delia floralis (Fallen) in response to potassium chloride, sucrose and sinigrin. The age of the fly did have an effect on the numbers of sensilla responding to the test stimuli and on the magnitude of the response, but there was no consistent pattern in these effects among sensilla. The labellar sensilla were more responsive to sucrose than the tarsal sensilla and the proportion of flies whose labellar sensilla responded to sucrose was initially low, but increased after day 2 of adult life. In contrast, the number of flies whose tarsal sensilla responded to stimulation with sucrose was initially high and decreased as the flies aged. There was a similar decline in the proportion of tarsal sensilla responding to potassium chloride. Neither the proportion of flies whose tarsal sensilla responded to sinigrin nor the magnitude of the response was influenced by the age of the fly. These finding are discussed in relation to the feeding and host selection behaviour of the fly.     

Ultrastructure and early development of the pore plate sensilla ofGymnomerus laevipes (Shuckard) (Vespoidea,Eumenidae)

Summary The oval pore plates (approx. 17 m long) are separated from the antennal cuticle by a furrow, the inner wall of which is flexible. The thin perforated plates are strengthened by an encircling and a middle ledge, the latter of which branches into about 100 almost parallel rims. Each pore plate is innervated by about 20 sense cells. The dendrites fork into numerous branches occupying the outer receptor lymph cavity below the perforated plate. Each pore plate is associated with one thecogen cell, two trichogen cells, one tormogen cell and one envelope cell 4. A so-called additional cell surrounds the sensillum in the imaginal stage. The envelope cells in the later of the two pupal stages examined, have reached an arrangement which immediately precedes the secretion of the cuticulin layer. The surface of the duplicate trichogen cells is almost equal in area to the completed perforated plate. A dendritic sheath, entirely reduced in the imago, protrudes into the exuvial space, where it encloses a single dendrite.In the younger pupal stage the Sensillenanlage forms a crater, whereby envelope cell 4 overtops the other envelope cells. The distal ends of the trichogen cells are divided into several appendages that form the bottom of the crater.     

The fine structure of the antennal sensilla of the pine saw flyNeodiprion sertifer (Insecta: Hymenoptera)

Summary There is a considerable sexual dimorphism as regards the development of the antenna inNeodiprion sertifer. In the male this is manifested in a larger antennal surface area and the possession of a great number of long single-walled sensilla (SW 1), which are located on the antennal branches. In the female the antennal branches are vestigial, and the single-walled sensilla, of a second type (SW 2), are shorter and present in lower numbers. Both sexes have in addition four types of sensilla in common:viz. a third type of single-walled sensilla (SW 3), terminal pore sensilla, double-walled sensilla, and poreless sensilla. These four sensillar types are characterized not only by their external appearance but also by their internal morphology. Especially the cells enveloping the sensory cells vary in number and appearance.Supported by joint grants from the Swedish Council for Planning and Coordination of Research, the Swedish Natural Science Research Council, and the Swedish Council for Forestry and Agricultural Research.     

Labial tip sensilla of Blissus leucopterus leucopterus (Hemiptera: Blissidae): Ultrastructure and behavior

The cuticular sensory receptors that are found on the apex of the labium of hemipterans play an important role in their feeding behavior. In this study we describe the ultrastructure, number, and distribution of sensilla on the labium apex of the chinch bug, Blissus leucopterus leucopterus. Each apical field of sensilla on the labium contains 11 uniporous peg sensilla and one sensillum chaeticum. The uniporous peg sensilla are innervated by 4–5 bipolar neurons that send dendrites in the lumen of each peg. Three neurons are associated with each sensillum chaeticum, two neurons have dendrites in the lumen of the sensillum, and the third dendrite ends in a tubular body at the base of the sensillum. Behavioral tests that involve chemical blockage of the sensory receptors show the importance of the labial sensilla in feeding behavior. Both morphological and behavioral evidence indicate that the labial sensilla have a chemosensitive function.     

The source of chilopod sensory information: External structure and distribution of antennal sensilla in Scutigera coleoptrata (chilopoda,Scutigeromorpha)

The investigation of the antennae of Scutigera coleoptrata (Linnaeus, 1758) by scanning electron microscopy (SEM) revealed the presence of five types of sensilla: sensilla trichodea, beak‐like sensilla, cone‐shaped sensilla brachyconica on the terminal article, sensory cones at the antennal nodes, and the shaft organ. Alongside the presence and absence of antennal sensillar types, three unique characters were found in the Scutigeromorpha: the presence of long antennae with nodes bearing sensory cones, the presence of a bipartite shaft including the shaft organ, and the presence of beak‐like sensilla. Neuroanatomical data showed that the animals' brains are equipped with well‐developed primary olfactory and mechanosensory centers, suggesting that the antennae must be equipped with specialized sensilla to perceive chemosensory and mechanosensory cues. With the evidence provided in this article for the Scutigeromorpha, SEM data are available at last on the antennal sensilla for all five chilopod taxa, allowing a comparative discussion of antennal morphology in Chilopoda. J. Morphol., 2011. © 2011Wiley‐Liss, Inc.