Etude topographique des interneurones ocellaires et de quelques uns de leurs prolongements chez Periplaneta americana

The topography of the largest ocellar interneurons in the brain of the cockroach Periplaneta americana was shown with cobalt chloride. The ocellar interneurons coloured from one nerve are confined to the ipsilateral side of the pars intercerebralis; their number and their position vary along the ocellar tract. If two ocellar nerves colour from the ocelli, the interneurons show a bilateral symmetry. Only one interneuron runs through the brain between each ocellus and the contralateral connective to the mesothoracic ganglion. When the injection of cobalt chloride is done without any current from the ocellus, the second-order ocellar neurons only are coloured, but when it is done using a current the higher order interneurons are also coloured.Axonal iontophoresis from a cervical connective back into the brain, has revealed that the cellular body of the contralateral higher-order interneuron is situated in the postero-ventral part of the protocerebrum. This pericaryon with a long cellular process is the largest of the ocellar ones (Ø = 50–60 μm). These results are discussed in relation to the ocellar and visual pathways of Schistocerca.     

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.     

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     

Spectral Sensitivity of Larval Mosquito Ocelli

The spectral sensitivity of lateral ocelli in both wild-type and white-eyed larvae of the yellow fever mosquito Aedes aegypti L. (reared in darkness) was measured by means of the electroretinogram. The spectral sensitivity is maximal at about 520 nm, with a small secondary peak near 370 nm. When allowance is made for some screening and filtering by the eye tissues, the spectral sensitivity is in reasonable agreement with the absorption spectrum of ocellar rhodopsin (λ_max = 515 nm).     

Phototaxis in Drosophila: R1–6 input and interaction among ocellar and compound eye receptors

All 3 photoreceptor types in the compound eye of Drosophila can evoke positive phototaxis. Here we describe input from R1–6 receptors which are very sensitive. Previous reports in this series of studies described input from R7 and R8, the other less sensitive receptors. Here we studied fast-walking phototaxis using extremely dim stimuli. We also studied input from the simple ocellar eyes. Thus, we can now summarize a complete synthesis of inputs and interactions among all compound eye and ocellar receptor types. Receptor-deficient mutants were used to establish receptor-specific input. Two other findings are presented: (1) eye colour pigments affect the spectral sensitivity for phototaxis; and (2) the ocelli interact to facilitate input from the compound eye receptor types. Possible mechanisms of receptor interaction are discussed in the light of these findings of positive input from all photoreceptor types in Drosophila.     

Electrophysiology of the Insect Dorsal Ocellus : III. Responses to flickering light of the dragonfly ocellus

The ERG of the dragonfly ocellus has been analyzed into four components, two of which originate in the photoreceptor cells, two in the ocellar nerve fibers (Ruck, 1961 a). Component 1 is a sensory generator potential, component 2 a response of the receptor axons. Component 3 is an inhibitory postsynaptic potential, component 4, a discharge of afferent nerve impulses in ocellar nerve fibers. Responses to flickering light are examined in terms of this analytic scheme. It has been found that the generator potential can respond to higher rates of flicker—up to 220/sec.—than can the receptor axon responses, the postsynaptic potential, or the ocellar nerve impulses. The maximum flicker fusion frequency as measured by fusion of the ERG is that of the sensory generator potential itself.     

The role of ocelli in circadian singing rhythms of crickets

ABSTRACT. . There is a direct quantitative relationship between the free-running period (r) of the circadian stridulation rhythm of male Australian field crickets, Teleogryllus commodus (Walker), and the intensity of the constant light conditions. Both T. commodus and the house cricket, Acheta domesticus (L.), show free-running periods of the singing rhythm of c. 24 h when the light intensity is 0.00025 lux. In both species the severance of the three ocellar nerves significantly slows the circadian period which is indicative of a reduced perception of the available light intensity. To test whether this period reduction is a peripheral or a central effect, electro-retinograms (ERGs) were recorded from compound eyes of male T. commodus with the ocelli fully functional, then occluded, and then uncovered. The size of the compound eye ERG is reduced by 20% with ocellar occlusion and can subsequently be fully restored to the intact level, which indicates that the ocellar effect is a peripheral one. Intensified CoCl₂ fills reveal one neurone in A. domesticus and two in T. commodus which travel from the lateral ocellar nerve out into the ipsilateral optic lobe of the compound eye. These neurones all terminate in or distal to the lobular neuropile. The data are interpreted to indicate a role for ocelli in modulating the light intensity perception of the compound eye. The final effect of the ocellar afferents is at a peripheral level prior to the input of the visual information to the optic lobe circadian pacemaker. Hence ocelli play an indirect role in circadian rhythmicity, augmenting the sensitivity of the primary photoreceptors to better perceive photic entrainment signals.     

Spectral sensitivity studies on the visual system of the praying mantis, Tenodera sinensis

In these studies a constant ERG response was used as a measure of visual sensitivity to different wavelengths of light. The dark-adapted compound eye of Tenodera sinensis is dominated by a single class of photoreceptors. with a major peak of sensitivity at about 510–520 nm, and with a minor peak of sensitivity in the near-ultraviolet region at about 370 nm. The dark-adapted dorsal ocellus does not contain a homogeneous population of sensory receptors. The sensitivity function of the dark-adapted ocellus to longer wavelength light (yellow and red) is determined by a single receptor with a major peak of sensitivity in the green at 510–520 nm with some sensitivity in the near-ultraviolet. Sensitivity at shorter wavelengths (near-ultraviolet and blue), however, involves the stimulation of both this and a near-ultraviolet-sensitive receptor with a maximum sensitivity at about 370 nm. Anatomically, the sensory cells of the dorsal ocellus of Tenodera were determined histologically to be grouped into two distinct regions, each group making its own separate contribution to the ocellar nerve. This may represent the separation of two different photoreceptor types in the ocellus of the mantis.     

Feedback synaptic interaction in the dragonfly ocellar retina

The intracellular response of the ocellar nerve dendrite, the second order neuron in the retina of the dragonfly ocellus, has been modified by application of various drugs and a model developed to explain certain features of that response. Curare blocked the response completely. Both picrotoxin and bicuculline eliminated the "off" overshoot. Bicuculline also decreased the size of response and the sensitivity. gamma-Aminobutyric acid (GABA), however, increased the size of response. The evidence indicates the possibility that the receptor transmitter is acetylcholine and is inhibitory to the ocellar nerve dendrite whereas the feedback transmitter from the ocellar nerve dendrite may be GABA and is facilitory to receptor transmitter release. The model of synaptic feedback interaction developed to be consistent with these results has certain important features. It suggests that the feedback transmitter is released in the dark to increase input sensitivity from receptors in response to dim light. This implies that the dark potential of the ocellar nerve dendrite may be determined by a dynamic equilibrium established by synaptic interaction between it and the receptor terminals. Such a system is also well suited to signalling phasic information about changes in level of illumination over a wide range of intensities, a characteristic which appears to be a significant feature of the dragonfly median ocellar response.     

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 Electrical Response of the Planarian Ocellus

The planarian ocellar potential (OP), an action potential evoked from the planarian ocellus by a light flash, was recorded with microelectrodes. OP amplitude, latency, and peak delay varied as a function of stimulus intensity and state of adaptation in a manner similar to the responses of other photoreceptors. Changes in the OP that occurred with different directions of incident light are described and attributed to screening effects of the ocellar pigment cells. The temperature coefficient (Q₁₀) of OP latency was 1.5; latency decreased continuously as temperature was increased to destructive levels. The energy of activation of the rate of OP formation was calculated to approximate 10 kcal. These findings suggest dependence of OP latency on ionic diffusion and of OP formation on a biocatalytic process.     

Spectral Sensitivity of the Planarian Ocellus

The ocellar potential (OP) of planaria was recorded using microelectrode techniques. The action spectrum and spectral sensitivity of the OP are described. Maximum OP sensitivity was found with 508 nm light. A moderate increase in sensitivity to blue light was observed. This is typical of many invertebrate photoreceptors and was shown, by selective chromatic adaptation, not to indicate the presence of a second pigment.     

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     

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.     

Neuronal pathways from the dorsal acelli of the house cricket,Acheta domesticus

Each ocellar nerve in the house cricket Acheta domesticus contains giant nerve fibers of 10-15 μ diameter, characterized in Golgi Cox preparations by a single row of short collaterals which runs along nearly the entire length of a fiber. Numerous long collaterals are given off by thin fibers in the ocellar nerve; medium-size fibers give off relatively few collaterals. The lateral ocellar tracts extend posteriorly through the dorsal protocerebrum, crossing the protocerebral bridge dorsally. The smaller median ocellar tract runs more ventrally through the pars intercerebralis; posterior to the bridge its fibers turn out toward the lateral nerves. Golgi and cobalt preparations reveal branching of giant and mediu_-size ocellar fibers posterior to the bridge at two levels, forming bilateral regions of ocellar neuropile. No ocellar processes appear to be given off to the corpora pedunculata, centra! body, nervi corporis cardiaci, antenna! lobes, or circumesophageal connectives; it is uncertain whether ocellar collaterals extend into the protocerebral bridge or optic lobes. Cell bodies of giant and medium-sized fibers are located in the pars intercerebralis.     

Convergence of antennal and ocellar inputs in the insect brain

Summary Unitary responses were recorded from the brain of the fleshfly, Boettcherisca peregrina, during olfactory or mechanical stimulation of the antenna, and simultaneous photic stimulation of the ocelli. Convergence from the two inputs, the antenna and the ocelli, was observed. The response to antennal stimulation was facilitated by photic stimulation in most units. The responses to the antennal stimuli were facilitated greatly at the peak of the photic response. Some units responded both to ocellar illumination and antennal stimulation. Their response to antennal stimulation seemed independent of the light-condition during the light-adapted state, but was facilitated at the onset of the ocellar illumination, and occluded just after its cessation. In addition, there were some units which responded to antennal stimulation but not to the ocellar illumination; some of them also showed facilitation of the response to antennal stimulation during ocellar illumination.     

Ocellar projections within the central nervous system of the worker honey bee,Apis mellifera

Summary The projections of ocellar fibres within the brain and thorax of the honey bee, Apis mellifera, were established using a modified cobalt sulphide technique, supplemented by serial sectioning of the brain for the light microscope.The results are: 5 large fibres in each lateral nerve and 12 in the median nerve have wide-field terminal arborisations in ocellar association areas on either side of the posterior slope area. 9 medium-sized fibres in each lateral nerve and 12 in the median nerve form a second ocellar association area on each side of the perioesophageal foramen. A group of fine fibres, stained via the ocellar nerves, arborise just below and anterior to the protocerebral bridge. 10 medium-sized fibres run from the level of the ocellar nerve tracts to the first and second thoracic ganglia, branching in a number of discrete areas within each ganglion. These fibres also form a restricted ocellar association area within the suboesophageal ganglion. A few fibres run between the higher-order optic centres and the ocellar tract. The large- and mediumsized fibres give off short, stout spines from their axons within the ocellar tracts.     

Ultraviolet light and puparial weight as factors in the autogeny of the fleshfly, Sarcophaga falculata

Light conditions and the puparial weight were assessed as factors that affect autogeny in Sarcophaga falculata. The frequency and degree of autogeny differed in flies originating from large or small puparia. The limitation of puparial weight range did not prevent the variation in the stage of autogeny. Autogeny was low in flies kept in complete darkness and was very high in uv irradiated flies. Removal of the ocelli before u.v. irradiation prevented most of the increase in autogeny, and it is assumed that the ocelli are the main transmitter of the u.v. effect on oögenesis. Neurosecretion was found within the cells of the ocellar nerve of adult flies. It is possible that this neurosecretion plays a rôle in the u.v. induced effect on autogeny.