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  • Electronic Resource  (8)
  • 1
    Electronic Resource
    Electronic Resource
    Posttranscriptional regulation of the immediate-early gene EGR1 by light in the mouse retina (2004)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 20 (2004), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Synaptic plasticity is modulated by differential regulation of transcription factors such as EGR1 which binds to DNA via a zinc finger binding domain. Inactivation of EGR1 has implicated this gene as a key regulator of memory formation and learning. However, it remains puzzling how synaptic input can lead to an up-regulation of the EGR-1 protein within only a few minutes. Here, we show by immunohistochemical staining that the EGR-1 protein is localized in synapses throughout the mouse retina. We demonstrate for the first time that two variants of Egr-1 mRNA are produced in the retina by alternative polyadenylation, with the longer version having an additional 293 base pairs at the end of the 3′UTR. Remarkably, the use of the alternative polyadenylation site is controlled by light. The additional 3′UTR sequence of the longer variant displays an even higher level of phylogenetic conservation than the coding region of this highly conserved gene. Additionally, it harbours a cytoplasmic polyadenylation element which is known to respond to NMDA receptor activation. The longer version of the Egr-1 mRNA could therefore rapidly respond to excitatory stimuli such as light or glutamate release whereas the short variant, which is predominantly expressed and contains the full coding sequence, lacks the regulatory elements for cytoplasmic polyadenylation in its 3′UTR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.2004.03811.x
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  • 2
    Electronic Resource
    Electronic Resource
    HOW A HARBOR SEAL SEES THE NIGHT SKY (2005)
    Oxford, UK : Blackwell Publishing Ltd
    Marine mammal science 21 (2005), S. 0 
    Details
    ISSN: 1748-7692
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Astronavigation is a possible mechanism of offshore orientation in marine mammals. However, the basic prerequisite for astronavigation is to see enough stars of the night sky. This cannot be taken for granted in seals as, due to adaptations of their dioptric apparatus to the optical properties of water, seals are supposed to be myopic and astigmatic when out of the water under low light conditions. Using various real and artificial stars in a go/no-go response paradigm we therefore determined the minimum brightness at which a harbor seal (Phoca vitulina) can detect stars. The dark-adapted seal was trained to look through an empty tube (“seal telescope”) and to retract its head only when a star appeared at the opposite aperture. The seal reliably detected Venus or Sirius becoming suddenly visible when the telescope was moved across the night sky. Detection thresholds were determined using artificial stars (parallel light identical to starlight coming from the universe) of predefined brightness generated by an optical system installed in front of the seal's telescope. The seal detected artificial stars down to 4.4 stellar magnitudes. Although these results cannot present evidence for astronavigation, they imply that seals should see enough stars to allow such orientation mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1748-7692.2005.tb01257.x
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  • 3
    Electronic Resource
    Electronic Resource
    Corneal accommodation in chick and pigeon (1987)
    Springer
    Journal of comparative physiology 160 (1987), S. 375-384 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We have investigated the role of changes in corneal radius of curvature in effecting accommodation in the bird's eye. It was found that in natural accommodation (measured by IR photoretinoscopy) changes of corneal radius of curvature (measured by IR photokeratometry) play an important role in both the chick and the pigeon. In the adult pigeon the cornea is indeed responsible for the largest part of natural accommodation (up to approx. 9 D). In this animal the corneal diameter (as seen from the optical axis of the eye) decreases in accommodation which can be taken to explain the change of corneal radius of curvature. In the chicken, corneal accommodation is combined with other mechanisms (total accommodative range 15–17 D, corneal accommodation about 8 D). The chicken's cornea is aspherical within the pupil area leading to large measurement variation in photokeratometry if the Purkinje images are not symmetrical to the pupillary axis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00613027
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  • 4
    Electronic Resource
    Electronic Resource
    Visual optics in toads (Bufo americanus) (1988)
    Springer
    Journal of comparative physiology 163 (1988), S. 201-213 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Aspects of visual optics were investigated in the American toad (Bufo americanus). The development of the refractive state of the eye during metamorphosis was followed with IR photoretinoscopy. Frozen sections documented the changes in optical parameters before and after metamorphosis. There is a difference in light sensitivity between juvenile and adult toads. Binocular accommodation in adult toads was observed. 1. IR photoretinoscopic measurements showed that the refractive state of the eye changed very rapidly during metamorphosis, about 10D/h while the animal entered the terrestrial habitat. 2. Frozen sections showed that the almost spherical lens in a tadpole eye had flattened in a just metamorphosed toad's eye while at the same time the distance of the lens to the retina had decreased. However, the morphological measurements were not sufficiently sensitive to record the relatively small changes in ocular dimensions that were responsible for the rapid changes in refractive state during metamorphosis. 3. Schematic eyes, with homogeneous and non homogeneous lenses, were constructed for tadpoles, juvenile toads, and adult toads. 4. Nonparaxial raytracing studies in schematic eyes suggested that the lenses of animals of the three developmental stages tadpole, juvenile toad, and adult are not homogeneous but have a refractive index gradient. The raytracing studies indicated that the refractive index gradient is different for the different developmental stages, being highest in the tadpole lens. 5. The observations of toads during feeding behavior at different light levels showed an increased light sensitivity in the adult nocturnal toads in contrast to the juvenile animals, which are diurnal. The increased light sensitivity could partly be explained with an increase in aperture and an increase in red rod outer segments. To fully explain the higher light sensitivity in adult toads, changes in neuronal parameters had to be assumed. 6. Retinoscopic measurements of the resting refractive state in the adult toad showed a hyperopic defocus of about +8D. By subtracting the measurement artefact for retinoscopy, the true resting focus was found to be nearly emmetropic. 7. The amount of natural accommodation in adult toads during normal feeding behavior was investigated with IR photoretinoscopy. Binocular accommodation of about 8D was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00612429
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  • 5
    Electronic Resource
    Electronic Resource
    Barn owls (Tyto alba) use accommodation as a distance cue (1991)
    Springer
    Journal of comparative physiology 169 (1991), S. 515-521 
    Details
    ISSN: 1432-1351
    Keywords: Vision ; Distance estimation ; Photorefraction ; Focus ; Pecking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We have investigated the role of ocular accommodation in the distance estimation during pecking in the barn owl (Tyto alba). Owls were trained to peck at pieces of food presented on a small platform (Fig. 2) while one eye was occluded to eliminate binocular distance cues (Fig. 1). The other eye was defocussed by spectacle lenses ( −4, −2, +2 diopters) or had normal vision. Pecking behavior was analyzed by video taping the owl from the side and drawing the owls' head position off-line frame-by-frame. Additionally, during some trials the owls' accommodation behavior was recorded continuously by infrared photoretinoscopy with a second camera. This camera was aligned with the line of sight of the owl so that the refractive state could be measured just prior to pecking. We made the following observations: 1. The lenses resulted in errors in distance estimation which were highly predictable from the power and sign of the lenses (Fig. 3). 2. The lenses also changed the position of the owls' head during the period of fixation (Fig. 4). This finding together with the observation that the owls closed their eyelids during pecking suggested that ‘pecking length’ is a pre-programmed parameter in the owls' pecking behavior (Figs. 5, 6). 3. The photorefractions showed that the owls' accommodative effort during fixation was highly correlated with the power of the lenses. During fixation, negative lenses caused the owl to accommodate more than positive lenses (Fig. 8). 4. The results demonstrate that the accommodative effort necessary to fixate the target is one of the parameters by which the owls can estimate distance (Fig. 9), at least under monocular viewing conditions. 5. The total range of accommodation in the barn owls measured in our experiments did not exceed 6 diopters. This may be one of the reasons why the owls did not get their targets into best optical focus during pecking. The results are discussed with respect to the depth of field in owls and accommodation behavior in other birds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00193542
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  • 6
    Electronic Resource
    Electronic Resource
    A negatively powered lens in the chameleon (1995)
    [s.l.] : Nature Publishing Group
    Nature 373 (1995), S. 692-694 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We have measured natural accommodation in two tame chameleons (Chamaeleo dilepis) sitting on a perch while they caught crickets presented by the investigator. We found that accommodation was very fast (up to 60 dioptres per second) and that accommodative ranges were larger than in other terrestrial ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/373692a0
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  • 7
    Electronic Resource
    Electronic Resource
    Das wachsende Auge - ein optisches System mit Autofokus (1999)
    Weinheim : Wiley-Blackwell
    Biologie in unserer Zeit 29 (1999), S. 238-246 
    Details
    ISSN: 0045-205X
    Keywords: Life and Medical Sciences
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Nur bei wenigen Wachstumsprozessen wird eine so groß Genauigkeit gefordert und erreicht wie bei der Abstimmung der Augenlänge auf die Brennweite von Linse und Hornhaut. Wenn das Auge um nur ein Prozent zu lang ist, besteht bereist eine Kurzsichtigkeit (Myopie) von fast einer Dioptrie (dpt). Dabei fällt die Sehschärfe in der Ferne auf etwa ein Drittel. ab. Ist das Auge daggen zu kurz (Weitsichtigkeit-Hyperopie), so kann man zwar in der Ferne meist noch gut sehen, aber die Arbeit in der Nähe wird schwierig, weil mehr Akkommodation aufgebracht werden muß. Die hat nichts mit der “Alterweitsichtigkeit” (Presbyopie) zu tun, wo zwar der Bau des Auges normal ist, aber der altersbedingte Verlust der Akkommodation scharfes Sehen in der Nähe unmöglich macht.Beim Menschen, einigen Afen und Vögeln erreicht die Abbildungsgüte im Bereich der Stelle des schärfsten Sehens (Fovea) die Grenze der physikalischen Möglichkeiten. Nicht optische Schwächen oder Ungenauigkeiten im Bau des Auges, sondern die Lichtbeugung an der Pupille, die zwangsläufig aus den Welleneigenschaften des Lichtes folgt, begrenzen weitere Auflösung. Es ist schwer vorstellbar, wie diese Genaukeit erreicht werden kann, wenn nicht eine Steuerung des Wachstums durch einen rückgekoppeltn Regelkreis erfolgt, der sein Fehlersignal aus dem Netzhautbild entnimmt. Bis vor wenigen Jahren herrschte dennoch die Meinnung vor, daß das Augenlängenwachstum weitgehend genetisch bestimmt ist. Inszwischen ist aber durch Experimente mit brillentragenden Hühnern und Affen gezigt worden, daß “normale” Seherfahrung tatsächlich Voraussetzung für genaues Wachtsum ist. Die zugrundeliegenden Mechanismen sind noch nicht vollständig aufgeklärt, ber bisherige Ergebnisse lassen Schlüsse über mögliche Ursachen von Kurzsichtigkeit zu.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/biuz.960290407
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  • 8
    Electronic Resource
    Electronic Resource
    Why are so many of the readers of this article short-sighted? Ciba Foundation Symposium 155: Myopia and the Control of Eye Growth (1990). Edited by Gregory R. Bock and Kate Widdows. John Wiley & Sons, Chichester. 256pp. £43.15 (1992)
    New York, NY : Wiley-Blackwell
    BioEssays 14 (1992), S. 69-69 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950140115
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