Neurogenic and antineurogenic effects from modifications at the Notch locus

The best studied mutations at the Notch locus produce a neurogenic phenotype, with a massive overgrowth of the nervous system at the expense of epidermis. We report here that, in the development of the adult peripheral nervous system, the Abruptex alleles of Notch have the opposite phenotype, namely an underproduction of sensory organs or sensilla. This arises primarily not from an arrest of the lineages that produce sensilla, from the degeneration of sensillar cells, or from the transformation into neurons of cells that normally secrete the cuticular components of a sensillum (as can happen in Notch alleles). Rather, our evidence argues strongly that the sensillar mother cells never form. This implies that the Notch protein plays a role in the process that first generates a difference between sensillar mother cells and ordinary epidermal cells. The number of sensilla formed on the wing of flies carrying multiple doses of Notch+ is virtually the same as that of wild type, i.e. the Abruptex phenotype is not reproduced to any significant extent. This suggests that the single amino acid substitutions that occur in Abruptex mutants confer on the protein some functionally distinctive feature, possibly more powerful intermolecular binding or altered stability.     

Diverse Filters to Sense: Great Variability of Antennal Morphology and Sensillar Equipment in Gall-Wasps (Hymenoptera: Cynipidae)

Comparative studies on antennal sensillar equipment in insects are largely lacking, despite their potential to provide insights into both ecological and phylogenetic relationships. Here we present the first comparative study on antennal morphology and sensillar equipment in female Cynipoidea (Hymenoptera), a large and diverse group of wasps, with special reference to the so-called gall-wasps (Cynipidae). A SEM analysis was conducted on 51 species from all extant cynipoid families and all cynipid tribes, and spanning all known life-histories in the superfamily (gall-inducers, gall-inquilines, and non-gall associated parasitoids). The generally filiform, rarely clavate, antennal flagellum of Cynipoidea harbours overall 12 types of sensilla: s. placoidea (SP), two types of s. coeloconica (SCo-A, SCo-B), s. campaniformia (SCa), s. basiconica (SB), five types of s. trichoidea (ST-A, B, C, D, E), large disc sensilla (LDS) and large volcano sensilla (LVS). We found a great variability in sensillar equipment both among and within lineages. However, few traits seem to be unique to specific cynipid tribes. Paraulacini are, for example, distinctive in having apical LVS; Pediaspidini are unique in having ≥3 rows of SP, each including 6–8 sensilla per flagellomere, and up to 7 SCo-A in a single flagellomere; Eschatocerini have by far the largest SCo-A. Overall, our data preliminarily suggest a tendency to decreased numbers of SP rows per flagellomere and increased relative size of SCo-A during cynipoid evolution. Furthermore, SCo-A size seems to be higher in species inducing galls in trees than in those inducing galls in herbs. On the other hand, ST seem to be more abundant on the antennae of herb-gallers than wood-gallers. The antennal morphology and sensillar equipment in Cynipoidea are the complex results of different interacting pressures that need further investigations to be clarified.     

Anatomical pathways connecting lip sensory structures and central nervous system in hirudinid leeches visualized by carbocyanine dyes and laser scanning confocal microscopy

Chemoreception inHirudo medicinalis is thought to be mediated by ciliated cells grouped in sensory structures, the sensilla, arranged in bands on the animal's dorsal lip (Elliott, 1986; Zipseret al., 1994). Furthermore, chemical and/or thermal stimulation of the dorsal lip in reduced preparations evokes changes in the electrical activity of the cephalic nerves that connect the head with the central nervous system. However, the complete trajectory by which the sensory afferents teach the cerebral ganglia has not been demonstrated anatomically. In this study, we traced these pathways following retrograde and/or anterograde transport of carbocyanine dyes (DiI, DiA and DiD) in the cephalic nerves ofHirudo medicinalis and a closely related species,Macrobdella decora. While information regardingMacrobdella's chemoreception is scarce, the two species show some differences with regard to their chemical preferences. Dyes were applied to the sensillar structures along the dorsal lip, or to the cut ends of individual cephalic nerves in fixed preparations that included the lip and attached nerves with or without the head ganglia. After a two week incubation, specimens were mounted and imaged using a confocal microscope.The results show that the axons of the sensory neurons in the sensilla project through the four pairs of cephalic nerves. The sensillar projections are however more numerous in the dorsal nerves than they are in the ventral ones. In addition, the organization of the sensillar bands, the morphology of the pathways and the sensory structures themselves appear to be identical forHirudo andMacrobdella and therefore the behavioral differences in response to appetitive stimuli cannot be readily explained by differences in morphology.     

Functional anatomy of sensory structures on the antennae of Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae)

The ultrastructure and distribution of sensilla on the antennae of the cabbage stem flea beetle, Psylliodes chrysocephala, were investigated using scanning and transmission electron microscopy techniques. Eight different sensillar types were distinguished. These were; hair plate sensilla, sensilla chaetica, three types of sensilla trichodea, sensilla basiconica, grooved peg sensilla and styloconic sensilla. The sensilla chaetica are known to be gustatory receptors. Ultrastructure indicates that the hair plate sensilla and sensilla trichodea type one are probably mechanoreceptors, whilst the sensilla styloconica are probably thermo-hygro receptors. These thermo-hygroreceptors are unusual in that they are innervated by two sensory cells (one hygroreceptor and one thermoreceptor) rather than the more usual triad. The remaining four sensillar types all have a porous hair shaft, indicating an olfactory role. One of these (the grooved peg sensillum) may also have a thermoreceptive function. No sexual dimorphism was found in the structure, number or distribution of the antennal sensilla.     

Electrophysiological evidence of synaptic interactions within chemosensory sensilla of scorpion pectines

The pectines of scorpions are ventral bilateral appendages supporting 10⁴–10⁵ chemosensory sensilla called pegs. Each peg contains 10–18 sensory neurons, some of which show ultrastructural evidence of axo-axonic synapses with other sensory neurons in the same sensillum. In extracellular recordings from single-peg sensilla, individual sensory units can be distinguished by impulse waveform and firing frequency. Cross-correlation analysis of impulse activity showed that at least two of these units, types `A1' and `A2', are inhibited during the 100-ms period immediately following activity of a third unit, type `B'. This interaction between sensory units in a single sensillum also occurs in surgically isolated pectines, indicating that it does not involve efferent feedback from the central nervous system. Other sensillar neurons appear to have excitatory interactions. Thus, in scorpion pectine, chemosensory information undergoes some form of processing within individual sensilla prior to its relay to the CNS, making this an unusually accessible preparation for study of first-order chemosensory processing events. Accepted: 12 April 1997     

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     

Fine structure and distribution of antennal sensilla of the desert locust, Schistocerca gregaria (Orthoptera: Acrididae)

The fine structure and distribution of various types of antennal sensilla in three nymphal stages and in adults of both solitary-reared (solitary) and crowd-reared (gregarious) phases of the desert locust, Schistocerca gregaria, were investigated by scanning and transmission electron microscopy. Four types of sensilla were identified: sensilla basiconica, s. trichodea, s. coeloconica and s. chaetica. S. basiconica contain up to 50 sensory neurons, each of which displays massive dendritic branching. The sensillar wall is penetrated by a large number of pores. In contrast, s. trichodea contain one to three sensory neurons that branch to give five or six dendrites in the sensillar lumen; the sensillum wall is penetrated by relatively few pores. The s. coeloconica are situated in spherical cuticular pits on the antennal surface. The s. coeloconica are of two types: one type contains one to three sensory neurons with double sensillar walls penetrated by slit-like pores, whereas the second type contains four sensory neurons with non-porous double sensillar walls. The s. chaetica have a flexible socket and a thick non-porous sensillum wall and contain four sensory neurons that send unbranched dendrites to a terminal pore. A fifth sensory neuron of the s. chaetica terminates in a tubular body at the base of the hair. S. basiconica and coeloconica are normally distributed over the entire antennal flagellum, with a concentration in the middle segments; s. trichodea have three areas of concentration on the 5th, 10th and 14th flagellar segments. Sensilla chaetica are most abundant on the terminal segment. Locusts raised in solitary conditions have more olfactory sensilla (s. basiconica and s. coeloconica) than crowd-reared locusts. The difference in sensillar numbers is more evident in adults than in nymphs. These results suggest that differences in the odour-mediated behaviour of nymphs and adults, and between the phases of S. gregaria, may be attributable to differences at the sensory input level.     

Fine structure of antennal sensilla of male Aedes aegypti (L.)

The terminal two antennal segments of male Aedes aegypti bear the same variety of sensillar types as the female's antenna, namely, sensilla chaetica, sensilla coeloconica, sensilla ampullacea, grooved pegs, and four types of sensilla trichodea: long and short, pointed-tipped trichodea and blunt-tipped types I and II. Each type of sensillum has a similar fine structure in both sexes. Of the 514 neurones which innervate these sensilla in the male, 91% are olfactory receptors, 7% mechanoreceptors, and 2% thermoreceptors. The total number of neurones in the male is about four times fewer than in the female, but the ratio of those responding to the various stimuli is similar.The sensilla studied herein probably mediate stimuli involved in location of suitable resting sites and nectar meals. In addition they are apparently involved in location of vertebrates as recent studies indicate that certain male mosquitoes are attracted to hosts to bring them into the proximity of the females for mating. This host finding behaviour of males would explain why they have the same sprectrum of sensillar types as do females.     

Physiology and glomerular projections of olfactory receptor neurons on the antenna of female Heliothis virescens (Lepidoptera: Noctuidae) responsive to behaviorally relevant odors

The neurophysiology and antennal lobe projections of olfactory receptor neurons housed within short trichoid sensilla of female Heliothis virescens F. (Noctuidae: Lepidoptera) were investigated using a combination of cut-sensillum recording and cobalt-lysine staining techniques. Behaviorally relevant odorants, including intra- and inter-sexual pheromonal compounds, plant and floral volatiles were selected for testing sensillar responses. A total of 184 sensilla were categorized into 25 possible sensillar types based on odor responses and sensitivity. Sensilla exhibited both narrow (responding to few odors) and broad (responding to many odors) response spectra. Sixty-six percent of the sensilla identified were stimulated by conspecific odors; in particular, major components of the male H. virescens hairpencil pheromone (hexadecanyl acetate and octadecanyl acetate) and a minor component of the female sex pheromone, (Z)-9-tetradecenal. Following characterization of the responses, olfactory receptor neurons within individual sensilla were stained with cobalt lysine (N=39) and traced to individual glomeruli in the antennal lobe. Olfactory receptor neurons with specific responses to (Z)-9-tetradecenal, a female H. virescens sex pheromone component, projected to the female-specific central large female glomerulus (cLFG) and other glomeruli. Terminal arborizations from sensillar types containing olfactory receptor neurons sensitive to male hairpencil components and plant volatiles were also localized to distinct glomerular locations. This information provides insight into the representation of behaviorally relevant odorants in the female moth olfactory system. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

The development of normal and ectopic sensilla in the wings of hairy and Hairy wing mutants of Drosophila.

We have utilized enhancer trap markers to follow the development of ectopic sensillar precursors in the wings of Drosophila induced by the mutations hairy and Hairy wing. Normal sensilla are still present in these mutations, and can be distinguished from ectopic sensilla based upon both the position and the timing of their development. This correlates well with the development of ectopic achaete expression in these mutations: such staining is detected only after the appearance of normal staining. Thus, neither mutation appears to alter the specification of proneural clusters in the wing, as identified with anti-achaete, or the specification of sensillar precursors within these clusters. Rather, both act to induce the formation of a temporally and spatially distinct phase of sensillar development.     

Sparse sensillar array on Trioza apicalis (Homoptera, Triozidae) antennae-an adaptation to high stimulus levels?

To investigate the morphological basis for olfactory reception in the carrot psyllid (Trioza apicalis) we used scanning and transmission electron microscopy. Our study reveals a very sparse sensillar setup. We identify and describe several different types of single-walled sensilla likely to have an olfactory function, as well as mechanosensory hairs and intracuticular sensilla. A T. apicalis antenna is about 0.6 mm long and has 10 segments. Apically on the flagellum there are two conspicuous multi-porous single-walled bristles. There are six cuticular cavities on the flagellum; two smaller on the apical flagellomere, and four larger located on the lateral side of the antenna on flagellomeres 2, 4, 6 and 7. Each cavity contains two sensilla and there are three varieties of cavity sensilla. Mechano- and chemosensory hairs appear in low numbers on all segments but the third. Carrot psyllids most likely use olfactory cues to locate their rather strongly smelling host plants, and we argue that the low number of olfactory sensilla found in this insect may accommodate high concentrations of odour stimuli. There is no sexual dimorphism in the sensillar setup. In concordance with this, no sex pheromones have been described in the Psylloidea so far.     

Structure and distribution of antennal sensilla in Oranmorpha guerinii (Gervais, 1837) (Diplopoda,Polydesmida)

Detailed information on sensory organs of Diplopoda especially on antennal sensilla are still sparse and fragmentary. The present study on the antennae of Oranmorpha guerinii (Polydesmida, Paradoxosomatidae) utilizing scanning electron microscopy revealed the presence of six sensillar types: (1) apical cones, (2) sensilla trichodea, (3) sensilla microtrichodea, (4) sensilla chaetica, (5) sensilla basiconica bacilliformia, and (6) sensilla basiconica spiniformia. External structure and distribution of cuticular antennal sensilla are compared with data from other diplopod species. We moreover discuss possible functions of antennal sensilla in millipedes.     

Sensory Organs in Ips typographus (Insecta: Coleoptera) Fine structure of the sensilla of the maxillary and labial palps*

The labial and maxillary palps of the bark beetle, Ips typographus, possess a diversified array of sensilla. There are four types of sensilla possessing a single tubular body indicating a mechanoreceptive function. The variation of the associated cuticular structures of these sensillar types ranges from long bristles to cavities within the cuticle. Terminal pore sensilla with a supposed mechanosensory/gustatory function and single-walled presumably chemoreceptive sensilla are found on the apical part of the terminal palp segments. A poreless sensillar type is found on the lateral side of the terminal segment of the maxillary palp. The functional capabilities of this sensillar type are presently unknown.     

木瓜榕传粉榕小蜂雌蜂触角感器的分布和超微形态

为探索木瓜榕传粉榕小蜂Ceratosolen emarginatus寄主定位机制, 应用扫描电镜和透射电镜观察了其雌蜂触角感器的类型、 分布和超微形态。结果显示： 木瓜榕传粉榕小蜂雌蜂触角呈膝状, 由柄节、 梗节和11个鞭小节组成的鞭节组成, 第3鞭小节着生一坚固的脊骨突。触角上共发现7类11种感器, 分别为毛形感器、 刺形感器、 锥形感器（包括单孔形和多孔形）、 多孔板形感器（包括长形和圆形）、 腔锥形感器（分为3种类型）、 栓锥形乳突状感器、 角锥形感器。结合表面特征和内部结构, 锥形感器、 多孔板形感器、 栓锥形乳突状感器和腔锥形感器类型1为有孔型, 为化学感器; 无孔型的毛形感器和刺形感器是机械感器, 但腔锥形感器类型2和3为本体感器或湿热压力感器; 最为特异的为角锥形感器, 其厚壁无孔, 逆向触角主轴, 为该科昆虫所特有, 推测可防止传粉榕小蜂进入榕果时滑脱。这些结果将有助于理解木瓜榕传粉榕小蜂特异性行为, 并为下一步开展电生理研究, 揭示其信息化学物质利用和分配模式奠定基础。     

Specific pathway selection by the early projections of individual peripheral sensory neurons in the embryonic medicinal leech

In leech, the central annulus of each midbody segment possesses seven pairs of sensilla, which are mixed clusters of primary peripheral sensory neurons that extend their axons into the CNS where they segregate into distinct fascicles. Pathway selection by individual afferent growth cones of sensillar neurons was examined by double labeling using intracellular dye-filling with anitobody labeling in early Hirudo medicinalis embryos. The monoclonal antibody Lan3–2 was used because sensillar neuronal tracts are specifically labeled by this antibody. Examining 68 individually filled neurons we found that sensillar neuron growth cones bifurcate within the CNS, that they project long filopodia capable to sampling the local environment, and that all of them appeared to choose a single particular CNS fascicle without apparent retraction or realignment of growth cones. Furthermore, each side of the bifurcating afferent growth cones always chose the same fascicle, implying a specific choice of a distinct labeled pathway. By dye-filling individual central neurons (P-cells), we show that there are centrally projecting axons present at the time sensillar afferents enter the ganglionic primordia and select a particular fascicle, and we confirm that at least the dorsal peripheral nerve is likely to be pioneered by central neurons, not by the peripheral afferent. In the sensillum studied here, we sound examples of sensory neurons extending axons into one of all the avilable fascicles. Thus, an individual embryonic sensillum possesses a heterogeneous population of afferents with respect to the central fascicle chosen. This is consistent with the idea that segregation into distinct axon fascicles may be based upon functional differences between individual afferent neurons. Our findings argue strongly in favor of specific pathway selection by afferents in this system and are consistent with previous suggestions that there exists a hierarchy of cues, including surface glycoconjugates that mediate navigation of the sensillar growth cones and the fasciculation of their axons. 1994 John Wiley & Sons, Inc.     

Re-Classification of Drosophila melanogaster Trichoid and Intermediate Sensilla Using Fluorescence-Guided Single Sensillum Recording

Drosophila olfactory receptor neurons are found within specialized sensory hairs on antenna and maxillary palps. The linking of odorant-induced responses to olfactory neuron activities is often accomplished via Single Sensillum Recordings (SSR), in which an electrode inserted into a single sensory hair records the neuronal activities of all the neurons housed in that sensillum. The identification of the recorded sensillum requires matching the neuronal responses with known odor-response profiles. To record from specific sensilla, or to systematically screen all sensillar types, requires repetitive and semi-random SSR experiments. Here, we validate an approach in which the GAL4/UAS binary expression system is used for targeting specific sensilla for recordings. We take advantage of available OrX-Gal4 lines, in combination with recently generated strong membrane targeted GFP reporters, to guide electrophysiological recordings to GFP-labeled sensilla. We validate a full set of reagents that can be used to rapidly screen the odor-response profiles of all basiconic, intermediate, and trichoid sensilla. Fluorescence-guided SSR further revealed that two antennal trichoid sensilla types should be re-classified as intermediate sensilla. This approach provides a simple and practical addition to a proven method for investigating olfactory neurons, and can be extended by the addition of UAS-geneX effectors for gain-of-function or loss-of-function studies.     

The cercal sensilla of the blowfly Lucilia cuprina. II. Structure of the enveloping cells and the basal regions of the sensory dendrites

The gustatory, olfactory, touch and stress receptors on the cerci of Lucilia cuprina Wied. (Diptera: Calliphoridae) have either two or three enveloping cells. The gustatory and olfactory sensilla have three enveloping cells: a tormogen, trichogen and thecogen cell. The tormogen and trichogen cells contribute to a sub-cuticular sensillar lumen which divides into two lobes basally. The thecogen cell forms a lumen around the dendrites. Distally the dendrites lie in the contents of the thecogen lumen within the dendritic sheath. Proximally the dendrites embed in the thecogen cell which has an expanded, microlamellate lumen basally. The sensillar lumen of the mechanosensory (trichoid mechanoreceptors and campaniform) sensilla is formed by a single enveloping cell: the presumptive tormogen cell. In trichoid mechanoreceptors the thecogen lumen is restricted to the region of the transitional region of the dendrite whereas the thecogen lumen of campaniform sensilla extends proximally although it is not as well-developed as that of the chemoreceptive sensilla. The dendrites of all sensillum types on the cerci have a granular body in the transitional region: a situation which has not been previously reported in chemoreceptive sensilla although common in the mechanoreceptors of Calliphoridae and Sarcophagidae.     

Flagellar sensilla of the eusocial gall-inducing thrips Kladothrips intermedius and its kleptoparasite, Koptothrips dyskritus (Thysanoptera: Phlaeothripinae)

Insect antennal flagella host a multitude of sensory organs fulfilling different functions. Chemoreception, for example, is essential for insects in many contexts. Both olfaction and contact chemoreception are involved in host-plant selection, as well as in the integrity of insect societies, especially for nestmate recognition. Kladothrips intermedius is a eusocial gall-inducing thrips with two castes: dispersers and soldiers. Koptothrips dyskritus is a specialist in invading Kl. intermedius galls, killing the occupants, and thereby gaining the food and shelter offered by galls. In this study, we compared the morphology and ultrastructure of the flagellar sensilla of Kl. intermedius and Ko. dyskritus via scanning and transmission electron microscopy in order to facilitate future investigations of their sensory ecology, with an emphasis on chemical ecology. The two species show a very similar sensillar array. There are a few mechanosensory trichoid and a second type of mechanosensory sensilla, thermo-hygroreceptive sensilla, olfactory single-walled basiconic and double-walled coeloconic sensilla as well as contact chemoreceptive chaetic sensilla. The latter are sexually dimorphic in Kl. intermedius. Dispersers and soldiers of Kl. intermedius do not present noteworthy morphological differences, but the ultrastructural investigations revealed that soldiers have fewer ORNs, possibly an adaptation to their gall-cloistered lifestyle.     

Neurons discovered in male Helicoverpa zea antennae that correlate with pheromone-mediated attraction and interspecific antagonism

Responses of single receptor neurons in the antennae of male Helicoverpa zea to sex pheromone components and to behavioral antagonists were recorded using a cut-sensillum extracellular recording technique. Three types of sensilla were identified from sampling 325 male-specific sensilla trichodea located at the lateral edge of antennomeres. The majority of these sensilla (71%) contained a receptor neuron tuned to the principal sex pheromone component (Z)-11-hexadecenal. A second sensillar type (10%) contained a receptor neuron that responded only to (Z)-9-tetradecenal. A third sensillar type (19%) contained a large-spiking neuron tuned to the secondary pheromone component (Z)-9-hexadecenal, but this neuron also could be stimulated to equivalent spike frequencies by the same emitted amounts of (Z)-9-tetradecenal. A smaller-spiking neuron in this sensillar type responded to two compounds known to act only as behavioral antagonists, (Z)-11-hexadecen-1-ol and (Z)-11-hexadecenyl acetate, and to (Z)-9-tetradecenal. Cross-adaptation studies confirmed the presence of one large- and one small-spiking neuron in the third sensillar type. Dose-response studies correlated to collected stimuli amounts showed that the large-spiking neuron in the third sensillar type was equally tuned to (Z)-9-hexadecenal and (Z)-9-tetradecenal, whereas the smaller-spiking neuron was far more sensitive to (Z)-11-hexadecen-1-ol and to (Z)-11-hexadecenyl acetate than to (Z)-9-tetradecenal. Accepted: 29 September 1997