Morphologic characteristics and responses of the neurons of the right parietal ganglion in Lymnaea stagnalis to stimulation of the sensory structures

Intracellular recordings have been made of the responses of 22 neurons of the central part of the dorsal surface of the right parietal ganglion of the snail Lymnaea stagnalis to adequate stimulation of chemo-, photo- and mechanoreceptor cells of the mantle and head skin including tentacles and lips. It was shown that the main bulk of the neurons investigated has broad receptive fields in the body wall and mantle, being able to respond to all types of the applied stimuli. Alongside, single neurons were revealed which receive single-mode input, either a mechanosensory or chemosensory one. Morphological studies indicate that the neurons are unipolar and have usually one, sometimes several projections. They differ in the pattern of branching as well as in the projections to peripheral nerves. However, almost all of them have vast dendritic regions in the central nervous system including central sensory nucleus of the right parietal ganglion.     

Octopaminergic neurons in the locust brain: morphological,biochemical and electrophysiological characterisation of potential modulators of the visual system

The two Protocerebral-Medulla 4 neurons (PM4a and b) in the locust brain have adjacent cell bodies in the medial deutocerebrum. They project through the posterior protocerebrum, forming limited arborisations en route, and enter the lobula and medulla of the ipsilateral optic lobe, where they form extensive, overlapping arborisations. The PM4a and b neurons are octopamine immunoreactive. Their octopamine content (approximately 25 pg per cell) is confirmed by gas chromatography-mass spectrometry; each cell contains approximately 25 pg p-octopamine. Simultaneous intracellular recording from exposed PM4a and b cell bodies reveals that the two cells are physiologically indistinguishable. They receive multimodal sensory inputs. Tactile/mechanosensory stimuli to much of the animal's body and head, acoustic stimuli, and simple visual stimuli all give rise to e.p.s.p.s and action potentials in the PM4 cell body. Simultaneous recording from the cell body in the deutocerebrum and the axon in the lobula demonstrates that action potentials are predominantly initiated in the deutocerebrum and propagate centrifugally, towards the optic lobe. Occasionally, bright light flashes will initiate an action potential in the axon in the optic stalk, which probably propagates bidirectionally: centripetally to the cell body, and centrifugally into the optic lobe. The extensive arborisations in the lobula and medulla are therefore likely to be sites of octopamine release. Because PM4 neurons are octopaminergic, project to the optic lobe, and receive modalities of sensory input known to dishabituate the Descending Contralateral Movement Detector (DCMD) visual interneuron, it is proposed that PM4 neurons are neuromodulatory — mediating dishabituation or arousal of the visual system.     

The anatomical pathways for antennal sensory information in the central nervous system of the cricket, Gryllus bimaculatus

Antennae are one of the major organs to detect chemo- and mechanosensory cue in crickets. Little is known how crickets process and integrate different modality of information in the brain. We thus used a number of different anatomical techniques to gain an understanding of the neural pathways extending from the antennal sensory neurons up to centers in the brain. We identified seven antennal sensory tracts (assigned as T1?C7) utilizing anterograde dye filling from the antennal nerve. Tracts T1?CT4 project into the antennal lobe (AL), while tracts T5 and T6 course into the dorsal region of the deutocerebrum or the suboesophageal ganglion, and finally, tract T7 terminates in the ventral area of flagellar afferent (VFA). By analyzing autofluorescence images of the AL, we identified 49 sexually isomorphic glomeruli on the basis of shape, relative position and size. On the basis of our sensory-tract data, we assigned the glomeruli into one of four separate groups. We then three-dimensionally reconstructed the internal structures in the AL (glomeruli) and the VFA (layers). Next in the protocerebrum, we identified both the tracts and their terminations from the AL and VFA. We found that 10 tracts originate in the AL, whereas there are at least eight tracts from the VFA. Several tracts from the AL share their routes with those from the VFA, but their termination areas are segregated. We now have a better anatomical understanding of the pathways for the antennal information in cricket.     

FMRFamide-like immunocytochemistry in the brain and subesophageal ganglion of <Emphasis Type="Italic">Triatoma infestans</Emphasis> (Insecta: Heteroptera). Coexpression with β-pigment-dispersing hormone and small cardioactive peptide B

The distribution of FMRFamide (FMRFa)-like immunoreactivity (LI) was studied in the brain and subesophageal ganglion of Triatoma infestans, the insect vector of Chagas disease. The neuropeptide displayed a widespread distribution with immunostained somata in the optic lobe, in the anterior, lateral, and posterior soma rinds of the protocerebrum, and around the antennal sensory and mechanosensory and motor neuropils of the deutocerebrum. FMRFa-immunoreactive profiles of the subesophageal ganglion were seen in the mandibular, maxillary, and labial neuromeres. Immunostained neurites were detected in the medulla and lobula of the optic lobe, the lateral protocerebral neuropil, the median bundle, the calyces and the stalk of the mushroom bodies, and the central body. In the deutocerebrum, the sensory glomeruli showed a higher density of immunoreactive processes than the mechanosensory and motor neuropil, whereas the neuropils of each neuromere of the subesophageal ganglion displayed a moderate density of immunoreactive neurites. Colocalization of FMRFa-LI and crustacean pigment-dispersing hormone-LI was found in perikarya of the proximal optic lobe, the lobula, the sensory deutocerebrum, and the labial neuromere of the subesophageal ganglion. The distribution pattern of small cardioactive peptide B (SCP_B)-LI was also widespread, with immunolabeled somata surrounding every neuropil region of the brain and subesophageal ganglion, except for the optic lobe. FMRFa- and SCP_B-LIs showed extensive colocalization in the brain of this triatomine species. The presence of immunolabeled perikarya displaying either FMRFa- or SCP_B-LI confirmed that each antisera identified different peptide molecules. The distribution of FMRFa immunostaining in T. infestans raises the possibility that FMRFa plays a role in the regulation of circadian rhythmicity. The finding of immunolabeling in neurosecretory somata of the protocerebrum suggests that this neuropeptide may also act as a neurohormone.This work was sponsored by the Facultad de Ciencias Biomédicas, Universidad Austral. Part of this work was performed at the Division of Neurobiology, Arizona Research Laboratories (Tucson, Arizona) with the support of a Fulbright Research Award to B.P.S.     

A chemosensory gene family encoding candidate gustatory and olfactory receptors in Drosophila

A novel family of candidate gustatory receptors (GRs) was recently identified in searches of the Drosophila genome. We have performed in situ hybridization and transgene experiments that reveal expression of these genes in both gustatory and olfactory neurons in adult flies and larvae. This gene family is likely to encode both odorant and taste receptors. We have visualized the projections of chemosensory neurons in the larval brain and observe that neurons expressing different GRs project to discrete loci in the antennal lobe and subesophageal ganglion. These data provide insight into the diversity of chemosensory recognition and an initial view of the representation of gustatory information in the fly brain.     

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。     

Central projections from contact chemoreceptors of the locust ovipositor and adjacent cuticle

Contact chemoreceptors (basiconic sensilla) located on the ovipositor and genital segments of the locust serve to control the chemical features of the substrate before and during oviposition. They occur dispersed and also crowded in fields between mechanosensory exteroceptors sensitive to touch or wind (trichoid and filiform sensilla). The central nervous projections of the four chemosensory and one mechanosensory neurons from single basiconic sensilla were stained selectively, focusing on receptors on the ovipositor valves, which usually contact the substrate during the pre-oviposition probing movements. All axons and neurites from one contact chemoreceptor usually stay close together in most of their projections. Segregation occurs mainly when single axons terminate in one neuromere while the others proceed to a different neuromere or ganglion. For projections from one chemoreceptor, there is evidence neither for functional segregation of mechanosensory from chemosensory afferent terminals nor for specific segregation between different chemosensory afferents. The projections from sensilla of dorsal cuticle tend to project rather uniformly along the midline of the terminal ganglion. Comparative staining of touch- and wind-sensitive hair receptor neurons shows mostly central projections, similar to those of neighbouring contact chemoreceptors. From the typical intersegmental projections of most primary afferents and from the lack of segregation into glomerular structures, we conclude that integration of chemosensory information from the genital segments is distributed in the terminal and the 7th abdominal ganglion.     

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     

棉铃虫幼虫脑和咽下神经节的三维结构构建

【目的】解剖棉铃虫Helicoverpa armigera (Hübner) 5龄幼虫脑和咽下神经节及其内部神经髓形态结构,并分析和构建幼虫脑和咽下神经节以及各神经髓的三维结构模型。【方法】采用免疫组织化学方法解剖脑和咽下神经节的内部神经髓结构,利用激光共聚焦显微镜获取脑和咽下神经节扫描图像,然后利用AMIRA 三维图像分析软件进行图像分析,从而构建脑和咽下神经节的三维结构模型,并测量脑和咽下神经节以及内部各神经髓的体积,并分析了相对比例。【结果】 棉铃虫5龄幼虫脑和咽下神经节由围咽神经索连接在一起。脑主要由前脑、中脑和后脑3部分组成。前脑内包括视叶、蕈形体和中央体等形态结构较明显的神经髓。此外,前脑还包括其他位于脑的左右两侧以及背侧和腹侧大量神经髓区域,约占脑总神经髓的59.65%。这些神经髓区域边界不明显。中脑主要包括1对触角叶;后脑位于脑的腹侧和触角叶的下方,体积较小。咽下神经节由3个神经节融合构成,从前到后分别为上颚神经节、下颚神经节和下唇神经节,由于融合的紧密程度高,3个神经节间的边界不明显。【结论】阐明了棉铃虫5龄幼虫脑和咽下神经节的神经髓形态结构,构建了脑和咽下神经节以及内部神经髓的三维结构模型。三维模型可以任意旋转,能从任何角度观察脑、咽下神经节和内部不同神经髓的结构及其它们之间的空间关系。本研究结果对研究棉铃虫脑和咽下神经节信息接收、处理及调控行为的机制奠定了解剖学基础。     

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.     

Combined effects of olfactory and mechanical inputs in antennal lobe neurons of the cockroach

Although it has been known that olfactory and mechanical inputs from the antenna converge in the antennal lobe of the deutocerebrum of the American cockroach, the capacity of antennal lobe neurons to integrate cues from these modalities was never examined. In the present study, neurons responsive to both the odor of lemon oil and to lateral displacement of the antenna were used to compare the effects of unimodal and bimodal stimulation. The combination of olfactory and mechanical stimuli produced increases over unimodal olfactory responses in 61% (30/49) of the neurons. In the remaining neurons the response either decreased (20%; 10/49), or no bimodal interaction was apparent (19%; 9/49). Dye injection (lucifer yellow) following physiological characterization revealed that these bimodal neurons are local neurons or projection neurons. The antennal lobe links the inputs from olfactory and mechanosensory systems and provides a substrate through which olfactory and mechanical stimuli influence one another's effects. Accepted: 29 September 1997     

Functional properties and projection areas of cutaneous receptors in catfish

Summary Neurophysiological studies were conducted in a species of catfish,Ictalurus nebulosus where specialized living habits are coupled with enlargement of certain nervous system structures. These fish, mainly lake bottom dwellers, recognize food only by touch. The entire body surface contains structures resembling mammalian taste buds; the ganglia of the fifth and seventh nerves (receiving input from barbel and head skin) are much larger than in other fish of similar size; the facial lobes, macroscopically invisible in most fish, are prominent. Early anatomical studies reported that the cutaneous buds, considered chemosensitive, project to the brainstem in parallel with tactile paths, but the two modalities remain separate. The facial lobes, the projection area of the cutaneous buds via the seventh nerve, were considered a pure chemosensory structure. In feeding behavior, the chemosensory system was proposed to distinguish sapid from nonsapid substances, the tactile system to localize the food substances.Response properties of single neurons to mechanical and chemical skin stimulations were determined in three successively activated sites: (1) sensory ganglion, (2) facial lobe, and (3) cerebellum. In each location, the majority of neurons were mechanosensitive; only a tiny fraction responded to chemical stimulation. Contrary to early anatomical studies, the two modalities were intermingled, and, particularly the enlarged facial lobes, cannot be considered pure chemosensory structures.Some degree of topographic organization occurred in the ganglion and facial lobe on comparing input from two peripheral barbel nerves. Among chemosensory neurons, some responded only to one, others to several of the applied test solutions. The latter generated distinctive spike trains in response to different test solutions (Fig. 2).Certain response properties, absent in the ganglion, occurred in the facial lobe after synaptic transmission: convergence of afferent fibers on single neurons, indicated by larger receptive fields and by spatial summation of input from two barbel nerves. Stimulation of a single peripheral nerve gave evidence of temporal summation at short conditioning-testing intervals and of inhibition at longer intervals (Fig. 5), suggesting that in many facial lobe units a single stimulus evokes a sequence of excitation followed by inhibition. The latencies of electrically driven units suggest that input from the barbels and head region project to the brainstem, and from there via a multisynaptic path to the cerebellum.This study was supported by U.S. Public Health Service Grants DE 02152 and DE 00248. I am indebted to Mr. R. Hansen, College of Fisheries, University of Washington, for obtaining the fish from Lake Washington.     

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

1. Single unimodal (olfactory) or multimodal (olfactory and mechanosensory) neurons in the antennal lobe of the deutocerebrum of the American cockroach were characterized functionally by microelectrode recording, and their morphological types and positions in the brain were established by dye injection. Thus individual, physiologically identified neurons of known shape could be mapped in reference to the areas of soma groups, glomeruli, tracts and their projection regions in the brain. 2. All of these neurons send processes to deutocerebral glomeruli, i.e., the regions in which the axons of antennal sensory cells terminate. Output neurons have axons that leave the deutocerebrum whereas local interneurons are anaxonic. 3. An output neuron innervates only one glomerulus, sending its axon into the calyces of the corpora pedunculata (CP) in the protocerebrum, where by multiple branching they reach many CP neurons. The same axons send collaterals into the lateral lobe of the protocerebrum. Because of this arrangement, each deutocerebral glomerulus is represented individually and separately in the two projection regions. The fine structure of the endings of the deutocerebral axons in the protocerebrum is described. In the CP calyces they form microglomeruli with typical divergent connectivity. 4. A local interneuron innervates many glomeruli without sending processes to other parts of the brain. 5. Unimodal olfactory and multimodal neurons can be either output neurons or local interneurons; multimodal information is sent to the protocerebrum directly, in parallel with the unimodal information. 6. At least one glomerulus--the macroglomerulus of the male deutocerebrum--is specialized so as to provide an exclusive topographic representation of certain olfactory stimuli not represented elsewhere (female sexual pheromone).     

Suboesophageal neurons involved in head movements and feeding in locusts.

The projections of nerves 6 and 7 of the locust suboesophageal ganglion (SOG) were stained by axonal filling with cobalt chloride. Nerve 6 contains two motoneurons which innervate neck muscles 50 and 51. Sensory neurons innervating hairs on the dorso-occipital region of the head also enter the ganglion through nerve 6 and terminate in a small bilateral plexus. The projections of the head hairs in nerve 6 do not overlap the arborizations of the motoneurons or the neurons of nerve 7, but lie in the same area as descending sensory neurons from wind-sensitive hairs of the front of the head. One branch of nerve 7 (7B) contains two fibres which innervate the salivary gland. These 'salivary' neurons (labelled SN1 and SN2) have their cell bodies in the ganglion. The second branch, 7A, contains sensory neurons from the submentum of the labium, which form four sensory plexuses, two dorsal and two ventral. The sensory plexuses from the submentum have specific regions of overlap with the salivary neurons and with the neck muscle motoneurons. We interpret these as indicating a flow of information from labial receptors signalling head and mouthpart movement to neurons involved in salivation and head movement. We further postulate that the anatomical separation of the various sensory plexuses is indicative of functional localization within the ganglion.     

Morphology of descending statocyst interneurons in the crayfish Procambarus clarkii Girard

Summary The morphological features of descending interneurons that responded to the artificial bending of statolith hairs were assessed with intracellular recording and staining techniques. Seven statocyst interneurons were identified on the basis of their structure and response characteristics and designated as interneurons S1 to S7. All seven identified interneurons project to the optic lobe, where the optic nerve also projects, and to the dorsal part of the tritocerebrum, where the eyestalk motoneurons originate. All except interneuron S6 also extend their major branches to other neuropilar regions. S2 projects to the dorsal part of the deutocerebrum, where the statocyst nerve terminates, and S3 to the dorsal part of deutocerebrum and the antennal lobe. Four other interneurons (S1, S4, S5, S7) also extend their branches to the parolfactory lobe to which the statocyst nerve projects as well as to the deutocerebrum and antennal lobe. The extensive dendritic projections of S1–S7 suggest that they are complex multimodal interneurons rather than simple relay interneurons, receiving at least visual and statocyst sensory information. The function of the antennal lobe branches, however, has yet to be determined since the functional role of antennal input in equilibrium control is unknown.     

Ultrastructure of the antennal sensorial appendage of larvae of Ophonus ardosiacus (Lutshnik, 1922) (Coleoptera, Carabidae) and possible correlations between size and shape and the larval feeding habits

The antennal sensory appendage morphology was studied in 19 species of carabid beetle larvae using scanning electron microscopy. Shape and size of the organ has been re-examined in selected taxa and are compared to figure out possible correlations between antennal sensory structures and larval morphoecological types. Morphometric analysis shows no correlation between antennal sensory appendage dimension and the four most common behavioural types. The ultrastructure of this sensory organ is described for larvae of Ophonus ardosiacus and the possible function is discussed. Olfactory function has been indicated as the most probable. The high number of chemosensory neurons of this multiporous organ suggests a possible ability of fine odour discrimination related to prey choice or host location.     

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.     

Postembryonic development of the antennal lobes in Periplaneta americana L.

Summary The postembryonic development of the antennal lobes of Periplaneta americana L. was examined with light- and electron-microscopical methods. There is no difference in the number of glomeruli and neurons in the antennal lobes of larval and adult animals. At hatching, the first larva already possesses the adult number of approximately 125 glomeruli and 500 to 560 deutocerebral neurons in the dorsolateral cell group of each antennal lobe. During postembryonic development the volume of the deutocerebral neurons increases three- to fourfold. The glomeruli of the first larva have about 7 % of the volume of the corresponding adult glomeruli. Since number, pattern, and size ratio of glomeruli (with the exception of the macroglomerulus) are constant in all larval stages and adult animals, it is possible to identify individual glomeruli. During the whole postembryonic development the ordinary glomeruli show a continuous volume increase, which parallels the increase in antennal sensory input. The macroglomerulus develops by way of special growth of two to four neuropil units, but not before the last three to four larval stages and only in males. Its growth precedes the formation of antennal pheromone receptors during the final molt; these receptors are known to project into the macroglomerulus. The development of the macroglomerulus in the last larval stages of the male may be caused by a genetically fixed growth program of specific deutocerebral neurons.Supported by the Deutsche Forschungsgemeinschaft (Scha 291/1)     

Localization of cholecystokinin-like immunoreactivity in the central nervous system of Triatoma infestans (Insecta: Heteroptera)

The distribution of cholecystokinin-like immunoreactivity was studied in the central nervous system of the heteropteran insect Triatoma infestans using high-sensitivity immunocytochemistry. In the protocerebrum, CCK-IR somata were observed in the anteromedial, anterolateral and posterior cell-body layers. The neuropils displayed different densities of immunoreactive neurites. Few immunoreactive somata were found in the optic lobe in both the medial and lateral soma rinds, as well as in the proximal optic lobe. Immunoreactive fibers were present in the medulla and lobula neuropils. The sensory deutocerebrum contained a higher number of immunopositive perikarya than the antennal mechanosensory and motor center. The antennal lobe glomeruli displayed a moderate density of immunoreactive fibers. With regard to the subesophageal ganglion, numerous CCK-IR somata were found close to the root of the mandibular nerve; others were present in the soma rind of the remaining neuromeres. CCK-IR perikarya were present in both thoracic ganglia, with the abdominal neuromeres containing the highest number of positive somata. The neuropils of both ganglia showed moderate densities of immunopositive processes. The distribution of CCK-LI in somata and neuropils of central nervous system of T. infestans is widespread suggesting that a CCK-like peptide may act mainly as a neuromodulator in the integration of information from distinct sensory receptors.     

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.