Activation of Protein Kinase C Modulates Light Responses in Horizontal Cells of the Turtle Retina

The effect of phorbol esters on the light-evoked responses of horizontal cells were studied in the turtle eyecup preparation. Phorbol esters caused a reduction in receptive field size and a significant decrease in the amplitude of responses to annular and full-field illumination; however, they caused only minor changes in responses to small spots in the receptive field centre. The dark membrane potential was not affected. The results suggest that phorbol esters may affect both coupling resistance and membrane resistance in horizontal cells. The effects of phorbol esters were blocked by the protein kinase C inhibitor staurosporine, and inactive phorbol ester had no effect, making it very likely that the phorbol ester effects were mediated through activation of protein kinase C. The above effects of the phorbol esters were considerably reduced by the dopamine antagonists haloperidol and fluphenazine, suggesting that they were in part mediated by release of dopamine.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73620/1/j.1460-9568.1992.tb00183.x.pd

Electrophysiological Characterization of GFP-Expressing Cell Populations in the Intact Retina

Studying the physiological properties and synaptic connections of specific neurons in the intact tissue is a challenge for those cells that lack conspicuous morphological features or show a low population density. This applies particularly to retinal amacrine cells, an exceptionally multiform class of interneurons that comprise roughly 30 subtypes in mammals1. Though being a crucial part of the visual processing by shaping the retinal output2, most of these subtypes have not been studied up to now in a functional context because encountering these cells with a recording electrode is a rare event

Влияние фазовых модификаций кремнезема на фильтрационно-емкостные свойства пород-коллекторов на газовых месторождениях

Фазовые модификации кремнезема из аморфной фазы в кристаллическую вызывают изменение порового пространства и проницаемости пород-коллекторов газовых месторождений. Данный переход к кремнезема определяет разработку и поиск газовых месторождений.Phase modifications of silica from the amorphous phase in the crystalline process of changing the threshold space and permeability of rock reservoirs of gas fields. This transition to silica determines the development and search for gas deposits

Lack of the Sodium-Driven Chloride Bicarbonate Exchanger NCBE Impairs Visual Function in the Mouse Retina

Regulation of ion and pH homeostasis is essential for normal neuronal function. The sodium-driven chloride bicarbonate exchanger NCBE (Slc4a10), a member of the SLC4 family of bicarbonate transporters, uses the transmembrane gradient of sodium to drive cellular net uptake of bicarbonate and to extrude chloride, thereby modulating both intracellular pH (pHi) and chloride concentration ([Cl-]i) in neurons. Here we show that NCBE is strongly expressed in the retina. As GABAA receptors conduct both chloride and bicarbonate, we hypothesized that NCBE may be relevant for GABAergic transmission in the retina. Importantly, we found a differential expression of NCBE in bipolar cells: whereas NCBE was expressed on ON and OFF bipolar cell axon terminals, it only localized to dendrites of OFF bipolar cells. On these compartments, NCBE colocalized with the main neuronal chloride extruder KCC2, which renders GABA hyperpolarizing. NCBE was also expressed in starburst amacrine cells, but was absent from neurons known to depolarize in response to GABA, like horizontal cells. Mice lacking NCBE showed decreased visual acuity and contrast sensitivity in behavioral experiments and smaller b-wave amplitudes and longer latencies in electroretinograms. Ganglion cells from NCBE-deficient mice also showed altered temporal response properties. In summary, our data suggest that NCBE may serve to maintain intracellular chloride and bicarbonate concentration in retinal neurons. Consequently, lack of NCBE in the retina may result in changes in pHi regulation and chloride-dependent inhibition, leading to altered signal transmission and impaired visual function

Chemical Clearing and Dehydration of GFP Expressing Mouse Brains

Generally, chemical tissue clearing is performed by a solution consisting of two parts benzyl benzoate and one part benzyl alcohol. However, prolonged exposure to this mixture markedly reduces the fluorescence of GFP expressing specimens, so that one has to compromise between clearing quality and fluorescence preservation. This can be a severe drawback when working with specimens exhibiting low GFP expression rates. Thus, we screened for a substitute and found that dibenzyl ether (phenylmethoxymethylbenzene, CAS 103-50-4) can be applied as a more GFP-friendly clearing medium. Clearing with dibenzyl ether provides improved tissue transparency and strikingly improved fluorescence intensity in GFP expressing mouse brains and other samples as mouse spinal cords, or embryos. Chemical clearing, staining, and embedding of biological samples mostly requires careful foregoing tissue dehydration. The commonly applied tissue dehydration medium is ethanol, which also can markedly impair GFP fluorescence. Screening for a substitute also for ethanol we found that tetrahydrofuran (CAS 109-99-9) is a more GFP-friendly dehydration medium than ethanol, providing better tissue transparency obtained by successive clearing. Combined, tetrahydrofuran and dibenzyl ether allow dehydration and chemical clearing of even delicate samples for UM, confocal microscopy, and other microscopy techniques

Connexin30.2:<i>In vitro</i> interaction with connexin36 in hela cells and expression in AII amacrine cells and intrinsically photosensitive ganglion cells in the mouse retina

Electrical coupling via gap junctions is an abundant phenomenon in the mammalian retina and occurs in all major cell types. Gap junction channels are assembled from different connexin subunits, and the connexin composition of the channel confers specific properties to the electrical synapse. In the mouse retina, gap junctions were demonstrated between intrinsically photosensitive ganglion cells and displaced amacrine cells but the underlying connexin remained undetermined. In the primary rod pathway, gap junctions play a crucial role, coupling AII amacrine cells among each other and to ON cone bipolar cells. Although it has long been known that connexin36 and connexin45 are necessary for the proper functioning of this most sensitive rod pathway, differences between homocellular AII/AII gap junctions and AII/ON bipolar cell gap junctions suggested the presence of an additional connexin in AII amacrine cells. Here, we used a connexin30.2-lacZ mouse line to study the expression of connexin30.2 in the retina. We show that connexin30.2 is expressed in intrinsically photosensitive ganglion cells and AII amacrine cells. Moreover, we tested whether connexin30.2 and connexin36 – both expressed in AII amacrine cells – are able to interact with each other and are deposited in the same gap junctional plaques. Using newly generated anti-connexin30.2 antibodies, we show in HeLa cells that both connexins are indeed able to interact and may form heteromeric channels: both connexins were co-immunoprecipitated from transiently transfected HeLa cells and connexin30.2 gap junction plaques became significantly larger when co-expressed with connexin36. These data suggest that connexin36 is able to form heteromeric gap junctions with another connexin. We hypothesize that co-expression of connexin30.2 and connexin36 may endow AII amacrine cells with the means to differentially regulate its electrical coupling to different synaptic partners

Ganglion Cell Adaptability: Does the Coupling of Horizontal Cells Play a Role?

Background: The visual system can adjust itself to different visual environments. One of the most well known examples of this is the shift in spatial tuning that occurs in retinal ganglion cells with the change from night to day vision. This shift is thought to be produced by a change in the ganglion cell receptive field surround, mediated by a decrease in the coupling of horizontal cells. Methodology/Principal Findings: To test this hypothesis, we used a transgenic mouse line, a connexin57-deficient line, in which horizontal cell coupling was abolished. Measurements, both at the ganglion cell level and the level of behavioral performance, showed no differences between wild-type retinas and retinas with decoupled horizontal cells from connexin57-deficient mice. Conclusion/Significance: This analysis showed that the coupling and uncoupling of horizontal cells does not play a dominant role in spatial tuning and its adjustability to night and day light conditions. Instead, our data suggest that anothe

Gap junctions in the eye: evidence for heteromeric, heterotypic and mixed-homotypic interactions

Some of the best evidence that different types of gap junction proteins (connexins) interact with each other in vivo has been found in the eye. This review focuses on three diverse ocular tissues that may contain heterotypic or heteromeric gap junction channels. Each of the tissues uses gap junctions in a superlative fashion: The crystalline lens has an exceptionally high density of gap junctions; the ciliary body expresses a surprising variety of connexins; the neural retina shows remarkable specificity in the patterns of intercellular coupling. (C) 2000 Elsevier Science B.V. All rights reserved

Short-term potentiation of off-responses in turtle horizontal cells

Depolarizing responses to light off were studied in turtle horizontal cells using intracellular recording in the everted eyecup preparation. In many cells the off-response showed two components (fast and slow) which could overshoot beyond the steady-state dark level. The peak amplitudes of the fast and slow components increased with increasing duration of the light stimulus. A similar enhancement of the off-responses could also be produced by repetitive stimulation with brief flashes. However, the degree of enhancement produced by repetitive stimulation was greater than could be produced by increasing stimulus duration, and the latency of the onset of depolarization was longer, suggesting that the enhancement produced by repetitive stimulation involves an additional mechanism. Dramatic enhancement of the off-response by stimuli which did not affect the on-response during light indicates that the off-response may contain information not present in the on-response. The fast component of the off-response was suppressed to a greater degree than other components by reducing extracellular calcium or in the presence of 500 [mu]M cobalt, suggesting that this component may involve a calcium current.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29381/1/0000451.pd