Optic lobe projections of marginal ommatidia in Calliphora erythrocephala specialized for detecting polarized light

Summary The structure of ommatidia at the dorsal eye margin of the fly, Calliphora erythrocephala is specialized for the detection of the e-vector of polarized light. Marginal zone ommatidia are distinguished by R7/R8 receptor cells with large-diameter, short, untwisted rhabdomeres and long axons to the medulla. The arrangement of the R7 microvillar directions along the marginal zone is fan-shaped. Ommatidia lining the dorsal and frontal edge of the eye lack primary screening pigments and have foreshortened crystalline cones. The marginal ommatidia from each eye view a strip that is 5 °–20 ° contralateral to the fly's longitudinal axis and that coincides with the outer boundaries of the binocular overlap.Cobalt injection into the retina demonstrates that photoreceptor axons arising from marginal ommatidia define a special area of marginal neuropil in the second visual neuropil, the medulla. Small-field neurons arising from the marginal medulla area define, in turn, a special area of marginal neuropil in the two deepest visual neuropils, the lobula and the lobula plate. From these arise local assemblies of columnar neurons that relay the marginal zones of one optic lobe to equivalent areas of the opposite lobe and to midbrain regions from which arise descending neurons destined for the the thoracic ganglia.Optically, the marginal zone of the retina represents the lateral edge of a larger area of ommatidia involved in dorsofrontal binocular overlap. This binocularity area is also represented by special arrangements of columnar neurons, which map the binocularity area of one eye into the lobula beneath the opposite eye. Another type of binocularity neuron terminates in the midbrain.These neuronal arrangements suggest two novel features of the insect optic lobes and brain: (1) Marginal neurons that directly connect the left and right optic lobes imply that each lobe receives a common input from areas of the left and right eye, specialized for detecting the pattern of polarized light. (2) Information about the e-vector pattern of sky-light polarization may be integrated with binocular and monocular pathways at the level of descending neurons leading to thoracic motor neuropil.     

A pair of descending neurons with dendrites in the optic lobes projecting directly to thoracic ganglia of dipterous insects

Summary The lobula descending neuron (LDN) of dipterous insects is a unique nerve cell (one on each side of the brain) that projects directly from the lobula complex of the optic lobes to neuropil in thoracic ganglia. In the supraoesophageal ganglia the LDN has two prominent groups of branches of which at least one is dendritic in nature. Postsynaptic branches are distributed in the lobula and some branches, the synaptic relations of which are not yet known, extend to the lobula plate. A second group of branches is found among dendrites of the descending neurons proper, in the lateral midbrain.The arborizations of LDN in the lobula (and lobula plate) map onto a retinotopic neuropil region subserving a posterior strip of the visual field of the compound eye. The arborizations in the lobula complex are extremely variable in size. The numbers of dendritic spines they possess vary greatly between left and right optic lobes of one animal, and between individual animals.     

Serotonin-like immunoreactivity in the optic lobes of three insect species

The cellular localization of 5-HT in the optic lobes of three insect species was assayed with the use of antibodies raised against 5-HT. In Schistocerca, Periplaneta, and Calliphora all neuropil regions of the optic lobe, the lamina, medulla and lobula, contain 5-HT-immunoreactive varicose fibres in different patterns, like columns and layers. Such fibres also connect the lobula to neuropil in the lateral protocerebrum. In Calliphora also 5-HT-positive fibres of the medulla and lobula plate have projections to the lateral protocerebrum, whereas the origin of the lamina fibres is not certain. In all species the processes displaying 5-HT-like immunoreactivity appear to be derived from a relatively small number of cell bodies, each neuron thus having processes over a large volume of the neuropil of the optic lobe in different layers.     

Binocular visual integration in the crustacean nervous system

Although the behavioral repertoire of crustaceans is largely guided by visual information their visual nervous system has been little explored. In search for central mechanisms of visual integration, this study was aimed at identifying and characterizing brain neurons in the crab involved in binocular visual processing. The study was performed in the intact animal, by recording intracellularly the response to visual stimuli of neurons from one of the two optic lobes. Identified neurons recorded from the medulla (second optic neuropil), which include sustaining neurons, dimming neurons, depolarizing and hyperpolarizing tonic neurons and on-off neurons, all presented exclusively monocular (ipsilateral) responses. In contrast, all wide field movement detector neurons recorded from the lobula (third optic neuropil) responded to moving stimuli presented to the ipsilateral and to the contralateral eye. In these cells, the responses evoked by ipsilateral or contralateral stimulation were almost identical, as revealed by analysing the number and amplitude of the elicited postsynaptic potentials and spikes, and the ability to habituate upon repeated visual stimulation. The results demonstrate that in crustaceans important binocular processing takes place at the level of the lobula.     

Immunocytochemical demonstration of S-antigen (arrestin) in the brain of the blowfly Calliphora vicina

S-Antigen (arrestin)-immunoreaction can be considered as a marker for retinal and extraretinal photoreceptors in both vertebrate and invertebrate species. The present immunocytochemical study with the blowfly Calliphora vicina revealed S-antigen immunoreaction in retinal photoreceptors and various groups of neurons bilaterally distributed in the optic lobes and in the proto-, deuto- and tritocerebrum. S-Antigen-immunoreactive processes and terminal formations were found in the lower division of the central body complex and in the neuropil of the mushroom body. Also neuropil regions of the optic lobe, the lamina, medulla and lobula displayed S-antigen-immunoreactive fibers which were arranged in different patterns. These immunocytochemical data suggest that extraocular photoreceptors may be located in various parts of the blowfly brain. They provide a structural basis for further experiments which are needed to identify definitely these elements as extraretinal photoreceptors.     

Genetic dissection of the anterior optic tract of Drosophila melanogaster

Electron microscopy shows that in wild-type Drosophila melanogaster the anterior optic tract (AOT) is formed by about 1260 fibers in males and slightly fewer in females. Golgi staining suggests that most AOT fibers connect the lobula with different regions of the central brain. In the sine oculis (so) and small optic lobes (sol) mutants the number of axons is drastically reduced, by 58% in sol and by 35% in so. In the double mutant sol:so there is a loss of up to 83% of the fibers in the AOT. Approximately half of the remaining 220 fibers form a well defined subbundle of very thin axons which is identifiable in wild type as well as in both single mutants. The fibers of this subbundle neither originate nor terminate in the visual ganglia: instead, they connect two different central brain regions. It is concluded that the combined action of the sol and so mutations abolishes more than 90% of the fibers of visual origin or destination in the AOT. Quantitative analysis of electron micrographs shows that the so and sol mutations act independently on nearly exclusive subsets of axons in the AOT.     

Aminergic neurons in the brain of blowflies and Drosophila: dopamine- and tyrosine hydroxylase-immunoreactive neurons and their relationship with putative histaminergic neurons

Summary The distribution and morphology of neurons reacting with antisera against dopamine (DA), tyrosine hydroxylase (TH) and histamine (HA) were analyzed in the blowflies Calliphora erythrocephala and Phormia terraenovae. TH-immunoreactive (THIR) and HA-immunoreactive (HAIR) neurons were also mapped in the fruitfly Drosophila melanogaster. The antisera against DA and TH specifically labeled the same neurons in the blowflies. About 300 neurons displayed DA immunoreactivity (DAIR) and THIR in the brain and subesophageal ganglion of the blowflies. Most of these neurons were located in bilateral clusters; some were distributed as bilateral pairs, and two ventral unpaired median (VUM) neurons were seen in the subesophageal ganglion. Immunoreactive processes were found in all compartments of the mushroom bodies except the calyces, in all divisions of the central body complex, in the medulla, lobula and lobula plate of the optic lobe, and in non-glomerular neuropil of protocerebrum, tritocerebrum and the subesophageal ganglion. No DA or TH immunoreactivity was seen in the antennal lobes. In Drosophila, neurons homologous to the blowfly neurons were detected with the TH antiserum. In Phormia and Drosophila, 18 HA-immunoreactive neurons were located in the protocerebrum and 2 in the subesophageal ganglion. The HAIR neurons arborized extensively, but except for processes in the lobula, all HAIR processes were seen in non-glomerular neuropil. The deuto- and tritocerebrum was devoid of HAIR processes. Double labeling experiments demonstrated that TH and HA immunoreactivity was not colocalized in any neuron. In some regions there wasm however, substantial superposition between the two systems. The morphology of the extensively arborizing aminergic neurons described suggests that they have modulatory functions in the brain and subesophageal ganglion.     

Compartmentalization of visual centers in the Drosophila brain requires Slit and Robo proteins

Brain morphogenesis depends on the maintenance of boundaries between populations of non-intermingling cells. We used molecular markers to characterize a boundary within the optic lobe of the Drosophila brain and found that Slit and the Robo family of receptors, well-known regulators of axon guidance and neuronal migration, inhibit the mixing of adjacent cell populations in the developing optic lobe. Our data suggest that Slit is needed in the lamina to prevent inappropriate invasion of Robo-expressing neurons from the lobula cortex. We show that Slit protein surrounds lamina glia, while the distal cell neurons in the lobula cortex express all three Drosophila Robos. We examine the function of these proteins in the visual system by isolating a novel allele of slit that preferentially disrupts visual system expression of Slit and by creating transgenic RNA interference flies to inhibit the function of each Drosophila Robo in a tissue-specific fashion. We find that loss of Slit or simultaneous knockdown of Robo, Robo2 and Robo3 causes distal cell neurons to invade the lamina, resulting in cell mixing across the lamina/lobula cortex boundary. This boundary disruption appears to lead to alterations in patterns of axon navigation in the visual system. We propose that Slit and Robo-family proteins act to maintain the distinct cellular composition of the lamina and the lobula cortex.     

Genetical analysis of visual system disorganizer (vid), a new gene involved in normal development of eye and optic lobe of the brain in Drosophila melanogaster

A neuroanatomical screening of a collection of P-element mutagenized flies has been carried out with the aim of finding new mutants affecting the optic lobe of the adult brain in Drosophila melanogaster. We have identified a new gene that is involved in the development of the adult axon array in the optic ganglia and in the ommatidia assembly. We have named this locus visual system disorganizer (vid). Reversional mutagenesis demonstrated that the vid mutant was the result of a P-element insertion in the Drosophila genome and allowed us to generate independent alleles, some of which resulted in semilethality, like the vid original mutant, while the others were completely lethal. A genetic somatic mosaic analysis indicated that the vid gene is required in the eye for its normal development by inductive effects. This analysis also suggests an inductive effect of the vid gene on the distal portion of the optic lobe, particularly the lamina and the first optic chiasma. Moreover, the absence of mutant phenotype in the proximal region of the optic ganglia, including the medulla, the second optic chiasma, and the lobula complex underlying mosaic eyes, is suggestive of an autonomously acting mechanism of the vid gene in the optic lobe. The complete or partial lethality generated by different mutations at the vid locus suggests that this gene's role may not be limited to the visual system, but may also affect a vital function during Drosophila development.     

Distribution of GABA-like immunoreactive neurons in the optic lobes of Periplaneta americana

Summary Specific antisera against protein-conjugated -aminobutyric acid (GABA) were used in immunocytochemical staining procedures to study the distribution of the putative GABA-like immunoreactive neurons in the optic lobes of Periplaneta. GABA-like immunoreactive structures are evident in all three optic neuropil regions. Six different populations of GABAergic neurons, whose perikarya are grouped around the medulla, are found within the optic lobe. The number of these immunoreactive cells varies greatly and corresponds to the number of ommatidia of the eye. In the proximal part of the lamina, a coarse network of GABA-positive fibres is recognizable. These are the processes of large field tangential cells whose fibres pass through the distal surface of the medulla. A second fibre population of the lamina is made up of the processes of the centrifugal columnar neurons whose perikarya lie proximally to the medulla. The medulla contains 9 layers with GABAergic elements of variable immunoreactivity. Layers 1, 3, 5, 7 and 9 exhibit strong labelling, as a result of partial overlapping of the processes of centrifugal and centripetal columnar neurons, tangential fibres and/or lateral processes of perpendicular fibres and (possibly) processes of amacrines. A strong immunoreactivity is found in the proximal and distal layers of the lobula.     

Circadian rhythms in cockroaches

Summary The driving oscillator, which mediates circadian locomotor rhythms in cockroaches, appears to reside in the protocerebrum of the brain. The evidence indicates that the optic lobes are crucial elements in this circadian system, and that control of rhythmicity is mediated through electrical, rather than hormonal, channels. Lesions were placed at various sites within the optic lobes in order to localize the areas controlling rhythmicity. It appears that the two innermost synaptic areas (the lobula and the medulla) constitute the crucial optic lobe elements. The outer synaptic area of the optic lobe (the lamina) is not necessary for the expression of rhythmicity, but does function as a coupling through which light cycles, transduced by the compound eyes, entrain the circadian clock.I would like to thank both Dr. Sue Binkley for her helpful comments in the preparation of this report, and Mr. Eli Levine for his assistance in photography. Support for this research was provided by a grant from the National Science Foundation (NS GB-30497).     

烟青虫成虫脑结构解剖和三维模型构建

【目的】解剖分析烟青虫 Helicoverpa assulta 成虫脑的结构,并构建脑三维结构数字化模型。【方法】利用神经突触蛋白抗体,对烟青虫成虫脑进行免疫组织化学染色标记,利用共聚焦激光扫描显微镜获得脑扫描数码图像,并结合三维图像分析软件对烟青虫脑结构进行识别分析,构建三维模型。【结果】突触蛋白抗体免疫染色将烟青虫脑和颚神经节的神经髓区域清晰标记出来。烟青虫成虫脑与颚神经节愈合而成为一体,中间具有一个孔洞,为食道穿过的通道。脑主要包括前脑、中脑和后脑3部分。依据染色标记结果识别和构建了至少16个脑神经髓结构。这些神经髓包括边界清晰的视叶、前视结节、蕈形体、中央复合体和触角叶及其亚结构。除此之外,还包括围绕这些神经髓的其他前脑神经髓区域,但这部分前脑神经髓内部边界模糊,不容易细分,而将其与颚神经节区域作为一个整体标记为中间脑,占脑总神经髓的55.05%。【结论】识别出烟青虫脑的主要功能结构区域,并成功构建了三维模型。该研究结果为进一步研究烟青虫脑接收、处理和整合感觉信息及调控行为的机制奠定了解剖学基础,并为研究烟青虫或其他昆虫脑结构发育、变异和重塑提供结构形态和体积大小依据。     

The optic lobes of Lepidoptera

Variants of the Golgi-Colonnier (1964) selective silver procedure have been used to show up neurons in insect brains. Neural elements are particularly clearly impregnated in the optic lobes. Three classes of nerve cells can be distinguished; perpendicular (class I), tangential (class II) and amacrine cells (class III). There are many types of neurons in each class which together have a very wide variety of form. Their components are related to specific strata in the optic lobe regions. Short visual cells from the retina terminate in the lamina in discrete groups of endings (optic cartridges). Pairs of long visual fibres from ommatidia pass through the lamina and end in the medulla. Class I cells link these two regions in parallel with the long visual fibres and groups of these elements define columns in the medulla. These in turn give rise to small-field fibres that project to the lobula complex. Tangential processes intersect the parallel arrays of class I cells at characteristic levels. Some are complex in form and may invade up to three regions. Another type provides a direct link between the ipsi- and contralateral optic lobe. Amacrine cells are intrinsic to single lobe regions and have processes situated at the same levels as those of classes I and II cells. A fifth optic lobe region, the optic tubercle, is connected to the medulla and lobula and also receives a set of processes from the mid-brain. There are at least six separate types of small-field relays which could represent the retina mosaic arrangement in the lobula.     

Anatomy of the ocellar interneurons of acridid grasshoppers

Summary The anatomy of the small ocellar interneurons in the brain of the acridid grasshopper Schistocerca vaga was revealed by cobalt-filling the three ocellar nerves and subsequent reconstructions from silver-intensified (Timm's method) serial sections.In total, 61 small ocellar interneurons were repeatedly identified with arborizations in many areas of the brain and optic lobe, including in particular the posterior neuropil, ocellar tracts, protocerebral bridge, lobula, ventral bridge and tritocerebral crotch, calyces, and antenno-glomerular tracts.Each ocellar nerve contains the axons of small cells that arborize in the other two ocellar tracts; these tracts are sites of ocellar integration. Direct interactions between the ocelli and compound eyes are suggested by the projections of small ocellar interneurons into the proximal lobula. Small cell arborizations from all three ocelli are distributed across much of the protocerebral bridge, implying a role for the bridge as an ocellar neuropil within the brain.Four of the small interneurons could be seen in whole-mount preparations and are demonstrated to be identical in five species of acridid grasshoppers of two different subfamilies: Schistocerca vaga, S. gregaria, Gastrimargus africanus, Trimerotropis pallidipennis, and Arphia conspersa.     

Pre-existing neuronal pathways in the developing optic lobes of Drosophila

We have identified a set of larval neurones in the developing adult optic lobes of Drosophila by selectively labelling cells that have undergone only a few mitoses. A cluster of three cells is located in each of the optic lobes near the insertion site of the optic stalk. Their axons fasciculate with fibres of the larval optic nerve, the Bolwig's nerve, and then form part of the posterior optic tract. These cells are likely to be first order interneurones of the larval visual system. Unlike the Bolwig's nerve, they persist into the adult stage. The possibility of a pioneering function of the larval visual system during formation of the adult optic lobe neuropil is discussed.     

Cell degeneration in the developing optic lobes of the sine oculis and small-optic-lobes mutants of Drosophila melanogaster

In the small-optic-lobes (sol) and sine oculis (so) mutants of Drosophila melanogaster extensive cell death occurs in the optic lobes during the first half of pupal development. Gynandromorph flies show that the sol mutation acts primarily on cells of the medulla cortex. Degeneration of medullar ganglion cells occurs at an early stage of cellular differentiation, when their axons have not yet participated in the formation of the second optic chiasma. The so gene, on the other hand, acts on the eye anlagen. The analysis of chimeric flies demonstrates that degeneration in the optic lobes of so flies is a consequence of eye reduction. At the level of the second optic chiasma extensive axonal degeneration can be observed in the mutant. Neurons seem to die after their failure to establish a sufficient number of functional contacts. In sol;so double mutants, the mutational effects are cumulative causing complete degeneration of columnar cell types in pupae without any eye anlage. The tiny rudiments of the optic lobes in eyeless double mutants still contain tangential neurons of the medulla and of the lobula complex. The central brain is reduced in size due to the missing visual fibers, however, its overall appearance is surprisingly normal.     

Brain development in the yellow fever mosquito Aedes aegypti: a comparative immunocytochemical analysis using cross-reacting antibodies from Drosophila melanogaster

Considerable effort has been directed towards understanding the organization and function of peripheral and central nervous system of disease vector mosquitoes such as Aedes aegypti. To date, all of these investigations have been carried out on adults but none of the studies addressed the development of the nervous system during the larval and pupal stages in mosquitoes. Here, we first screen a set of 30 antibodies, which have been used to study brain development in Drosophila, and identify 13 of them cross-reacting and labeling epitopes in the developing brain of Aedes. We then use the identified antibodies in immunolabeling studies to characterize general neuroanatomical features of the developing brain and compare them with the well-studied model system, Drosophila melanogaster, in larval, pupal, and adult stages. Furthermore, we use immunolabeling to document the development of specific components of the Aedes brain, namely the optic lobes, the subesophageal neuropil, and serotonergic system of the subesophageal neuropil in more detail. Our study reveals prominent differences in the developing brain in the larval stage as compared to the pupal (and adult) stage of Aedes. The results also uncover interesting similarities and marked differences in brain development of Aedes as compared to Drosophila. Taken together, this investigation forms the basis for future cellular and molecular investigations of brain development in this important disease vector.     

Rôle of eyes,optic lobes,and pars intercerebralis in locomotory and stridulatory circadian rhythms of Teleogryllus commodus

Locomotory and stridulatory activity rhythms of male crickets (Teleogryllus commodus) were assayed simultaneously following various experimental procedures. These included (a) severing the pathways between the ocelli and the brain, between the ommatidia and the optic lobes, or between the optic lobes and the brain, and (b) RF cauterization of the pars intercerebralis. The results indicate that (1) light-dark cycles which entrain both rhythms are perceived by the compound eyes and not by the ocelli; (2) loss of connexion between the brain and the optic lobes leads to arrhythmicity in both behaviours, but a single optic lobe can maintain rhythmicity; (3) absence of neurosecretory cells in the pars intercerebralis is correlated with loss of stridulatory activity and arrhythmicity in locomotory behaviour. It is suggested that the pars intercerebralis serves as a site of coupling between a circadian pacemaker and various overt behaviours. However, intermediate control by the pars intercerebralis is assumed to be exerted via channels that can be either hormonal or purely neuronal in nature.