Spatial organization of the antennal lobe in Cylindroiulus punctatus (Leach) (Myriapoda : Diplopoda)

The topography of the antennal afferent pathway has been studied in detail for the first time in a myriapod, Cylindroiulus punctatus, by cellular staining, following localized application of cobalt chloride to the cut end of one antenna. At the lateral entrance of the sensory antennal nerve into the deutocerebrum, 3 main groups of tracts have been distinguished. In the antennal lobe, there are two groups of glomeruli: a ventral group of 3 glomeruli and a dorsal group of 15 or 16 glomeruli. The number, position and dimensions of the glomeruli indicate that the glomerular organization is globally invariant (5 individuals).     

Constancy and variability of identified glomeruli in antennal lobes: computational approach in <Emphasis Type="Italic">Spodoptera littoralis</Emphasis>

The primary olfactory centres share striking similarities across the animal kingdom. The most conspicuous is their subdivision into glomeruli, which are spherical neuropil masses in which synaptic contacts between sensory and central neurons occur. Glomeruli have both an anatomical identity (being invariant in location, size and shape) and a functional identity (each glomerulus receiving afferents from olfactory receptor neurons that express the same olfactory receptor). Identified glomeruli offer a favourable system for analysing quantitatively the constancy and variability of the neuronal circuits, an important issue for understanding their function, development and evolution. The noctuid moth Spodoptera littoralis with its well-studied pheromone communication system has become a model species for olfaction research. We analyse here its glomerular organisation based on ethyl-gallate-stained and synapsin-stained preparations. Although we have confirmed that the majority of glomeruli can be individually identified in various antennal lobes, we have recognised several types of biological variability. Some glomeruli are absent, possibly indicating the lack of the corresponding receptor neuron type or its misrouting during development. The antennal lobes vary in global shape and, consequently, the spatial location of the glomerular changes. Although they do not prevent glomerulus identification when quantitative analysis methods are used, these variations place limits on the straightforward identification of glomeruli in functional studies, e.g. calcium-imaging or single-cell staining, when using conventional three-dimensional maps of individual antennal lobes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users. This work was supported by research grants from INRA (Projet Jeune Equipe and Projet S.P.E.) to S.A. and J.P.R. and from ANR-BBSRC 07 BSYS 006 (Pherosys) to J.P.R. and S.A. and by a PhD grant from INRA Departments M.I.A. and S.P.E. to L.C.     

Deutocerebrum of the cockroach Blaberus craniifer burm. Quantitative study and automated identification of the glomeruli

The glomerular organization of the hemideutocerebrum is analyzed quantitatively, using only spatial position, in four individuals (eight hDTCs) after a visual identification of glomeruli on graphic reconstructions. In order to assess directly the invariance of the neuropil in an insect brain the following is done: (1) The position of each glomerulus is compared to the position A′ it should occupy if the hDTCs were identical. It is shown that in 80 and 71% of the cases, respectively, intra- and interindividual comparisons in the studied glomerulus is the nearest to A′. (2) The actual position is equally compared to the theoretical location A″ each glomerulus should occupy if its absolute position could be changed but not its relative position with respect to its neighbors. The calculation of A″ is based on process (3). In 86 and 80% of the cases, respectively, it is found that the actual position is that which is nearest to A″. (3) An automated identification process, based on absolute and relative locations, but completely independent of visual identification, is described. It allows the identification of 77 and 74% of glomeruli, respectively. These matchings are in 96 and 90% of the cases identical to the visual matchings. The location predictability of most glomeruli is discussed to show the existence, nature, and limits of the hemideutocerebral invariance.     

Comparative study of the antennal lobes and their afferent pathway in the worker bee and the drone (Apis mellifera)

Summary The topography of the antennal afferent path-ways was studied comparatively in the worker bee and the drone of Apis mellifera L. by cellular marking, following localized application of cobalt chloride to the cut end of one antenna. This study dealt principally with the first relay of the afferent pathway in the glomeruli of the antennal lobe. The counting and measurement of all the glomeruli were performed on 5 worker bees and 5 drones. An important sexual dimorphism, represented by 4 large and easily identifiable glomerular complexes, was demonstrated in the drone. In both worker bee and drone, four main regions of the glomerular neuropil were distinguished according to corresponding afferent bundles. The worker possessed 166 glomeruli and the drone 103. The number, position and dimensions of the glomeruli indicated that the glomerular organization was unvarying in worker bees and in drones. Concerning the internal structure of the glomeruli, two types were distinguished: the great majority (95%) exhibited a cortical layer, whereas in the 7 posterior glomeruli the synaptic fields of association seemed to be scattered throughout the whole volume. The main results of this work (glomerular invariance, sexual dimorphism) support the hypothesis of the functional unit of the glomeruli.Unité de Recherche Associée au CNRS, UA 483     

Morphology of the olfactory system in the predatory mite Phytoseiulus Persimilis

The predatory mite Phytoseiulus persimilis locates its prey, the two-spotted spider mite, by means of herbivore-induced plant volatiles. The olfactory response to this quantitatively and qualitatively variable source of information is particularly well documented. The mites perform this task with a peripheral olfactory system that consists of just five putative olfactory sensilla that reside in a dorsal field at the tip of their first pair of legs. The receptor cells innervate a glomerular olfactory lobe just ventral of the first pedal ganglion. We have made a 3D reconstruction of the caudal half of the olfactory lobe in adult females. The glomerular organization as well as the glomerular innervation appears conserved across different individuals. The adult females have, by approximation, a 1:1 ratio of olfactory receptor cells to olfactory glomeruli.     

Influence of 3 beta-blockers on the diameter of glomeruli isolated from the renal cortex of rats

The purpose of the study was to determine a direct vascular effect of beta-blockers on isolated glomeruli of rat kidney. The glomeruli were isolated by sieving and their diameters measured with a micrometer before and after addition of each of three beta-blockers. The diameter of the glomeruli increases (6,7%) with verapamil, a calcium inhibitor, but remains unchanged in the same experimental conditions as well with propranolol, drug which decreases renal plasma flow, than with nadolol and tertatolol, drug increasing renal haemodynamics. The location and the mechanism of the glomerular vasoactivity of these different beta-blockers are discussed.     

Organization of the teleostean nucleus rotundus.

The nucleus rotundus of 21 species of teleosts was studied by a modified Bodian and the Golgi method to clarify the histological organization, with special reference to the cell lamination and the glomerular formation. The common components of the nucleus in all species are as follows: a thick fiber bundle which comes from the commissura horizontalis and enters the nucleus from the dorsal surface, many small cells, large cells, glomeruli, and a surrounding fibrous capsule. The nuclei of all species studied are classified into three types mainly on the distribution of the small cells, and to a lesser degree on the location of the large cells and the glomeruli. The first type of nucleus has small cells, large cells and glomeruli throughout its extent. In the second type of nucleus, many small cells form a peripheral cell layer, while the large cells and glomeruli are found all over the nucleus. The third type of nucleus is clearly laminated. It is composed of four layers arranged concentrically around a central fiber net in the following order: a glomerular layer, a fibrous layer, a small-cell layer, and a peripheral fibrous capsule. In some species, the large cells are located in the fibrous capsule, and all glomeruli contain a star-like structure, which corresponds to the tips of the large cell dendrites.     

Multiple factors shape development of olfactory glomeruli: Insights from an insect model system

The antennal system of the moth Manduca sexta is a useful model for studies of the development of olfactory glomeruli, the complex synaptic structures that typically underlie the initial processing of olfactory input in vertebrates and invertebrates. In this review, we summarize cellular events in the construction of glomeruli in Manduca and highlight experiments that reveal factors that influence glomerulus development. By methodically manipulating each of various cell types, both neuronal and glial, that contribute to glomerular architecture, we have found that: olfactory receptor axons lay a template for developing glomeruli, stabilization of the template by glial cells is necessary to permit subsequent steps in development of the glomeruli, and the hormone that regulates adult development causes production of adequate numbers of glial cells. Neither electrical activity nor the presence of a serotonin-containing neuron that persists throughout development is required for a glomerular pattern to develop; these factors might, however, influence the synaptic organization of individual glomeruli. © 1996 John Wiley & Sons, Inc.     

Demonstration of 2 distinct glomerular populations by a sieving technic in the kidney cortex of the pig

Amelioration of sieving technics for glomeruli isolation aims at obtention of purer and more homogeneous preparations, presenting a high preservation degree for glomerular functional studies. We have recently demonstrated the necessity to use sieves adapted to the glomeruli size of different considered animals as well as to use kidneys having exactly the same weight in order to obtain very homogeneous glomeruli suspensions. This study presents a new amelioration in the homogeneity of the glomeruli diameter through a preliminary dissection of the renal cortex in order to isolate glomeruli situated in the same particular cortical zone. Pig renal cortex, because of its size, agrees well with a fine dissection in order to dissociate the superficial and the juxta-medullary zones. Glomeruli are isolated with 160/120 micro mesh sieves. Diameter mean value is 218.8 +/- 30.1 micro in superficial glomeruli and 270.4 +/- 30.1 micro in juxta-medullary ones, highly significant difference, (p less than 0.001). Moreover, repartition frequency histograms of the juxta-medullary glomerular populations diameter presents a large shifting to higher values. This renal dissection preceding the glomeruli isolation sieving technique contributes to better the homogeneity of the isolated glomeruli suspensions and opens the way to the original study of the comparative in vitro vasoreactivity of these two different glomerular populations after incubation with physiological or pharmacological reagents.     

Constancy and variability of glomerular organization in the antennal lobe of the silkmoth

We investigated the anatomical organization of glomeruli in the antennal lobes (ALs) of male silkmoths. We reconstructed 10 different ALs and established an identification procedure for individual glomeruli by using size, shape, and position relative to anatomical landmarks. Quantitative analysis of these morphological characteristics supported the validity of our identification strategy. The glomerular organization of the ALs was roughly conserved between different ALs. However, we found individual variations that were reproducibly observed. The combination of a digital atlas with other experimental techniques, such as electrophysiology, optical imaging, and genetics, should facilitate a more in-depth analysis of sensory information processing in silkmoth ALs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Tomoki Kazawa and Shigehiro Namiki contributed equally to this work. This research was supported by Grant-in-Aid for Scientific Research from the Japan Ministry of Education, Culture, Sports, Science, and Technology (area no. 454, to R.K.).     

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.     

Caste- and sex-specific adaptations within the olfactory pathway in the brain of the ant Camponotus floridanus

Olfaction plays a key role in mediating ant behavior, and ant societies are characterized by caste- and sex-specific division of labor. We propose that caste- and sex-specific adaptations in the olfactory pathway promote differences in olfactory behavior. This study compares olfactory centers in the brain of large (major) workers, small (minor) workers, virgin queens, and males of the carpenter ant Camponotus floridanus. The number of glomeruli in the antennal lobe was similar in the female castes, although the glomerular volumes differed. Males had approximately 45% fewer glomeruli compared to females (approximately 258 and approximately 434) and one antennal sensory tract was absent. A dual output pathway to the mushroom bodies was present in males. In contrast to females, however, the number of glomeruli connected to the medial antennocerebral tract was substantially smaller than those associated with the lateral tract. All glomeruli in the male antennal lobe contained serotonergic processes, whereas in the female castes glomeruli in the large tract six cluster lacked serotonergic innervations. We conclude that differences in general glomerular organization are subtle among the female castes, but sex-specific differences in the number, connectivity and neuromodulatory innervation of glomeruli are substantial and likely to underlie differences in olfactory processing and learning.     

Glomerular interactions in olfactory processing channels of the antennal lobes

An open question in olfactory coding is the extent of interglomerular connectivity: do olfactory glomeruli and their neurons regulate the odorant responses of neurons innervating other glomeruli? In the olfactory system of the moth Manduca sexta, the response properties of different types of antennal olfactory receptor cells are known. Likewise, a subset of antennal lobe glomeruli has been functionally characterized and the olfactory tuning of their innervating neurons identified. This provides a unique opportunity to determine functional interactions between glomeruli of known input, specifically, (1) glomeruli processing plant odors and (2) glomeruli activated by antennal stimulation with pheromone components of conspecific females. Several studies describe reciprocal inhibitory effects between different types of pheromone-responsive projection neurons suggesting lateral inhibitory interactions between pheromone component-selective glomerular neural circuits. Furthermore, antennal lobe projection neurons that respond to host plant volatiles and innervate single, ordinary glomeruli are inhibited during antennal stimulation with the female’s sex pheromone. The studies demonstrate the existence of lateral inhibitory effects in response to behaviorally significant odorant stimuli and irrespective of glomerular location in the antennal lobe. Inhibitory interactions are present within and between olfactory subsystems (pheromonal and non-pheromonal subsystems), potentially to enhance contrast and strengthen odorant discrimination.     

Development of the cerebellar glomeruli in the ontogeny of hens

By means of light and electron microscopy development of the cerebellar glomeruli has been studied in the hen ontogenesis. Two successive stages have been revealed: protoglomerular (the 16th-18th days of incubation) and glomerular (the 19th day of incubation--the end of the 3d week after hatching). Specific peculiarities of their structural organization are presented. A suggestion is made on an inductive effect of the afferent mossy fibers on processes of morphological formation of the cerebellar glomeruli.     

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     

Spatial representation of odours in the antennal lobe of the moth Spodoptera littoralis (Lepidoptera: Noctuidae)

Glomeruli within the antennal lobe (AL) of moths are convergence sites for a large number of olfactory receptor neurons (ORNs). The ORNs target single glomeruli. In the male-specific cluster of glomeruli, the macroglomerular complex (MGC), the input is chemotypic in that each glomerulus of the MGC receives information about a specific component of the conspecific female sex pheromone. Little is known about how neurons that detect other odorants arborize in and amongst glomeruli. The present study focuses on how sex pheromones and biologically relevant semiochemicals are represented in the ALs of both sexes of the moth Spodoptera littoralis. To assess this, we optically measured odour-evoked changes of calcium concentration in the ALs. Foci of calcium increase corresponded in size and shape with anatomical glomeruli. More than one glomerulus was normally activated by a specific non-pheromonal odorant and the same glomerulus was activated by several odorants. All odorants and pheromone components tested evoked unique patterns of glomerular activity that were highly reproducible at repeated stimulations within an individual. Odour-evoked patterns were similar between individuals for a given odorant, implicating a spatial olfactory code. In addition, we demonstrated that activity patterns evoked by host-plant related volatiles are similar between males and females.     

Functional divergence of spatially conserved olfactory glomeruli in two related moth species

In different moth species, the number and spatial arrangement of olfactory glomeruli in the antennal lobe (AL) vary widely, but the spatial map within a species is thought to be invariant, making it possible to identify single glomeruli across individuals. We investigated the relationship between the physiological tuning of pheromone-selective interneurons and their association with specific, identified glomeruli in the macroglomerular complex (MGC) of the noctuid moth, Heliothis subflexa. Three odorants that are required for pheromone-source location in this species were tested individually and in blends. Recordings from 27 pheromone-specific projection neurons (PNs) indicated that the majority (48%) were selectively activated by the major pheromone component of this species, Z-11-hexadecenal (Z11-16:Ald), with 33% primarily tuned to Z-9-hexadecenal and 19% to Z-11-hexadecenol. Intracellular staining revealed that the dendrites of PNs tuned to Z11-16:Ald always branched within the largest glomerulus of the MGC, the cumulus. Similarly, each of the other two classes of PN was associated with a different 'satellite' glomerulus in the MGC. The spatial configuration of the four-glomerulus H. subflexa MGC was indistinguishable from that previously reported in the closely related species, Heliothis virescens. Hence, as these two species diverged, changes in the association of satellite MGC glomeruli with particular odorants have occurred without a measurable change in the anatomical arrangement of the glomerular array.     

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.