Reflectance Speckle of Retinal Nerve Fiber Layer Reveals Axonal Activity
ABSTRACT PURPOSE: This study investigated the retinal nerve fiber layer (RNFL) reflectance speckle and tested the hypothesis that temporal change of RNFL speckle reveals axonal dynamic activity. METHODS: RNFL reflectance speckle of isolated rat retinas was studied with monochromatic illumination. A series of reflectance images were collected every five seconds for about 15 min. Correlation coefficients (CC) of selected areas between a reference and subsequent images were calculated and plotted as a function of the time intervals between images. An exponential function fit to the time course was used to evaluate temporal change of speckle pattern. To relate temporal change of speckle to axonal activity, in vitro living retina perfused at a normal (34°C) and a lower (24°C) temperature, paraformaldehyde-fixed retina and retina treated with microtubule depolymerization were used. RESULTS: RNFL reflectance was not uniform; rather nerve fiber bundles had a speckled texture that changed with time. In normally perfused retina, the time constant of the CC change was 0.56 ± 0.26 min. In retinas treated with lower temperature and microtubule depolymerization, the time constants increased by 2 - 4 times, indicating that the speckle pattern changed more slowly. The speckled texture in fixed retina was stationary. CONCLUSIONS: Fixation stops axonal activity; treatments with either lower temperature or microtubule depolymerization are known to decrease axonal transport. The results obtained in this study suggest that temporal change of RNFL speckle reveals structural change due to axonal activity. Assessment of RNFL reflectance speckle may offer a new means of evaluating axonal function.
SourceAvailable from: Samuel D Crish[Show abstract] [Hide abstract]
ABSTRACT: Glaucoma is an age-related optic neuropathy involving sensitivity to ocular pressure. The disease is now seen increasingly as one of the central nervous system, as powerful new approaches highlight an increasing number of similarities with other age-related neurodegenerations such as Alzheimer's and Parkinson's. While the etiologies of these diseases are diverse, they involve many important common elements including compartmentalized programs of degeneration targeting axons, dendrites and finally cell bodies. Most age-related degenerations display early functional deficits that precede actual loss of neuronal substrate. These are linked to several specific neurochemical cascades that can be linked back to dysregulation of Ca(2+)-dependent processes. We are now in the midst of identifying similar cascades in glaucoma. Here we review recent evidence on the pathological progression of neurodegeneration in glaucoma and some of the Ca(2+)-dependent mechanisms that could underlie these changes. These mechanisms present clear implications for efforts to develop interventions targeting neuronal loss directly and make glaucoma an attractive model for both interrogating and informing other neurodegenerative diseases.Neuroscience 03/2011; 176:1-11. DOI:10.1016/j.neuroscience.2010.12.036 · 3.33 Impact Factor
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ABSTRACT: In diverse cell types, microtubule (MT) and actin filament networks cooperate functionally during a wide variety of processes, including vesicle and organelle transport, cleavage furrow placement, directed cell migration, spindle rotation, and nuclear migration. The mechanisms by which MTs and actin filaments cooperate to mediate these different processes can be grouped into two broad categories: coordinated MT- and actin-based transport to move vesicles, organelles, and cell fate determinants; and targeting and capture of MT ends at cortical actin sites. Over the past several years, a growing number of cellular factors that bridge these cytoskeletal systems have been identified. These include 'hetero-motor' complexes (physically associated myosin and kinesin), myosin-CLIP170 complexes, formin homology (FH) proteins, dynein and the dynactin complex, Kar9p, coronin, Kelch repeat-containing proteins, and ERM proteins.Current Opinion in Cell Biology 03/2000; 12(1):63-71. DOI:10.1016/S0955-0674(99)00058-7 · 8.74 Impact Factor
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ABSTRACT: To develop an isolated rat retina preparation suitable for the study of the reflectance of the mammalian retinal nerve fiber layer (RNFL). A rat retina with a short piece of optic nerve attached was dissected free from the eye and stretched over a slit in a black membrane. The retina was placed in a black chamber perfused with warmed and oxygenated physiologic solution. Imaging microreflectometry was used to acquire images of the RNFL at wavelengths from 400 to 830 nm and over time. At all wavelengths the isolated retina provided high-contrast images of nerve fiber bundles against a uniform, dark background. The nerve fiber bundles had a speckled texture, especially at long wavelengths. Time-lapse movies showed that over a period of several minutes the speckle pattern slowly changed. Although the general appearance of the bundles was similar at two closely spaced wavelengths (660 and 680 nm), the detailed patterns were completely different. The isolated retina preparation is well suited to the study of the optical properties of the RNFL. The speckled texture of nerve fiber bundles probably results from optical interference in the scattered light. The slow change in pattern implies that the size and/or shape of the scattering structures must change with time.Journal of Glaucoma 03/1999; 8(1):31-7. DOI:10.1097/00061198-199902000-00008 · 2.43 Impact Factor