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ABSTRACT: The widely used botulinum neurotoxin A (BoNT/A) blocks neurotransmission via cleavage of the synaptic protein SNAP-25 (synaptosomal-associated protein of 25 kDa). Recent evidence demonstrating long-distance propagation of SNAP-25 proteolysis has challenged the idea that BoNT/A remains localized to the injection site. However, the extent to which distant neuronal networks are impacted by BoNT/A retrograde trafficking remains unknown. Importantly, no studies have addressed whether SNAP-25 cleavage translates into structural and functional changes in distant intoxicated synapses. Here we show that the BoNT/A injections into the adult rat optic tectum result in SNAP-25 cleavage in retinal neurons two synapses away from the injection site, such as rod bipolar cells and photoreceptors. Retinal endings displaying cleaved SNAP-25 were enlarged and contained an abnormally high number of synaptic vesicles, indicating impaired exocytosis. Tectal injection of BoNT/A in rat pups resulted in appearance of truncated-SNAP-25 in cholinergic amacrine cells. Functional imaging with calcium indicators showed a clear reduction in cholinergic-driven wave activity, demonstrating impairments in neurotransmission. These data provide the first evidence for functional effects of the retrograde trafficking of BoNT/A, and open the possibility of using BoNT/A fragments as drug delivery vehicles targeting the central nervous system.
Traffic 04/2012; 13(8):1083-9. · 4.92 Impact Factor
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ABSTRACT: Increased intraocular pressure (IOP) is a major risk factor for glaucoma, and its contribution to neuronal damage appears multi-factorial. An open issue is whether pressure effects on blood vessels contribute to neuronal damage. In particular, little is known about pressure effects on capillaries, which are the site of most metabolic exchange in the retina, but cannot be easily visualized in vivo. To address this issue, here we have imaged retinal capillaries in acutely isolated living rat retinas, and measured alterations in capillary viability, caliber and response to vasoactive stimuli after controlled pressure stimuli. We found that capillary viability, diameter and response to vasodilator stimulation are not affected after pressure increments; yet, a prolonged lack of capillary response to the vasoconstrictor Endothelin-1 (Et-1) is observed. Considering that Et-1 is a major component of the endogenous control of retinal blood flow the present data lead to the hypothesis that prolonged or repeated IOP elevation could induce capillary disregulation contributing to neuronal damage over time.
Experimental Eye Research 09/2009; 90(1):33-40. · 3.26 Impact Factor
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ABSTRACT: Patterns in nature have always fascinated human beings. They convey the idea of order, organization and optimization, and, to the enquiring mind, the alluring promise that understanding their building rules may uncover the forces that shaped them. In the retina, two patterns are outstanding: the stacking of cells in layers and, within the layers, the prevalent arrangement of neurons of the same type in orderly arrays, often referred to as mosaics for the crystalline-like order that some can display. Layers and mosaics have been essential keys to our present understanding of retinal circuital organization and function. Now, they may also be a precious guide in our exploration of how the retina is built. Here, we will review studies addressing the mechanisms controlling the formation of retinal mosaics and layers, illustrating common themes and unsolved problems. Among the intricacies of the building process, a world of physical forces is making its appearance. Cells are extremely complex to model as "physical entities", and many aspects of cell mechanotransduction are still obscure. Yet, recent experiments, focusing on the mechanical aspects of growth and differentiation, suggest that adopting this viewpoint will open new ways of understanding retinal formation and novel possibilities to approach retinal pathologies and repair.
Progress in Retinal and Eye Research 06/2008; 27(3):260-83. · 9.45 Impact Factor
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Valentina Resta,
Elena Novelli,
Giovanni Vozzi,
Cristiano Scarpa,
Matteo Caleo,
Arti Ahluwalia,
Anna Solini,
Eleonora Santini,
Vincenzo Parisi,
Francesco Di Virgilio, Lucia Galli-Resta
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ABSTRACT: Elevated intraocular pressure may lead to retinal ganglion cell injury and consequent visual deficits. Chronic intraocular pressure increase is a major risk factor for glaucoma, a leading blinding disease, and permanent visual deficits can also occur following acute pressure increments due to trauma, acute glaucoma or refractive surgery. How pressure affects retinal neurons is not firmly established. Mechanical damage at the optic nerve head, reduced blood supply, inflammation and cytotoxic factors have all been called into play. Reasoning that the analysis of retinal neurons soon after pressure elevation would provide useful cues, we imaged individual ganglion cells in isolated rat retinas before and after short hydrostatic pressure increments. We found that slowly rising pressure to peaks observed in trauma, acute glaucoma or refractive surgery (50-90 mmHg) did not damage ganglion cells, whereas a rapid 1 min pulse to 50 mmHg injured 30% of these cells within 1 h. The severity of damage and the number of affected cells increased with stronger or repeated insults. Degrading extracellular ATP or blocking the P2X receptors for ATP prevented acute pressure-induced damage in ganglion cells. Similar effects were observed in vivo. A short intraocular pressure transient increased extracellular ATP levels in the eye fluids and damaged ganglion cells within 1 h. Reducing extracellular ATP in the eye prevented damage to ganglion cells and accelerated recovery of their response to light. These data show that rapid pressure transients induce acute ganglion cell injury and unveil the causal role of extracellular ATP elevation in such injury.
European Journal of Neuroscience 06/2007; 25(9):2741-54. · 3.63 Impact Factor
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ABSTRACT: The precise assembly of neuronal circuits requires that the correct number of pre- and postsynaptic neurons form synaptic connections. Neuronal cell number is thus tightly controlled by cell death during development. Investigating the regulation of cell number in the retina we found an ATP gated mechanism of neuronal death control. By degrading endogenous extracellular ATP or blocking the P2X(7) ATP receptors we found that endogenous extracellular ATP triggers the death of retinal cholinergic neurons during normal development. ATP-induced death eliminates cholinergic cells too close to one another, thereby controlling the total number, the local density and the regular spacing of these neurons.
Development 07/2005; 132(12):2873-82. · 6.60 Impact Factor
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ABSTRACT: Most regions of the nervous system derive their power of processing from a modular architecture. The retina is an outstanding example of modular circuit design. Retinal neurons are stacked in layers and within each layer neurons of the same type commonly form orderly arrays, or mosaics. Here we review current knowledge on the mechanisms of retinal mosaic formation, and discuss the hypothesis that retinal mosaics are the building blocks in the assembly of retinal circuitry.
Progress in brain research 02/2005; 147:141-53. · 3.04 Impact Factor
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ABSTRACT: To test whether retinal mosaics develop through interactions that are restricted primarily to the mosaic cells, we studied the horizontal cell mosaic in mutant mice (rd/rd and rd/bcl2) displaying severe retinal abnormalities. These mutants show that the horizontal cell mosaic develops normally even if these cells lack part of their synaptic input, have anomalous morphologies, eventually decrease in number, and reside in an abnormally packed retinal layer. These data strongly support a developmental design in which the final position of each cell in a retinal mosaic is controlled by interactions between homotypic cells and is independent of other cell types. The present analysis is also an investigation of the effects of photoreceptor degeneration on the horizontal cells in an established animal model of retinitis pigmentosa, the rd/rd mouse. We find that the organization of the horizontal cell mosaic resists photoreceptor degeneration and, furthermore, that bcl2 overexpression prevents the partial loss of horizontal cells secondary to photoreceptor loss. Secondary degeneration hampers attempts to restore retinal function by transplanting photoreceptors or promoting their survival. The anti-apoptotic gene bcl2 appears to be a promising tool to rescue inner retinal neurons, increasing the probability that photoreceptor rescue or substitution may be beneficial to subjects suffering from retinal degenerative diseases.
Journal of Neuroscience 11/2003; 23(30):9924-8. · 7.11 Impact Factor
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Lucia Galli-Resta
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ABSTRACT: Development of the nervous system can be schematically summarized as (1) making the necessary cells, (2) putting these cells in the right places, and then (3) connecting them appropriately. Each of these steps represents an enormous challenge to our understanding. Focusing on the vertebrate retina, I will consider the question of what defines the right place for a neuron to go. I will illustrate data pointing to the prominent role played by short-range cellular interactions, possibly coordinated by global factors, and will discuss how a few sets of local rules could control cell positioning and proper wiring in retinal circuits.
Trends in Neurosciences 01/2003; 25(12):638-43. · 14.23 Impact Factor
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ABSTRACT: In the vertebrate retina cell layers support serial processing, while monolayered arrays of homotypic neurones tile each layer to allow parallel processing. How neurones form layers and arrays is still largely unknown. We show that monolayered retinal arrays are dynamic structures based on dendritic interactions between the array cells. The analysis of three developing retinal arrays shows that these become regular as a net of dendritic processes links neighbouring array cells. Molecular or pharmacological perturbations of microtubules within dendrites lead to a stereotyped and reversible disruption of array organization: array cells lose their regular spacing and the arrangement in a monolayer. This leads to a micro-mechanical explanation of how monolayers of regularly spaced 'like-cells' are formed.
Development 09/2002; 129(16):3803-14. · 6.60 Impact Factor
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ABSTRACT: Individual types of retinal nerve cell are spaced across the retina in an orderly manner, ensuring a uniform sampling of the visual field. This regularity in cellular spacing has been commonly attributed to fate determination mechanisms operating around the time of cell birth, an hypothesis presuming that the position of a nerve cell is fixed within the plane of the retina from the time of its determination. At odds with this view, recent results from X-inactivation mosaic mice indicate that certain classes of retinal nerve cell, those known to form orderly mosaics in the adult retina, disperse tangentially during development. Furthermore, studies defining the spatial characteristics of developing and mature retinal mosaics suggest that cell-cell interactions around the time of morphological differentiation lead to mutual repulsion. Modelling studies in turn show that nothing more than a simple minimal spacing rule between neighboring cells of the same type is sufficient for the creation of the global patterning observed in biological retinal mosaics. For some cell types, the size of this "exclusion zone" surrounding individual cells is shown to be an intrinsic characteristic of each cell type, invariant across the retina, and accounting for the variation in mosaic regularity across changes in cell density. These results show how short-distance movements driven by intercellular interactions at the local level may mediate the emergence of the global patterning characteristic of retinal mosaics during development.
Progress in Retinal and Eye Research 04/2002; 21(2):153-68. · 9.45 Impact Factor
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ABSTRACT: We analysed the spatial organization of the cholinergic amacrine cell mosaics in the mouse retina, as part of a general study of the major mouse retinal arrays, aiming at providing intrinsic cellular reference grids to monitor anomalies in retinal growth and/or functional organization in mouse models of retinal degeneration. The spatial organization of the cells was analysed by means of the nearest neighbour distance analysis, as well as by the analysis of Voronoi and Delaunay tesselations. We found non random cell spacing in both cholinergic arrays, although the mosaic in the ganglion cell layer tiles the retina scarcely better than a random distribution. Autocorrelation analysis revealed no detectable pattern in cell positioning, but there was a tendency towards a minimal spacing between array elements. Finally, we found no correlation in the spatial organization of the two arrays.
European Journal of Neuroscience 09/2000; 12(10):3819 - 3822. · 3.63 Impact Factor
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ABSTRACT: The horizontal cells are known to form a mono-layered mosaic in the adult retina, but are scattered at different retinal depths in early development. To help clarifying when and which spatial constraints appear in the relative positioning of these cells, we have performed a quantitative analysis of the three-dimensional (3D) organization of the horizontal cell mosaic at different developmental stages in the postnatal rat retina. We first analyzed the two-dimensional (2D) distribution of the horizontal cell projections onto a plane parallel to the upper retinal surface in retinal flat-mounts, and thus to the future mature horizontal cell mosaic. We found that this 2D distribution was non random since postnatal day 1 (P1), and had a subsequent stepwise improvement in regularity. This preceded the alignment of cells in a single monolayer, which was observed on P6. We then computed true horizontal cell spacing in 3D, finding non-random 3D positioning already on P1. Simulation studies showed that this order might simply derive from the 2D order observed in the projections of the cells in flat-mount, combined with their limited spread in retinal depth. Throughout the period analyzed, the relative positions of horizontal cells are in good agreement with a minimal spacing rule in which the exclusion zone corresponds to the average size of the inner core of the cell dendritic tree estimated from P1 samples. These data indicate the existence of different phases in the process of horizontal cell 3D spatial ordering, supporting the view that multiple mechanisms are involved in the development of the horizontal cell mosaic.
Visual Neuroscience 24(1):91-8. · 2.23 Impact Factor
