Light adaptation of cones in rabbits and guinea pigs

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenObjective: During light adaptation of the retina, cone electroretinograms (ERGs) can be obtained. It is known that during light adaptation considerable changes occur in the cone ERGs of man, monkeys and mice. All these species have vascular retinae. In the present study we examined whether the same applies to mammalian species with a limited retinal vasculature (rabbits) or avascular retinae (guinea pigs), and which both have two types of cones but scotopic ERGs with completely different morphology. Material and methods: ERGs were recorded from anaesthetized rabbits and guinea pigs with corneal electrodes made from steal wire. Copper wire placed in the mouth of the animal served as reference electrode, and a subcutaneous needle as ground. Recordings were amplified 1000-fold, with bandwidth settings at 1-1000 Hz, and fed into a computer via an A/D converter. Corneas were anaesthetized with a topical application of proparacaine, and pupils dilated with topical application of tropicamide. ERGs were elicited with brief (10 msec) light flashes, and the retina light adapted with a steady white background light. Results: The scotopic b-wave is more than twice the amplitude of the a-wave in rabbits, while the scotopic b-wave in guinea pigs is only slightly larger than the a-wave. The b-wave of the cone ERG is twice the amplitude of the cone a-wave in both species. Once a background light has been turned on, the amplitude increases in both species and the process of light adaptation reaches a peak about 10 minutes thereafter. The b-wave implicit time is shortened by light adaptation in rabbits, but not in guinea pigs. Oscillatory potentials are present in guinea pig ERGs when recorded in dark but not when recorded in light. Conclusions: Mammals that have avascular retinae and which are without long-wavelength cones show evidence of light adaptation of the cone ERG. In guinea pigs the cone ERG increases in amplitude during light adaptation without concomitant shortening of the implicit time. These changes occur at similar rate in rabbits and guinea pigs. The oscillatory potentials in rabbits increase in amplitude but not in guinea pigs. These results suggest that different mechanisms determine the light adaptation of the cone ERG in guinea pigs than in rabbits.Tilgangur: Þegar sjónhimna er aðlöguð að ljósi er hægt að skrá sjónhimnurit (electroretinogram, ERG) keilna. Vitað er að við ljósaðlögun verða miklar breytingar í sjónhimnuriti keilna hjá mönnum, öpum og músum. Þessar tegundir hafa æðar í sjónhimnu. Í þessari rannsókn var athugað hvort sama eigi við um tegundir spendýra með lítið af æðum í sjónu (kanínur) eða engar (marsvín) æðar í sjónu og sem hafa tvær tegundir keilna en alls ólík sjónhimnurit í rökkri. Efniviður og aðferðir: Sjónhimnurit voru skráð frá svæfðum kanínum og marsvínum með skráningarskautum úr stálvír, sem staðsett voru á hornhimnu augans. Koparvír staðsettur í munni var notaður sem viðmiðunarskaut og nál undir húð sem jarðtenging. Skráning var mögnuð 1000-falt, með bandvídd 1-1000 Hz, og niðurstöður fluttar í tölvu með A/D breytikorti. Hornhimna var staðdeyfð með próparakaíni, sjáaldur víkkað með trópikamíð dropum. Sjónhimnurit var vakið með stuttum (10msek) ljósblikkum, og sjónhimna aðlöguð að stöðugu hvítu bakgrunnsljósi. Niðurstöður: Í rökkri er b-bylgja meir en helmingi stærri en a-bylgja í sjónhimnuriti kanína, en b-bylgja aðeins eilítið stærri en a-bylgja hjá marsvínum. Í sjónhimnuriti keilna er hins vegar b-bylgja helmingi stærri en a-bylgja hjá báðum tegundum. Eftir að kveikt er á bakgrunnsljósi eftir aðlögun að rökkri hækkar spenna svara og nær hámarki eftir um 10 mínútur í báðum tegundum. Dvöl b-bylgju styttist hjá kanínum, en ekki hjá marsvínum. Í sjónhimnuriti keilna hjá kanínum eru sveifluspennur (oscillatory potentials), sem stækka að spennu við aðlögun að ljósi. Sveifluspennur eru í sjónhimnuriti marsvína, þegar það er skráð í rökkri, en engar í sjónhimnuriti keilna. Ályktanir: Spendýr með æðalausa sjónhimnu og engar langbylgjukeilur sýna ljósaðlögun sjónhimnurits keilna. Í marsvínum eykst sjónhimnurit keilna að spennu án þess að dvöl breytist við ljósaðlögun. Þessar breytingar eru svipaðar í tíma í kanínum og marsvínum. Sveifluspennur aukast að spennu í kanínum en ekki marsvínum. Niðurstöður benda til að önnur ferli ráði ljósaðlögun sjónhimnurits keilna hjá marsvínum en kanínum

Reinterpretation of the RRISP-77 Iceland shear-wave profiles

Two shear-wave profiles, E and G, collected during the 1977 Reykjanes Ridge Iceland Seismic Experiment have played an important role in models of the Icelandic crust. They were originally interpreted as indicating very low shear-wave velocities and abnormally low shear-wave quality factors in the 10–15 km depth range. These attributes, which are indicative of near-solidus temperatures, were used to support the hypothesis that the crust of Iceland is relatively thin (10–15 km) and underlain by partially molten material. More recent seismic data, however, contradict this hypothesis and suggest that the crust is thicker (20–30 km) and cooler. A re-examination of the RRISP-77 data indicates that the low shear-wave velocities are artefacts arising from source static anomalies (in the case of profile G) and misidentification of a secondary shear phase, SmS, as S (in the case of profile E). Furthermore, the attenuation occurs at ranges when rays from the shots pass near the Askja (profile E) and Katla and Oraefajokull (profile G) volcanoes. It may therefore have a localized source, and not be diagnostic of Icelandic crust as a whole. This new interpretation of the RRISP-77 shear-wave data is consistent with models having a thick, cold crust.We thank 0. Flovenz, one of the principal investigators of the SIST experiment, G. Foulger and B. Julian, principal investigators of the Hengill experiment, and the Incorporated Research Institutions for Seismology for providing us with copies of the data. Lamont Doherty Contribution Number 5513Peer Reviewe

Concocting Ulysses in the North

The first Icelandic publications of works by James Joyce were translations of two stories from Dubliners (“A Little Cloud” and “Counterparts”) in 1946 and 1961.1 A third short story, “Eveline” was translated in 1962 by Sigur"ur A. Magnússon, who later would become the Joyce translator in Iceland, rendering Dubliners as a whole in 1982, Ulysses in 1992-93 (two volumes), and Portrait of the Artist as a Young Man in 2000

Mouse microphthalmia-associated transcription factor (Mitf) mutations affect the structure of the retinal vasculature

Funding Information: The findings of this study were presented at the ARVO annual meeting in May, 2018. Supported by the Helga Jónsdóttir and Sigurlidi Kristjánsson Memorial Fund, The Richard P. Theodórs and Dora Sigurjónsdóttir Memorial Fund, University of Iceland Research Fund. Publisher Copyright: © 2022 The Authors. Acta Ophthalmologica published by John Wiley & Sons Ltd on behalf of Acta Ophthalmologica Scandinavica Foundation.Purpose: Mice carrying pathogenic variants in the microphthalmia transcription factor (Mitf) gene show structural and functional changes in the retina and retinal pigment epithelium. The purpose of this study was to assess the vascular changes in Mitf mice carrying pathogenic variants by determining their retinal vessel diameter. Methods: Mice examined in this study were: B6-Mitfmi-vga9/+ (n = 6), B6-Mitfmi-enu22(398) /Mitfmi-enu22(398) (n = 6) and C57BL/6J wild type mice (n = 6), all 3 months old. Fundus images were taken with a Micron IV camera after intraperitoneal injection of fluorescein salt. Images were adjusted to enhance contrast and a custom written MATLAB program used to extract the mean vascular diameter at a pre-defined distance from the optic disc. The number of vessels, mean diameter and mean total diameter were examined. Results: The mean diameter of retinal veins in Mitfmi-enu22(398)/Mitfmi-enu22(398) mice was 18.8% larger than in wild type (p = 0.026). No differences in the mean diameter of the retinal arteries were found between the genotypes. Mitfmi-enu22(398)/Mitfmi-enu22(398) mice have 17.2% more retinal arteries (p = 0.026), and 15.6% more retinal veins (p = 0.041) than wild type. A 24.8% increase was observed in the mean combined arterial diameter in mice with the Mitfmi-enu22(398)/Mitfmi-enu22(398) compared to wild type mice (p = 0.024). A 38.6% increase was found in the mean combined venular diameter in mice with the Mitfmi-enu22(398)/Mitfmi-enu22(398) pathogenic variation as compared to wild type (p = 0.004). The mean combined retinal venular diameter in the Mitfmi-vga9/+ mice was 17.8% larger than in wild type (p = 0.03). Conclusion: An increase in vascularization of the retina in Mitfmi-enu22(398) /Mitfmi-enu22(398) mice was found, indicating an increased demand for blood flow to the retina.Peer reviewe

The microphthalmia-associated transcription factor (Mitf) gene and its role in regulating eye function.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked DownloadMutations in the microphthalmia-associated transcription factor (Mitf) gene can cause retinal pigment epithelium (RPE) and retinal dysfunction and degeneration. We examined retinal and RPE structure and function in 3 month old mice homo- or heterozygous or compound heterozygous for different Mitf mutations (Mitfmi-vga9/+, Mitfmi-enu22(398)/Mitfmi-enu22(398), MitfMi-Wh/+ and MitfMi-Wh/Mitfmi) which all have normal eye size with apparently normal eye pigmentation. Here we show that their vision and retinal structures are differentially affected. Hypopigmentation was evident in all the mutants while bright-field fundus images showed yellow spots with non-pigmented areas in the Mitfmi-vga9/+ mice. MitfMi-Wh/+ and MitfMi-Wh/Mitfmi mice showed large non-pigmented areas. Fluorescent angiography (FA) of all mutants except Mitfmi-vga9/+ mice showed hyperfluorescent areas, whereas FA from both Mitf-Mi-Wh/+ and MitfMi-Wh/Mitfmi mice showed reduced capillary network as well as hyperfluorescent areas. Electroretinogram (ERG) recordings show that MitfMi-Wh/+ and MitfMi-Wh/Mitfmi mice are severely impaired functionally whereas the scotopic and photopic ERG responses of Mitfmi-vga9/+ and Mitfmi-enu22(398)/Mitfmi-enu22(398) mice were not significantly different from wild type mice. Histological sections demonstrated that the outer retinal layers were absent from the MitfMi-Wh/+ and MitfMi-Wh/Mitfmi blind mutants. Our results show that Mitf mutations affect eye function, even in the heterozygous condition and that the alleles studied can be arranged in an allelic series in this respect.Icelandic Research Fund National University Hospital Research Fund Helga Jonsdottir and Sigurlioi Kristjansson Memorial Fun

Progressive Cone-Rod Dystrophy and RPE Dysfunction in Mitfmi/+ Mice

Funding Information: A.G.-L. acknowledges financial support provided by a Postdoctoral Fellowship Grant from the Icelandic Research Fund (217796-052). T.E. acknowledges financial support from the Landspitali National Hospital Research Fund (986862). Publisher Copyright: © 2023 by the authors.Mutations in the mouse microphthalmia-associated transcription factor (Mitf) gene affect retinal pigment epithelium (RPE) differentiation and development and can lead to hypopigmentation, microphthalmia, deafness, and blindness. For instance, an association has been established between loss-of-function mutations in the mouse Mitf gene and a variety of human retinal diseases, including Waardenburg type 2 and Tietz syndromes. Although there is evidence showing that mice with the homozygous Mitfmi mutation manifest microphthalmia and osteopetrosis, there are limited or no data on the effects of the heterozygous condition in the eye. Mitf mice can therefore be regarded as an important model system for the study of human disease. Thus, we characterized Mitfmi/+ mice at 1, 3, 12, and 18 months old in comparison with age-matched wild-type mice. The light- and dark-adapted electroretinogram (ERG) recordings showed progressive cone-rod dystrophy in Mitfmi/+ mice. The RPE response was reduced in the mutant in all age groups studied. Progressive loss of pigmentation was found in Mitfmi/+ mice. Histological retinal sections revealed evidence of retinal degeneration in Mitfmi/+ mice at older ages. For the first time, we report a mouse model of progressive cone-rod dystrophy and RPE dysfunction with a mutation in the Mitf gene.Peer reviewe

Mitf Links Neuronal Activity and Long-Term Homeostatic Intrinsic Plasticity

Publisher's versionNeuroplasticity forms the basis for neuronal circuit complexity and differences between otherwise similar circuits. We show that the microphthalmia-associated transcription factor (Mitf) plays a central role in intrinsic plasticity of olfactory bulb (OB) projection neurons. Mitral and tufted (M/T) neurons from Mitf mutant mice are hyperexcitable, have a reduced A-type potassium current (IA) and exhibit reduced expression of Kcnd3, which encodes a potassium voltage-gated channel subunit (Kv4.3) important for generating the IA. Furthermore, expression of the Mitf and Kcnd3 genes is activity dependent in OB projection neurons and the MITF protein activates expression from Kcnd3 regulatory elements. Moreover, Mitf mutant mice have changes in olfactory habituation and have increased habituation for an odorant following long-term exposure, indicating that regulation of Kcnd3 is pivotal for long-term olfactory adaptation. Our findings show that Mitf acts as a direct regulator of intrinsic homeostatic feedback and links neuronal activity, transcriptional changes and neuronal function.This work was supported by the Icelandic Research Fund, Rannís Grants 152715-053 and 163068-051Peer reviewe