Destruction in vivo de neurones ocellaires chez la Blatte, Periplaneta americana

Cobalt chloride has on the ocellus of the cockroach Periplaneta americana, the same destroying effect as a thermocauterisation or electrocoagulation. When an iontophoretic diffusion of cobalt chloride is done without any current from the ocelli, the second-order ocellar neurons are destroyed yet no modification is observed in the vital functions of the cockroach. Cobalt chloride iontophoresis could be used to destroy ocellar neurons only if these ocellar neurons are not going to be immediately replaced. Experiments show that the ocellar neuron killed is replaced after apolysis, but if the substitute neuron is destroyed in its turn, the destruction is definitive. These results suggest two methods of destruction for second-order ocellar neurons: one for larvae and one for adult cockroaches.     

Interneurones subserving ocelli in two species of trichopterous insects: morphology and central projections

Summary The central projections of ocellar interneurones in two species of trichopterous insects Agrypnia varia F. and Limnephilus flavicornis F. were analysed by use of cobalt iontophoresis. The interneurones were classified into three groups: large-, medium- and small-caliber neurones based on the diameters of the axons. Seven large-diameter neurones project from each lateral ocellus into the central nervous system. Of these, four neurones terminate in the posterior slope (three ipsilateral and one contralateral). Three neurones possess branches in the contralateral posterior slope and proceed down the cervical connective into the thoracic ganglia. Medium-sized neurones connect the neuropiles of the three ocelli to each other. Small-diameter neurones contact the contralateral lobula and medulla of the optic lobes and connect the three ocellar neuropiles. Large-diameter neurones of the median ocellus were found to terminate bilaterally or ipsilaterally in the posterior slope. In the posterior slope four different subregions can be recognised: (1) the dorso-lateral, (2) the ventro-lateral, (3) the lateral, into which large-diameter interneurones of the lateral ocelli send branches, and (4) the medial, innervated by interneurones of the median ocellus. Interneurones of the median ocellus send branches into the lateral region as well.     

Lateral ocellar nerve projections in the dragonfly brain

Summary The central projections of the lateral ocellar neurons of the dragonfly were examined using whole nerve cobalt iontophoresis, supplemented by sectioning of the nerve and brain for inspection in the light and electron microscopes. At E.M. level the presence of cobalt in filled axon profiles and cell bodies was confirmed by analysis of X-ray energy spectra in the microscope.The pathways, cell body sites and terminal arborizations of four large (7–25 m diameter) lateral ocellar neurons are described. Two of these fibers arborize in the ipsilateral posterior neuropil of the protocerebrum and two cross the brain and arborize in the contralateral posterior neuropil. Within each half of the posterior neuropil, two spatially separated regions of ocellar input have been identified. These regions receive median ocellar input plus input from either the ipsi- or contralateral ocellus, but not both. The arborizations of the contralateral fibers are more extensive than those of the ipsilateral fibers.One of the contralateral neurons crosses the brain in the region of the protocerebral bridge giving off a collateral in that region before descending to the posterior neuropil. This collateral arborizes almost immediately in a region receiving input from arborizations of a number of small ocellar neurons (those less than 5 m in diameter) from the ipsilateral ocellar nerve, together with small neurons from the median ocellar nerve, forming a region in each half of the brain which receives input from all three ocelli. The small lateral ocellar neurons associated with these arborizations have cell bodies adjacent to the lateral ocellar tracts.This work was supported in part by National Institute of Health Grants 2 RO1 EY-00777 and 1 KO4 EY-00040     

东方蜜蜂背单眼的结构和胚后发育

本研究通过形态解剖和BrdU免疫组织化学方法对东方蜜蜂Apis cerana Fabricius背单眼的胚后发育过程进行了比较研究,结果表明:东方蜜蜂的每一个背单眼都包括角膜晶体、角膜生成细胞、小网膜细胞以及后部的单眼神经。蜜蜂的背单眼起源自头壳上皮;其胚后发育的高峰期集中在蛹发育的前3d;其新细胞主要来源于上皮细胞和圆锥形单眼囊周围细胞的有丝分裂;单眼同脑的联系在P1期前后就已经建立;角膜晶体的形成在P5以后。说明单眼的结构和发育同其功能密切相关。     

Central projections of first-order ocellar interneurons in the bug Triatoma infestans (Heteroptera: Reduviidae)

The projections of first-order ocellar interneurons were analyzed in the hematophagous bug Triatoma infestans by cobalt filling. The axons run between the calyces of the mushroom bodies and dorsal of the central body to different regions of the brain and the subesophageal and thoracic ganglia. The interneurons can be grouped into large L cells and small S cells. The L cells have cell bodies ranging from 11.5 to 25 μm and axons ranging from 8 to 25 μm diameter (measured in the ocellar nerve); the S cells have smaller cell bodies of 9 μm or less and axon diameters less than 5 μm. The projections of ten L cells are described in detail; they project to the protocerebral posterior slope (PS), the other ocellus (O), the optic neuropile, and the subesophageal, pro-, meso-, and metathoracic ganglia, either to ipsi- (PS I, II), or contra- (PS IV, V), or bilateral areas. In this case projections occur to the same areas (PSO, PS III) or different areas at each side (PSOE; E = eye). Large-descending (LD) first-order interneurons project to the contralateral posterior slope of the protocerebrum, the deutocerebrum, and subesophageal, pro-, mesa-, and metathoracic areas (LD I-III). Cell bodies are located in the dorsal protocerebral lobes and pars intercerebralis, except the PS II neuron and three LD cells, which are located in the ipsilateral posterior protocerebrum. This is the first report about ocellar pathways in Hemiptera. Their adaptive function is discussed with reference to the bugs' behavior as Chagas disease vectors. © 1996 Wiley-Liss, Inc.     

Lobula plate and ocellar interneurons converge onto a cluster of descending neurons leading to neck and leg motor neuropil in Calliphora erythrocephala

Summary In the fly, Calliphora erythrocephala, a cluster of three Y-shaped descending neurons (DNOVS 1–3) receives ocellar interneuron and vertical cell (VS4–9) terminals. Synaptic connections to one of them (DNOVS 1) are described. In addition, three types of small lobula plate vertical cell (sVS) and one type of contralateral horizontal neuron (Hc) terminate at DNOVS 1, as do two forms of ascending neurons derived from thoracic ganglia. A contralateral neuron, with terminals in the opposite lobula plate, arises at the DNOVS cluster and is thought to provide heterolateral interaction between the VS4–9 output of one side to the VS4–9 dendrites of the other. DNOVS 2 and 3 extend through pro-, meso-, and metathoracic ganglia, branching ipsilaterally within their tract and into the inner margin of leg motor neuropil of each ganglion. DNOVS 1 terminates as a stubby ending in the dorsal prothoracic ganglion onto the main dendritic trunks of neck muscle motor neurons. Convergence of VS and ocellar interneurons to DNOVS 1 comprises a second pathway from the visual system to the neck motor, the other being carried by motor neurons arising in the brain. Their significance for saccadic head movement and the stabilization of the retinal image is discussed.     

The tritocerebral commissure ''dwarf'' (TCD): a major GABA-immunoreactive descending interneuron in the locust

Summary The minor branch of the tritocerebral commissure of the locust,Locusta migratoria, contains only two axons which are from interneurons in the brain descending to the ventral cord ganglia. The smaller of these two neurons, the tritocerebral commissure dwarf (TCD), is immunoreactive to GABA, suggesting that it may be an inhibitory interneuron. We have exploited the accessibility of its axon in the commissure, first, to fill it with cobalt to define its morphology, and second, to record its input characteristics. It has a cell body and arborization of fine branches in the deutocerebrum of the brain, its axon passes contralateral through the tritocerebral commissure and it forms bilateral arborizations in the suboesophageal and three thoracic ganglia. It receives mechanosensory input from many regions of the ipsilateral body and head, and it is sensitive to illumination levels, generally showing greater spontaneous activity in the dark.It is one of the largest GABA-immunoreactive descending interneurons in the locust, suggesting it plays a prominent role in behaviour. Since it is easily accessible for physiological recording, its roles in circuits for particular components of behaviour should be amenable to investigation.     

Sensory interneurons: some observations concerning the physiology and related structural significance of two cells in the crayfish brain

Two large interneurons in the crayfish brain which are sensitive to vibrational stimuli were injected with the fluorescent dye Procion Yellow. The dendritic branching profiles reflect the directional sensitivity of their respective mechanoreceptive fields on the cephalic appendages and integument. One interneuron branches exclusively on the contralateral side of the brain and receives monosynaptic input from the contralateral antenna; the second interneuron branches primarily on the ipsilateral side and is more sensitive to input from ipsilateral receptors although its receptive field is bilateral. The data suggest that these cells are primary and secondary sensory interneurons, respectively.     

Central projections of first-order ocellar interneurons in two orthopteroid insects Acheta domesticus and Periplaneta americana

Summary The central projections of ocellar first-order interneurons in the cricket, Acheta domesticus, and the cockroach, Periplaneta americana, were examined in silver-intensified cobalt preparations. Ten morphologically different types of ocellar interneurons among a total of 44 are recognized in the cricket, and five different types among a total of 26 in the cockroach, indicating that these species have simpler ocellar systems than those described previously in locusts. Ocellar interneurons arborize in the following regions of neuropil in both the cricket and cockroach: the ocellar foci of the posterior protocerebrum, the posterior deutocerebrum, the protocerebral bridge, the ocellar synaptic plexus, ocellar nerves and tracts, and the lobula and medulla of the optic lobes. Ocellar first-order interneurons thus project predominantly to sites where they are likely to synapse with other ocellar and optic-lobe interneurons.     

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.     

The contribution of the pleural type 12 interneuron to swim acceleration in Clione limacina

The pteropod mollusc, Clione limacina, swims by alternate dorsal–ventral flapping movements of its wing-like parapodia. The basic swim rhythm is produced by a network of pedal swim interneurons that comprise a swim central pattern generator (CPG). Serotonergic modulation of both intrinsic cellular properties of the swim interneurons and network properties contribute to swim acceleration, the latter including recruitment of type 12 interneurons into the CPG. Here we address the role of the type 12 interneurons in swim acceleration. A single type 12 interneuron is found in each of the pleural ganglia, which contributes to fast swimming by exciting the dorsal swim interneurons while simultaneously inhibiting the ventral swim interneurons. Each type 12 interneuron sends a single process through the pleural–pedal connective that branches in both ipsilateral and contralateral pedal ganglia. This anatomical arrangement allowed us to manipulate the influence of the type 12 interneurons on the swim circuitry by cutting the pleural–pedal connective followed by a “culture” period of 48 h. The mean swim frequency of cut preparations was reduced by 19% when compared to the swim frequency of uncut preparations when stimulated with 10⁻⁶ M serotonin; however, this decrease was not statistically significant. Additional evidence suggests that the type 12 interneurons may produce a short-term, immediate effect on swim acceleration while slower, modulatory inputs are taking shape.     

Structure predicts synaptic function of two classes of interneurons in the thoracic ganglia of Locusta migratoria

Summary The relationship between synaptic function and structure was examined for 32 spiking interneurons (13 inhibitory and 19 excitatory) in the meso- and metathoracic ganglia of the locust, Locusta migratoria. In no instance was the structure of an excitatory interneuron similar to that of an inhibitory interneuron. However, 12 of the 13 inhibitory interneurons shared a number of structural features, namely a ventromedially located soma, axon(s) projecting into contralateral connective(s), and a laterally bowed primary neurite. Structurally the excitatory interneurons formed a more heterogeneous group. Even so, 12 of the 19 had a combination of structural features in common, namely laterally located somata and axon(s) projecting into contralateral connective(s). The clear differences in structure of the two main groups of inhibitory and excitatory interneurons suggest that other neurons with structures similar to members of these two groups can be classified as inhibitory and excitatory, respectively. Thus we propose that structure predicts synaptic function for two distinct groups of interneurons in the thoracic ganglia of locusts. Present address: Department of Biology, McGill University, Montreal, Qubeck, Canada     

The organization of exteroceptive sensory inputs to interneurons of the flight neuropil in locusts

1. Thirty-seven pairs of mesothoracic interneurons respond selectively to visual or ocellar stimuli corresponding to deviations from course in flight, expressed as angular rotation around the three spatial axes. 2. Sensitivities to roll and yaw are very strongly associated. All interneurons showing a directional preference for yaw rotations showed the same preference for roll rotations. A few roll-sensitive cells were not directionally sensitive to yaw. Some interneurons respond exclusively to pitch rotations, most to both pitch and roll/yaw. 3. Approximately equal numbers of interneurons prefer pitch up, pitch down, roll/yaw to the ipsilateral side and roll/yaw to the contralateral side. All four possible combinations of pitch (up or down) with roll/yaw (ipsilateral or contralateral) preferences occur with equal probability. 4. No relationship between neuronal structure and directional properties could be discerned. 5. The average latency of the ocellar EPSPs recorded in the interneurons is not significantly different from the average latency of the ocellar spike in the descending neurons (at the same temperature and in the same ganglion). The average ocellar IPSP latency is 8.5 ms longer. The data support the hypothesis that most EPSPs are derived from monosynaptic inputs from the DNs, and most IPSPs from polysynaptic inputs. A few EPSPs are also derived from polysynaptic inputs. 6. Most of these neurons are sensitive to wind, at least some directionally so, in a manner functionally compatible with their visual or ocellar directionality, and most are excited. Two neurons respond to movement of small objects in the visual field, and 5 to high frequency sound.     

Effects of excitatory amino acid antagonists on synaptic transmission in the ampullae of Lorenzini of the skate Raja clavata

Summary The spectral sensitivity of the ocellus in the cucumber looper moth, Anadevidia peponis, was investigated by recording electroretinograms (ERGs). The peak sensitivities were observed at 340 nm in the ultraviolet and at 520–540 nm in the green. Selective spectral adaptation revealed the existence of at least two receptor types in the ocellar retina. The ratio of green to ultraviolet sensitivities for an ocellus whose ocellar nerve was cut was higher than that for an intact ocellus. It is suggested that efferent signals which control the spectral sensitivity of the ocellus are present in the ocellar nerve.Abbreviations ERG electroretinogram - GR/UV green to ultraviolet sensitivities - ON ocellar nerve     

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     

Second-order ocellar neurons in the brain of the honeybee (Apis mellifera)

Summary Electrophoretic injection of Procion Yellow M-R4 into the ocellar tract of the worker bee has revealed the following:Two types of giant axon run from the lateral ocellus to the circumesophageal neuropile, where one branches ipsilaterally and the other contralaterally. A third type comes from the median ocellus and can be traced into the cervical connectives. The largest dendritic complex is in the circumesophageal neuropile; in addition, fiber endings have been demonstrated in the following areas: in the subretinal region, along the optic commissure, in the medulla interna, in the subesophageal ganglion and between the neurosecretory cells of the pars intercerebralis. — The giant fibers are enclosed in a glial sheath.Three types of cell body are described. One is associated with the glia; another, larger cell type comprises giant-axon somata. The third type of cell is small, and cannot yet be identified.Some of the histological results are discussed with respect to the possible function of the ocellus.     

Neuronal connections in the ocellus of the wasp (Paravespula vulgaris L.)

Summary Studies of the dorsal ocelli of the wasp Paravespula vulgaris (L.) led to the following results: Under a biconvex corneal lens, 150 m in thickness, about 600 receptor cells are located. The rhabdomeres of two adjacent cells form a closed plate-like rhabdom (0.5–1.0 m in thickness, 6 m in width and 10–25 m in depth or length).In the lateral ocellus the receptor cells synapse up to 8 ocellar nerve fibers, and in the median ocellus they synapse up to 16 (20–30 m thick) ocellar nerve fibers.The ocellar synaptic plexus may display three types of synapses between the two types of neurons: (i) Receptor-cell axons are presynaptic to dendrites of the first-order interneurons. (ii) Dendrites of the first-order interneurons are presynaptic to receptor-cell axons. (iii) The subunits of a dendrite of first-order interneurons form synapses with each other.The present work was partially supported by the Stiftung Volkswagenwerk     

Sound localisation in crickets

Intracellular recordings were made in the brain of the cricket Gryllus bimaculatus from an ascending auditory interneuron (AN1). Acoustic stimuli with calling song temporal pattern were delivered via earphones in a preparation with the acoustic trachea cut (attenuation of crossing sound > 30 dB). The input-output function of this cell was then determined by recording its responses to stimulation of the ipsilateral ear alone, of the contralateral ear alone and to stimulation of both ears simultaneously with the same or different carrier frequencies and intensities.This interneuron was excited by the ear ipsilateral to its axon and dendritic field and unresponsive to stimuli presented to the axon-contralateral ear alone. However, in binaural stimulation experiments, the response to a constant ipsilateral stimulus was progressively reduced as the intensity of a simultaneous contralateral stimulus was increased, above a threshold intensity.Tuning curves for threshold of this inhibition, determined in binaural stimulation experiments, indicated significant inhibition in the range 3–20 kHz with lowest threshold at 4–5 kHz. The inhibition was unaffected by sectioning of the contralateral circumoesophageal or neck connective, indicating that the inhibitory influence crosses the midline at the level of the prothoracic ganglion. Intracellular recordings from AN1 in the prothoracic ganglion confirmed that it was indeed neurally inhibited by inputs from the contralateral ear.Tuning curves for excitation of an omega neuron (ON1) by the ear ipsilateral to its soma and also the tuning of inhibition of ON1 by its contralateral ON1 partner, closely match the tuning of inhibition of AN1 and to a lesser extent, of AN2. This was taken as evidence that each AN1 is inhibited by the contralateral ON1. The significance of this interaction for directional hearing and phonotaxis is discussed.Abbreviations AP/CHP action potentials per chirp - AN1, AN2 ascending auditory interneurons 1, 2 - ON1 omega neuron 1 - ipsi ipsilateral contra contralateral - PTG prothoracic ganglion loc lateral ocellar nerve - On optic nerve an antennal nerve - coc circum-oesophageal connective so sound off