Frederick Crescitelli

The visual pigment sensitivity hypothesis: further evidence from fishes of varying habitats.

SummaryVisual pigments were extracted from the retinas of 8 species of marine teleosts and 4 species of elasmobranchs and a comparison was made of the pigment properties from these fishes, some inhabiting surface waters, others from the mesopelagic zone, and a few migrating vertically between these two environments. An association was found between the spectral position of the absorbance curve and the habitat depth or habitat behavior, with the blue-shifted chrysopsins being the pigments of the twilight zone fishes and the rhodopsins with fishes living near the surface. The retina of the swell shark (Cephaloscyllium ventriosum) yielded extracts with two photopigments; one, a rhodopsin at 498 nm; the second, a chrysopsin at 478 nm. This fish has been reported to practice seasonal vertical migrations between the surface and the mesopelagic waters. In addition to the spectral absorbance, several properties of these visual pigments were examined, including the meta-III product of photic bleaching, regeneration with added 11-cis and 9-cis retinals, and the chromophoric photosensitivity. The chrysopsin properties were found to be fundamentally similar to those of typical vertebrate rhodopsins. Correlating the spectral data with the habitat and habitat behavior of our fishes gives us confidence in the idea that the scotopic pigments have evolved as adaptations to those aspects of their color environment that are critical to the survival of the species.

A correlation of ultrastructure and function in the developing retina of the frog tadpole

The first electroretinographic response to light in developing tadpoles (Rana pipiens) was a purely cornea-negative slow potential which corresponded in time of first appearance with the first appearance of retinal receptor outer segments as revealed by electron microscopy. At this stage (6–7 days after fertilization) the receptors possessed a minimal number of developing outer segment disks, which are known to house the visual pigment molecules. The inner segments, in turn, possessed all the structural components typical of the adult receptor cell. No signs were noted of receptor synaptic structures or of the outer plexiform layer. We interpret these findings as indicating that the visual receptors at this stage of development are able to generate a potential in response to a light flash, but are unable to propagate this excitation inward to the neuronal layers. The initial negative potential may be, therefore, an isolated receptor potential. The appearance of the positive potential somewhat later in development was correlated in time with the maturation of the receptor synaptic apparatus. The correlation in times of appearance of the positive potential and the mature synaptic apparatus confirms our earlier results with Rana catesbeiana, a species characterized by a slower rate of development.

Changes in ultrastructure and electroretinogram of bullfrog retina during development

A study has been made with the purpose of attempting to correlate the ultrastructural and electroretinographic changes in the retina of the bullfrog during embryonic growth. On day 8 after fertilization, when we first examined the eyes for electrical responses to light, we obtained slow, cornea-negative waves. These persisted for the following 2 days and on day 11 a rapid negative deflection was added to the ERG. Cornea-positivity appeared on day 12 and remained thereafter. Electron microscopy revealed that during the period of negative responses the visual cells were well developed except for the synaptic apparatus, which reached maturity later than did the outer segments, the inner segments, and the visual cell nuclei. On day 12, when positivity was first recorded, the synaptic terminals of the receptors completed development, showing many synaptic ribbons and numerous synaptic vesicles within the synaptic body The meaning of the sequential development of the visual cells, in relation to the retinal origins of the a- and b-waves of the ERG is discussed.

Delayed off-responses recorded from the isolated frog retina

Using the isolated frog retina perfused with a glucose-containing physiological fluid, it is possible to demonstrate, by electrical recording, the presence of a delayed and slow off-potential, having the same sign as theb-wave and with TTP values (time from cessation of stimulus to peak of the slow wave) whichincrease with increase in stimulus intensity. Delays of about 20 sec have been recorded with stimulus illuminance at 150 lux. This unusually delayed off-effect appearsbefore exposure of a retina to a bleaching light andafter such exposure, although the properties of this component are somewhat different for the two conditions. The characteristics of this new potential are such as to clearly distinguish it from the usual components of the classical ERG. In fact, it is possible by proper adjustment of the stimulus parameters, to demonstrate in the same recordingsboth d-wave and this delayed off-effect in various stages of compounding together. The amplitude and TTP values for this component follow the Roscoe-Bunsen Law of photochemical reactions below flash durations of about one second. The spectral sensitivity of the delayed off-effect agrees with the rhodopsin absorbance curve suggesting that this response is mediatedvia the rhodopsin rods. This occurs even when the rhodopsin of the retina is reduced by bleaching to a level only 3–5% of normal. This late slow wave is accompanied by spike discharges and is probably not the result of abnormal activity. We speculate that the greater delay at higher stimulus magnitudes is related to an inhibition which is revealed by a persistent negativity following theb-wave.

The electroretinogram of the antelope ground squirrel

Abstract The electroretinogram (ERG) of this ground squirrel, an animal with a purecone type of retina, was found to have a prominent a-wave , a relatively fast b-wave and no c-wave . The d-wave was also large and it showed the familiar dependency on duration of stimulation that is characteristic of off-effects. The key finding was the demonstration that the b-wave was duplex, consisting of two components (b 1 , b 2 ) which were present in responses to flashes at all wavelengths from 454 m/gm to 631 m/gm. These two components showed independence in so far as their behavior to changes in light intensity and to light adaptation was concerned. The significance of this finding is that the human ERG also has two separate b-components which are usually assigned to separate activity in rods and cones. This cannot be the explanation for the two b-waves of the ground squirrel since only cones are present. Evidently a duplex b-system , behaving in some respects like the rod-cone system of the human retina, can occur in a retina with a single morphological type visual cell.

Color Vision in the Antelope Ground Squirrel

Antelope ground squirrels (Citellus leucurus) were able, after conditioning, to respond correctly to a port illuminated with light at a wavelength of 460 nanometers. This color randomly presented at one of two positions, was correctly selected in reference to a second port illuminated with light at 500, 520, 569, and 600 nanometers, or with white light of varying intensity. Luminosity was not a factor in the discrimination.

The eyespot of euglena gracilis: a microspectrophotometric study

The eyespots in cells of streptomycin-bleached strains and of dark-grown cultures of Euglena gracilis, were examined by means of fluorescence microscopy and microspectrophotometry. When viewed with light in the region of 380-500 nm, the stigma appeared as a dark spot. Adjacent to this was a second spot, not seen with white light, but which was seen to fluoresce when excited with radiation at 370 +/- 20 nm. This fluorescence proved to be polarized in contrast to other fluorescing bodies in the cell. The absorption curves, obtained by microspectrophotometry of individual eyespots, were found to consist of two spectral maxima, an A-band in the blue and a B-band in the green. Unlike the A-band, the B-band provided evidence of originating from an anisotropic structure. Relating these data to literature findings, we conclude that the B-band is the absorbance of a pigment in the quasi-crystalline paraflagellar body and the A-band perhaps a pigment in the orange-red stigma. The spectrum of the B-band does not appear to be that of a flavoprotein or of a free carotenoid but its resemblance to the spectrum of rhodopsin is significant in relation to published data for the Chlamydomonas eyespot that suggests the presence of a rhodopsin-like pigment as the photosensitive system responsible for phototaxis in this alga.

The visual pigment system ofXenopus laevis: Tadpoles and adults

Abstract The extraction procedure revealed that the retinal pigment system of Xenopus laevis , an entirely aquatic anuran, is not constant throughout its life cycle. The larvae have both porphyropsin and rhodopsin but the adult is characterized by a system wholly or predominantly porphyropsin. This implies that Xenopus metamorphosis, unlike that of certain other anurans, is accompanied by a changeover from an A 1 - to an A 2 -pigment. For an entirely aquatic anuran, this is contrary to expectations based on the nature of the habitat. The explanation may lie, not in its present mode of life, but in its past history i.e. Xenopus , though aquatic now, may have origins from a terrestrial ancestor. Rhodopsin may be just a vestigial indicator of past events rather than an adaptation to a present mode of life.

The visual pigments of birds: I. The Turkey

Abstract Digitonin extracts of the retinae of sixty-five Broad Breasted Bronze turkeys were found to possess two photopigments: a red-sensitive component (iodopsin) with absorption maximum in the region of 562 mμ and a typical rhodopsin with a maximum at about 504 mμ. Both are retinene 1 pigments. Iodopsin comprised about one-third of the total photopigment content of the extract. The results are in agreement with data previously obtained with the chicken retina but they did not include the finding of a photopigment at 544 mμ as reported for the pigeon retina.

The gecko visual pigments: a microspectrophotometric study

1. A dual system of visual pigments having absorbance maxima in the green and blue respectively has been found in the retinas of geckos both by single cell microspectrophotometry and by the method of extraction. Microspectrophotometry has shown the system to be present in four species of geckos representing four genera. Along with previous work with extracts (Crescitelli, 1972) this indicates a fundamental property in this family of lizards. No other photopigments have been detected.