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     

Electroretinogram Characteristics and the Spectral Mechanisms of the Median Ocellus and the Lateral Eye in Limulus polyphemus

Electrical responses (ERG) to light flashes of various wavelengths and energies were obtained from the dorsal median ocellus and lateral compound eye of Limulus under dark and chromatic light adaptation. Spectral mechanisms were studied by analyzing (a) response waveforms, e.g. response area, rise, and fall times as functions of amplitude, (b) slopes of amplitude-energy functions, and (c) spectral sensitivity functions obtained by the criterion amplitude method. The data for a single spectral mechanism in the lateral eye are (a) response waveforms independent of wavelength, (b) same slope for response-energy functions at all wavelengths, (c) a spectral sensitivity function with a single maximum near 520 mµ, and (d) spectral sensitivity invariance in chromatic adaptation experiments. The data for two spectral mechanisms in the median ocellus are (a) two waveform characteristics depending on wavelength, (b) slopes of response-energy functions steeper for short than for long wavelengths, (c) two spectral sensitivity peaks (360 and 530–535 mµ) when dark-adapted, and (d) selective depression of either spectral sensitivity peak by appropriate chromatic adaptation. The ocellus is 200–320 times more sensitive to UV than to visible light. Both UV and green spectral sensitivity curves agree with Dartnall's nomogram. The hypothesis is favored that the ocellus contains two visual pigments each in a different type of receptor, rather than (a) various absorption bands of a single visual pigment, (b) single visual pigment and a chromatic mask, or (c) fluorescence. With long duration light stimuli a steady-state level followed the transient peak in the ERG from both types of eyes.     

Ultrastructure and migration of screening pigments in the retina of Pieris rapae L. (Lepidoptera,Pieridae)

Summary The retinal morphology of the butterfly, Pieris rapae L., was investigated using light and electron microscopy with special emphasis on the morphology and distribution of its screening pigments. Pigment migration in pigment and retinula cells was analysed after light-dark adaptation and after different selective chromatic adaptations. The primary pigment cells with white to yellow-green pigments symmetrically surround the cone process and the distal half of the crystalline cone, whilst the six secondary pigment cells, around each ommatidium, contain dark brown pigment granules. The nine retinula cells in one ommatidium can be categorised into four types. Receptor cells 1–4, which have microvilli in the distal half of the ommatidium only, contain numerous dark brown pigment granules. On the basis of the pigment content and morphology of their pigment granules, two distal groups of cells, cells 1, 2 and cells 3, 4 can be distinguished. The four diagonally arranged cells (5–8), with rhabdomeric structures and pigments in the proximal half of the cells, contain small red pigment granules of irregular shape. The ninth cell, which has only a small number of microvilli, lacks pigment. Chromatic adaptation experiments in which the location of retinula cell pigment granules was used as a criterium reveal two UV-receptors (cells 1 and 2), two green receptors (cells 3 and 4) and four cells (5–8) containing the red screening pigment, with a yellow-green sensitivity.     

Spectral responses of sustaining fibers in the optic tracts of crayfish (Procambarus)

Summary Spectral response curves were recorded for 60–70 individual sustaining fibers in the optic nerve of the crayfish Procambarus. These cells belong to at least 8 of the 14 classes of sustaining fibers described by Wiersma and Yamaguchi (1966) on the basis of receptive fields. About 90 percent of the cells receive predominant input from yellow-green receptors and are maximally sensitive at 560 to 570 nm; a much smaller number receive principal input from blue receptors and are maximally sensitive near 460 nm.The wavelength sensitivity of optic fibers receiving their major input from yellow-green receptors depends on the state of dark adaptation of the animal and the intensity of illumination. Early in dark adaptation and at high intensities of stimulation the spectral response curve is distorted by light which has been filtered through the sleeves of red-brown shielding pigment. During dark adaptation a shift in maximum spectral response to shorter wavelengths parallels the retraction of the migratory pigment to the dark position and the development of retinal glow. The effects are reversed by injecting into a dark-adapted animal an extract of eyestalks containing the hormone controlling pigment migration: the pigment sleeves lengthen, retinal glow disappears, and shoulders or peaks of sensitivity appear in the red region of the spectrum.This work was supported by USPHS research grant EY 00222 to Yale University. A. E. R. W. was aided by a Fulbright-Hays travel grant. We are grateful to Prof. C. A. G. Wiersma and Dr. R. M. Glantz for a helpful demonstration of the recording technique.     

Studies on the Relation between the Pigment Migration and the Sensitivity Changes during Dark Adaptation in Diurnal and Nocturnal Lepidoptera

The functional significance of the pigment migration in the compound insect eye during dark adaptation has been studied in diurnal and nocturnal Lepidoptera. Measurements of the photomechanical changes were made on sections of eyes which had been dark-adapted for varying periods of time. In some experiments the sensitivity changes during dark adaptation were first determined before the eye was placed in the fixation solution. No change in the position of the retinal pigment occurred in Cerapteryx graminis until the eye had been dark-adapted for about 5 minutes. The start of the migration was accompanied by the appearance of a break in the dark adaptation curve. During longer periods of dark adaptation the outward movement of the pigment proceeded in parallel with the change in sensitivity, the migration as well as the adaptive process being completed within about 30 minutes. In the diurnal insects chosen for the present study (Erebia, Argynnis) the positional changes of the retinal pigment were insignificant in comparison with the movement of the distal pigment in Cerapteryx graminis. On the basis of these observations the tentative hypothesis is put forward that the second phase of adaptive change in nocturnal Lepidoptera is mediated by the migration of the retinal pigment while the first phase is assumed to be produced by the resynthesis of some photochemical substance. In diurnal insects which have no appreciable pigment migration the biochemical events alone appear to be responsible for the increase in sensitivity during dark adaptation.     

The effect of light adaptation on the dynamic properties of phototransduction in the fly,Phormia regina

The static and dynamic characteristics of phototransduction were studied in photoreceptors of the compound eye of the fly Phormia regina (Calliphoridae) using a green light emitting diode driven by a controlled current source. The LED provides sufficiently intense light to investigate the behaviour of the receptors over about half of the dark adapted range of the response versus log intensity curve. The effects of constant adapting light intensities upon the step response and upon the frequency response and coherence functions were examined. Using both methods the effect of light adaptation upon receptor sensitivity can be closely approximated by a similar linear dependence of log sensitivity upon log adapting intensity. However, there was no reliably detectable effect of light adaptation upon the time constant of the response over the range of adapting intensities used.Abbreviation LED Light Emitting Diode     

Colour receptors in the eye of the digger wasp,Sphex cognatus Smith: Evaluation by selective adaptation

Summary Pigment granule migration in pigment cells and retinula cells of the digger wasp Sphex cognatus Smith was analysed morphologically after light adaptation to natural light, dark adaptation and after four selective chromatic adaptations in the range between 358 nm and 580 nm and used as the index of receptor cell sensitivity. The receptor region of each ommatidium consists of nine retinula cells which form a centrally located rhabdom. Two morphologically and physiologically different visual units can be described, defined by the arrangement of the rhabdomeric microvilli, the topographical relationship of the receptor cells with respect to the eye axes and the unique retinula cell screening pigmentation. These two different sets of ommatidia (type A and B) are randomly distributed in a ratio of 13 throughout the eye (Ribi, 1978b). Chromatic adaptation experiments with wavelengths of 358 nm, 443 nm, 523 nm and 580 nm and subsequent histological examination reveal two UV receptors, two blue receptors and four yellow-green receptors in type A ommatidia and two UV receptors and six green to yellow-green receptors in type B ommatidia. The pigments in cells surrounding each ommatidium (two primary pigment cells, 20 secondary pigment cells and four pigmented cone extensions) were not affected significantly by the adaptation experiments.     

Spectral absorption and sensitivity measurements in single ommatidia of the green crab,Carcinus

Summary Rhabdoms of the green crabCarcinus maenas were examined by microspectrophotometry and found to contain a visual pigment with _max at 502–506 nm. Upon irradiation, a stable metarhodopsin formed with unchanged _max and molar extinction coefficient. In the presence of 5% glutaraldehyde the rhabdoms were photobleached. Partial bleaching experiments indicate that in the rhabdoms studied, only one visual pigment was present, with an absorption spectrum appropriate for a hypothetical rhodopsin from Dartnall's (1953) nomogram.Retinular (photoreceptor) cells were studied with microelectrodes. They had negative resting potentials of 30–65 mV and responded to light with depolarizing receptor potentials. All cells had maximum sensitivity at ~493 nm, as did the ERG (electroretinogram). Selective adaptation failed to alter the spectral sensitivity functions of single cells or the ERG. If these spectral sensitivity data are pooled with Wald's (1968), the average sensitivity of the dark-adapted eye is accounted for adequately by the pigment of the rhabdom.The results of this work do not support the hypothesis of Horridge (1967) that each ommatidium ofCarcinus has two color receptors.This work was supported by U.S. P.H.S. grant EY 00222.     

The eyes of a “nobody”,Anoplodactylus petiolatus (Pantopoda; Anoplodactylidae)

The fine structure of the four ocelli ofAnoplodactylus petiolatus was examined using serial longitudinal and transversal sections of the eye hill. Each pigment cup ocellus is composed of a (planconvex) cuticular lens, lens forming hypodermal cells, inverse retinula cells with latticed rhabdom and surrounding tapetum and pigment layers. Within the retinula cells a distal “vitreous” zone, a nucleus zone and a proximal rhabdomeric zone can be distinguished. Retinula cell axons originate proximally. The tapetum cells contain several layers of reflecting crystals. Distally, they have a common microvillous region. The intraretinal “vitreous” zone contains glycogen-like particles in the centre and rough ER in the periphery. Contrary to other Pantopoda vitreous cells, a praeretinal membrane and a vertical lens groove have not been observed inAnoplodactylus. While the presence of four (median) ocelli appears to be a primitive characteristic, the inverse orientation of the retinula cells in combination with a tapetum lucidum represents a highly derived characteristic among arthropod median eyes.     

Multiple predator effects on size-dependent behavior and mortality of two species of anuran larvae

This study examined the effects of multiple predators on size‐specific behavior and mortality of two species of anuran larvae. Particularly, we focused on how trait changes in predators and prey may be transmitted to other species in the food web. In laboratory experiments, we examined the effects of bluegill sunfish, Lepomis macrochirus, and the odonate larva Anax junius on behavior and mortality of tadpoles of the bullfrog, Rana catesbeiana, and the green frog R. clamitans. Experiments were conducted with predators alone and together to assess effects on behavior and mortality of the tadpoles. The experiments were replicated on five size classes of the tadpoles to evaluate how responses varied with body size.
Predation rates by Anax were higher on bullfrogs than on green frogs, and both bullfrogs and green frogs suffered greater mortality from Anax than from bluegill. Bluegill only consumed green frogs. Predation rates by both predators decreased with increasing tadpole size and decreased in the non‐lethal (caged) presence of the other predator. Both anuran larvae decreased activity when exposed to predators. Bullfrogs, however, decreased activity more in the presence of Anax than in the presence of bluegill, whereas green frogs decreased activity similarly in the presence of both predators. The largest size class of green frogs, but not of bullfrogs, exhibited spatial avoidance of bluegill. These responses were directly related to the risk posed by the different predators to each anuran species. Anax activity (speed and move frequency) also was higher when alone than in the non‐lethal presence of bluegill. We observed decreased predation rate of each predator in the non‐lethal presence of the other, apparently caused by two different mechanisms. Bluegill decreased Anax mortality on tadpoles by restricting the Anax activity. In contrast, Anax decreased bluegill mortality on tadpoles by reducing tadpole activity. We discuss how the activity and spatial responses of the tadpoles interact with palatability and body size to create different mortality patterns in the prey species and the implications of these results to direct and indirect interactions in this system.     

A retinal substrate for colour discrimination in crabs

Summary In crabs, there is behavioural evidence for colour discrimination from the portunidCarcinus and severalUca species, but in the same and related species only a single visual pigment has been found in the rhabdoms by microspectrophotometry. Micro-electrode recordings of the spectral sensitivity of single portunid photoreceptors may throw some light on this apparent inconsistency. Large changes in spectral sensitivity occur with light adaptation in the crabScylla serrata. Selective adaptation experiments rule out the possibility that the changes may be caused by the presence of a number of visual pigments or of antenna pigments. The results suggest that inScylla the absorption of a single visual pigment type is modified by different coloured filters in different photoreceptors and that this makes colour discrimination possible.     

Extracellular laccases in ascomycetes<Emphasis Type="Italic">Trichoderma atroviride</Emphasis> and<Emphasis Type="Italic">Trichoderma harzianum</Emphasis>

Laccase activity inTrichoderma harzianum and in our own isolateTrichoderma atroviride was correlated with the production of the green pigment in conidial spores. The laccases of the two fungal species exhibit comparable kinetic parameters, pH optima and thermal sensitivity but differed in physiological properties, such as their catalytic activity during growth.     

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.     

The contribution of different colour receptors to a motor output in the fly

Summary A light flash given to the eye ofCalliphora leads to a movement of the legs (light induced leg reflex) which most likely normally initiates flight of the animal. This reflex has a short latency (12 to 30 ms, depending upon light intensity) and is quite reproducible without habituation. The spectral sensitivity of the reflex shows that receptors R1-6 most likely govern the input to the reflex in dark adaptation, a contribution of receptors R7 can be demonstrated with selective chromatic adaptation.     

The anatomy of the median ocellus of Limulus

Summary The median ocellus of Limulus consists of irregular groups of large photoreceptor cells which form a cup-shaped retina around the ocellar lens. Each group is surrounded and penetrated by guanophores and glia. The photoreceptor cells have extensive rhabdomeric regions, both along infoldings of cell membranes and between cells. Five-layered junctions occur between rhabdomeric microvilli. An occasional arhabdomeric (AR) cell is associated with a group of photoreceptors. Fine dendritic branches of the AR cell penetrate the rhabdomeric regions and form five-layered junctions with photoreceptor rhabdomeres. Axons of photoreceptor cells, and of at least some AR cells, gather at the proximal side of the cup to form an optic nerve.Supported in part by NIH EY00312 and EY00377.We would like to thank Dr. W. K. Stell, Dr. A. C. Bell, and Dr. W. H. Fahrenbach for their helpful discussions.     

Action spectra and chromatic mechanisms of cells in the median ocelli of dragonflies

Spectral sensitivities were recorded intracellulary in median ocelli of Anax junius, Aeschnatuberculifera, and Libellulapulcella. All cells had peak sensitivities at 360 and 500 nm while UV-blue+green cells found only in Anax had a third peak sensitivity at 440 nm. Ratios of UV-to-green sensitivities varied from cell to cell in each ocellus, but no UV-only or green-only cells were recorded. Half of the cells tested had a reverse Purkinje shift: They were more sensitive in the green at low illuminations but more sensitive in the UV at high illuminations; their intensity-response curves at 370 and 520 nm crossed but became parallel for large responses. Wave-lengths 420 nm and shorter elicited a family of low intensity-response curves with one slope; wavelengths 440 nm and longer elicities a family of curves with another slope. Orange-adapting lights selectively adapted sensitivity in the green, but UV-adapting lights had little selective effect. Amounts of log-selective adaptation were proportional to log orange-adapting intensity. It is concluded that two spectral mechanisms can be recorded from each cell, possibly by coupling of UV and green cells or possibly because each cell contains two visual pigments. Selective chromatic adaptations may provide the ocellus with a kind of "authomatic color control," while the reverse Purkinje shift could extend the ocellus' sensitivity to prevailing skylight.     

The micromorphology of the nauplius eye of the estuarine calanoid copepod, Sulcanus conflictus Nicholls (Crustacea)

The nauplius eye consists of one median and two lateral ocelli, each within a pigment cup. The three pigment cups are made up from two multi-nucleate pigment cells: each cell forming one lateral cup and half of the median cup. The three cups are lined on the insides by tapetal cells which contain layers of reflectile crystals. Each of the ocelli contains six sensory cells which protrude from the rims of the pigment cups and the protruding parts are sheathed by the conjunctiva cells. The whole eye is enveloped by a thin membrane which also sheaths the proximal parts of the five nerve bundles that leave the eye. All the sensory cells of the lateral ocelli are similar and have rhabdomeric microvilli on the terminal end, and contain phaosomes and a multitude of other organelles and cytoplasmic inclusions. The complex median ocellus contains a superior group of three retinular cells, linked by interdigitating processes, and an inferior group consisting of a large central cell enclosed in two cup-shaped peripheral retinular cells. A two-tiered rhabdome arrangement exists, with a rather complex inferior rhabdome set made up of a central rhabdomere and two hemi-annulate rhabdomeres. The cytoplasm of the retinular cells of the median ocellus lack phaosomes but instead contain double-walled tubular elements, possibly formed by the inpushings of microvilli into adjacent cells. The possible functional significance of the unique arrangement seen in the median ocellus is discussed. The retinular cells are of the inverse type. There are no efferent nerve fibres from the brain nor any nervous connection between the lateral and the median ocelli.     

Remodeling of the Nauplius Eye into the Adult Ocelli during Metamorphosis of the Barnacle, Balanus amphitrite hawaiiensis

The planktonic barnacle larva has a single median ocellus (nauplius eye), while the adult possesses two distinct sets of photoreceptors; a pair of lateral ocelli and a single median ocellus. The nauplius eye of the cypris larva of Balanus amphitrite hawaiiensis is composed of 14 visual cells grouped into three components (a pair of lateral components and a single ventral component) surrounding two centrally located pigment cells; each lateral component consists of 5 visual cells and the ventral component, 4 visual cells. In each component, the rhabdom is made up of apposing microvilli arising directly from the neighboring visual cell bodies.
During metamorphosis into the adult form, the three components of the median ocellus become separated. Each lateral component migrates laterally on the mantle and is remodeled into the adult lateral ocellus, losing two visual cells but gaining new pigment and tapetum cells in the process. The ventral component remains in the mid portion and becomes the adult median ocellus without fundamental modification in composition. The visual cells in both ocelli undergo a marked increase in volume and form many finger-like dendrites. Rhabdomes are made up of interdigitating microvilli arising from the the dendrite tips.     

Single and Multiple Visual Systems in Arthropods

Extraction of two visual pigments from crayfish eyes prompted an electrophysiological examination of the role of visual pigments in the compound eyes of six arthropods. The intact animals were used; in crayfishes isolated eyestalks also. Thresholds were measured in terms of the absolute or relative numbers of photons per flash at various wavelengths needed to evoke a constant amplitude of electroretinogram, usually 50 µv. Two species of crayfish, as well as the green crab, possess blue- and red-sensitive receptors apparently arranged for color discrimination. In the northern crayfish, Orconectes virilis, the spectral sensitivity of the dark-adapted eye is maximal at about 550 mµ, and on adaptation to bright red or blue lights breaks into two functions with λ_max respectively at about 435 and 565 mµ, apparently emanating from different receptors. The swamp crayfish, Procambarus clarkii, displays a maximum sensitivity when dark-adapted at about 570 mµ, that breaks on color adaptation into blue- and red-sensitive functions with λ_max about 450 and 575 mµ, again involving different receptors. Similarly the green crab, Carcinides maenas, presents a dark-adapted sensitivity maximal at about 510 mµ that divides on color adaptation into sensitivity curves maximal near 425 and 565 mµ. Each of these organisms thus possesses an apparatus adequate for at least two-color vision, resembling that of human green-blinds (deuteranopes). The visual pigments of the red-sensitive systems have been extracted from the crayfish eyes. The horse-shoe crab, Limulus, and the lobster each possesses a single visual system, with λ_max respectively at 520 and 525 mµ. Each of these is invariant with color adaptation. In each case the visual pigment had already been identified in extracts. The spider crab, Libinia emarginata, presents another variation. It possesses two visual systems apparently differentiated, not for color discrimination but for use in dim and bright light, like vertebrate rods and cones. The spectral sensitivity of the dark-adapted eye is maximal at about 490 mµ and on light adaptation, whether to blue, red, or white light, is displaced toward shorter wavelengths in what is essentially a reverse Purkinje shift. In all these animals dark adaptation appears to involve two phases: a rapid, hyperbolic fall of log threshold associated probably with visual pigment regeneration, followed by a slow, almost linear fall of log threshold that may be associated with pigment migration.     

Trichromatic visual system in an insect and its sensitivity control by blue light

Summary The spectral sensitivity of the visual cells in the compound eye of the mothDeilephila elpenor was determined by electrophysiological mass recordings during exposure to monochromatic adapting light. Three types of receptors were identified. The receptors are maximally sensitive at about 350 nm (ultraviolet), 450 nm (violet), and 525 nm (green). The spectral sensitivity of the green receptors is identical to a nomogram for a rhodopsin with _max at 525 nm. The spectral sensitivity of the other two receptors rather well agrees with nomograms for corresponding rhodopsins. The recordings indicate that the green receptors occur in larger number than the other receptors. The ultra-violet and violet receptors probably occur in about equal number.The sensitivity after monochromatic adapting illumination varies with the wavelength of the adapting light, but is not proportional to the spectral sensitivity of the receptors. The sensitivity is proportional to the concentration of visual pigment at photoequilibrium. The equilibrium is determined by the absorbance coefficients of the visual pigment and its photoproduct at each wavelength. The concentration of the visual pigment, and thereby the sensitivity, is maximal at about 450 nm, and minimal at wavelengths exceeding about 570 nm.The light from a clear sky keeps the relative concentration of visual pigment in the green receptors, and the relative sensitivity, at about 0.62. The pigment concentration in the ultra-violet receptors is about 0.8 to 0.9, and that in the violet receptors probably about 0.6. At low ambient light intensities a chemical regeneration of the visual pigments may cause an increase in sensitivity. At higher intensities the concentrations of the visual pigments remain constant. Due to the constant pigment concentrations the input signals from the receptors to the central nervous system contain unequivocal information about variations in intensity and spectral distribution of the stimulating light.The work reported in this article was supported by the Swedish Medical Research Council (grant no B 73-04X-104-02B), by Karolinska Institutet, and by a grant (to G. Höglund) from Deutscher Akademischer Austauschdienst, and by the Deutsche Forschungsgemeinschaft, Schwerpunktsprogramm Rezeptorphysiologie HA 258-10, and SFB 114.