121 research outputs found
Fusion of secretory vesicles isolated from rat liver
Secretory vesicles isolated from rat liver were found to fuse after exposure to Ca2+. Vescle fusion is characterized by the occurrence of twinned vesicles with a continuous cleavage plane between two vesicles in freeze-fracture electron microscopy. The number of fused vesicles increases with increasing Ca2+-concentrations and is half maximal around 10–6 m. Other divalent cations (Ba2+, Sr2+, and Mg2+) were ineffective. Mg2+ inhibits Ca2+-induced fusion. Therefore, the fusion of secretory vesiclesin vitro is Ca2+ specific and exhibits properties similar to the exocytotic process of various secretory cells.
Various substances affecting secretionin vivo (microtubular inhibitors, local anethetics, ionophores) were tested for their effect on membrane fusion in our system.
The fusion of isolated secretory vesicles from liver was found to differ from that of pure phospholipid membranes in its temperature dependence, in its much lower requirement for Ca2+, and in its Ca2+-specificity. Chemical and enzymatic modifications of the vesicle membrane indicate that glycoproteins may account for these differences
Histological Evaluation of Diabetic Neurodegeneration in the Retina of Zucker Diabetic Fatty (ZDF) Rats
In diabetes, retinal dysfunctions exist prior to clinically detectable vasculopathy, however the pathology behind these functional deficits is still not fully established. Previously, our group published a detailed study on the retinal histopathology of type 1 diabetic (T1D) rat model, where specific alterations were detected. Although the majority of human diabetic patients have type 2 diabetes (T2D), similar studies on T2D models are practically absent. To fill this gap, we examined Zucker Diabetic Fatty (ZDF) rats - a model for T2D - by immunohistochemistry at the age of 32 weeks. Glial reactivity was observed in all diabetic specimens, accompanied by an increase in the number of microglia cells. Prominent outer segment degeneration was detectable with changes in cone opsin expression pattern, without a decrease in the number of labelled elements. The immunoreactivity of AII amacrine cells was markedly decreased and changes were detectable in the number and staining of some other amacrine cell subtypes, while most other cells examined did not show any major alterations. Overall, the retinal histology of ZDF rats shows a surprising similarity to T1D rats indicating that despite the different evolution of the disease, the neuroretinal cells affected are the same in both subtypes of diabetes
Understanding the retinal basis of vision across species
The vertebrate retina first evolved some 500 million years ago in ancestral marine chordates. Since then, the eyes of different species have been tuned to best support their unique visuoecological lifestyles. Visual specializations in eye designs, large-scale inhomogeneities across the retinal surface and local circuit motifs mean that all species' retinas are unique. Computational theories, such as the efficient coding hypothesis, have come a long way towards an explanation of the basic features of retinal organization and function; however, they cannot explain the full extent of retinal diversity within and across species. To build a truly general understanding of vertebrate vision and the retina's computational purpose, it is therefore important to more quantitatively relate different species' retinal functions to their specific natural environments and behavioural requirements. Ultimately, the goal of such efforts should be to build up to a more general theory of vision
Pan-retinal characterisation of Light Responses from Ganglion Cells in the Developing Mouse Retina
International audienceWe have investigated the ontogeny of light-driven responses in mouse retinal ganglion cells (RGCs). Using a large-scale, high-density multielectrode array, we recorded from hundreds to thousands of RGCs simultaneously at pan-retinal level, including dorsal and ventral locations. Responses to di erent contrasts not only revealed a complex developmental pro le for ON, OFF and ON-OFF responses, but also unveiled di erences between dorsal and ventral RGC responses. At eye-opening, dorsal RGCs of all types were more responsive to light, perhaps indicating an environmental priority to nest viewing for pre-weaning pups. The developmental pro le of ON and OFF responses exhibited antagonistic behaviour, with the strongest ON responses shortly after eye-opening, followed by an increase in the strength of OFF responses later on. Further, we found that with maturation receptive eld (RF) center sizes decrease, spike-triggered averaged responses to white noise become stronger, and centers become more circular while maintaining di erences between RGC types. We conclude that the maturation of retinal functionality is not spatially homogeneous, likely re ecting ecological requirements that favour earlier maturation of the dorsal retina
Photopigment coexpression in mammals: comparative and developmental aspects
In mammals, each cone had been thought to
contain only one single type of photopigment. It was not
until the early 1990s that photopigment coexpression
was reported. In the house mouse, the distribution of
color cones shows a characteristic division. Whereas in
the upper retinal field the ratio of short wave to middleto-
long wave cones falls in the usual range (1:10), in the
ventral retinal field M/L-pigment expression is
completely missing. In the transitional zone, numerous
dual cones are detectable (spatial coexpression). In other
species without retinal division, dual cones appear
during development, suggesting that M/L-cones develop
from S-cones. Dual elements represent a transitory stage
in M/L-cone differentiation that disappear with
maturation (transitory coexpression). These two
phenomena seem to be mutually exclusive in the species
studied so far.
In the comparative part of this report the retinal cone
distribution of eight rodent species is reported. In two
species dual cones appear in adult specimens without
retinal division, and dual elements either occupy the
dorsal peripheral retina, or make up the entire cone
population. This is the first observation proving that all
cones of a retina are of dual nature. These species are
good models for the study of molecular control of opsin
expression and renders them suitable sources of dual cones for investigations on the role and neural
connections of this peculiar cone type.
In the developmental part, the retinal maturation of
other species is examined to test the hypothesis of
transitory coexpression. In these species S-pigment
expression precedes that of the M/L-pigment, but dual
cones are either identified in a small number or they are
completely missing from the developing retina. These
results exclude a common mechanism for M/L-cone
maturation: they either transdifferentiate from S-cones or
develop independently
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