Sensory processing of ambient CO<Subscript>2</Subscript> information in the brain of the moth<Emphasis Type="Italic"> Manduca sexta</Emphasis>

Insects use information about CO₂ to perform vital tasks such as locating food sources. In certain moths, CO₂ is involved in oviposition behavior. The labial palps of adult moths that feed as adults have a pit organ containing sensory receptor cells that project into the antennal lobes, the sites of primary processing of olfactory information in the brain. In the moth Manduca sexta and certain other species of Lepidoptera, these receptor cells in the labial-palp pit organ have been shown to be tuned to CO₂, and their axons project to a single, identified glomerulus in the antennal lobe, the labial-palp pit organ glomerulus. At present, however, nothing is known about the function of this glomerulus or how CO₂ information is processed centrally. We used intracellular recording and staining to reveal projection (output) neurons in the antennal lobes that respond to CO₂ and innervate the labial-palp pit organ glomerulus. Our results demonstrate that this glomerulus is the site of first-order processing of sensory information about ambient CO₂. We found three functional types of CO₂-responsive neurons (with their cell bodies in the antennal lobe or the protocerebrum) that provide output from the antennal lobe to higher centers in the brain. Some physiological characteristics of those neurons are described.Abbreviations AL Antennal lobe - AN Antennal nerve - CMB Calyces of the mushroom body - IPSP Inhibitory postsynaptic potential - LC-I Dorsal cluster of the lateral group of AL neuronal somata - LH Lateral horn of the protocerebrum - LPN Labial-palp nerve - LPO Labial-palp pit organ - LPOG LPO glomerulus - PC Protocerebrum - PI AL neuron that projects to the PC through the inner antenno-cerebral tract - PN Projection neuron     

Fine structure and primary sensory projections of sensilla located in the labial-palp pit organ of Helicoverpa armigera (Insecta)

The fine structure and primary sensory projections of sensilla located in the labial-palp pit organ of the cotton bollworm Helicoverpa armigera (Insecta, Lepidoptera) are investigated by scanning electron and transmission electron microscopy combined with confocal laser scanning microscopy. The pit organ located on the third segment of the labial palp is about 300 μm deep with a 60-μm-wide opening, each structure containing about 1200 sensilla. Two sensillum types have been found, namely hair-shaped and club-shaped sensilla, located on the upper and lower half of the pit, respectively. Most sensilla possess a single dendrite. The dendrite housed by the club-shaped sensilla is often split into several branches or becomes lamellated in the outer segment. As reported previously, the sensory axons of the sensilla in the labial pit organ form a bundle entering the ipsilateral side of the subesophageal ganglion via the labial palp nerve and project to three distinct areas: the labial pit organ glomerulus in each antennal lobe, the subesophageal ganglion and the ventral nerve cord. In the antennal lobe, the labial pit organ glomerulus is innervated by sensory axons from the labial pit organ only; no antennal afferents target this unit. One neuron has been found extending fine processes into the subesophageal ganglion and innervating the labial palp via one branch passing at the base of the labial palp nerve. The soma of this assumed motor neuron is located in the ipsilateral cell body layer of the subesophageal ganglion. Our results provide valuable knowledge concerning the neural circuit encoding information about carbon dioxide and should stimulate further investigations directed at controlling pest species such as H. armigera.     

Development of the labial pit organ glomerulus in the antennal lobe of the moth Manduca sexta: The role of afferent projections in the formation of identifiable olfactory glomeruli

Iterated neuropil modules called glomeruli are characteristic of primary olfactory centers in both vertebrates and invertebrates. To gain insight into the developmental mechanisms underlying the formation of such structured, organized neuropil, we have examined the development of an identified glomerulus in the olfactory (antennal) lobe of the moth Manduca sexta. The labial pit organ glomerulus (LPOG) receives bilateral sensory projections from the labial pit organs in the labial palps of the mouthparts, while other glomeruli in the antennal lobe receive unilateral projections from the antenna. Here, we chronicle the development of the LPOG under normal and perturbed conditions. Our findings suggest that the sensory axons of the labial pit organ, like those of the antenna, induce and shape growth of interneuronal arborizations, but specific features of interneuronal arborizations such as the relative position of glomerular arborizations within the antennal lobe are independent of both classes of afferent innervation. Labial pit organ axons and antennal axons exhibit a high degree of specificity for their respective target regions, independent of the presence or absence of the other class of afferent axon or the route taken to the antennal lobe. Specification of glomerular position is intrinsic to the antennal lobe rather than a consequence of competition between afferent axons. © 1999 John Wiley & Sons, Inc. J Neurobiol 40: 28–44, 1999     

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.     

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。     

Development of the labial pit organ glomerulus in the antennal lobe of the moth Manduca sexta: the role of afferent projections in the formation of identifiable olfactory glomeruli.

Iterated neuropil modules called glomeruli are characteristic of primary olfactory centers in both vertebrates and invertebrates. To gain insight into the developmental mechanisms underlying the formation of such structured, organized neuropil, we have examined the development of an identified glomerulus in the olfactory (antennal) lobe of the moth Manduca sexta. The labial pit organ glomerulus (LPOG) receives bilateral sensory projections from the labial pit organs in the labial palps of the mouthparts, while other glomeruli in the antennal lobe receive unilateral projections from the antenna. Here, we chronicle the development of the LPOG under normal and perturbed conditions. Our findings suggest that the sensory axons of the labial pit organ, like those of the antenna, induce and shape growth of interneuronal arborizations, but specific features of interneuronal arborizations such as the relative position of glomerular arborizations within the antennal lobe are independent of both classes of afferent innervation. Labial pit organ axons and antennal axons exhibit a high degree of specificity for their respective target regions, independent of the presence or absence of the other class of afferent axon or the route taken to the antennal lobe. Specification of glomerular position is intrinsic to the antennal lobe rather than a consequence of competition between afferent axons.     

Antennal lobe projection destinations of Helicoverpa zea male olfactory receptor neurons responsive to heliothine sex pheromone components

We used single sensillum recordings to define male Helicoverpa zea olfactory receptor neuron physiology followed by cobalt staining to trace the axons to destination glomeruli of the antennal lobe. Receptor neurons in type A sensilla that respond to the major pheromone component, (Z)-11-hexadecenal, projected axons to the cumulus of the macroglomerular complex (MGC). In approximately 40% of these sensilla a second receptor neuron was stained that projected consistently to a specific glomerulus residing in a previously unrecognized glomerular complex with six other glomeruli stationed immediately posterior to the MGC. Cobalt staining corroborated by calcium imaging showed that receptor neurons in type C sensilla sensitive to (Z)-9-hexadecenal projected to the dorsomedial posterior glomerulus of the MGC, whereas the co-compartmentalized antagonist-sensitive neurons projected to the dorsomedial anterior glomerulus. We also discovered that the olfactory receptor neurons in type B sensilla exhibit the same axonal projections as those in type C sensilla. Thus, it seems that type B sensilla are anatomically type C with regard to the projection destinations of the two receptor neurons, but physiologically one of the receptor neurons is now unresponsive to everything except (Z)-9-tetradecenal, and the other responds to none of the pheromone-related odorants tested.     

Identification of serotonin- and vasopressin immunoreactivities in the suprachiasmatic nucleus of four mammalian species

Summary Cobalt fills from small, defined regions of the antenna in D. melanogaster show that the three types of sensilla on the third segment, the flagellum, and a fourth sensillum located in the arista, project into the glomeruli of the antennal lobe. We have identified 19 glomeruli in each lobe, according to their location, shape, and size. At least ten of these represent major projection areas of flagellar or aristal sensilla. The large majority of glomeruli is innervated from both antennae, but a small group of five receive exclusively ipsilateral input. A particular sensory fiber appears to terminate only in one specific glomerulus, either in the ipsilateral or in both lobes. Fills from flagellar regions bearing a single type of sensillum, yield a specific pattern of glomeruli containing stained terminals. Aristal projections remain strictly ipsilateral, whereas those from the other sensilla consist of an ipsilateral and a bilateral component. When filling from different points in an area bearing one type of sensillum, similar projections are produced, suggesting that projection patterns observed reflect predominantly the type of sensillum rather than its location on the flagellum. Accordingly, individual glomeruli might represent functional units, each receiving antennal input in a characteristic combination.We are indebted to Dr. H. Tobler for critical comments. R.F.S. was supported by the Swiss National Foundation (Grant No. 3.541-0.79) as well as a Travel Aid by the Swiss Academy of Sciences     

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.     

粘虫下唇须陷窝器及其感器的形态、类型与分布

【目的】明确我国重要农业害虫粘虫Mythimna separata Walker下唇须和陷窝器形态结构以及陷窝器内部感器的形态、类型与分布。【方法】利用光学显微镜观察粘虫成虫下唇须及陷窝器形态结构,利用扫描电子显微镜观察陷窝器内部的感器。【结果】结果表明,粘虫成虫下唇须似管状,具3节,各节形态和长度不同,其中第2节最长。粘虫下唇须长度雌雄异形,雌性的下唇须长度为2 463.50±143.65 μm,显著短于雄性的（2 566.11±70.28 μm）（t=2.722, df=34, P=0.012）。陷窝器凹坑深约280 μm,开口处直径约50 μm,内部直径约32 μm,雌雄间无显著差异。陷窝器内部的感器主要包括毛形感器和棒状感器2种类型。毛形感器位于陷窝器凹坑的上半部分,而棒状感器分布在陷窝器凹坑的下半部分。雌性毛形感器长为18.20±0.84 μm,显著短于雄性的21.24±0.34 μm（t=3.335, df=30, P=0.003）。而雌性的棒状感器长为14.69±0.48 μm,显著长于雄性的12.31±0.49 μm（t=3.452, df=21, P=0.002）。【结论】粘虫下唇须陷窝器感器分属2大类型,分布于陷窝器内不同的区域,其长度具有性别差异性。本文报道的这些形态学观察结果为进一步研究粘虫下唇须陷窝器感器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。     

Evolution and ultrastructure of the bovine spermatogonia precursor cell line

We have used a cytochemical technique to investigate the distribution of acetylcholinesterase (AChE) activity in the deutocerebrum of the brain of the sphinx moth Manduca sexta. To distinguish between extra-and intracellular pools of the enzyme, some brains were treated prior to histochemical staining with echothiophate, an irreversible AChE inhibitor which penetrates cell membranes very slowly and, therefore, inhibits only extracellular AChE. In the antennal nerve, fascicles of presumably mechanosensory fibers show echothiophateinsensitive AChE activity. They bypass the antennal lobe and project to the antennal mechanosensory and motor center of the deutocerebrum. In the antennal lobe, fibers in the coarse neuropil, cell bodies in the lateral cell group, and all glomeruli exhibit AChE activity. In most ordinary glomeruli, echothiophate-sensitive AChE activity is concentrated in the outer cap regions, corresponding to the terminal arborizations of olfactory afferents. A previously unrecognized glomerulus in the ventro-median antennal lobe shows uniform and more intense AChE-specific staining that the other glomeruli. No AChE activity appeared to be associated with malespecific pheromone-sensitive afferents in the macro-glomerular complex. About 67 interneurons with somata in the lateral cell group of the antennal lobe show echo-thiophate-insensitive AChE activity. These neurous seem to be members of two types of antennal-lobe projection neurons with fibers passing through the outer-antenno-cerebral tract to the protocerebrum. AChE-stained arborizations of these neurons appear to invade all glomeruli, including three distinguishable subunits of the male-specific macroglomerular complex. In echothiophate-treated animals, the projections of one of these types of fiber form large terminals in the lateral horn of protocerebrum, which partly protrude into the adjacent glial cell layer. The results suggest that extracellularly accessible AChE is associated with ordinary olfactory receptor terminals but apparently not with pheromone-sensitive afferents. Intracellular AChE appears to be present in antennal mechanosensory fibers and in two types of olfactory projection neurons of the antennal lobe. The study provides further evidence for cholinergic neurotransmission of most antennal afferents. The AChE-containing interneurons might be cholinergic as well or use the enzyme for functions unrelated to hydrolysis of acetylcholine.Abbreviations ACh acetylcholine - AChE acetylcholinesterase - AL antennal lobe - AMMC antennal mechanosensory and motor center - ChAT choline acetyltransferase - IACT inner antenno-cerebral tract - MGC macroglomerular complex     

Sexual dimorphism in neuronal projections from the antennae of silk moths (Bombyx mori,Antheraea polyphemus) and the gypsy moth (Lymantria dispar)

Summary The antennal lobe of both sexes of the silk moth Bombyx mori contains 55–60 ventrally located antennal glomeruli; in addition, that of the male contains a dorsal macroglomerular complex (MGC). A group of identifiable glomeruli consisting of two lateral large glomeruli (LLG) and four medial small glomeruli (MSG) is present in both sexes, but the LLG are greatly enlarged in the female. A MGC is also present in the male gypsy moth Lymantria dispar and male giant silk moth Antheraea polyphemus. The MGC in all of these species is organized into 3–4 distinct levels of glomeruli. Antennal sensory fibers were stained by cobalt backfills in B. mori, A. polyphemus, and L. dispar. Most fibers stained from cut long hairs (sensilla trichodea) projected to MGC in males and LLG in both sexes of B. mori. The distribution of fibers in the MGC of B. mori was topographically biased in that a majority of fibers from anterior branches projected medially in MGC while most fibers from posterior branches projected laterally or anteriorly. Terminal arborizations of single fibers were each restricted to a single glomerular level of the MGC. Fibers projecting to the posterior antennal center were frequently stained in cut-hair and control preparations, apparently by uptake of cobalt through intact sensilla on flagellar branches.     

Development of an identified serotonergic neuron in the antennal lobe of the moth and effects of reduction in serotonin during construction of olfactory glomeruli

Each olfactory (antennal) lobe of the moth Manduca sexta contains a single serotonin (5-HT) immunoreactive neuron whose processes form tufted arbors in the olfactory glomeruli. To extend our present understanding of the intercellular interactions involved in glomerulus development to the level of an individual, identified antennal lobe neuron, we first studied the morphological development of the 5-HT neuron in the presence and absence of receptor axons. Development of the neuron's glomerular tufts depends, as it does in the case of other multiglomerular neurons, on the presence of receptor axons. Processes of the 5-HT neuron are excluded from the region in which the initial steps of glomerulus construction occur and thus cannot provide a physical scaffolding on which the array of glomeruli is organized. Because the neuron's processes are present in the antennal lobe neuropil throughout postembryonic development, 5-HT could provide signals that influence the pattern of development in the lobe. By surgically producing 5-HT-depleted antennal lobes, we also tested the importance of 5-HT in the construction of olfactory glomeruli. Even in the apparent absence of 5-HT, the glomerular array initiated by the receptor axons was histologically normal, glial cells migrated to form glomerular borders, and receptor axons formed terminal branches in their normal region within each glomerulus. In some cases, 5-HT-immunoreactive processes from abnormal sources entered the lobe and formed the tufted intraglomerular branches typical of most antennal lobe neurons, suggesting that local cues strongly influence the branching patterns of developing antennal lobe neurons. © 1995 John Wiley & Sons, Inc.     

Species and sexual differences in antennal lobe architecture and glomerular organization in two parasitoids with different degree of host specificity, Microplitis croceipes and Cotesia marginiventris

The endoparasitic wasps (Hymenoptera: Braconidae), Microplitis croceipes (specialist) and Cotesia marginiventris (generalist), are parasitoids of lepidopteran larvae and differ in their degree of host specificity. Recent studies have reported key differences between the two species in the abundance of antennal olfactory sensilla and their response to host-related volatiles. Here, we have compared antennal lobe architecture and glomerular organization in the two parasitoid species by using a combination of axonal tract tracing techniques and confocal microscopy. In M. croceipes, the medial half of the antennal lobe is larger with a greater number of glomeruli compared with the lateral half, whereas in C. marginiventris, the lateral half is larger than the median half. The volume of the antennal lobe is approximately 2.5 times greater in M. croceipes than in C. marginiventris. However, the number of glomeruli per antennal lobe is only slightly higher in M. croceipes (females: 219–222; males: 220–224) than in C. marginiventris (females: 192–194; males: 193–196). A comparison of males and females within each species demonstrated a striking sexual difference in terms of an enlarged glomerulus (macroglomerulus or MG) at the entrance of the antennal nerve and of a complex of 3–4 MG (CMG) in the posterior region of the antennal lobe of males of both species. Being specific to males, both the MG and CMG might be involved in the detection of female-related odor.     

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.     

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

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

Physiological and morphological characterization of honeybee olfactory neurons combining electrophysiology,calcium imaging and confocal microscopy

The insect antennal lobe is the first brain structure to process olfactory information. Like the vertebrate olfactory bulb the antennal lobe is substructured in olfactory glomeruli. In insects, glomeruli can be morphologically identified, and have characteristic olfactory response profiles. Local neurons interconnect glomeruli, and output (projection) neurons project to higher-order brain centres. The relationship between their elaborate morphology and their physiology is not understood. We recorded electrophysiologically from antennal lobe neurons, and iontophoretically injected a calcium-sensitive dye. We then measured their spatio-temporal calcium responses to a variety of odours. Finally, we confocally reconstructed the neurons, and identified the innervated glomeruli. An increase or decrease in spiking frequency corresponded to an intracellular calcium increase or decrease in the cell. While intracellular recordings generally lasted between 10 and 30 min, calcium imaging was stable for up to 2 h, allowing a more detailed physiological analysis. The responses indicate that heterogeneous local neurons get input in the glomerulus in which they branch most strongly. In many cases, the physiological response properties of the cells corresponded to the known response profile of the innervated glomerulus. In other words, the large variety of response profiles generally found when comparing antennal lobe neurons is reduced to a more predictable response profile when the innervated glomerulus is known.Abbreviations ACT antenno-cerebralis-tract - AL antennal lobe - AP action potential - l-ACT lateral ACT - LN local neuron - LPL lateral protocerebral lobe - m-ACT medial ACT - MB mushroom body - OSN olfactory sensory neuron - PN projection neuron - T1 tract 1 of the antennal nerve     

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.