Development of leg chordotonal sensory organs in normal and heat shocked embryos of the cricket Teleogryllus commodus (Walker)

This paper describes the embryonic development of some parts of the sensory peripheral nervous system in the leg anlagen of the cricket Teleogryllus commodus in normal and heat shocked embryos. The first peripheral neurons appear at the 30% stage of embryogenesis. These tibial pioneer neurons grow on a stereotyped path to the central nervous system and form a nerve which is joined by the growth cones of axons that arise later, including those from the femoral chordotonal organ, subgenual organ and tympanal organ. The development of these organs is described with respect to the increase in number of sensory receptor cells and the shape and position of the organs. At the 100% stage of embryogenesis all three organs have completed their development in terms of the number of sense cells and have achieved an adult shape. To study the function of the tibial pioneer neurons during embryogenesis a heat shock was used to prevent their development. Absence of these neurons has no effect on the development of other neurons and organs proximal to them. However, the development of distal neurons and organs guided by them is impaired. The tibial pioneer neurons grow across the segmental boundary between femur and tibia early in development, and the path they form seems to be essential for establishing the correct connections of the distal sense organs with the central nervous system.     

Sensory organs of the thoracic legs of the moth Manduca sexta

Summary The thoracic legs of the moth Manduca sexta acquire a new form and develop a new complement of sensory organs and muscles during metamorphosis from larva to adult. Because of our interest in the reorganization of neural circuitry and the acquisition of new behaviors during metamorphosis, we are characterizing sensory elements of larval and adult legs so that we may determine the contribution of new sensory inputs to the changes in behaviors. Here we describe the sensory structures of adult legs using scanning electron microscopy to view the external sensilla and cobalt staining to examine innervation by underlying sensory neurons. We find that, in contrast to larval legs, the adult legs are covered with a diverse array of sensilla. All three pairs of thoracic legs contain scattered, singly innervated scalelike sensilla. Campaniform sensilla occur singly or in clusters near joints. Hair plates, consisting of numerous singly innervated hairs, are also present near joints. Other more specialized sensilla occur on distal leg segments. These include singly innervated spines, two additional classes of singly innervated hairs, and three classes of multiply innervated sensilla. Internal sensory organs include chordotonal organs, subgenual organs, and multipolar joint receptors.     

Metamorphic changes in the central projects of hair sensilla inTenebrio molitor L. (Insecta: Coleoptera)

Summary This paper describes the afferent projections of hair sensilla of the pro- and mesothoracic legs and the lateral thoracic sclerites of larval and adultTenebrio molitor and the corresponding set of pupal hair sensilla. The sensory neurons that innervate the hair sensilla of larval or adult insects project somatotopically into the thoracic neuropil. Different types of sensilla on the same region of the body surface project to the same zone of the ipsilateral thoracic ventral neuropil but exhibit different arborization patterns. Although there is a profound reorganization of body surface sensilla, the basic somatotopic layout of the larva is maintained in the adult. The sensory neurons that innervate the pupal hair sensilla possess central projections similar to those of the corresponding adult sensory neurons. The central projections of pupal sensory neurons are somatotopically oriented. Their projection pattern is serially homologous in the thoracic and the abdominal ganglia. The central projection pattern of the described pupal sensory neurons is constant throughout pupation. MAb 22C10 immunoreactivity allows an estimate of the timing of the early differentiation of the imaginal sensory neurons originating during pupation. Ablation experiments indicate that pupal sensory neurons influence the central projection pattern of the differentiating imaginal sensory neurons.     

Changes taking place in the electrophoretic haemolymph protein pattern during metamorphosis of Polytela gloriosae (Lepidoptera)

The haemolymph proteins of the larva, pupa and adult of Polytela gloriosae have been fractioned by Polyacrylamide gel disc electrophoresis. In the haemolymph of the fifth instar larval stage a total of ten protein fractions have been detected. The concentration of the protein fractions 2, 3, 4, 9 and 10 shows oscillations in their concentration in the early fifth instar, middle fifth instar and late fifth instar larval stage. In all 11 protein fractionswere detected in the haemolymph of different stages of the pupa. The protein bands 1, 7 and 10 of the pupa appear newly in the haemolymph as these bands were not found in the haemolymph of the larvae. The protein fraction 9 of larva was not found in the pupa. In the haemolymph of adult insect sexual difference was observed in the haemolymph protein pattern. In the haemolymph of adult female a total of 10 protein fractions were detected while from the male haemolymph a total of 8 protein fractions were detected. The pupal band 7 was not found in the adults of both the sexes. In the haemolymph of larva and adult one pigmented protein fraction was observed. No pigmented protein fraction was found in the haemolymph of pupa. Iron - containing protein fraction and the acid mucopolysaccharides were not found in the haemolymph. The protein fractions 3, 4, 5, 6 and 7 of adult haemolymph were darkly stained by the Schiff reagent and, thus, they are the fractions of glycoprotein. One protein fraction of lipoprotein was also found in the haemolymph.     

Fine structure of the galeal styloconic sensilla of larval Lymantria dispar (Lepidoptera: Lymantriidae)

Lepidopteran larvae possess two pairs of styloconic sensilla located on the maxillary galea. These sensilla, namely the lateral and medial styloconic sensilla, are each comprised of a smaller cone, which is inserted into a style. They are thought to play an important role in host-plant selection and are the main organs involved in feeding. Ultrastructural examination of these sensilla of fifth instar Lymantria dispar (L.) larvae reveal that they are each approximately 70 um in length and 30 um in width. Each sensillum consists of a single sensory peg inserted into the socket of a large style. Each peg bears a slightly subapical terminal pore averaging 317 nm in lateral and 179 nm in medial sensilla. Each sensillum houses five bipolar neurons. The proximal dendritic segment of each neuron gives rise to an unbranched distal dendritic segment. Four of these dendrites terminate near the tip of the sensillum below the pore and bear ultrastructural features consistent with contact chemosensilla. The fifth distal dendrite terminates near the base of the peg and bears ultrastructural features consistent with mechanosensilla. Thus, these sensilla each bear a bimodal chemo-mechanosensory function. The distal dendrites lie within the dendritic channel and are enclosed by a dendritic sheath. The intermediate and outer sheath cells enclose a large sensillar sinus, whereas the smaller ciliary sinus is enclosed by the inner cell. The neurons are ensheathed successively by the inner, intermediate, and outer sheath cells.     

Sensorimotor pathways processing vibratory signals from the femoral chordotonal organ of the stick insect

The femoral chordotonal organ of stick insects senses position and velocity of movements in the femur-tibia joint, as well as tibial vibration. While sensory information about large-scale tibial movements is processed by a well-known neuronal network and elicits resistance reflexes in extensor and flexor tibiae motoneurons, it is not yet known how sensory information about vibration of the tibia is processed. We investigated the transmission of vibration stimuli to tibial extensor motoneurons and their premotor interneurons. Vibration stimuli applied to the femoral chordotonal organ evoked responses in tibial extensor and flexor muscles. During ongoing vibration this response adapted rapidly. This adaptation had no effect on the motoneuronal response to large-scale tibial movements. Recording from premotor interneurons revealed that vibratory signals were processed in part by the same interneuronal pathways as (large-scale) velocity and position information. While only certain parts of the interneuronal reflex pathways showed little or no response during vibration stimuli, most neurons responded to both position or velocity stimuli and vibration at the femoral chordotonal organ. We conclude that sensory information about vibration of the tibia shares part of the interneuronal pathways that transmit sensory information about large-scale tibial movements to the motoneurons. Accepted: 25 April 1999     

Embryogenesis of peripheral nerve pathways in grasshopper legs. I. The initial nerve pathway to the CNS

The founding of the first nerve path of the grasshopper metathoracic leg was examined at the level of identified neurons, using intracellular dye fills, immunohistochemistry, Nomarski optics, and scanning and transmission electron microscopy. The embryonic nerve is established by the axonal trajectory of a pair of afferent pioneer neurons, the tibial 1 (Ti1) cells. Following a period of profuse filopodial sprouting, the Ti1 axonal growth cones, possessing 75- to 100-microns-long filopodia, navigate a stereotyped path across the limb bud epithelium to the base of the appendage and into the CNS. The Ti1 axons grow from cell to cell along a chain of preaxonogenesis neurons spaced at intervals along the pathway, forming dye-passing junctions with them. The contacted neurons subsequently undergo axonogenesis and follow the pioneer axons into the CNS. Later arising neurons project their axons onto the cell bodies of the chain, thereby establishing the principal branch points of the nerve. Among the later arising afferents are the sensory neurons of the femoral chordotonal and subgenual organs. The morphology of the adult nerve appears to be determined by the stereotyped positioning of neurons in the differentiating limb bud and by the resultant axonal trajectories established during the first 10% of peripheral neurogenesis.     

A dual function of the Notch gene in Drosophila sensillum development

We have investigated the function of the neurogenic gene Notch (N) during development of the adult sensilla of Drosophila. Heat pulses were applied to flies carrying the temperature-sensitive Notch allele Nts1 at different larval and pupal stages. We can show that the reduction of Notch+ function during a short interval prior to the onset of sensillum precursor division, resulting from a heat pulse between 0 and 14 hr after puparium formation (apf), leads to an increase in microchaete precursors at the expense of epidermal cells. The structure and cellular composition of the sensilla produced by these supernumerary precursors are normal. Later heat pulses which include the interval immediately after sensillum precursor division (14-20 hr apf) lead, among the progeny of the sensillum precursors, to a hyperplasia of sensory neurons, at the expense of accessory cells. The resulting "sensilla" consist of neurons only and lack the external cuticular structures (i.e., shaft, socket). These results demonstrate that similar mechanisms both of which involve the function of the Notch gene may be operating to sort out (premitotic) sensillum precursors from epidermal precursors and (postmitotic) sensory neurons from accessory cells. They further show that in postmitotic sensillum cells the differentiative fate is not yet irreversibly fixed, but presumably requires cell-cell interaction to become established.     

Developmental changes of the antenna and its neurons in the silkworm,Bombyx mori,with special regard to larval-pupal transformation

The larval antenna of Bombyx mori has 13 sensilla and about 52 sensory neurons in its distal portion. The axons form two nerve cords which unite in the cranial hemocoel to supply the brain as the olfactory nerve. The antennal imaginal disc, which is a thick pseudostratified epithelium continuous with the antennal epidermis, thickens markedly during the 5th instar by rapid cell proliferation. At the prepupal stage cell proliferation ceases and the disc everts to form a large pupal antenna. Simultaneously, an extensive cell rearrangement occurs in the antennal epidermis and the disc tissue becomes much thinner because of the abrupt expansion of antennal surface area. The two larval nerve cords thin down markedly by degeneration of axons, but they do not disintegrate totally even after the onset of pupation. The epidermis of the larval antenna forms the distal portion of the pupal antenna, while the imaginal disc forms the more basal portion. Development to the adult antenna occurs almost immediately after the onset of pupation; many adult neurons appear in the simple epidermis facing toward the thick outer side of the newly formed pupal cuticle. By 12 hours after the onset of pupation, these neurons align themselves in many transverse rows which are the first sign of the adult antennal configuration. Addition of these neuronal axons to the once-thinned nerve cords causes resumed thickening of the cords during the first 24 hours and thereafter. Differentiation of adult sensilla begins in the next 24 hours and is almost completed at the third day of pupation, which requires a total of 10 days.     

Microscopic analysis of mechanosensory system monitoring the dynamic claw actions in the tenebrionid beetle Zophobas atratus

Many insects have a pair of claws on each leg. The distribution of mechanoreceptors that monitor claw actions was examined in the tenebrionid beetle Zophobas atratus. Each claw has 25–45 campaniform sensilla (CS) that detect the claw’s deformation due to substrate engagement. Five CS clusters are observed around the end of the 5th tarsomere (Ta5) in a concave, socket-like structure. The 1st cluster, containing 2–5 CS, is embedded in the unguifer to which the claws are articulated. The symmetrical 2nd and 3rd clusters, each containing two CS, are located bilaterally in the ventrolateral grooves of the sidewall of the socket, into which the unguis retractor plate slides. The 4th and 5th clusters, containing 1–2 CS with two hair sensilla, are localized near the ventrolateral ridges of the socket into which the basal portion of the claw is pressed during maximal claw flexion. In addition, Ta5 has a chordotonal organ of six sensory cells to monitor claw extension. These results suggest that the mechanoreceptor system may directly monitor the precise mechanical states of individual claws and provide the central nervous system with the sensory information required for fine feedback control of movements of the pretarsus and other leg segments for locomotion and other purposes.     

Synaptic connections between sensory afferents and the common inhibitory motoneuron in crayfish

The sensory inputs to the common inhibitory motoneuron that innervates every leg muscle of the crayfish Procambarus clarkii (Girard) were analyzed by performing intracellular recordings from its neurite within the neuropil of the 5th thoracic ganglion. Two types of sensory inputs involved in locomotion were studied, those from a movement coding proprioceptor (the coxobasal chordotonal organ) and those from sensory neu rons coding contact forces exerted at the tip of the leg on the substrate (the dactyl sensory afferents). Sinusoidal movements applied to the chordotonal organ strand induced a stable biphasic response in the common inhibitory motoneuron that consisted of bursts of spikes during release and stretch of the strand, corresponding to raising and lowering of the leg, respectively. Using ramp movements imposed on the chordotonal strand, we demonstrated that only movement-coding chordotonal afferents produce excitatory post-synaptic potentials in the common inhibitory motoneuron; these connections are monosynaptic. Mechanical or electrical stimulation of the dactyl sensory afferents resulted in an increase in the tonic discharge of the common inhibitory motoneuron through polysynaptic excitatory pathways. These two types of sensory cues reinforce the central command of the common inhibitory motoneuron and contribute to enhancing its activity during leg movements, and thus facilitate the relaxation of tonic muscle fibres during locomotion.Abbreviations ADR anterior distal root - A Lev anterior levator nerve - CB coxo-basipodite joint - CBCO coxo-basal chordotonal organ - CI common inhibitory motoneuron - Dep depressor nerve - DSA dactyl sensory afferents - EPSP excitatory post-synaptic potential - IN interneuron - MN motoneuron - PDR posterior distal root - P Lev posterior levator nerve - Pro promotor nerve - Rem remotor nerve     

Factors influencing the developmental capacity of Galleria larval epidermis

The nature of the cuticle secreted by integument from a day-1 penultimate instar larval Galleria when cultured in vivo in the abdomen of a last instar larva varied with the age of the host. When placed in a day-5 last instar larva, the implanted integument secreted a pupal cuticle at the time the host metamorphosed and became a pupa. However, when placed in a day-7 last instar larva the implant, from the same stage donor, secreted a larval cuticle at the time the host pupated. Experimental studies involving implantation of the integument for a 24 hr period, into various developmental stages of normal and ligated last instar larvae, pupae, and pharate adults, prior to placing it in a day-7 last instar larva suggest that a non-hormonal factor present in day-4 and -5 last instar larvae is important to initiate pupal syntheses.     

Development of the sensory system in larvae and pupae of Chaoborus crystallinus (DeGeer, 1776; Diptera, Chaoboridae): sensory cells, nerves and ganglia of the tail region

Using various microscopical techniques, we have studied changes in the sensory equipment and architecture of the peripheral nervous system (PNS) around the first metamorphic molt from larva to pupa in the phantom midge Chaoborus. The transparent larvae and pupae of this dipteran with ancestral features allow us to investigate sensilla and their central projections from whole-mount preparations of complete groups of segments. Each sensillum on the posterior larval and pupal segments was identified using its external shape and position, and the morphology of the abdominal ganglia and segmental nerves was investigated. In addition, retrograde fills with the carbocyanine dye DiI were used to trace the axonal paths of most of the extero- and proprioreceptors. These findings were combined to produce maps of the sensory elements of larval and pupal abdomens that were analyzed at three levels: seriality (homonomy), ontogenetic changes of individual sensilla, and homology of the PNS between different species. Comparison of different segments shows for both stages that primarily there is a homonomous basic design of the PNS, but segment-specific modifications are evident in segments 8-10. Comparison of corresponding larval and pupal segments shows that many sensilla retain their internal structure and axonal projections. However, their external cuticular parts are changed in relation to the different life habits of larvae and pupae. Furthermore, some sensilla are completely reduced during the pupal molt, especially those of the tenth segment which appears as a distinct larval structure (caenogenesis). Comparison between species indicates that despite the varying types of sensilla their basic segmental arrangement and their axonal trajectories are conserved.     

Intersegmental interneurons serving larval and pupal mechanosensory reflexes in the moth Manduca sexta

1. Intersegmental interneurons (INs) that participate in the larval bending reflex and the pupal gin trap closure reflex were identified in the isolated ventral nerve cord of Manduca sexta. INs 305, 504, and 703 show qualitatively different responses in the pupa than in the larva to electrical stimulation of sensory neurons that are retained during the larval-pupal transition to serve both reflexes. Action potentials produced by current injected into the 3 interneurons excite motor neurons that are directly involved in the larval and pupal reflexes. The excitation of the motor neurons is not associated with EPSPs at a fixed latency following action potentials in the interneurons, and thus there do not seem to be direct synaptic connections between the interneurons and the motor neurons. 2. IN 305 (Fig. 2) has a lateral soma, processes in most of the dorsal neuropil ipsilateral to the soma, and a crossing neurite that gives rise to a single contralateral descending axon. IN 305 is excited by stimulation of the sensory nerve ipsilateral to its soma in the larva and the pupa. Stimulation of the sensory nerve contralateral to its soma produces an inhibitory response in the larva, but a mixed excitatory/inhibitory response to the identical stimulus in the pupa. 3. IN 504 (Fig. 3) has a lateral soma, processes throughout most of the neuropil ipsilateral to the soma, and a crossing neurite that bifurcates to give rise to a process extending to the caudal limit of the neuropil and an ascending axon. IN 504 is excited by stimulation of the sensory nerve ipsilateral to its soma in both larvae and pupae, while the response to stimulation of the sensory nerve contralateral to its soma is inhibitory in the larva but mixed (excitatory/inhibitory) in the pupa. 4. IN 703 has a large antero-lateral soma, a neurite that extends across to the contralateral side giving rise to processes located primarily dorsally in both ipsilateral and contralateral neuropils, and two axons that ascend and descend in the connectives contralateral to the soma (Fig. 4). IN 703 responds to stimulation of the sensory nerves on either side of the ganglion, but the form of the response changes during the larval-pupal transition. In the larva, the response consists of very phasic (0-2 spikes) excitation, but in the pupa there is a prolonged excitation that greatly outlasts the stimulus (Fig. 6).(ABSTRACT TRUNCATED AT 400 WORDS)     

Structure and sensory physiology of the leg scolopidial organs in Mantophasmatodea and their role in vibrational communication

Individuals of the insect order Mantophasmatodea use species-specific substrate vibration signals for mate recognition and location. In insects, substrate vibration is detected by mechanoreceptors in the legs, the scolopidial organs. In this study we give a first detailed overview of the structure, sensory sensitivity, and function of the leg scolopidial organs in two species of Mantophasmatodea and discuss their significance for vibrational communication. The structure and number of the organs are documented using light microscopy, SEM, and x-ray microtomography. Five scolopidial organs were found in each leg of male and female Mantophasmatodea: a femoral chordotonal organ, subgenual organ, tibial distal organ, tibio-tarsal scolopidial organ, and tarso-pretarsal scolopidial organ. The femoral chordotonal organ, consisting of two separate scoloparia, corresponds anatomically to the organ of a stonefly (Nemoura variegata) while the subgenual organ complex resembles the very sensitive organs of the cockroach Periplatena americana (Blattodea). Extracellular recordings from the leg nerve revealed that the leg scolopidial organs of Mantophasmatodea are very sensitive vibration receptors, especially for low-frequency vibrations. The dominant frequencies of the vibratory communication signals of Mantophasmatodea, acquired from an individual drumming on eight different substrates, fall in the frequency range where the scolopidial organs are most sensitive.     

Structure and development of antennae in a moth,Manduca sexta

The antenna of the moth, Manduca sexta, comprises two small basal segments and a long (2 cm) flagellum, which is divided into nearly 80 annuli. The annuli bear cuticular scales and small sensory organs, sensilla. A trachea, a blood vessel, and two nerve trunks run through the lumen of the antenna and into the head. Sensilla are arranged in an orderly pattern that is repeated on each flagellar annulus. Each flagellum bears about 10⁵ sensilla, which contain about 2.5 × 10⁵ primary sensory neurons. Clumps of undifferentiated cells (imaginal disks), present in the larva, form pupal antennae during the larval-pupal molt. During the subsequent metamorphic development of the adult, cell divisions, changes in cell shape, and cellular differentiation transform pupal into adult antennae. Sensilla and scales arise and differentiate in the antenna during metamorphosis; regions in which sensilla and scales will arise can be recognized before overt differentiation occurs. All of the flagellar annuli develop synchronously. The dense innervation and neuronal simplicity of antennal flagella, as well as their synchronous development at a late and accessible stage in the animal's life cycle, suit them for studies of neuronal differentiation.     

Range fractionation in the locust metathoracic femoral chordotonal organ

Summary Insect femoral chordotonal organs are internal proprioceptors which monitor the position and movements of the femur-tibia joint of the leg. The locust (Locusta migratoria) metathoracic femoral chordotonal organ is composed of approximately 100 neurones with a variety of response properties. In this study intracellular recordings were used to examine the range fractionation of phasic and tonic responses to tibial movements. Some neurones responded across the full range of leg angles, while others had restricted response ranges, and could therefore act as labeled lines. Neurones with maximal firing at mid-angles are described for the first time in a locust femoral chordotonal organ. Responses are discussed in terms of underlying structural constraints on signal transduction.Abbreviation (mt) FCO (metathoracic) femoral chordotonal organ     

Proliferation pattern of postembryonic neuroblasts in the brain of Drosophila melanogaster.

The spatio-temporal proliferation pattern of postembryonic neuroblasts in the central brain region of the supra-esophageal ganglion of Drosophila melanogaster was studied by labeling DNA replicating cells with 5-bromo-2'-deoxyuridine (BrdU). There are five proliferating neuroblasts per hemisphere in larvae just after hatching: one in the ventro-lateral, and the other four in the postero-dorsal region of the brain. Dividing neuroblasts increase during the late first-late second instar larval stages, reaching a plateau of about 85 neuroblasts per hemisphere. Most neuroblasts cease dividing 20-30 hr after puparium formation (APF), while only four in the postero-dorsal region continue making progenies until 85-90 hr APF. The four distinct neuroblasts proliferating in the early larval and late pupal stages are identical; they lie in the cortex above the calyces of the mushroom bodies (corpora pedunculata), proliferating over a period twice as long as that for the other neuroblasts. Their daughter neurons project into the mushroom body neuropile, and hence are likely to be the Kenyon cells. The cell-cycle period of the four neuroblasts (named mushroom body neuroblasts: MBNbs) is rather constant (1.1-1.5 hr) during the mid larval-early pupal stages and is longer before and after that. The total number of the MBNb progenies made throughout the embryonic and postembryonic development was estimated to be 800-1200 per hemisphere.     

Femoral chordotonal organ in the legs of an insect,Chrysoperla carnea(Neuroptera)

The femoral chordotonal organ (FCO) inChrysoperla carneais situated in the distal part of the femur and consists of two scoloparia, which are fused at their distal end. The distal scoloparium contains 17-20 scolopidia, and the proximal one six scolopidia. Each scolopidium consists of two sensory cells and three types of enveloping cells (glial, scolopale and attachment cell). The sensory cells of different scolopidia do not lie at the same level in the FCO. Therefore the attachment cells of different scolopidia have different lengths. In the FCO, three types of ciliary roots are found in different sensory cells. The dendrite of the sensory cell terminates in a distal process, which has the structure of a modified cilium (9x2+0). The very distal part of the cilium is surrounded by an extracellular electron dense material, the cap, and ends in a terminal dilation. The scolopale cell contains the electron dense scolopale rods, consisting of plentiful microtubules. In their middle third the scolopale rods are fused and form the scolopale. In the FCO septate junctions, desmosomes and hemidesmosomes are found.