Imaging of rat optic nerve axons in vivo (original) (raw)
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Axon types classified by morphometric and multivariate analysis in the rat optic nerve
Brain Research, 1992
Calibers of the rat optic nerve axons distribute unimodally and it is difficult to distinguish groups among them. However, these fibers arose from 3 types of ganglion cells and showed 3 conduction velocities. Performing a cluster analysis over several uitrastructural parameters we found 3 main groups of fibers. These groups are present in a very similar proportion to the ganglion cells groups described in the rat retina.
Proceedings of the National Academy of Sciences of the United States of America, 2012
The mature optic nerve cannot regenerate when injured, leaving victims of traumatic nerve damage or diseases such as glaucoma with irreversible visual losses. Recent studies have identified ways to stimulate retinal ganglion cells to regenerate axons part-way through the optic nerve, but it remains unknown whether mature axons can reenter the brain, navigate to appropriate target areas, or restore vision. We show here that with adequate stimulation, retinal ganglion cells are able to regenerate axons the full length of the visual pathway and on into the lateral geniculate nucleus, superior colliculus, and other visual centers. Regeneration partially restores the optomotor response, depth perception, and circadian photoentrainment, demonstrating the feasibility of reconstructing central circuitry for vision after optic nerve damage in mature mammals.
Growth of injured rabbit optic axons within their degenerating optic nerve
The Journal of Comparative Neurology, 1990
Spontaneous growth of axons after injury is extremely limited in the mammalian central nervous system (CNS). It is now clear, however, that injured CNS axons can be induced to elongate when provided with a suitable environment. Thus injured CNS axons can elongate, but they do not do so unless their environment is altered.
Experimental Neurology, 1988
The diameter-based rate of degeneration in the rat's optic nerve was examined using coordinated morphological and electrophysiological techniques. Long-Evans, male rats were implanted with indwelling stimulating electrodes in the optic chiasm and recording electrodes in the stratum opticum of the superior colliculus. After 1 week, unilateral enucleation was performed with the unoperated side serving as the control. Electrically evoked recordings, obtained on the day of enucleation (De), displayed three distinct peaks, Pre, Nl and P3, with peak latencies of 1.22, 2.22, and 4.04 ms, respectively. In a parallel set of rats, morphological analysis of the optic nerve over Die7 was performed. Electron micrographs were taken of cross sections of the entire optic nerve from both the enucleated and unoperated (i.e., control) side. Computer-linked morphometric analysis of the ultrastructurally normal axons from each nerve was assembled in three-dimensional, diameter-based histograms at each time point. The control population consisted of axons with diameters ranging from ~0.5-5.0 pm with a modal peak of 1.5 I.crn and a well developed tail in the 3.5-5.0 pm range. By Di,r, a selective loss of large diameter (>3.5 pm) axons occurred in the optic nerve, with medium diameter (2.0-3.5 pm) axons degenerating at Dg and smaller diameter populations (~2.0 pm) persisting until later time points (D5-7). A linear regression analysis showed an exponential rate of degeneration which was a direct function of axonal diameter. In summary, this study demonstrates that the fiber population of the optic nerve is separable electrophysiologically and by its rate of degeneration, with larger diameter fibers degenerating faster in response to transection.
Investigative Ophthalmology & Visual Science, 2013
Injured retinal ganglion cell (RGC) axons do not regenerate spontaneously, causing loss of vision in glaucoma and after trauma. Recent studies have identified several strategies that induce long distance regeneration in the optic nerve. Thus, a pressing question now is whether regenerating RGC axons can find their appropriate targets. Traditional methods of assessing RGC axon regeneration use histological sectioning. However, tissue sections provide fragmentary information about axonal trajectory and termination. To unequivocally evaluate regenerating RGC axons, here we apply tissue clearance and light sheet fluorescence microscopy (LSFM) to image whole optic nerve and brain without physical sectioning. In mice with PTEN/SOCS3 deletion, a condition known to promote robust regeneration, axon growth followed tortuous paths through the optic nerve, with many axons reversing course and extending towards the eye. Such aberrant growth was prevalent in the proximal region of the optic nerve where strong astroglial activation is present. In the optic chiasms of PTEN/SOCS3 deletion mice and PTEN deletion/Zymosan/cAMP mice, many axons project to the opposite optic nerve or to the ipsilateral optic tract. Following bilateral optic nerve crush, similar divergent trajectory is seen at the optic chiasm compared to unilateral crush. Centrally, axonal projection is limited predominantly to the hypothalamus. Together, we demonstrate the applicability of LSFM for comprehensive assessment of optic nerve regeneration, providing in-depth analysis of the axonal trajectory and pathfinding. Our study indicates significant axon misguidance in the optic nerve and brain, and underscores the need for investigation of axon guidance mechanisms during optic nerve regeneration in adults.
European Journal of Neuroscience, 1989
Calibres and microtubule contents of the non-medullated and myelinated domains of optic nerve axons of adult rats were studied with the electron microscope. The cross-sectional areas of the non-medullated domain was 0.25 μm2, and that of the myelinated domain 0.40 μm2, that is, greater by 59%. The increase in size was uneven across the axonal population; it was marked in fine and medium sized axons, and modest in the largest axons. The number of microtubules increased with axonal size; the density, however, decreased from 85 mirotubules/μm2 axons to about 20 in 1.2 μm2 axons. In axons of equal cross sectional area, the microtubular density of the myelinated and non-medullated domains was the same. Microtubular density values of optic axons resemble those of dorsal roots more than those of peripheral nerve axons of equal calibre. The facts that optic axons increase in size and gain microtubules behind the eyeball while the microtubular packing decreases suggest a local regulation of the axonal cytoskeleton.
Ultra structural evidence of axonal regeneration following intracranial transection of optic nerve
Neuro endocrinology letters, 2010
The present work was aimed at studying the ultra structural changes of the proximal (retinal) stump of the intracranially transected optic nerve of the rat for any possible regenerative ability. Specimens were collected one (1 wpo) and four weeks(4 wpo) after the transection and the cross sections of the stumps were studied by electron microscopy by dividing them into three zones, (1) the central zone, (2) the intermediate zone, and (3) the peripheral zone. The present results showed evident morphological changes in these zones both in the 1 wpo and 4 wpo groups. The signs of degeneration were more marked in the central zone than in the peripheral zone and they were more prominent in the 1 wpo group than in the 4 wpo group. The most prominent sign of the degeneration was loss or lack of the healthy myelinated axons. The main evidence of the regenerative ability was the reappearance of the apparently healthy myelinated axonal profiles, with a parallel decrease of the non myelinated o...