Movement on dark–light adaptation in beetle eyes of the neuropteran type

1971 ◽  
Vol 179 (1054) ◽  
pp. 73-85 ◽  
Keyword(s):  
Outer Layer ◽  
Light Adaptation ◽  
Pigment Cells ◽  
Retinula Cell ◽  
Clear Zone ◽  
Dark Light ◽  
Light Guides

Beetles of several species belonging to the families Carabidae, Dytiscidae, Gyrinidae and Hydrophilidae have an eye of the neuropteran type which is characterized as follows. In the dark-adapted state a long column formed by retinula cells (in these families numbering seven) stretches from the cone tip to the rhabdom layer. In the light a crystalline tract, formed from the outer layer of the cone, extends about 100 µ m from the cone and is surrounded by pigment cells. Scarabaeid beetles examined are similar but lack the distal rhabdomere always found in the above groups. All have a basal retinula cell with rhabdomere. In the scarabaeids the retinula cell columns have a content of solids greater than the surrounding cells, suggesting that they act as light guides across the clear zone.

The dorsal eye of the mayfly Atalophlebia (Ephemeroptera)

1978 ◽  
Vol 200 (1139) ◽  
pp. 137-150 ◽  
Keyword(s):  
Visual Pigment ◽  
Current Flow ◽  
Yellow Pigment ◽  
The Other ◽  
Retinula Cell ◽  
Clear Zone ◽  
Large Size ◽  
Sharp Focus ◽  
Pigment Distribution ◽  
Light Guides

The dorsal eye of Atalophlebia has two unusual features, the sensitivity only to ultraviolet (u. v.) light, and the candelabra-shaped rhabdom. In addition, the crystalline cone is surrounded to its tip by a yellow pigment, and the tip tapers gradually as a dense fibre. These details, particularly the pigment distribution, indicate that a superposition image cannot be formed by u. v. light. Also, there is no refracting or reflecting structure that could form a sharp superposition image. Instead, it is suggested that u. v. rays are sharply focused on the cone tip and conducted by the retinula cell columns acting as light guides across the clear zone. Light of longer wavelength, on the other hand, is partially focused through the yellow pigment, and, although it is not seen by the insect, it is available to photoregenerate the visual pigment. This method of boosting sensitivity is appropriate for a pure u. v. eye and does not require a sharp focus of the regenerative rays, although the clear zone is an essential part of the mechanism. The rhabdom has an extraordinary shape like a flat 5-armed candelabra in cross section, with five posteriorly directed arms which are formed by six retinula cells. There is also a 7th retinula cell without a rhabdomere. This cell penetrates laterally the rhabdom of the other six, and also forms a sheath around half of its own ommatidium and half of the the adjacent ommatidium. The exceptional relations between this cell, and the other six, together with the orientated candelabra pattern of the rhabdom, and the large size of the 7th retinula axon, is interpreted as a way of enhancing the current flow down the 7th axon which runs direct to the medulla, bypassing the lamina.

The ommatidium of the dorsal eye of Cloeon as a specialization for photoreisomerization

1976 ◽  
Vol 193 (1110) ◽  
pp. 17-29 ◽  
Keyword(s):  
Large Scale ◽  
Light Adaptation ◽  
Clear Zone ◽  
Angular Sensitivity ◽  
Cell Column ◽  
Screening Pigment ◽  
Double Function ◽  
Corneal Lens ◽  
Visible Wavelengths ◽  
Light Guides

The turbanate dorsal eyes of Cloeon have thin biconvex corneal facets, large crystalline cones, and long retinula cells which cross the clear zone. There is no large-scale movement of screening pigment upon adaptation. The combination of anatomical features suggests that the eye operates with high visual acuity because the corneal lens is focused on the tip of the cone, from which light is guided by the retinula cell column across the clear zone. By this means the eye could function near the diffraction limit. The suggestion that the main visual path is by light guides has some experimental support from examination of embedded shoes of the eye, but leaves no function for the clear zone, as there is negligible movement of pigment upon light adaptation. A clue to the function of the clear zone is provided by the unique appearance of a distal collection of rhabdom microvilli which are formed by all seven retinula cells around the tip of the crystalline cone. This distal rhabdom necessarily acts as a filter for light which crosses the clear zone. It is suggested that this light is utilized in the photoregeneration of the visual pigment after the effective visible wavelengths have been reduced. Filtering at this level could prevent unfocused regenerative rays, which cross the clear zone, from interfering with the angular sensitivity of the receptors. In other clear zone eyes, screening pigment around the cone tip could similarly serve a double function by acting as the aperture of the light guide and at the same time transmitting photoregenerative rays which cross the clear zone outside the light guides.

Eye structure and optics in the pelagic shrimp Acetes sibogae (Decapoda, Natantia, Sergestidae) in relation to light-dark adaptation and natural history

1986 ◽  
Vol 313 (1160) ◽  
pp. 251-270 ◽  
Keyword(s):  
Natural History ◽  
Basement Membrane ◽  
Focal Length ◽  
Pigment Cells ◽  
Retinula Cell ◽  
Maximum Diameter ◽  
Membrane Turnover ◽  
Image Brightness ◽  
Crystalline Cone ◽  
Cone Cells

The structure and optics of the compound eyes of the neritic sergestid shrimp, Acetes sibogae , are described. The eyes are nearly spherical and heavily pigmented. The facets are square, indicating that the eye operates by the recently recognized mechanism of reflecting superposition. The most distal portion of each ommatidium is the corneal lens, which is secreted by two underlying corneagenous cells. These two cells surround the crystalline cone and cone stalk and the four cells of which they are composed and extend proximally at least as far as the distal rhabdom. Near the base of the cone stalk the extensions of the corneagenous cells swell and enclose spheres which bear on their surfaces small particles similar to ribosomes in appearance. Beneath the corneagenous cells lie four crystalline cone cells, parts of which differentiate to form the crystalline cone and cone stalk. The latter structures are compound, one quarter of each being contributed by each crystalline cone cell. Distally the crystalline cone cells send a small projection, which is surrounded by the corneagenous cells, to the cornea. Proximal extensions of each of the four parts of the cone stalk extend between the retinula cells and meet within the basement membrane. Between the base of the cone stalk and the regularly layered rhabdom lies the distal rhabdom. It is surrounded by a cell that we have termed retinula cell eight (R8), by analogy with other crustacean systems, and consists of unordered microvilli projecting from the cell membrane into the extracellular space above the layered rhabdom. In addition to R 8, which contributes only to the distal rhabdom, seven other retinula cells contribute to the proximal rhabdom, which consists of alternating ordered layers of orthogonally arranged microvilli. Four of these retinula cells are arranged orthogonally and extend far distally along the crystalline tract. The other three do not extend as far distally and alternate with the first four in their position around the axis of the ommatidium. R8 is located still further proximally at the level of the distal rhabdom. All seven of the retinula cells which contribute to the proximal rhabdom contain proximal pigment and extend through the basement membrane. The basement membrane consists of a meshwork grid with each intersection supporting a rhabdom so at this point the retinula cell axons project into different squares of the meshwork. Tapetal pigment cells are present in the vicinity of the basement membrane and extend downward to the lamina. The granules of tapetal pigment are covered or exposed by movements of the proximal pigment and also change their intracellular distribution depending on illumination. In addition to the proximal (retinula cell) pigment and the tapetal pigment the eye contains four types of distal pigment. Moving inward from the cornea these are the distal yellow pigment (DYP) which surrounds the entire eye; the distal reflecting pigment (DRP), which forms a thin layer and is continuous with the tapetal pigment at the edge of the eye; and the black distal pigment and the mirror pigment (MP) both contained within distal pigment cells (DPC). In the light-adapted state the proximal pigment moves distally, surrounding the rhabdoms, and the tapetal pigment granules move proximally so that they are mainly found beneath the basement membrane. Movements of the distal pigments are less clearcut, but they all appear to move somewhat proximally in the light-adapted state. Multivesicular bodies are more abundant in the retinula cells shortly after dawn, and are possibly related to membrane turnover. Interommatidial angle, as measured on both fixed and fresh material, varied from 2.8 to 3.8° in different parts of the eye. The crystalline cones were found to have a uniform refractive index radially, which, combined with their square shape, indicates that they function by reflecting superposition. Total internal reflection from the sides of the cones is adequate to explain the maximum diameter of the eyeshine from the dark-adapted eye at night without the need for additional mirrors. Nevertheless, from its organization and appearance the mirror pigment could act as a reflector in the dark-adapted eye. Also, the size of the glow patch indicates that there would be a gain of nearly two log units in image brightness in going from the light-adapted to the dark-adapted state. Each corneal facet was found to act as a weak converging lens, with a focal length of approximately 300 μm. The eye structure of Acetes is discussed in relation to that of other shrimp and to the natural history of Acetes .

Light guides in the dorsal eye of the male mayfly

1982 ◽  
Vol 216 (1202) ◽  
pp. 25-51 ◽  
Keyword(s):  
Ultraviolet Light ◽  
Compound Eye ◽  
Lucifer Yellow ◽  
Single Units ◽  
Polarization Sensitivity ◽  
Clear Zone ◽  
Tight Coupling ◽  
Acceptance Angle ◽  
Yellow Light ◽  
Light Guides

(i) The dorsal eyes are sensitive to ultraviolet light, which is focused by the corneal lens into crystalline cones in the region where these taper progressively to columns across the clear zone. The action of these columns as light guides can be observed in fixed eyes embedded in polymerized resin. In life the light guide part of the column is surrounded by watery non-cellular haemolymph. (ii) Shadowing the eye surface with a thin wire (three facets wide) while recording from individual receptor units shows that ultraviolet light reaches each receptor by its own facet as in an apposition eye, and not, as in a superposition eye, by a group of many facets. (iii) As shown by the dye Lucifer Yellow injected from a microelectrode, the electrophysiological unit consists of all seven retinula cells in the rhabdom region. Consistent with this tight coupling of retinula cells there is no polarization sensitivity. The peak spectral sensitivity of all single units is at 345-365 nm in the ultraviolet. The acceptance angle is 2.0–2.5°. The sensitivity at the spectral peak to a point source on the optical axis of the unit is poor compared to that in other insects tested with the same equipment. (iv) The acceptance angles (∆ ρ ) in the dorsal eye are at the theoretical minimum for the facet diameter and wavelength from diffraction theory. Ultraviolet vision, therefore, has made possible a reduction in facet size but the interommatidial angle ∆ ϕ is greater than expected from the optimum sampling theory of the diffraction limited compound eye. In fact ∆ ρ ≈ ∆ ϕ ≈ 2°. (v) The dorsal eye is effectively a foveal region with greater sampling density and narrower receptive fields but less overlap of fields than the lateral eye. (vi) The square cones and yellow screening pigment strongly suggest that there is superposition by reflexion of yellow light that spreads between ommatidia across the clear zone. This yellow light might photoreisomerize the visual pigment. Attempts to prove this theory during the recording from single units have so far failed but no better function for the clear zone has been suggested.

The ommatidium of the lacewing Chrysopa (Neuroptera)

1976 ◽  
Vol 192 (1108) ◽  
pp. 259-271 ◽  
Keyword(s):  
Signal To Noise Ratio ◽  
Visual Fields ◽  
Neural Mechanism ◽  
Retinula Cell ◽  
Cell Nuclei ◽  
Clear Zone ◽  
Parallel Beam ◽  
Cell Column ◽  
Spatial Frequencies ◽  
Different Levels

The eye is a clear zone eye with extensive movement of retinula cells on adaptation to light. The ommatidium has three types of rhabdomere, at different levels, so that the eye necessarily abstracts at least three kinds of information simultaneously from the incoming rays. In the lightadapted state light can enter each ommatidium only via a crystalline tract that is surrounded by dense pigment grains. A small distal rhabdomere (cell 7) always lies at the end of this tract. In the dark-adapted eye the retinula cell nuclei and distal rhabdomere move to the cone tip and the crystalline tract is drawn into the cone. There is then a region of the retinula cell column, between cone tip and proximal rhabdoms, across which there is no structure that could act as a light guide. A key question, therefore, is how the light is focused across this clear zone in the darkadapted state. As shown by the wide angular distribution of eyeshine when a parallel beam is incident on the dark-adapted eye, rays are poorly focused upon the columns of the large rhabdoms. The wide visual fields of receptors 1-6 in the dark-adapted eye, inferred from the observation of eyeshine, are seen as a way of narrowing the bandwidth of spatial frequencies, so that only the largest objects in the visual field contribute to motion-detection. This would improve the signal-to-noise ratio, not in the receptors themselves, but in the neural mechanism, by simplifying the incoming signal.

scholarly journals Modulation of crayfish retinal function by red pigment concentrating hormone

1995 ◽  
Vol 198 (7) ◽  
pp. 1447-1454 ◽  
Author(s):  
A Garfias ◽  
L Rodríguez-Sosa ◽  
H Aréchiga
Keyword(s):  
Circadian Rhythm ◽  
Light Adaptation ◽  
Retinal Pigment ◽  
Physiological Role ◽  
Pigment Cells ◽  
Red Pigment ◽  
Retinal Activity ◽  
Retinal Photoreceptors ◽  
Dose Dependent

The role of the crustacean octapeptide red pigment concentrating hormone (RPCH) in the control of crayfish retinal activity was explored. RPCH injection into intact animals resulted, after a latency of 10­30 min, in a dose-dependent enhancement of electroretinogram (ERG) amplitude lasting 60­120 min. RPCH was able to potentiate ERG amplitude in both light-adapted and dark-adapted animals. Following light-adaptation, responsiveness to RPCH was five times higher than following dark-adaptation. In conjunction with ERG enhancement, in light-adapted animals, RPCH injection elicited a dose-dependent retraction of distal retinal pigment, but did not affect proximal retinal pigment position. The effects of RPCH were blocked by a polyclonal antibody raised against a tyrosinated form of RPCH (A-tyr-RPCH). The antibody was also capable of partially blocking the nocturnal phase of the circadian rhythm of ERG amplitude and the darkness-induced retraction of distal retinal pigment. These results suggest that RPCH acts both on the retinal photoreceptors and on the distal pigment cells, playing a physiological role as a mediator of the effects induced by darkness and by the nocturnal phase of the circadian rhythm.

Alternatives to superposition images in clear-zone compound eyes

1971 ◽  
Vol 179 (1055) ◽  
pp. 97-124 ◽  
Keyword(s):  
Scattered Light ◽  
Retinula Cell ◽  
Compound Eyes ◽  
Clear Zone ◽  
Light Effect ◽  
Angular Sensitivity ◽  
Dim Light ◽  
Optical Pathway ◽  
Receptor Layer

The clear zone between the cones and the receptor layer in dark -adapted eyes of insects that are active in dim light has formerly been explained as a space to allow formation of a superposition image. Although erect images have been seen in Ephestia (Lepidoptera) and Hydrophilus (Coleoptera), new experiments show that they are accompanied by scattered light and that the angular sensitivity of individual receptors must be wide in the dark-adapted state. Alternatives to the superposition theory are examined, and it is concluded that in eyes with crystalline cones the clear zone (in general, in the numerous shapes and sizes of eyes of nocturnally active insects) enables light entering by many facets to sum upon individual receptors on the far side of the clear zone. In addition to the scattered light effect, light is carried across the clear zone in crystalline tracts or retinula cell columns, which provide a separate optical pathway for each ommatidium also in the light-adapted state.

Änderungen der Feinstruktur im Komplexauge von Formica polyctena bei der Helladaptation / Ultrastructural Variations during Light Adaptation in the Complex Eye of Formica polyctena

1971 ◽  
Vol 26 (4) ◽  
pp. 357-359 ◽  
Author(s):  
Randolf Menzel ◽  
Gisela Lange
Keyword(s):  
White Light ◽  
Functional Significance ◽  
Light Adaptation ◽  
Pigment Cells ◽  
Plasma Zone ◽  
Wide Margin ◽  
Formica Polyctena ◽  
Long Time

The dark adapted rhabdom is surrounded lengthwise by a wide margin of large vacuoles (“palisades”). The pigment granula within the retinula cells are uniformly distributed in the plasma outside of the palisades. Illumination of the eye with white light from a xenon-arc (15 · 10 -4 cal/cm2 · min) caused the pigment granula in the retinula cells to wander distally and to accumulate close to the rhabdom. The vacuole margin remained more proximal but was separated from the rhabdom by a wider plasma zone. After long-time illumination (30 min) the long pigment-cells expanded while the retinula cells simultaneously became thinner. Reference is made to the functional significance of these variations.

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