Maxillary palp glomeruli and ipsilateral projections in the antennal lobe of<Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

The antennal lobe was examined by Golgi-silver impregnation to differentiate the glomeruli depending on the source and types of inputs. Thirty-five of the 43 ‘identified’ olfactory glomeruli were Golgi-silver impregnated in the present study. Seven glomeruli compared to three, reported previously, were found to be targets of maxillary palp chemosensory neurons. These include glomeruli VA3, VC2, VM5, VA7m/VA7l of the ventral antennal lobe and DC2, DC3, DM5 of the dorsal antennal lobe. The number of glomeruli receiving the maxillary palp sensory projections tallies with the number ofDrosophila olfactory receptors (seven) reported to be expressed exclusively in the maxillary palp. Twenty-eight Golgi-impregnated glomeruli were found to receive input from the antennal nerve. The ratio of glomeruli serving the maxillary palp to those serving the antenna (∼1:5) matches with the ratio ofDrosophila olfactory receptors expressed in these two olfactory organs respectively. In addition to glomerulus V, glomeruli VP1-3, VL1, VL2a/2p and VC3m/3l were found to receive ipsilateral projections. Thus, additional ipsilateral glomeruli have been identified.     

Olfactory physiology in the Drosophila antenna and maxillary palp: acj6 Distinguishes two classes of odorant pathways

This article provides characterization of the electrical response to odorants in the Drosophila antenna and provides physiological evidence that a second organ, the maxillary palp, also has olfactory function in Drosophila. The acj6 mutation, previously isolated by virtue of defective olfactory behavior, affects olfactory physiology in the maxillary palp as well as in the antenna. Interestingly, abnormal chemosensory jump 6 (acj6) reduces response in the maxillary palp to all odorants tested except benzaldehyde (odor of almond), as if response to benzaldehyde is mediated through a different type of odorant pathway from the other odorants. In other experiments, different parts of the antenna are shown to differ with respect to odorant sensitivity. Evidence is also provided that antennal response to odorants varies with age, and that odorants differ in their age dependence. © 1992 John Wiley & Sons, Inc.     

Development and organization of the Drosophila olfactory system: An analysis using enhancer traps

Drosophila uses different olfactory organs at different developmental stages. The larval and adult olfactory organs are morphologically dissimilar and have different developmental origins: the antenno-maxillary complex (AMC), which houses the larval olfactory organ, is histolyzed during metamorphosis; the third antennal segment—the principal adult olfactory organ—derives from an imaginal disc. A screen for genes expressed in both larval and adult olfactory organs, but in relatively few other tissues, has been carried out. Seven enhancer trap lines showing reporter gene expression in both the larval AMC and in certain subsets of the adult antenna are described. The antennal staining pattern of one line shows a striking change over the first few days of adult life, with a time course comparable to that of the development of sexual maturity. A pronounced sexual dimorphism in antennal staining pattern is seen in another line. Some staining patterns resemble the patterns of certain classes of antennal sensilla; others show expression restricted to only a small number of cells. Some lines also show expression associated with other chemosensory organs at either the larval or adult stage, including the maxillary palps, labellum, and anterior wing margin. One line, which also shows staining in the male reproductive tract, is male sterile. The significance of these results is considered in terms of (1) the molecular organization of the olfactory system; (2) the recruitment of olfactory genes for use in two developmental contexts; (3) the sharing of genes among different sensory modalities; (4) the role of olfaction in sexual behavior; and (5) posteclosional changes in the olfactory system. © 1992 John Wiley & Sons, Inc.     

Central projections of olfactory receptor neurons from single antennal and palpal sensilla in mosquitoes

In insects, olfactory receptor neurons (ORNs) are located in cuticular sensilla, that are present on the antennae and on the maxillary palps. Their axons project into spherical neuropil, the glomeruli, which are characteristic structures in the primary olfactory center throughout the animal kingdom. ORNs in insects often respond specifically to single odor compounds. The projection patterns of these neurons within the primary olfactory center, the antennal lobe, are, however, largely unknown.We developed a method to stain central projections of intact receptor neurons known to respond to host odor compounds in the malaria mosquito, Anopheles gambiae. Terminal arborizations from ORNs from antennal sensilla had only a few branches apparently restricted to a single glomerulus. Axonal arborizations of the different neurons originating from the same sensillum did not overlap.ORNs originating from maxillary palp sensilla all projected into a dorso-medial area in both the ipsi- and contralateral antennal lobe, which received in no case axon terminals from antennal receptor neurons. Staining of maxillary palp receptor neurons in a second mosquito species (Aedes aegypti) revealed unilateral arborizations in an area at a similar position as in An. gambiae.     

Multimodal chemosensory integration through the maxillary palp in Drosophila

Drosophila melanogaster has an olfactory organ called the maxillary palp. It is smaller and numerically simpler than the antenna, and its specific role in behavior has long been unclear. Because of its proximity to the mouthparts, I explored the possibility of a role in taste behavior. Maxillary palp was tuned to mediate odor-induced taste enhancement: a sucrose solution was more appealing when simultaneously presented with the odorant 4-methylphenol. The same result was observed with other odors that stimulate other types of olfactory receptor neuron in the maxillary palp. When an antennal olfactory receptor was genetically introduced in the maxillary palp, the fly interpreted a new odor as a sweet-enhancing smell. These results all point to taste enhancement as a function of the maxillary palp. It also opens the door for studying integration of multiple senses in a model organism.     

Olfactory physiology in the Drosophila antenna and maxillary palp: acj6 distinguishes two classes of odorant pathways.

This article provides characterization of the electrical response to odorants in the Drosophila antenna and provides physiological evidence that a second organ, the maxillary palp, also has olfactory function in Drosophila. The acj6 mutation, previously isolated by virtue of defective olfactory behavior, affects olfactory physiology in the maxillary palp as well as in the antenna. Interestingly, abnormal chemosensory jump 6 (acj6) reduces response in the maxillary palp to all odorants tested except benzaldehyde (odor of almond), as if response to benzaldehyde is mediated through a different type of odorant pathway from the other odorants. In other experiments, different parts of the antenna are shown to differ with respect to odorant sensitivity. Evidence is also provided that antennal response to odorants varies with age, and that odorants differ in their age dependence.     

Temporal target restriction of olfactory receptor neurons by Semaphorin-1a/PlexinA-mediated axon-axon interactions

Axon-axon interactions have been implicated in neural circuit assembly, but the underlying mechanisms are poorly understood. Here, we show that in the Drosophila antennal lobe, early-arriving axons of olfactory receptor neurons (ORNs) from the antenna are required for the proper targeting of late-arriving ORN axons from the maxillary palp (MP). Semaphorin-1a is required for targeting of all MP but only half of the antennal ORN classes examined. Sema-1a acts nonautonomously to control ORN axon-axon interactions, in contrast to its cell-autonomous function in olfactory projection neurons. Phenotypic and genetic interaction analyses implicate PlexinA as the Sema-1a receptor in ORN targeting. Sema-1a on antennal ORN axons is required for correct targeting of MP axons within the antennal lobe, while interactions amongst MP axons facilitate their entry into the antennal lobe. We propose that Sema-1a/PlexinA-mediated repulsion provides a mechanism by which early-arriving ORN axons constrain the target choices of late-arriving axons.     

Development and organization of the Drosophila olfactory system: an analysis using enhancer traps.

Drosophila uses different olfactory organs at different developmental stages. The larval and adult olfactory organs are morphologically dissimilar and have different developmental origins: the antenno-maxillary complex (AMC), which houses the larval olfactory organ, is histolyzed during metamorphosis; the third antennal segment--the principal adult olfactory organ--derives from an imaginal disc. A screen for genes expressed in both larval and adult olfactory organs, but in relatively few other tissues, has been carried out. Seven enhancer trap lines showing reporter gene expression in both the larval AMC and in certain subsets of the adult antenna are described. The antennal staining pattern of one line shows a striking change over the first few days of adult life, with a time course comparable to that of the development of sexual maturity. A pronounced sexual dimorphism in antennal staining pattern is seen in another line. Some staining patterns resemble the patterns of certain classes of antennal sensilla; others show expression restricted to only a small number of cells. Some lines also show expression associated with other chemosensory organs at either the larval or adult stage, including the maxillary palps, labellum, and anterior wing margin. One line, which also shows staining in the male reproductive tract, is male sterile. The significance of these results is considered in terms of (1) the molecular organization of the olfactory system; (2) the recruitment of olfactory genes for use in two developmental contexts; (3) the sharing of genes among different sensory modalities; (4) the role of olfaction in sexual behavior; and (5) posteclosional changes in the olfactory system.     

Olfactory physiology in the Drosophila maxillary palp requires the visual system gene rdgB

We describe the kinetics of odorant response in the maxillary palp of Drosophila, and show that the rate of recovery from odorant stimulation is affected by mutation of the rdgB (retinal degeneration B) gene. We use immunocytochemistry to confirm that the rdgB gene product is expressed in the maxillary palp. rdgB has recently been shown to encode a protein with Ca²⁺-binding sites and sequence similarity to rat brain phosphatidylinositol transfer protein; it is located near the rhabdomeric membranes in photoreceptor cells, where it has been suggested to play a role in membrane transport. The delay in recovery kinetics that we observe in olfactory tissue may reflect a defect in membrane restoration at the conclusion of the olfactory transduction cascade. The use of common molecules in the physiology of two olfactory organs, and in both visual and olfactory physiology, is discussed.Abbreviations EAG electroantennogram - EPG electropalpogram - ERG electroretinogram - norpA no receptor potential A - PBS phosphate buffered saline - rdgB retinal degeneration B - PI phosphatidylinositol     

Timing of Wingless signalling distinguishes maxillary and antennal identities in Drosophila melanogaster

The Drosophila adult head mostly derives from the composite eye-antenna imaginal disc. The antennal disc gives rise to two adult olfactory organs: the antennae and maxillary palps. Here, we have analysed the regional specification of the maxillary palp within the antennal disc. We found that a maxillary field, defined by expression of the Hox gene Deformed, is established at about the same time as the eye and antennal fields during the L2 larval stage. The genetic program leading to maxillary regionalisation and identity is very similar to the antennal one, but is distinguished primarily by delayed prepupal expression of the ventral morphogen Wingless (Wg). We find that precociously expressing Wg in the larval maxillary field suffices to transform it towards antennal identity, whereas overexpressing Wg later in prepupae does not. These results thus indicate that temporal regulation of Wg is decisive to distinguishing maxillary and antennal organs. Wg normally acts upstream of the antennal selector spineless (ss) in maxillary development. However, mis-expression of Ss can prematurely activate wg via a positive-feedback loop leading to a maxillary-to-antenna transformation. We characterised: (1) the action of Wg through ss selector function in distinguishing maxillary from antenna; and (2) its direct contribution to identity choice.     

An accessory olfactory pathway in Lepidoptera: the labial pit organ and its central projections in Manduca sexta and certain other sphinx moths and silk moths

Summary In the hawkmoth, Manduca sexta, the third segment of each labial palp contains a pit, which houses a densely packed array of sensilla. We have named this structure the labial pit organ (LPO). The sensilla within the pit are typical of olfactory receptors, characterized by a grooved surface, wall pores, and pore tubules. Axons arising from receptor cells that innervate these sensilla project bilaterally to a single glomerulus in each antennal lobe. We have compared this central projection with that in three other species of Manduca (M. quinquemaculata, M. dilucida, and M. lanuginosa) and in the silkmoths Antheraea polyphemus and Bombyx mori. A bilateral projection to a single glomerulus in each antennal lobe is present in all cases. We suggest that the LPO serves as an accessory olfactory organ in adult Lepidoptera.     

Atlas of olfactory organs of Drosophila melanogaster: 1. Types,external organization,innervation and distribution of olfactory sensilla

The third antennal segment (funiculus) and the maxillary palp are the main and accessory olfactory sense organs of Drosophila melanogaster. Cryofixed antennae and palps revealed a superior preservation of the sensory dendrites and other cellular details as compared to conventional chemical fixation. Extensive cross-section series through funiculus and palp were studied in order to obtain as complete an evaluation as possible of the sensillar complement on these appendages. About 75% of all sensilla on the male and female funiculus were individually studied and their position on the antennal surface mapped. Dimensions of the cuticular apparatus of the various types of sensilla are provided as well as the number of innervating receptor neurons. Particular attention has been paid to the cuticular pores important for stimulus transport and to the sensory dendrites. On the funiculus surface, all sensilla have multiple wall pores: sensilla (s.) trichodea and s. basiconica are single-walled, s. coeloconica are double-walled. The distribution of s. trichodea and s. basiconica follows opposing gradients along a diagonal axis parallel to the axis of the arista from proximo-medial to disto-lateral. In this disto-lateral direction the density of s. trichodea increases while that of the s. basiconica decreases. S. trichodea occur in three subtypes with one, two or three receptor neurons. Basiconic sensilla can be subdivided into three subtypes of large s. basiconica (with two or four receptor neurons), three subtypes of thin s. basiconica (with mostly two, rarely four neurons), and one subtype of small s. basiconica with two receptor neurons. Large s. basiconica occur only in the most proximal region (the ‘LB-zone’); thin s. basiconica are most common in a belt that borders the LB-zone distally, while small s. basiconica are most numerous even further distally along the mentioned diagonal axis in between the s. trichodea. S. intermedia are single-walled, multiporous sensilla which combine features of s. trichodea and s. basiconica; they are found in two subtypes with two or three receptor neurons, in the same region where s. trichodea abound. The s. coeloconica are irregularly distributed over the funicular surface, and occur in two subtypes with two or three receptor neurons. Sexual dimorphism on the antenna is moderate, the female funiculus is a bit longer and carries a larger number of small s. basiconica and large s. basiconica of the LB-I subtype; the male funiculus, however, has more s. trichodea than the female. On the maxillary palp, besides mechanoreceptive s. chaetica, there are only s. basiconica with two receptor neurons. According to the fine structure of their sensory dendrites, three subtypes can be discriminated which are distributed in a random pattern. The functional significance of the described structures and distribution awaits future immunocytochemical and electrophysiological experiments.     

Odorant response of individual sensilla on theDrosophila antenna

We have documented odor responses of all morphological classes of sensilla on the surface of theDrosophila antenna: sensilla basiconica, sensilla trichodea, and sensilla coeloconica. Both subtypes of s. basiconica, large and small, respond to odors. S. trichodea fall into different functional types. Type 1 appears narrowly tuned, as it responded only tocis-vaccenyl acetate, believed to be a pheromone. Type 2 responded totrans-2-hexenal and 4-methyl cyclohexanol. These two types of s. trichodea are differentially distributed on the antennal surface, and have dramatically different frequencies of spontaneous action potentials. Likewise, there are multiple types of s. coeloconica. One type is broadly tuned, responding most strongly to a test stimulus of butyric acid, but also to a variety of other odors; it is restricted to the dorso-medial portion of the third antennal segment. A second type gave detectable responses only totrans-2-hexenal. These results demonstrate that all classes of sensilla are olfactory, and they reveal the organizational complexity of theDrosophila olfactory system.     

亚洲小车蝗触角转录组及化学感受蛋白基因表达谱分析(英文)

【目的】化学感受蛋白(chemosensory proteins, CSPs)是一类小分子的可溶性蛋白,在昆虫中发挥多种作用。本研究旨在组装中国北方主要草原害虫之一——亚洲小车蝗Oedaleus asiaticus的触角转录组,鉴定出化学感受蛋白基因以及分析其在成虫不同组织中的表达水平。【方法】利用RNA-s eq 亚洲小车蝗成虫触角进行转录组测序和组装;通过筛选转录组数据库、克隆及测序,鉴定出化学感受蛋白基因;应用qPCR分析CSP基因在成虫不同组织(触角、去除触角和口器的头、上唇、去掉下唇须的下唇、下唇须、下颚须、胸部、跗节、翅和腹部)中的表达模式。【结果】成功构建了亚洲小车蝗成虫触角转录组,共获得61 629个unigenes,平均长度为733 nt,总长度和N50分别为45 175 449和1 130 nt。其中26 064个unigenes(42.29％)注释到6个数据库(NR, NT, Swiss-Prot, KEGG, COG和GO)。通过Blast验证、克隆和测序鉴定出17个CSP基因;BlastP和系统发育分析表明亚洲小车蝗CSPs(OasiCSPs)与东亚飞蝗Locusta migratoria CSPs(LmigCSPs)和沙漠蝗Schistocerca gregaria CSPs(SgreCSPs)关系最密切。qPCR分析表明,8个CSP基因在成虫不同组织中的表达水平存在显着差异,特别是,OasiCSP8在下唇须和下颚须中高表达,而OasiCSP11和OasiCSP13在触角中表达量最高。OasiCSP15在化学感受器官(触角、上唇、去掉下唇须的下唇、下唇须、下颚须和跗节)中的表达量远高于非化学感受器官(去掉触角和口器的头部、胸部、翅和腹部)中的表达量,而OasiCSP12在几乎所有测定的组织中具有相似的表达分布。【结论】OasiCSPs在亚洲小车蝗化学感受和发育过程中可能起着多种作用,这些结果为进一步研究这些化学感受蛋白在亚洲小车蝗中的功能奠定了基础。     

The olfactory responses of the antenna and maxillary palp of the fleshfly,Neobellieria bullata (Diptera: Sarcophagidae), and their sensitivity to blockage of nitric oxide synthase

The relative sensitivities of the olfactory receptors in the antenna and maxillary palp of the fleshfly, Neobellieria bullata, were assessed using simultaneous electroantennograms (EAGs) and electropalpograms (EPGs). In general, the antennae and maxillary palps were more sensitive to odors related to animals (blood extract and saturated carboxylic acid) than to odors that were plant-derived (citral, hexenol, hexenal). In addition, the maxillary palps were relatively less sensitive to plant-derived odorants than the antennae, perhaps related to their anatomical position. Scanning electron microscopy was also used to assess the types of sensilla found on the two organs. In addition, NADPH-diaphorase histochemistry was used in an attempt to localize the enzyme nitric oxide synthase (NOS) in the antenna and the maxillary palps. We found evidence of NADPH-diaphorase staining in both organs, with localized staining in the antennal cells and more general staining in the maxillary palps. When NOS was selectively blocked using the antagonist L-NAME, the amplitude of the EAGs and EPGs to odorants fell by 30-50%. In contrast, application of the inactive enantiomer, D-NAME, did not change the amplitude of the EAGs or the EPGs. Our results indicate that NOS is involved in the function of olfactory receptor cells in the fleshfly.     

Quantifying relative importance of maxillary palp information on the olfactory behavior of Drosophila melanogaster

Maxillary palps have been proposed as secondary olfactory organs, after the antennae, in Drosophila melanogaster. Our study tries to establish the quantitative importance of both organs as olfactory information mediators. Dose-response curves for three odorants: ethyl acetate, propionaldehyde and benzaldehyde were carried out for comparing olfaction in either complete animals or flies surgically deprived of antennae. Antennaless flies tested in our behavioral assay showed indifferent, attractant and repellent responses depending on concentration, similarly as normal flies do. However, they clearly displayed less sensitivity than normal flies. The range of concentrations they were able to perceive was correlated to antennal sensitivity approximately by a factor 110 for ethyl acetate and benzaldehyde, and between 110 and 1100 at high concentrations of propionaldehyde. A complementary experiment was performed to test changes in olfactory behavior produced by removing maxillary palps in the presence of antennae. At high concentrations of odorant, responses to ethyl acetate and propionaldehyde experienced small changes when both palps were removed. Results are compatible with a summation model of all olfactory information reaching the brain either through antennae or palps.Abbreviations ANOVA analysis of variance - EAG electroantennogram, extracellular recording of electrical changes produced on the antenna in response to odorant stimulation - EPG electropalpogram, extracellular recording of electrical changes produced on the maxillary palp in response to odorant stimulation - IO Olfactory index     

A spatial map of olfactory receptor expression in the Drosophila antenna

Insects provide an attractive system for the study of olfactory sensory perception. We have identified a novel family of seven transmembrane domain proteins, encoded by 100 to 200 genes, that is likely to represent the family of Drosophila odorant receptors. Members of this gene family are expressed in topographically defined subpopulations of olfactory sensory neurons in either the antenna or the maxillary palp. Sensory neurons express different complements of receptor genes, such that individual neurons are functionally distinct. The isolation of candidate odorant receptor genes along with a genetic analysis of olfactory-driven behavior in insects may ultimately afford a system to understand the mechanistic link between odor recognition and behavior.     

蚊虫嗅觉识别的神经机制

蚊虫主要依赖嗅觉系统与外界环境进行化学信息交流。蚊虫通过嗅觉感受系统寻找食物、 配偶和产卵场所, 进而做出相应的行为反应。本文综述了近年来蚊虫嗅觉系统对气味信号神经传导机制的研究进展。蚊虫的嗅觉感器主要位于触角和下颚须, 触角上的毛形感器和锥形感器感受氨水、 乳酸、 羧酸类化合物等人体和其他动物释放的微量气味物质, 下颚须上的锥形感器则感受呼出的二氧化碳以及一些其他的挥发性物质; 蚊虫嗅觉感器内部有受体神经细胞, 其上分布有嗅觉受体蛋白, 蚊虫对外界环境的化学感受就是通过气味物质与这些受体蛋白互作而得以实现; 根据对不同气味物质的反应谱差异, 嗅觉神经细胞被分为不同的功能类型; 来自嗅觉神经细胞的神经信号进一步从外周传导至中枢神经中脑触角叶内的神经小球, 在此对信息进行初步的处理, 通过评估嗅觉神经细胞的反应和触角叶内的神经小球相应被激活的区域, 不同小球被分别命名; 最后, 神经信号继续整合, 由投射神经传向前脑, 最终引发一系列昆虫行为反应。这些研究从理论上剖析了气味信号在蚊虫嗅觉系统中的神经转导通路, 对于我们深刻理解蚊虫的嗅觉系统具有重要意义, 同时也有助于进一步理解其他昆虫甚至人类的气味识别机制及进行更深层次神经科学的探索。     

Analysis of immunocytochemical staining patterns in the antennal system of Drosophila melanogaster

By immunizing mice with homogenized brains, heads, or a mixture of heads and antennae of D. melanogaster, we obtained six monoclonal antibodies (mabs) that bind to the olfactory system of Drosophila with various degrees of specificity. They can be divided into three groups with respect to their staining pattern: (1) The antibodies ca51/2, na21/2, and nb230 label both in the third (olfactory) antennal segment and in the visual ganglia. All of them bind to antennal structures that can be correlated with basiconic sensilla. The antibody ca51/2 labels sensory neurons of these sensilla. In the antenna of the lozenge ³ mutant, which lacks basiconic sensilla, no labeling is present. In Western blots ca51/2 recognizes in the antenna an antigen of 43.5 kDa, which is expressed in the antenna only in the presence of basiconic sensilla. The antibody na21/2 binds to basiconic and coeloconic sensilla, most likely to the apical part of sheath cells. In immunoblots it recognizes in the antenna two antigens of 42.2 kDa and 46.7 kDa. The latter appears to be correlated in the antenna with the presence of basiconic sensilla. (2) The staining pattern of antibody nc10 is associated with the sheath cells of basiconic and coeloconic sensilla. Moreover, nc10 binds to a subset of glomeruli in the antennal lobe. (3) The staining pattern of the antibodies VG2 and I24B5 is restricted to the antenna. I24B5 recognizes coeloconic sensilla and VG2 recognizes both coeloconic and basiconic sensilla. Staining patterns in both cases include sheath cells.