The organization of the chemosensory system in Drosophila melanogaster: a rewiew

This review surveys the organization of the olfactory and gustatory systems in the imago and in the larva of Drosophila melanogaster, both at the sensory and the central level. Olfactory epithelia of the adult are located primarily on the third antennal segment (funiculus) and on the maxillary palps. About 200 basiconic (BS), 150 trichoid (TS) and 60 coeloconic sensilla (CS) cover the surface of the funiculus, and an additional 60 BS are located on the maxillary palps. Males possess about 30% more TS but 20% fewer BS than females. All these sensilla are multineuronal; they may be purely olfactory or multimodal with an olfactory component. Antennal and maxillary afferents converge onto approximately 35 glomeruli within the antennal lobe. These projections obey precise rules: individual fibers are glomerulus-specific, and different types of sensilla are associated with particular subsets of glomeruli. Possible functions of antennal glomeruli are discussed. In contrast to olfactory sensilla, gustatory sensilla of the imago are located at many sites, including the labellum, the pharynx, the legs, the wing margin and the female genitalia. Each of these sensory sites has its own central target. Taste sensilla are usually composed of one mechano-and three chemosensory neurons. Individual chemosensory neurons within a sensillum respond to distinct subsets of molecules and project into different central target regions. The chemosensory system of the larva is much simpler and consists essentially of three major sensillar complexes on the cephalic lobe, the dorsal, terminal and ventral organs, and a series of pharyngeal sensilla.     

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.     

Inactivation of olfactory sensilla of a single morphological type differentially affects the response of Drosophila to odors

The olfactory organs on the head of Drosophila, antennae and maxillary palps, contain several hundred olfactory hairs, each with one or more olfactory receptor neurons. Olfactory hairs belong to one of three main morphological types, trichoid, basiconic, and coeloconic sensilla, and show characteristic spatial distribution patterns on the surface of the antenna and maxillary palps. Here we show that targeting expression of the cell-death gene reaper to basiconic sensilla (BS) causes the specific inactivation of most olfactory sensilla of this type with no detectable effect on other types of olfactory sensilla or the structure of the antennal lobe. Our data suggest that BS are required for a normal sensitivity to many odorants with a variety of chemical structures, through a wide range of concentrations. Interestingly, however, in contrast to other odorants tested, the behavioral response of ablated flies to intermediate concentrations of propionic and butyric acids is normal, suggesting the involvement of sensilla unaffected by ectopic reaper expression, probably coeloconic sensilla that respond strongly to these two organic acids. As inactivation of BS causes an underestimation of the concentration of both acids detectable at both the highest and lowest odorants concentrations, our results suggest that concentration coding for these two odorants relies on the integration of signals from different subsets of sensilla, most likely of different morphological types.     

Sensing the Underground - Ultrastructure and Function of Sensory Organs in Root-Feeding Melolontha melolontha (Coleoptera: Scarabaeinae) Larvae

Introduction

Below ground orientation in insects relies mainly on olfaction and taste. The economic impact of plant root feeding scarab beetle larvae gave rise to numerous phylogenetic and ecological studies. Detailed knowledge of the sensory capacities of these larvae is nevertheless lacking. Here, we present an atlas of the sensory organs on larval head appendages of Melolontha melolontha. Our ultrastructural and electrophysiological investigations allow annotation of functions to various sensory structures.

Results

Three out of 17 ascertained sensillum types have olfactory, and 7 gustatory function. These sensillum types are unevenly distributed between antennae and palps. The most prominent chemosensory organs are antennal pore plates that in total are innervated by approximately one thousand olfactory sensory neurons grouped into functional units of three-to-four. In contrast, only two olfactory sensory neurons innervate one sensillum basiconicum on each of the palps. Gustatory sensilla chaetica dominate the apices of all head appendages, while only the palps bear thermo-/hygroreceptors. Electrophysiological responses to CO₂, an attractant for many root feeders, are exclusively observed in the antennae. Out of 54 relevant volatile compounds, various alcohols, acids, amines, esters, aldehydes, ketones and monoterpenes elicit responses in antennae and palps. All head appendages are characterized by distinct olfactory response profiles that are even enantiomer specific for some compounds.

Conclusions

Chemosensory capacities in M. melolontha larvae are as highly developed as in many adult insects. We interpret the functional sensory units underneath the antennal pore plates as cryptic sensilla placodea and suggest that these perceive a broad range of secondary plant metabolites together with CO₂. Responses to olfactory stimulation of the labial and maxillary palps indicate that typical contact chemo-sensilla have a dual gustatory and olfactory function.     

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.     

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。     

Larval chemosensory projections and invasion of adult afferents in the antennal lobe of Drosophila

We have studied the fate of olfactory afferents during metamorphic transformation of Drosophila melanogaster. Intracellular labeling of afferents from larval head chemosensilla suggests that the larval antennal lobe may be an olfactory target, whereas tritocerebral and suboesophageal centers are likely targets of gustatory sensilla. Application of monoclonal antibody 22C10 shows that the larval antennal nerve is the precursor of the adult antennal nerve and is used as a centripetal pathway for the adult afferents. Likely guidance cues are larval olfactory afferents that persist during early metamorphosis. P[GAL4] enhancer trap lines are introduced as efficient markers to follow the establishment of adult sensory projections. β-Galactosidase and the bovine TAU protein were used as reporter proteins, and their expression patterns are compared. P[GAL4] lines MT14 and KL116 demonstrate that adult antennal afferents have arrived in the antennal lobe 24 h after pupariation and extend to the contralateral lobe 6 h later. Line MT14 expresses GAL4 mostly in basiconic sensilla and in certain trichoid sensilla, whereas KL116 is specific for trichoid and a small subset of basiconic sensilla. In the antennal lobe, largely complementary subsets of glomeruli are labeled by the two lines, in agreement with the observation that particular types of sensilla project to particular target glomeruli. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 281–297, 1997.     

Morphological and ultrastructural characterization of olfactory sensilla in Drosophila suzukii: Scanning and transmission electron microscopy

Drosophila suzukii is a serious horticultural and quarantine pest, damaging various berry crops. Although the active use of olfactory communication in D. suzukii is well-known, their olfactory sensory system has not been comprehensively reported. Therefore, the present study was carried out to understand the morphology, distribution and ultrastructure of olfactory sensilla present in the antennae and maxillary palps of D. suzukii, through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The olfactory sensilla on the antennae of D. suzukii in both sexes could be classified into three major morphological types, basiconic, trichoid and coeloconic sensilla, according to their shapes. The antennal basiconic sensilla were further divided into three subtypes and the antennal trichoid sensilla into two subtypes, respectively, according to the size of individual sensillum. In contrast to the antennal olfactory sensilla showing diverse morphology, basiconic sensilla was the only type of olfactory sensilla in the maxillary palps of D. suzukii. The basiconic sensilla in the maxillary palps could be further classified into three subtypes, based on their size. Our SEM and TEM observations indicated that multiple nanoscale pores are present on the surface of all types of olfactory sensilla in the antennae and maxillary palps, except coeloconic sensilla. The difference in the morphological types and the distribution of olfactory sensilla suggests that their olfactory functions are different between antennae and maxillary palps in D. suzukii. The results of this study provide useful information for further studies to determine the function of olfactory sensilla in D. suzukii and to understand their chemical communication system.     

Behavioral and electroantennogram analysis of olfactory stimulation inlozenge: ADrosophila mutant lacking antennal basiconic sensilla (Diptera: Drosophilidae)

Two alleles of the mutant lozengeof Drosophila melanogaster, lzand lz³,lack basiconic sensilla on the antennal funiculus. To elucidate the role of these sensilla for the perception of food odors, we studied the locomotor behavior and the electroantennogram (EAG) activity of lozenge flies in response to olfactory stimuli. The significance of basiconic sensilla on the maxillary palps was assessed by testing the locomotion of flies surgically deprived of their palps. The behavioral data suggest that antennal and maxillary basiconic sensilla may be important receptors for short chain alcohols and organic acids but less crucial receptors for acetates, aldehydes, and ketones. In agreement with this interpretation, EAG responses to alcohols (but not to esters) were found to be markedly lower in lozengethan in the wild type.     

Cephalic sensory pathways in the central nervous system of larval Manduca sexta (Lepidoptera : Sphingidae)

Central projections of neurons innervating sensory structures on the head of larval Manduca sexta were traced by using methods of anterograde cobalt-diffusion. Regions of the deutocerebrum and tritocerebrum in the brain receive input from the antenna, labrum, maxilla, labial palps, hypopharynx and other unidentified regions of the buccal cavity. Antennal, maxillary and labial inputs project to the larval antennal centre (LAC) of the deutocerebrum. Stemmatal neurons and a few antennal neurons project into the protocerebrum. The suboesophageal ganglion (SEG) receives input from mechanosensory neurons in all parts of the head and its sensory appendages. Some mechanosensory neurons project further to the first thoracic ganglion. In addition to receiving input from chemosensory neurons of the maxilla, the SEG may also receive chemosensory input from epipharyngeal sensilla of the labrum.     

Sexual dimorphism in the antennal lobe of the ant Camponotus japonicus

The carpenter ant, a social hymenopteran, has a highly elaborated antennal chemosensory system that is used for chemical communication in social life. The glomeruli in the antennal lobe are the first relay stations where sensory neurons synapse onto interneurons. The system is functionally and structurally similar to the olfactory bulbs of vertebrates. Using three-dimensional reconstruction of glomeruli and subsequent morphometric analyses, we found sexual dimorphism of the antennal lobe glomeruli in carpenter ants, Camponotus japonicus. Female workers and unmated queens had about 430 glomeruli, the highest number reported so far in ants. Males had a sexually dimorphic macroglomerulus and about 215 ordinary glomeruli. This appeared to result from a greatly reduced number of glomeruli in the postero-medial region of the antennal lobe compared with that in females. On the other hand, sexually isomorphic glomeruli were identifiable in the dorsal region of the antennal lobe. For example, large, uniquely shaped glomeruli located at the dorso-central margin of the antennal lobe were detected in all society members. The great sexual dimorphism seen in the ordinary glomeruli of the antennal lobe may reflect gender-specific tasks in chemical communications rather than different reproductive roles.     

Sensory organs on the body parts of the bed-bug Cimex hemipterus fabricius (Hemiptera : Cimicidae) and the anatomy of its central nervous system

Anatomy of the sensory organs on the prominent body parts of the adult bed-bug Cimex hemipterus (Hemiptera: Cimicidae) and its central nervous system (CNS) was studied by light, transmission, or scanning electron microscopy. The distal tips of antenna and rostrum were found to have rich complements of sensilla. The antenna has both olfactory and gustatory sensilla. Olfactory sensilla project to the antennal lobe organized in the form of glomeruli, while the 2nd component, presumably from gustatory sensilla, projects to the suboesophageal ganglion. The ultrastructure of the sensory pegs on the rostrum of C. hemipterus does not resemble the chemosensilla of adult insects; rather they resemble the larval sensilla of Drosophila melanogaster in the maxillary organ. Earlier we believed this to be a gustatory organ. A few similar sensilla also occur on the antenna, indicating its multimodal role. Amongst the 3 types of sensory hairs located on legs, there are only a few gustatory hairs (7–10 hairs) on the tibia. The pointed and serrate mechanosensory hair types occur in abundance; the serrate type are prominently present on the lateral surface of the legs. On other parts of the body such as the thorax or abdomen, serrate hairs are most abundant. Both the distal segment of antenna and rostrum are invested by 2 nerves, where the axon counts of the 2 antennal nerves are 380 and 425, while each rostral nerve on average has 205 axons. Abundant clusters of microtubules were found in the brain, thoracio-abdominal ganglia, leg-nerves, and the space between muscles and cuticle. These conspicuous microtubule-clusters occur in interaxonal space, mainly glial cells, in the nervous system. In addition, the glial cells have osmiophilic junctions amongst themselves. A novel “hinge and joint” system, which controls the cross-section of the food canal and the salivary duct in an inversely related manner, was found in the rostrum of the bed-bug.     

Evidence of age-related changes in the antennal glomeruli of Drosophila melanogaster using monoclonal antibodies

As a tool to better understand the organization of the olfactory pathway three monoclonal antibodies have been isolated and characterized each having a unique staining pattern in the antenna and antennal lobe of Drosophila melanogaster. Monoclonal antibody F14-2D6 stains sensilla coeloconica and thick sensilla basiconica in the funiculus, Y1-3D10 stains only a few sensilla especially in and around the sacculus, while F15-12E8 stains all the sensilla. All three antibodies stain a subset of the glomeruli in the antennal lobe, of which 11 glomeruli are stained in common by all three antibodies. These antibodies could be used to study projection patterns of the sensilla into the antennal lobe. Glomerular staining was observed at different developmental times with the different antibodies. F15-12E8 stains all the glomeruli at eclosion, Y1-3D10 stains only a few glomeruli at eclosion but most glomeruli are stained by the first day after eclosion. F14-2D6 stains all glomeruli only after eclosion. F15-12E8 also stains the mushroom bodies. The antigen recognized by F14-2D6 in the glomeruli shows an increase with age of the flies, measured as increased intensity of staining. These observations suggest that age-related changes continue in the antennal lobe of the flies even after eclosion. These antibodies could therefore serve as unique markers for other studies on the development of the olfactory system.     

Physiology and antennal lobe projections of olfactory receptor neurons from sexually isomorphic sensilla on male <Emphasis Type="Italic">Heliothis virescens</Emphasis>

The neurophysiology and antennal lobe projections of olfactory receptor neurons (ORNs) within sexually isomorphic short trichoid sensilla of male Heliothis virescens (Noctuidae: Lepidoptera) were investigated using cut-sensillum recording and cobalt-lysine staining. A total of 202 sensilla were sorted into 14 possible sensillar categories based on odor responses and physiology of ORNs within. Seventy-two percent of the sensilla identified contained ORNs stimulated by conspecific odors. In addition, a large number of ORNs were specifically sensitive to ß-caryophyllene, a plant-derived volatile (N = 41). Axons originating from ORNs associated with individual sensilla were stained with cobalt lysine (N = 67) and traced to individual glomeruli in the antennal lobe. ORNs with responses to female sex pheromone components exhibited similar axonal projections as those previously described from ORNs in long sensilla trichodea in male H. virescens. Antennal lobe axonal arborizations of ORNs sensitive to hairpencil components were also located in glomeruli near the base of the antennal nerve, whilst those sensitive to plant odorants projected to more medial glomeruli. Comparisons with ORNs described from female H. virescens supports the notion that glomeruli at the base of the antennal nerve are associated with conspecific and interspecific odorants, whereas those located medially are associated with plant volatiles.     

Phenotypic plasticity in number of glomeruli and sensory innervation of the antennal lobe in leaf‐cutting ant workers (A. vollenweideri)

In the leaf‐cutting ant Atta vollenweideri, the worker caste exhibits a pronounced size‐polymorphism, and division of labor is dependent on worker size (alloethism). Behavior is largely guided by olfaction, and the olfactory system is highly developed. In a recent study, two different phenotypes of the antennal lobe of Atta vollenweideri workers were found: MG‐ and RG‐phenotype (with/without a macroglomerulus). Here we ask whether the glomerular numbers are related to worker size. We found that the antennal lobes of small workers contain ～390 glomeruli (low‐number; LN‐phenotype), and in large workers we found a substantially higher number of ～440 glomeruli (high‐number; HN‐phenotype). All LN‐phenotype workers and some small HN‐phenotype workers do not possess an MG (LN‐RG‐phenotype and HN‐RG‐phenotype), and the remaining majority of HN‐phenotype workers do possess an MG (HN‐MG‐phenotype). Using mass‐staining of antennal olfactory receptor neurons we found that the sensory tracts divide the antennal lobe into six clusters of glomeruli (T1–T6). In LN‐phenotype workers, ～50 glomeruli are missing in the T4‐cluster. Selective staining of single sensilla and their associated receptor neurons revealed that T4‐glomeruli are innervated by receptor neurons from the main type of olfactory sensilla, the Sensilla trichodea curvata. The other type of olfactory sensilla (Sensilla basiconica) exclusively innervates T6‐glomeruli. Quantitative analyses of differently sized workers revealed that the volume of T6 glomeruli scales with the power of 2.54 to the number of Sensilla basiconica. The results suggest that developmental plasticity leading to antennal‐lobe phenotypes promotes differences in olfactory‐guided behavior and may underlie task specialization within ant colonies. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 70: 222–234, 2010.     

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.     

小菜蛾成虫下唇须感器的超微结构及其神经元中枢投射

【目的】明确小菜蛾Plutella xylostella成虫下唇须感器的形态结构及感器神经元的投射。【方法】利用光学显微镜观察和扫描电子显微镜观察下唇须结构和感器类型,利用神经回填技术和激光共聚焦显微镜观察下唇须感器神经元在脑部的投射。【结果】小菜蛾成虫下唇须共3节,其上存在Böhm氏鬃毛、钟形感器、鳞形感器、锥形感器、微毛形感器5种不同类型的感器和一个陷窝器结构。Böhm氏鬃毛短小尖细,钟形感器形如顶部凹陷的圆帽,两种感器均分布于下唇须第1节,且大小上均无雌雄二型差异;鳞形感器形同柳叶,锥形感器粗而直,均散生于下唇须的第2和3节,两种感器在大小上均存在雌雄二型差异,其中雌性的鳞形感器显著大于雄性的,根据其雌雄二型差异现象推测雌蛾的鳞形感器可能与感受寄主植物挥发物有关;下唇须第3节中上部具有一个圆形陷窝器结构,雄虫的陷窝器内径为5.68±0.33μm,雌虫的为6.03±0.23μm,雌雄间无显著性差异;凹坑内长有表面光滑的微毛形感器。小菜蛾下唇须感器神经元主要投射于脑部咽下神经节、每个触角叶的下唇须陷窝器神经纤维球和腹神经索3条通路。【结论】阐明了小菜蛾下唇须感器的类型、分布和形态特征及其感器神经元在脑部的投射形态,为深入了解小菜蛾下唇须感器的生理和功能奠定了基础。     

利用单感器记录与神经元示踪结合对棉铃虫主要性信息素感器内神经元投射的鉴定

【目的】鉴定雄性棉铃虫Helicoverpa armigera成虫触角性信息素感器嗅觉受体神经元的功能、形态及中枢投射路径。【方法】利用单感器记录技术记录棉铃虫嗅觉受体神经元对性信息素的反应,同时采用荧光染料作为示踪剂染色标记嗅觉受体神经元;使用免疫组织化学方法处理相应的脑组织,标记脑内触角叶的神经纤维球结构;用激光扫描共聚焦显微镜获取图像数据,使用图形软件ZEN和Amira 4.1.1进行三维结构重建。【结果】记录到雄性棉铃虫成虫触角上长毛形感器对主要性信息素成分Z11-16∶Ald产生明显的电生理反应,并成功染色标记了该感器内的嗅觉受体神经元。染色标记显示该感器内具有两个嗅觉受体神经元,其轴突通过触角神经分别投射触角叶内的云状体神经纤维球和普通神经纤维球。【结论】单感器记录与神经元示踪两技术结合能够用于鉴定昆虫触角嗅觉受体神经元的功能、形态和投射至神经纤维球的路径。与赖氨酸钴方法比较,使用荧光染料法进行神经元示踪,操作更简便,且易于进行三维空间分析,为调查棉铃虫其他嗅觉神经元的投射路径以明确外周气味受体感受与中枢系统的联系提供了有力技术支持。     

Neuronal architecture of the antennal lobe in Drosophila melanogaster

Summary Computer reconstruction of the antennal lobe of Drosophila melanogaster has revealed a total of 35 glomeruli, of which 30 are located in the periphery of the lobe and 5 in its center. Several prominent glomeruli are recognizable by their location, size, and shape; others are identifiable only by their positions relative to prominent glomeruli. No obvious sexual dimorphism of the glomerular architecture was observed. Golgi impregnations revealed: (1) Five of the glomeruli are exclusive targets for ipsilateral antennal input, whereas all others receive afferents from both antennae. Unilateral amputation of the third antennal segment led to a loss of about 1000 fibers in the antennal commissure. Hence, about 5/6 of the approximately 1200 antennal afferents per side have a process that extends into the contralateral lobe. (2) Afferents from maxillary palps (most likely from basiconic sensilla) project into both ipsi-and contralateral antennal lobes, yet their target glomeruli are apparently not the same as those of antennal basiconic sensilla. (3) Afferents in the antennal lobe may also stem from pharyngeal sensilla. (4) The most prominent types of interneurons with arborizations in the antennal lobe are: (i) local interneurons ramifying in the entire lobe, (ii) unilateral relay interneurons that extend from single glomeruli into the calyx and the lateral protocerebrum (LPR), (iii) unilateral interneurons that connect several glomeruli with the LPR only, (iv) bilateral interneurons that link a small number of glomeruli in both antennal lobes with the calyx and LPR, (v) giant bilateral interneurons characterized by extensive ramifications in both antennal lobes and the posterior brain and a cell body situated in the midline of the suboesophageal ganglion, and (vi) a unilateral interneuron with extensive arborization in one antennal lobe and the posterior brain and a process that extends into the thorax. These structural results are discussed in the context of the available functional and behavioral data.Abbreviations AC antennal commissure - AMMC antennal mechanosensory and motor center - iACT, mACT, oACT inner/middle/outer antenno-cerebral tract - bACTI, uACTI bilateral/unilateral ACT relay interneuron - AN antennal nerve - AST antenno-suboesophageal tract - FAI fine arborization relay interneuron - GSI giant symmetric relay interneuron - LI local interneuron - LPR lateral protocerebrum - SOG suboesophageal ganglion - TI thoracic relay interneuron - bVI bilateral V-relay interneuron