Neural organisation in the first optic ganglion of the nocturnal bee <Emphasis Type="Italic">Megalopta genalis</Emphasis>

Each neural unit (cartridge) in the first optic ganglion (lamina) of the nocturnal bee Megalopta genalis contains nine receptor cell axons (6 short and 3 long visual fibres), and four different types of first-order interneurons, also known as L-fibres (L1 to L4) or lamina monopolar cells. The short visual fibres terminate within the lamina as three different types (svf 1, 2, 3). The three long visual fibres pass through the lamina without forming characteristic branching patterns and terminate in the second optic ganglion, the medulla. The lateral branching pattern of svf 2 into adjacent cartridges is unique for hymenopterans. In addition, all four types of L-fibres show dorso-ventrally arranged, wide, lateral branching in this nocturnal bee. This is in contrast to the diurnal bees Apis mellifera and Lasioglossum leucozonium, where only two out of four L-fibre types (L2 and L4) reach neighbouring cartridges. In M. genalis, L1 forms two sub-types, viz. L1-a and L1-b; L1-b in particular has the potential to contact several neighbouring cartridges. L2 and L4 in the nocturnal bee are similar to L2 and L4 in the diurnal bees but have dorso-ventral arborisations that are twice as wide. A new type of laterally spreading L3 has been discovered in the nocturnal bee. The extensive neural branching pattern of L-fibres in M. genalis indicates a potential role for these neurons in the spatial summation of photons from large groups of ommatidia. This specific adaptation in the nocturnal bee could significantly improve reliability of vision in dim light. B.G. is grateful for travel awards from the Royal Physiographic Society, the Per Westlings Fond, the Foundation of Dagny and Eilert Ekvall and the Royal Swedish Academy of Sciences. E.J.W. acknowledges the receipt of a Smithsonian Short-Term Research Fellowship and thanks the Swedish Research Council, the Crafoord Foundation, the Wenner–Gren Foundation and the Royal Physiographic Society of Lund for their ongoing support. W.T.W. was supported by general research funds from the Smithonian Tropical Research Institute     

Fine structure of the first optic ganglion (lamina) of the cockroach, Periplaneta americana

The structural organization of the first optic ganglion (lamina) of the cockroach (Periplaneta americana) was investigated by the use of light and electron microscopy. Each compound eye of the cockroach is composed of up to 2000 visual units (ommatidia) of the fused rhabdom type. The ommatidia themselves consist of eight receptor cells which terminate as axons in either the first or second optic ganglion. Three different short visual fibre types end in two separate strata in the lamina, and one long fibre type ends in the second optic ganglion. Monopolar second-order neurons with wide field branching patterns in the middle stratum of the first synaptic region have postsynaptic contacts with short visual fibres. Horizontal fibre elements with branching patterns at different levels of the lamina apparently form three horizontal plexuses with presynaptic and/or postsynaptic connections to first- and secondorder neurons. The lack of well-organized fibre cartridges containing a constant number of first and second order neurons in each fascicle and the presence of only unistratified wide field monopolar cells could represent, as compared to other insect orders, a primitive stage in the development of the first optic ganglion.     

A neural network to improve dim-light vision? Dendritic fields of first-order interneurons in the nocturnal bee <Emphasis Type="Italic">Megalopta genalis</Emphasis>

Using the combined Golgi-electron microscopy technique, we have determined the three-dimensional dendritic fields of the short visual fibres (svf 1–3) and first-order interneurons or L-fibres (L1-4) within the first optic ganglion (lamina) of the nocturnal bee Megalopta genalis. Serial cross sections have revealed that the svf type 2 branches into one adjacent neural unit (cartridge) in layer A, the most distal of the three lamina layers A, B and C. All L-fibres, except L1-a, exhibit wide lateral branching into several neighbouring cartridges. L1-b shows a dendritic field of seven cartridges in layers A and C, dendrites of L2 target 13 cartridges in layer A, L3 branches over a total of 12 cartridges in layer A and three in layer C and L4 has the largest dendritic field size of 18 cartridges in layer C. The number of cartridges reached by the respective L-fibres is distinctly greater in the nocturnal bee than in the worker honeybee and is larger than could be estimated from our previous Golgi-light microscopy study. The extreme dorso-ventrally oriented dendritic field of L4 in M. genalis may, in addition to its potential role in spatial summation, be involved in edge detection. Thus, we have shown that the amount of lateral spreading present in the lamina provides the anatomical basis for the required spatial summation. Theoretical and future physiological work should further elucidate the roles that this lateral spreading plays to improve dim-light vision in nocturnal insects. B.G. is grateful for grants from the Royal Physiographic Society, the Per Westlings Fond, the Foundation of Dagny and Eilert Ekvall and the Royal Swedish Academy of Sciences. E.J.W. would like to thank the Smithsonian Tropical Research Insitute, the Swedish Research Council, the Crafoord Foundation, the Wenner-Gren Foundation and the Royal Physiographic Society of Lund for their ongoing support.     

Cholinergic neurons in the lamina ganglionaris of the blowfly Calliphora erythrocephala

Summary The distribution of putative cholinergic neurons in the lamina of the blowfly Calliphora erythrocephala was studied by immunocytochemical and histochemical methods. Three different antibodies directed against the AChsynthesizing enzyme, choline acetyltransferase (ChAT), revealed a cholinergic population of fibres running parallel to the laminar cartridges, which have branch-like structures at the distal lamina border. Cell bodies in the chiasma next to the lamina border were also labelled by the anti-ChAT antibodies. Monopolar cell bodies in the nuclear layer were faintly labelled. The distribution of the acetylcholine hydrolyzing enzyme, acetylcholine esterase (AChE), was revealed by histochemical staining and was similar to the ChAT immunocytochemistry. The arrangement of ChAT positive fibres in transverse and longitudinal sections and the distribution of AChE stained fibres indicate that the amacrine cells of the lamina are cholinergic cells.We dedicate this work to Prof. F. Zettler who passed away in fall 1988: K.-H. Datum, I. Rambold     

The superposition eye of Cloeon dipterum: The organization of the lamina ganglionaris

Summary The lamina ganglionaris of the superposition eye of Cloeon dipterum is composed of separate optic cartridges arranged in a hexagonal pattern. Each optic cartridge consists of one central, radially branched monopolar cell (Li) surrounded by a crown of seven retinula cell terminals and two more unilaterally branched monopolar cells (La1/La2) situated close together outside the cartridge. Projections to neighbouring cartridges have not been observed.In most cases, synaptic contacts could be seen between a presynaptic retinula cell and more than two other postsynaptic profiles, which belong to monopolar cells or sometimes to glial cells.Seven retinula cell fibers of one ommatidium pass in a bundle through the basement membrane, run into their respective cartridges without changing orientation and terminate at approximately equal levels in the lamina. Long visual fibers with endings in the medulla are not visible in the superposition eye lamina, but are present in the lateral apposition eye. The relationship between the behaviour of the animal, optic mechanisms of the superposition eye and the structure of the lamina is discussed.     

Anatomical identification of spectral receptor types in the retina and lamina of the Australian orchard butterfly,Papilio aegeus aegeus D.

Summary The nine receptor cells examined in each ommatidium of the butterfly Papilio aegeus aegeus can be named according to their positional orientation across the fused rhabdom. Six of them end as short visual fibres (svf) in the second stratum of the lamina, whereas the remaining three retinula cells (lvf) pass together with the lamina fibres (L-fibres) the first optic ganglion and the outer chiasma to end in the three most distal layers of the second optic ganglion, the medulla. The organization of the retinula-cell axons within the pseudocartridge and the cartridge remains almost uniform throughout the first optic ganglion. Five L-fibres, which have their origin in the fenestrated layer (FL), join each laminar cartridge before entering the neuropil of the first optic region. Four of these L-fibres (L-1, L-2, L-3 and L-4) could be definitely located and characterized using Golgi-stained light- and electron-microscopic techniques. Whereas L-1 and L-3 show a lateral branching pattern reaching only fibres of the same cartridge, L-2 and L-4 have long collaterals interconnecting several neighbouring cartridges in a characteristic pattern. Serial sections of silver-impregnated retinula-cell axons as well as L-fibres were investigated for their synaptic connectivity patterns between and within these fibres. These cellular interactions and possible information processing are discussed.     

Characterization of the fibrillar layer at the epithelial-mesenchymal junction in tooth germs

A characteristic layer containing numerous fibrils is associated with the basement membrane of the inner enamel epithelium during the early stages of odontogenesis. However, its nature is not well understood. In this study, the layer was examined with high-resolution electron microscopy and immuno-histochemical staining. Tooth germs of monkeys (Macaca fuscata) were studied and each fibril in the layer was found to be a tubular structure, 8–9 nm in width, resembling a basotubule, the tubular structure previously observed in various basement membranes. The space between the fibrils was filled with a network formed by irregular anastomosing strands with an average thickness of 4 nm; these strands resembled the cords forming the network in the lamina densa of basement membranes. After immunoperoxidase staining, fine threads immunoreactive for laminin staining were seen winding along the strands of the network, and 1.5-nm wide filaments, immunoreactive for type IV collagen, took the form of a network arrangement. The 5-nm-wide ribbon-like structures associated with the strands were identified as heparan sulfate proteoglycan by immunostaining. These results are similar to those obtained for the cord network of the lamina densa. The fibrillar layer therefore represents a highly specialized lamina fibroreticularis of the basement membrane of the inner enamel epithelium, and rich in basotubules.     

Neuronal connectivity patterns in the compound eyes of Artemia salina and Daphnia magna (Crustacea: Branchiopoda)

Summary The neuronal types and patterns in the visual system of the species Artemia salina and Daphina magna have been studied with the Golgi method and electron microscopy. The lamina contains five classes of neurons: photoreceptor axons, monopolar, centrifugal, tangential and amacrine neurons. The terminals of the receptor axons are distributed in two (A. salina) or three (D. magna) layers. The dilated terminals have an extensive and wide array of fine branches. One axon from each ommatidium bypasses the lamina and terminates in the medulla in A. salina. A. salina has four types of monopolar neurons, two of which are stratified, whereas in D. magna only two types are found, one of which is bistratified. Tangential T-neurons connect the lamina with the protocerebrum. D. magna has in addition one tangential T-neuron connecting both the lamina and the medulla with the protocerebrum. In both species monopolar-type centrifugal neurons connect the medulla and the lamina, whereas that of A. salina has a wide laminar distribution. Both species also have amacrine cells in the lamina. The medulla contains, besides those shared with the lamina, transmedullary neurons (two types in A. salina), amacrine cells and neurons originating in the protocerebrum.Cartridge-type synaptic compartments are lacking in the investigated species, although a periodic arrangement is discernible in the distal portion of the lamina of A. salina. The receptors from three types of specialized contacts in Artemia, one of which involves a dyad. D. magna has only one-to-one synapses. Neurosecretory fibres are absent in A. salina.The investigation was supported by the Swedish Natural Science Research Council (Grant No. 2760-009)     

The organization of the lamina ganglionaris of the hemipteran insects,Notonecta glauca,Corixa punctata and Gerris lacustris

Summary Neuronal elements, i.e. first and second order neurons, of the first optic ganglion of three waterbugs, N. glauca, C. punctata and G. lacustris, are analyzed on the basis of light and electron microscopy.Eight retinula cell axons, leaving each ommatidium, disperse to different cartridges as they enter the laminar outer plexiform layer. Such a pattern of divergence is one of the conditions for neuronal superposition; it is observed for all three species of waterbugs. The manner in which the receptors of a single bundle of ommatidia split of within the lamina, whereby information from receptors up to three or five horizontal rows away can converge upon the same cartridge, differs among the species. Six of the eight axons of retinula cells R1-6, the short visual fibers end at different levels within the bilayered lamina, whereas the central pair of retinula cells R7/8, the long visual fibers, run directly through the lamina to a corresponding unit of the medulla. Four types of monopolar cells L1–L4 are classified; their branching patterns seem to be correlated to the splitting and termination of retinula cell axons. The topographical relationship and synaptic organization between retinula cell terminals and monopolar cells in the two laminar layers are identified by examination of serial ultrathin sections of single Golgi-stained neurons.An attempt is made to correlate some anatomical findings, especially the neuronal superposition, to results from physiological investigations on the hemipteran retina.     

The unusual visual system of the Strepsiptera: external eye and neuropils

Adult males of the insect order Strepsiptera are characterized by an unusual visual system that may use design principles from compound as well as simple eyes. The lenses of this eye are unusually large and focus images onto extended retinae. The light-gathering ability of the lens is sufficient to resolve multiple points of an image in each optical unit. We regard each unit as an independent image-forming eye that contributes an inverted partial image. Each partial image is re-inverted by optic chiasmata between the retinae and the lamina, where the complete image could be assembled from the neighboring units. The lamina, medulla and lobula are present, but their organization into cartridges is not clearly discernable. Fluorescent fills, whole-tissue stains, and synaptotagmin immunohistochemistry show that the optic neuropils nevertheless are densely packed, and that several parallel channels within the medulla underlie each of the lenses. The size and shape of the rhabdoms, as well as a relatively slow flicker-fusion frequency could suggest that these eyes evolved through a nocturnal life stage.Abbreviations O object size - U object distance - I image size - f focal length - A lens aperture - D lens diameter - interommatidial angle - S light sensitivity of optical system     

Sur la structure des parois de l'appareil circulatoire dePhoronis psammophila Cori (Phoronida,Lophophorata)

Resume Trois types de parois ont été décrits dans l'appareil circulatoire du tronc dePhoronis psammophila. La succession des diverses couches de chaque type est la suivante: 1. cellules péritonéales — lame basale — rares cellules endothéliales; 2. cellules myoépithéliales — lame basale — rares cellules endothéliales; 3. une couche de muscles circukires, puis une de muscles longitudinaux — épaisse lame basale — endothélium continu.

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On the wall structure of the circulatory system inPhoronis psammophila Cori (Phoronida, Lophophorata)

Summary Three types of wall structure of blood vessels have been described. It consists of the following distinct layers, from exterior to interior: 1. peritoneal cells — thin basal lamina — some endothelial cells; 2. myoepithelial cells resting on a basal lamina — some endothelial cells; 3. circular and longitudinal muscle layers of myoepithelial cells — thick basal lamina — continuous endothelial lining.

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Abréviations C capillaire - ce cavité coelomique - ce cellule endothéliale - cm cellule myoépithé'liale - cp cellule péritonéale - fc fibre musculaire circulaire - fl fibre musculaire longitudinale - gs globule sanguin - lb lame basale - m myofibrille - mf myofilament - tvp tissu vasopéritonéal - V vaisseau sanguin     

Proliferation pattern and early differentiation of the optic lobes in Drosophila melanogaster

Summary The larval and early pupal development of the optic lobes in Drosophila is described qualitatively and quantitatively using [³H]thymidine autoradiography on 2-m plastic sections. The optic lobes develop from 30–40 precursor cells present in each hemisphere of the freshly hatched larva. During the first and second larval instars, these cells develop to neuroblasts arranged in two epithelial optic anlagen. In the third larval instar and in the early pupa these neuroblasts generate the cells of the imaginal optic lobes at discrete proliferation zones, which can be correlated with individual visual neuropils.The different neuropils as well as the repetitive elements of each neuropil are generated in a defined temporal sequence. Cells of the medulla are the first to become postmitotic with the onset of the third larval instar, followed by cells of the lobula complex and finally of the lamina at about the middle of the third instar. The elements of each neuropil connected to the most posterior part of the retina are generated first, elements corresponding to the most anterior retina are generated last.The proliferation pattern of neuroblasts into ganglion mother cells and ganglion cells is likely to include equal as well as unequal divisions of neuroblasts, followed by one or two generations of ganglion mother cells. For the lamina the proliferation pattern and its temporal coordination with the differentiation of the retina are shown.     

A dynamic model of a two-synapse feedback loop in the vertebrate retina

The theoretical properties of synapses such as those in the retina which operate on graded potentials are developed using work on tetrodotoxin-treated synapses as a basis. A linearized model of a two-synapse negative feedback loop analogous to the bipolaramacrine feedback loop in the retina possesses a frequency response which developes an increasingly prominent resonance peak at higher input levels and under some circumstances shows instability. Psychophysical studies have shown that the visual system also exhibits this behaviour suggestive of progressive underdamping in a harmonic oscillator. Evidence in favor of the hypothesis that resonance originates in the loop is presented, the conclusions being that the loop functions to tune the retina to a range of temporal frequencies.Symbol Table V millivolts depolarisation relative to resting membrane potential - V _n , V _out pre-synaptic, post-synaptic depolarisation respectively - V _e , V _i reversal potential or e.m.f. of post-synaptic battery of excitatory, inhibitory synapses respectively - V _out (max) maximal post-synaptic depolarisation defined by Eq.(10c) - V ₀ input depolarisation for feedback loop - depolarisation potential normalised with respect to V _out(max) - I milliamperes of depolarising current - I _s post-synaptic membrane current - I _c cable current - I ₀ input depolarising current for feedback loop - I _max maximal physiological value for I ₀ =V _e ·G ₀ - i depolarising current normalised with respect to I_max - e reversal potential normalised with respect to V _e - r _i specific resistivity of internal medium - R _m membrane resistance - C _m membrane capacitance - cable space constant = R _m /2R _i - g ₀ characteristic cable conductance = 2/R _m ·R _i - G conductance of post-synaptic membrane - G _s maximal post-synaptic membrane conductance - g fraction of receptors occupied by transmitter = G/G _s - r the ratio G _s/G ₀ - membrane time constant = R _m·C_m - ₁ time constant of transmitter release in response to presynaptic depolarisation [Eq. (6)] - ₂ time constant of decay of g [Eq. (7a)] - _{2 2}·[1+k·exp(b·v _in)]^–1 - k equilibrium constant for transmitter-receptor interaction [Eq. (7a)] - b constant determining increase in rate of transmitter release with pre-synaptic depolarisation [Eq. (6)] - c concentration of transmitter in synaptic cleft normalised with respect to resting concentration - H _jk (s) linearised transfer function for synaptic transmission from neurone j to neurone k - G(s) H₁₂(s) - H(s) -H₂₁(s) - F(s) linearised closed-loop transfer function - _x 2 times spatial frequency of counterphase grating pattern - the ratio (1+s)/(_x)₂ - a the product (1+r)·k - d density of bipolars per unit area     

Arsenic‐induced NFκβ transactivation through Erks‐ and JNKs‐dependent pathways in mouse epidermal JB6 cells

Carnosine, a alanylLhistidine dipeptide with antioxidant properties is present at high concentrations in skeletal muscle tissue. In this study, we report on the antioxidant activity of carnosine on muscle lipid and protein stability from both in vitro and in vivo experiments. Carnosine inhibited lipid peroxidation and oxidative modification of protein in muscle tissue prepared from rat hind limb homogenates exposed to in vitro Fenton reactant (Fe²⁺, H₂O₂)generated free radicals. The minimum effective concentrations of carnosine for lipid and protein oxidation were 2.5 and 1 mM, respectively. Histidine and alanine, active components of carnosine, showed no individual effect towards inhibiting either lipid or protein oxidation. Skeletal muscle of rats fed a histidine supplemented diet for 13 days exhibited a marked increase in carnosine content with a concomitant reduction in muscle lipid peroxidation and protein carbonyl content in skeletal muscle caused by subjecting rats to a Fenitrilotriacetate administration treatment. This significant in vitro result confirms the in vivo antioxidant activity of carnosine for both lipid and protein constituents of muscle under physiological conditions.     

The role of cotyledonary tissue in the differentiation of shoots and roots from cotyledon explants of Brassica juncea (L.) Czern.

In cotyledon cultures of Brassica juncea, shoots and roots invariable differentiate at the cut end of the petiole. Organogenesis occurred only if the proximal cut end of the petiole was in contact with the medium. In the absence of the petiole, differentiation from the lamina was rare. Hence investigations were carried out to study the influence of the cotyledonary lamina on regeneration of shoots and roots from the petiolar cut end. The lamina tissue was surgically removed from the cotyledon explants at different durations (0–10 days) after culturing them on either root-forming (basal medium) or shoot-forming (basal medium containing 5.0 M N⁶-benzyladenine) media. The differentiation of roots or shoots from the petioles was dependent on the presence of the lamina for at least 7 days of culture. Quantitative removal of the laminar tissue had a corresponding negative effect on shoot bud differentiation from the petiole. The nature of the lamina factor was found to be auxin-like.     

The first optic ganglion of the bee

Summary The arrangement of first and second order neurons in an optic cartridge and the topographical relationships of the second order neurons within a cartridge and to groups of surrounding cartridges have been analyzed in the visual system of the bee, Apis mellifera, from light and electron microscope studies on Golgi preparations. At the level of the monopolar cell body layer, the nine retinula cell fibres of each ommatidium, the six short visual fibres arranged in a circle surrounding the three long visual fibres, become cartridges as a consequence of the appearance of the second order neurons (L-fibres) which join the R-fibre bundles. Two of the four different L-fibre types, L-1 and L-2, remain together in the centre of the cartridge throughout the lamina. The axons of the L-3 and L-4 fibres, however, have their position integrated into the circle formed by the endings of the short visual fibres. On the basis of further examination of light and especially electron microscopical Golgi material, the different L-fibres can be classified into four types which appear in each cartridge. The clear stratification in the first synaptic region (A, B and C) seems to be the best criterion for a morphological classification since such a classification necessarily also includes a functional basis. According to a naming system based on the position of the lateral processes, L-fibres with side branches in strata A, B and C are called L-1 fibres. Fibres with lateral processes in strata A and B are L-2 fibres; monopolar cell fibres with branches only in the second stratum B are L-fibres of type 3; and all monopolar cells with branches only in stratum C are called L-4 fibres. In addition to the branching pattern covering only the parent cartridge, two of the four fibre types (L-2 and L-4) have long collaterals reaching neighbouring cartridges: L-2 in stratum A and L-4 in stratum C. These collaterals presumably form a substrate for lateral interactions.     

Spectral and polarized light sensitivity of photoreceptors in the compound eye of the cricket (Gryllus bimaculatus)

Summary Retinula cells in the compound eye of the cricket (Gryllus bimaculatus) were recorded intracellularly and stained with Lucifer yellow. Two different methods were used to determine the spectral sensitivity of these cells: a) the spectral scanning method, and b) the conventional flash method. Three spectral types, with S()-curves close to the rhodopsin-absorption functions, were found with _max at 332 nm (UV), 445 nm (blue) and 515 nm (green), respectively.Blue receptors were only recorded in the anatomically specialized dorsal rim area (DRA), and UV and green receptors in the dorsal region of the pigmented part of the eye, whereby green receptors were only found in the ventral eye. On the basis of these results, model calculations are presented for di- and trichromatic colour vision in the cricket.The fluorescence markings revealed green receptors whose axons project with short visual fibres to the lamina, and a UV receptor with a long visual fibre which projects through the lamina to the medulla. The blue receptors send their axons either to the lamina and medulla (long visual fibres) or only to the lamina (short visual fibres).The temporal dynamics of the three receptor types were examined. The blue receptors lack a phasic component of the receptor potential, and the time from stimulus on-set to peak potential is strongly increased compared to the UV and green receptors. Light adaptation reduces the latency to less than half of the dark adapted state.Spectral adaptation experiments revealed an unidirectional coupling between UV and green receptors, and it was found that polarization sensitivity (PS) in blue cells was much higher (PS= 6.5±1.5) than that of UV (PS=1.76±0.05) and green (2.26±0.57) receptors. The functional aspects of the three receptor types are discussed with respect to the presented physiological and morphological data.Abbreviations DA dorsal area - DRA dorsal rim area - PS polarization sensitivity     

A Golgi-electron-microscopical study of the structure and development of the lamina ganglionaris of the locust optic lobe

Summary The gross structure as well as the neuronal and non-neuronal components of the lamina ganglionaris of the locust Schistocerca gregaria are described on the basis of light- and electron-microscopical preparations of Golgj (selective silver) and ordinary histological preparations. The array of optic cartridges within the lamina neuropile — their order and arrangement — and the composition of the cartridges are described. There are six types of monopolar neurons: three whose branches reach to other cartridges and three whose branches are confined to their own cartridges. Retinula axons terminate either in the lamina or the medulla neuropiles. There are three types of centrifugal neurons, two types of horizontal neuron, as well as glia and trachea in the lamina neuropile. The development of the lamina neuropile is described in terms of developing monopolar and centrifugal axons, growing retinula fibres, and composition of the developing optic cartridges.MSN was supported in part by a Fulbrights-Hays Scholarsship. We are grateful to the Science Research Council for its grant to PMJS.