Photomechanical Changes Research Articles

In-situ Monitoring of Photocontrollable Wrinkle Erasure in Azobenzene-based Supramolecular Systems.

In this contribution, dynamic photoinduced wrinkle erasure enabled by photomechanical changes in supramolecular polymer-azo complexes was characterized via confocal microscopy. Different photoactive molecules, disperse yellow 7 (DY7) and 4,4'-dihydroxyazobenzene (DHAB), were compared to 4-hydroxy-4'-dimethylaminoazobenzene (OH-azo-DMA). The characteristic erasure times of wrinkles were quickly assessed by using an image processing algorithm. The results confirm that the photoinduced movement on the topmost layer can be successfully transferred to the substrate. Furthermore, the chosen supramolecular strategy allows decoupling the effect of molecular weight of the polymer and photochemistry of the chromophore, allowing quantitative comparison of wrinkling erasure efficiency of different materials and providing a facile way to optimize the system for specific applications.

Nanoindentation study of optically patterned surface relief grating of azobenzene polymers.

We present the light-controlled hierarchical mechanical properties of optically patterned azobenzene thin films through a nanoindentation study. In this study, we inscribed holographic surface relief grating (SRG) of azopolymers by two-beam coupling-based light interference lithography. The resultant morphological profile of azopolymers was monitored by atomic force microscope (AFM), followed by the nanoindentation study. From the load-displacement curve of the indentation procedure, photomechanical changes of the azopolymers along grating patterns were evaluated in terms of hardness and modulus at the crest and trough of the SRG, respectively. The results revealed that the surface height as well as the mechanical properties was modulated according to the light interference pattern.

The eye of the parthenogenetic and minute moth Ectoedemia argyropeza (Lepidoptera: Nepticulidae)

Ectoedemia argyropeza (Zeller, 1839) possesses a compound eye that exhibits features of both apposition and superposition type eyes. Like apposition eyes, the eye of E. argyropeza lacks a clear-zone, which in superposition eyes separates the distal dioptric from the proximal light-perceiving structures. On the other hand, a tracheal layer around the proximal ends of the rhabdom as well as a well-developed corneal nipple array on the corneal surfaces are features that E. argyropeza shares with the larger moths. Unique, and so far only seen to this extreme degree in any insect, is the hourglass-shape of E. argyropeza's rhabdom, in which two almost equally voluminous regions (one distal, one proximal and formed in both cases by seven rhabdomeres) are connected by a narrow waist-like region of the retinula. An eighth retinula cell, not participating in rhabdom formation, is developed as a basal cell, just above the basement membrane. The eye responds with photomechanical changes to dark/light adaptation, but while the proximal rhabdom moiety slightly expands (as expected) in the dark, the distal rhabdom increases its diameter only upon light-adaptation. Owing to the tandem position of the two rhabdom moities, it is in the light-adapted state that the distally-placed rhabdom is favoured, while the proximal rhabdom plays a more important role at low ambient light levels. With screening pigments withdrawn, tracheal tapetum exposed, and distal rhabdom diameters reduced, the proximal and in the dark enlarged rhabdom is then in a position to capture photons that have entered the eye through not only the ommatidial window above, but other facets as well even in the absence of a clear-zone and superposition optics.

Sexual dimorphism and light/dark adaptation in the compound eyes of male and female Acentria ephemerella (Lepidoptera: Pyraloidea: Crambidae)

In the highly sexual-dimorphic nocturnal moth, Acentria ephemerella Denis & Schiffermuller 1775, the aquatic and win- gless female possesses a refracting superposition eye, whose gross structural organization agrees with that of the fully-winged male. The possession of an extensive corneal nipple array, a wide clear-zone in combination with a voluminous rhabdom and a reflecting tracheal sheath are proof that the eyes of both sexes are adapted to function in a dimly lit environment. However, the ommatidium of the male eye has statistically significantly longer dioptric structures (i.e., crystalline cones) and light-perceiving elements (i.e., rhab- doms), as well as a much wider clear-zone than the female. Photomechanical changes upon light/dark adaptation in both male and female eyes result in screening pigment translocations that reduce or dilate ommatidial apertures, but because of the larger number of smaller facets of the male eye in combination with the structural differences of dioptric apparatus and retina (see above) the male eye would enjoy superior absolute visual sensitivity under dim conditions and a greater resolving power and ability to detect movement during the day. The arrangement of the microvilli in the rhabdom of both genders suggests that their eyes are polarization-sensitive, an ability they would share with many aquatic insects that have to recognize water surfaces. Although sexual recognition in A. ephe- merella is thought to chiefly rely on pheromones, vision must still be important for both sexes, even if the females are wingless and never leave their watery habitat. Females swim actively under water and like their male counterparts, which fly above the surface of the water, they would have to see and avoid obstacles as well as potential predators. This, together with a small incidence of winged females, we believe, could be the reason why the eyes of female A. ephemerella are less regressed than those of other sexually dimorphic moths, like for instance Orgyia antiqua. Another, but difficult to test, possibility is that male and female A. ephemerella have diverged in their behaviour and habitat preferences less long ago than other sexually dimo rphic moths.

The compound eye of Orgyia antiqua (Lepidoptera: Lymantriidae): Sexual dimorphism and light/dark adaptational changes

Structure and photomechanical changes upon light/dark adaptation in the superposition compound eyes of the highly sexu- ally dimorphic Orygia antiqua were studied by light and electron microscopy. The eyes of the fully winged male differ from those of the wingless, sedentary female in several respects: they are significantly larger, display a more regular ommatidial array, have a wider clearzone and possess a much more substantial tracheal tapetum. However, the eyes of the female exhibit more pronounced photomechanical changes upon light/dark adaptation than those of the male. We believe that for females, on account of their limited mobility, it is necessary that their eyes can cope with widely fluctuating brightnesses, but that visual sensitivity and resolving power are less important to them than to the actively flying males. Although the latter may be attracted to the females by pheromones, males in their diurnal searches will have to visually avoid obstacles and predators. Moreover, because of their ability to fly, males can seek shelters or shaded areas and unlike the sedentary females avoid prolonged exposures to potentially hazardous light levels. This could explain why the eyes of the females exhibit more pronounced photomechanical responses to changes in ambient light lev- els.

Post-embryonic photoreceptor development and dark/light adaptation in the spittle bug Philaenus spumarius (L.) (Homoptera, Cercopidae)

The aims of this paper have been to describe (1) the general structure of the compound eye of the spittle bug Philaenus spumarius, (2) the eye's post-embryonic development, (3) photomechanical changes upon dark/light adaptation in the eye, and (4) how leaving the semi-aquatic foam bubble and turning into an adult affects the organization of the eye. Spittle bugs, irrespective of size or sex, possess apposition type compound eyes. The eye's major components (i.e. facet, cornea, cone and rhabdom) grow rather isometrically from the smallest nymph to the adult. Photomechanical changes can occur during both nymphal and adult phases and manifest themselves through pigment granules and mitochondria migrating to and away from the rhabdom, and rhabdom diameters varying with time of day and ambient light level. When a nymph transforms into an adult, its compound eyes’ dorsoventral axes widen, facet diameters increase, facet shapes turn from circular to pentagonal and hexagonal, the cornea thickens and the rhabdoms become thinner. The agile adults, free from the foam that surrounds the nymphs, can be expected to need their vision more than the nymphs, and the changes in eye structure do, indeed, indicate that the adults have superior visual acuity. A thicker cornea in the adults reduces water loss and protects the compound eye from mechanical and light-induced damage: protection given to the nymphs by their foam bubbles.

Post-embryonic photoreceptor development and dark/light adaptation in the stick insect Carausius morosus (Phasmida, Phasmatidae)

The aims of this paper have been (a) to document postembryonic eye growth in the common laboratory stick insect Carausius morosus and (b) to examine whether the capacity of the eye to adapt to changing light intensities varied with age. We found that number of facets, corneal thickness, ommatidial diameter, widths of cone and retinal layers, and rhabdom volume increased linearly. Interommatidial angles, pigment grain sizes, and microvillar diameters, however, remained approximately the same. On the basis of the morphometric data we calculated that sensitivity in the adult stick insect eye was at least tenfold that of the eye of first instar nymphs and could show that adults would be able to perceive a similar amount of detail at considerably dimmer ambient light than the smaller individuals. In terms of resolving power this means that light- and dark-adapted first instar stick insects possess acceptance angles of 5.3° and 8°, respectively and that the corresponding figures for the adult eye are 4.7° and 7.3°. The bigger (and more light-sensitive) eye of fully grown C. morosus makes protection against radiation damage a more serious issue in the adult individual than the small first instar. The findings explain why smaller (=younger) stick insects are less nocturnal than mature, fully-grown individuals. It is, thus, not surprising to see that dark/light adaptational photomechanical changes affecting pigment position and rhabdom widths, are more pronounced in the eyes of the adults.

Grouped, stacked rods and tapeta lucida in the retina of Japanese anchovy Engraulis japonicus

: Morphology of the photoreceptor cells and tapetum of the Japanese anchovy Engraulis japonicus was studied by histologically and by chemical analysis. The Japanese anchovy has a duplex retina. The cones form parallel rows consisting of alternately placed long cones and bifid cones. Both types of cones are intimately associated and form triple units that are regularly spaced along the row of cones. The rods are grouped and stacked. This fish has a retinal tapetum lucidum composed of guanine and hypoxanthine. Three structures of the tapetum lucidum were recognized: platelet, diamond and rod types. Photomechanical changes include movements of the photoreceptor cells and the retinal tapetum. The retina of the Japanese anchovy is thought to be highly sensitive and well adapted to a dim light environment.

Effect of photic manipulation on the level of melatonin in the retinas of frogs ( Rana tigrina regulosa)

The level of melatonin in the frog ( Rana tigrina regulosa) retina was studied at midlight and middark in a 12L:12D cycle and under different lighting conditions. It was found that the frog displayed a diurnal rhythm of melatonin in the retina with high levels in the dark period. When the animal was subjected to an extended dark period, the level of retinal melatonin was significantly ( P < 0.05) increased. In addition, the normal low level of retinal melatonin in the light period was significantly ( P < 0.05) increased after dark treatment, and the normal high level of retinal melatonin in the dark period was significantly ( P < 0.05) lowered following light exposure. These results suggest that synthesis and secretion of melatonin in the frog retina is controlled by environmental lighting. This supports the hypothesis that melatonin plays an important role in the regulation of the photomechanical changes of eye pigmentation, an important element in the control of light sensitivity and acuity in the eyes of vertebrates. Moreover, these findings suggest that the photoreceptor may be a neuroendocrine or neurohumoral transducer which transduces the environmental lighting into neuroendocrine or neurohumoral secretion, melatonin.

An Endogenous Crepuscular Rhythm of Rainbow Trout (Salmo Gairdneri) Photomechanical Movements

ABSTRACT The position of the epithelial pigment and cones in the retina of Salmo gairdneri was determined during extended periods of darkness in fish entrained to both artificial and natural light/dark cycles. An endogenous rhythm of such photomechanical movements, unique among species so far examined, was observed in both groups of fish, with two peaks of light adaptation coincident with dawn and dusk. It is suggested that such an apparently non-adaptive physiological rhythm is related to the behavioural pattern of trout and reveals a basic crepuscular organisation. No endogenous rhythm was observed in continual light. These results suggest that control of photomechanical changes in rainbow trout has two components : an endogenous component, that causes the bimodal pattern in maintained darkness, and a direct effect of light, that maintains light adaptation throughout a normal day.

The Function of Photomechanical Movements in the Retina of the Rainbow Trout (Salmo Gairdneri)

ABSTRACT The function of photomechanical movements in the retina of rainbow trout (Salmo gairdneri) was investigated by determining both the effect of light on the level of extractable visual pigment, and the electroretinographic b-wave sensitivity, during various stages of photomechanical light and dark adaptation. Dark-adapted fish, light-adapted fish, and dark-adapted fish exposed to ten minutes direct sunlight had on average visual pigment concentrations of 100, 82 and 36% respectively. The intensity of illumination required to bleach a specified amount of visual pigment in the light-adapted retina was found to be 1·29 log units higher than that needed to bleach the same amount of visual pigment in a dark-adapted eye. The level of extractable visual pigment was observed to be relatively constant over natural twilight periods. A close temporal correlation was observed between the time course of electroretinographic adaptation, measured by the b-wave sensitivity, and photomechanical changes. All these observations tend to support the hypothesis that photo-mechanical movements serve, at least in part, to protect the rod visual pigment from overstimulation in the light-adapted retina.

A diurnal rhythm of N-acetylserotonin in the retina of rats

Diurnal variation of N-acetylserotonin in the retina was studied in male rats housed under a photoperiod of 12 h light and 12 h darkness (lights on at 06.00 h) for two weeks. N-acetylserotonin was extracted from the retina by ethyl acetate at pH ≤ 3 and was determined by radioimmunoassay. There is a diurnal rhythm of N-acetylserotonin in the retina with high at night and low in the daytime. It is suggested that N-acetylserotonin in the retina may contribute partly to the levels of circulating N-acetylserotonin and may play a role in the regulation of photomechanical changes in the eye of rats.

Cone myoid elongation and rod myoid contraction are inhibited by colchicine in the trout retina.

Retinal photoreceptors of lower vertebrates undergo photomechanical changes (elongation or shortening) in response to light or dark. Colchicine, a microtubule-disrupting drug, blocks cone, but not rod elongation. Instead, rod shortening is blocked by this drug, thus suggesting that different mechanisms mediating these responses are involved in rods and cones.

Photomechanical changes in the retina and choroid of guinea pigs, Cavia porcellus

Pigmented guinea pigs were killed under illumination at noon and following 3 h light-adaptation and in total darkness at midnight and following 4 h dark-adaptation. The guinea pigs that were killed under illumination had light pigmentation in the pigment epithelium of the retina and elongated chromatophores in the choroid, whereas the guinea pigs that were killed in darkness had heavy pigmentation in the pigment epithelium and the chromatophores of the choroid showed various degrees of clumping suggesting photomechanical changes in the eye pigmentation of guinea pigs.

Retinal Structure and Function in the Walleye (Stizostedion vitreum vitreum) and Sauger (S. canadense)

In the sauger, Stizostedion canadense, the tapetum lucidum of the retina was found to be more highly developed than in the walleye, S. vitreum vitreum. The tapetum is uniformly distributed throughout the sauger's eye, whereas it reaches a comparable development only in the ventral region of the walleye's retina. Other structural differences also suggested that the sauger's retina is more sensitive to light than the walleye's. In both species, photomechanical changes in response to light- and dark-adaptation were restricted to the retinal epithelial pigment (melanin) and the rods. Electroretinographic recordings appeared to be correlated with the differences in tapetal development and habits of the two species. Key words: Percidae, Stizostedion vitreum vitreum, S. canadense, light intensity, retinal structure, histology, electrophysiology, behavior

A Photo-Mechanical Technique for the Production of Drainage Density Maps

AbstractThe importance of drainage density has long been recognised, but no rapid and inexpensive method exists for mapping its spatial distribution. A method based upon photo-mechanical changes of line weight is suggested. This is based upon the use of a whirling illuminator, and offers an effective means of mappi1lg density. Some of the problems inherent in the technique are outlined, and its use is illustrated by a map of the drainage density of the London region.

A Photo-Mechanical Technique for the Production of Drainage Density Maps

The importance of drainage density has long been recognised, but no rapid and inexpensive method exists for mapping its spatial distribution. A method based upon photo-mechanical changes of line weight is suggested. This is based upon the use of a whirling illuminator, and offers an effective means of mappi1lg density. Some of the problems inherent in the technique are outlined, and its use is illustrated by a map of the drainage density of the London region.

Photomechanical changes in the ommatidia of theLimulus lateral eye during light and dark adaptation

1. The photomechanical changes which occur inLimulus lateral eye during long-term (8 hours or longer) dark-light adaptation were studied via light microscopy. 2. The results indicated that, in addition to the migration of protective pigment granules previously observed, morphological changes occur in cone cells, retinular cell rhabdomeral membranes and eccentric cell dendrites during adaptation (Figs. 1, 2 and 3). These changes were confined to the illuminated (or light-deprived) portion of the eye and did not depend on intact neural connections with the brain. 3. Eyes excised during daylight hours from animals maintained in darkness appeared partially “light-adapted” suggesting circadian effects (Fig. 4). 4. Large vacuole-Iike structures formed in retinular cells during prolonged (24–48 hour) exposure to fluorescent room light and disappeared during a subsequent dark period (Fig. 5). 5. It is possible that the changes which occur in the rhabdomeral membranes of retinular cells and the eccentric cell dendrite during light-dark adaptation affect the electrotonic coupling which exists between these cells.

Melatonin levels in developing Xenopus laevis

1. 1. Spectrophotofluormetric determinations of melatonin levels in embryonic stages of the amphibian Xenopus laevis have been made. 2. 2. Significant changes occur at the times of first embryonic movement, hatching and active larval swimming. 3. 3. There is some indication that a fivefold increase in melatonin, occurring at the time of active larval swimming, is the result of enzyme activity in the retina of the eye. 4. 4. The suggestion is made that melatonin metabolism is related to photomechanical changes in retinal cells.

RHYTHMIC MOVEMENTS OF CONES IN THE RETINA OF BLUEFISH, POMATOMUS SALTATRIX, HELD IN CONSTANT DARKNESS

1. The retina of bluefish, Pomatomus saltatrix, undergoes photomechanical changes in response to light and darkness. Complete light-adaption requires between 15 and 30 minutes, complete dark-adaption between 30 and 60 minutes.2. Retinal cones of juvenile bluefish held under continuous darkness for two days exhibited a diurnal retinomotor rhythm. The epithelial pigment layer remained in a dark-adapted condition throughout the two days and displayed no discernible expansion.3. Results were related with activity rhythms of bluefish and suggested that internal control of a retinomotor rhythm may predispose the eye to environmental changes in light intensity.