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.     

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     

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.     

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.     

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.     

Fine structure and primary sensory projections of sensilla on the maxillary palp of Drosophila melanogaster Meigen (Diptera : Drosophilidae)

Three types of hairs were identified on the maxillary palp of Drosophila melanogaster Meigen (Diptera : Drosophilidae): (i) single-walled, multiporous sensilla basiconica, which constitute 75% of the innervated hairs; (ii) thick walled non-porous sensilla trichodea, which make up the remaining 25% of the innervated hairs; and (iii) numerous spinules, which are un-innervated. These sensilla basiconica uniformly contain 2 bipolar sense cells, whereas sensilla trichodea have a single dendrite with a tubular body at the base of each hair. A majority of the sensilla basiconica is located on the distal half of the dorsal surface, whereas sensilla trichodea are positioned on the tip and entire ventrolateral ridge of the palp. Approximately 125 axons of the sense cells join to form a single nerve. The structure of sensilla basiconica and sensilla trichodea suggests that they are olfactory and mechanosensory respectively. The contact chemoreceptors (gustatory sensilla) are conspicuously absent on the maxillary palp.Golgi silver impregnations and cobalt fills show that the primary sensory fibres from sensilla trichodea and sensilla basiconica on the maxillary palp project in the posterior suboesophageal ganglion (SOG) and the antennal lobe respectively. A single fibre projects separately either in the SOG or in the antennal lobe. In the antennal lobe, the input received from sensilla basiconica is usually bilateral and at least 5 glomeruli are innervated symmetrically on either side from both the palps.This study suggests that the sensory neurons are capable of making selective projections in the specific regions of the brain. Accordingly, the fibres from a sensillum project to the brain with respect to their functions and the individual glomeruli represent functional units of the brain, receiving inputs in a characteristic combination.     

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.     

The macroglomerular complex of the antennal lobe in the tobacco budworm moth Heliothis virescens : specified subdivision in four compartments according to information about biologically significant compounds

The functional organisation of the male specific macroglomerular complex in Heliothis virescens has been studied by tip recordings of sensilla trichodea type 1 combined with cobalt-lysine stainings and by intracellular recordings of antennal lobe projection neurons combined with neurobiotin stainings. The antennal lobe, the macroglomerular complex and the stained axons/dendrites were reconstructed by camera-lucida. Some were further computer reconstructed in three dimensions. The results showed that: 1) The macroglomerular complex consisted of four anatomically separated compartments; 2) A large compartment (the cumulus) at the entrance of the antennal nerve received input from receptor neurons responding to the major pheromone component; 3) Another large compartment, located dorso-medially of the cumulus (the dorso-medial compartment) received input from receptor neurons tuned to the second pheromone component; 4) Two ventrally located compartments received input from two receptor neuron types, co-localized in the same sensillum. Each neuron type responded strongest to one of two interspecifically acting signals, shown to interrupt the pheromone attraction. 5) The function of the dorso-medial compartment was further verified by selective arborizations in this compartment by a projection neuron showing strong response to antennal stimulation with the second pheromone component. At low concentration, the neuron responded synergistically to stimulation with the binary pheromone mixture. Accepted: 29 July 1998     

Projection pattern of poreplate sensory neurones in honey bee worker,Apis mellifera L. (Hymenoptera : Apidae)

The projections of olfactory receptor cells of the poreplate sensilla were studied in the worker honey bee, Apis mellifera L. (Hymenoptera : Apidae) by filling single sensilla iontophoretically with cobalt chloride. Successful fillings of individual sensilla lead to staining of one to 22 sensory neurones. All stained receptor cell axons are uniglomerular. Seven fillings of poreplates from the 5th flagellar segment in different animals were compared to analyse the distribution patterns of the receptor cell axons in the antennal lobe. The sensory neurones of individual poreplates project to widely distributed glomeruli in the antennal lobe. The projection patterns of different poreplates are not the same, but may be overlapping.     

Distinct Projections of Two Populations of Olfactory Receptor Axons in the Antennal Lobe of the Sphinx Moth Manduca sexta

The central projections of olfactory receptor cells associatedwith two distinct types of antennal sensilla in the sphinx mothManduca sexta were revealed by anterograde staining. In bothsexes, receptor axons that arise from sexually isomorphic, type-IItrichoid sensilla (and possibly some basiconic sensilla) projectto the spheroidal glomeruli in the ipsilateral antennal lobe.Each axon terminates in one glomerulus. Axons from a limitedregion of the antenna project to glomeruli throughout the lobe,arguing against strict topographic mapping of antennal receptorcells onto the array of glomeruli. Axons of sex-pheromone-selectivereceptor cells in the male-specific type-I trichoid sensillaproject exclusively to the sexually dimorphic macroglomerularcomplex (MGC). Axons from sensilla on the dorsal surface ofthe antenna are biased toward the medial MGC and those fromventral sensilla, toward the lateral MGC. Some receptor-cellaxons branch before reaching the MGC, but their terminals arealways confined to one of the two main glomerular divisionsof the MGC, the cumulus and toroid. These findings confirm thatprimary-afferent information about pheromonal and non-pheromonalodors is segregated in the antennal lobe and suggest that thereis a functional correspondence between particular olfactoryreceptor cells and specific glomeruli. Chem. Senses 20: 313–323,1995.     

The antennal lobe of Libellula depressa (Odonata,Libellulidae)

Here we describe the antennal lobe of Libellula depressa (Odonata, Libellulidae), identified on the basis of the projections of the afferent sensory neurons stemming from the antennal flagellum sensilla. Immunohistochemical neuropil staining as well as antennal backfills revealed sensory neuron terminal arborizations covering a large portion of the antennal lobe. No clear glomerular structure was identified, thus suggesting an aglomerular antennal lobe condition as previously reported in Palaeoptera. The terminal arbors of backfilled sensory neurons do, however, form spherical knots, probably representing the connections between the few afferent neurons and the antennal lobe interneurons. The reconstruction revealed that the proximal part of the antennal nerve is divided into two branches that innervate two spatially separated areas of the antennal lobe, an anterioventral lobe and a larger posteriodorsal lobe. Our data are consistent with the hypothesis that one tract of the antennal nerve of L. depressa contains olfactory sensory neurons projecting into one of the sublobes, while the other tract contains thermo-hygroreceptive neurons projecting into the other sublobe.     

The antennae of neopseustid moths: Morphology and phylogenetic implications, with special reference to the sensilla (Insecta, Lepidoptera, Neopseustidae)

The antennae of Lepidoptera Neopseustidae were examined with the scanning electron microscope. The studied species, Nematocentropus cfr. omeiensis, Neopseustis meyricki, Synempora andesae, Apoplania valdiviana and Apoplania penai possess nine types of antennal flagellum sensilla: multiporous large sensilla basiconica, multiporous thin sensilla basiconica, multiporous small sensilla basiconica, multiporous sensilla trichodea, multiporous sensilla coeloconica; uniporous sensilla chaetica; aporous sensilla chaetica, aporous stylus-shaped sensilla chaetica, aporous sensilla styloconica.The multiporous sensillum type here termed “multiporous large sensillum basiconicum” is unknown from other Lepidoptera and probably constitutes an autapomorphy of the family Neopseustidae. This sensillum type is remarkable by having a single base in female Apoplania and Synempora while in male Apoplania it has a bifid or trifid base, and in male Synempora it is composed of two or three incompletely separated hairs. This may be the first recorded example of a sexually dimorphic lepidopteran sensillum type. The stylus-shaped sensillum chaeticum is a primitive type which occurs only in some lower Lepidoptera.     

Structure and development of the insect antennodeutocerebral system

The structure and postembryonic development of antennae and deutocerebrum in various insect orders are reviewed. First, the number and/or size of system components, i.e. antennal sensilla, neuroreceptors, deutocerebral neurons and synaptic complexes (glomeruli), are compared in adult insects. Second, the neuronal organization of the system is examined. Evidence of projection of the neuroreceptors from the 2 basal antennal segments (scape and pedicel) in the antennal mechanosensory and motor center and from the distal segments (flagellum) in the antennal lobe is discussed. Third, the types of cerebral neurons found in the antennal lobe are described. Fourth, all synaptic contacts between neurons in the antennal lobe take place in discrete glomeruli whose ultrastructure and neurotransmitters are examined. Evidence of individual identifiability of glomeruli is given. Fifth, various sexual dimorphisms present in the antenna and antennal lobe, related or not to sex pheromone perception, are described at sensillar, neuronal, and glomerular levels. Sixth, the postembryonic development of neurons and glomeruli is analyzed in holo- and hemimetabolous insects. In conclusion, the columnar organization of the system is emphasized, alternative models of antennal-neuron projection into glomeruli are considered, and the functional significance of identified glomeruli is discussed.     

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。     

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.     

A neuroanatomical study on the organization of the central antennal pathways in insects

Summary Receptor cell axons from the antennal flagellum terminate in the glomeruli of the ipsilateral deutocerebrum in Periplaneta americana and Locusta migratoria. Processes from several groups of deutocerebral neurons also enter the glomeruli and terminate in characteristic branching patterns. There, they contact the antennal axons. Connections are both convergent and divergent. Not only do single central neurons collect the inputs from many receptor cells, but receptor axons were often observed to branch and terminate at more than one deutocerebral neuron. The axons from a portion of the neurons go to form the deutocerebral bundle of the tractus olfactorioglobularis. These axons of the bundle terminate in the ipsilateral calyx of the corpus pedunculatum and in the lateral lobus protocerebri. The processes of the majority of the deutocerebral neurons stay within the deutocerebrum itself and may serve as local interneurons. Part of some antennal fibers terminate in the lobus dorsalis. The lobus glomeratus receives inputs from the maxillary palps and also from processes of deutocerebral neurons.Electron microscopy of synaptic connections and anatomical experiments reveal a complicated pattern of connections between receptor axons and higher order neurons as well as between higher order neurons themselves within the glomeruli.The ratio of the number of antennal fibers to that of relay fibers could easily lead to the interpretation, that the deutocerebrum merely serves as a device for reducing the number of transmission channels. However, coupled with physiological data, anatomical details such as conand divergence of input and interconnections between input channels suggest rather a filtering system and a highly complicated integrative network.     

Antennal sensory system of Periplaneta americana L.

The morphology of the antennal hair-sensilla of Periplaneta americana, their distribution and frequency on the antennal flagellum have been examined by transmission- and scanning-electron microscopy. The types of sensilla were distinguished with respect to physiologically relevant criteria such as wall structure and number of sensory cells. Among the sensilla of the antenna of the adult male, long, single-walled sensilla with four sensory cells (types sw B), Probably responsible for reception of sexual pheromones, are most frequent, representing about 54% of the antennal sensilla. About half of these sensilla are newly-formed at the imaginal ecdysis; the other half are derived from the shorter type sw B sensilla of the nymphal antenna. Short type sw B sensilla are present in all larval stages of both sexes and in adult females as well. During the imaginal ecdysis of males, however, the length of these sensilla increases to double that found in nymphs. Dendritic branches also increase in number. During postembryonic development, the number of sensory fibers in the antennal flagellum increases nearly 20-fold, from 14,000 in the first larval instar to about 270,000 in the adult male. The greatest increase, approximately 90%, occurs during the last developmental stage.     

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     

Antennal movements induced by odour and central projection of the antennal neurones in the honey-bee

Movements of the antennae induced by odour were investigated. Odour presented to the antenna of one side induced both antennae to move to that side. The EMGs recorded from the flexor muscles of both scapes showed that the latency of the movement of the ipsilateral flagellum when induced by odour was about 71 msec shorter than that of the contralateral flagellum. Recording electrical activities from the antennal nerve showed that there are more than 14 neurones in the antenno-motor externus.The distribution of the antennal nerve in the brain was investigated histologically by the injection of fluorescent dye. Antennal sensory neurones terminated at the glomeruli in the antennal lobe, in the dorsal lobe, in the protocerebrum, and in the commissural part of the suboesophageal ganglion. Injection of the fluorescent dye into the antennal nerve after degeneration of the antennal sensory neurones showed that the antennal motoneurones run in the ventral side of the antennal and dorsal lobes, and terminate in the marginal region of the ipsilateral oesophageal connective.The difference in latency of odour-induced flagellar movements is discussed in relation to the histological results and the unitary responses in the brain reported previously.     

Physiological responses and central nervous projections of antennal olfactory receptor neurons in the adult desert locust, Schistocerca gregaria (Orthoptera: Acrididae)

Olfactory receptor neurons present in two morphological sensillum types on the male Schistocerca gregaria antenna were for the first time investigated physiologically when stimulated with behaviourally relevant odours. Neurons present in trichoid/basiconic sensilla showed clear excitatory responses to compounds present in the male-produced aggregation pheromone and also to a plant produced compound. Sensilla could be categorised physiologically according to the responses of their receptor neurons to the tested stimuli. Also receptor neurons present in sensilla coeloconica responded to aggregation pheromone components, but always in an inhibitory fashion. These neurons could, however, be excited by a plant produced compound and by some acids present in the nymphal odour. The antennal lobe of the male S. gregaria was observed to contain about 1000 very small glomerular structures. Single receptor neurons were stained from the antenna to the antennal lobe using a cobalt lysine technique. These stainings revealed a multi glomerular axonal branching pattern of antennal receptor neurons.Abbreviations AN antennal nerve - AL antennal lobe - RN receptor neuron