Wallerian degeneration in the optic nerve of the rabbit

Determining Direction of Axonal Flow in the Equine Ramus Communicans by Ultrastructural Examination of the Plantar Nerves 2 Months after Transecting the Ramus

The ramus communicans, neural connection between medial and lateral plantar nerves of the horse, was transected to determine the degree to which medial and lateral plantar nerves contribute to the plantar ramus. After 2 months, sections of plantar nerves immediately proximal and distal to the communicating branch were collected and processed for electron microscopy. All examined nerves had undergone Wallerian degeneration and contained regenerating and mature fibers. Layers of the myelin sheath were separated by spaces and vacuoles, indicating demyelination of medial and lateral plantar nerves. Shrunken axons varied in diameter and were surrounded by an irregular axolemma. Shrunken axoplasm of both myelinated and non-myelinated fibers contained ruptured mitochondria and cristae, disintegrating cytoskeleton, and vacuoles of various sizes. The cytoplasm of neurolemmocytes contained various-sized vesicles, ruptured mitochondria within a fragile basal lamina and myelin whorls of multilayered structures indicative of Wallerian degeneration. These ultrastructural changes, found proximal and distal to the ramus in medial and lateral plantar nerves, suggest that axonal flow is bi-directional through the ramus communicans of the pelvic limbs of horses, a previously unreported finding. As well, maturity of nerves proximal and distal to the ramus indicates that all nerve fibers do not pass through the ramus.

Wallerian-like axonal degeneration in the optic nerve after excitotoxic retinal insult: an ultrastructural study

Background

Excitotoxicity is involved in the pathogenesis of a number neurodegenerative diseases, and axonopathy is an early feature in several of these disorders. In models of excitotoxicity-associated neurological disease, an excitotoxin delivered to the central nervous system (CNS), could trigger neuronal death not only in the somatodendritic region, but also in the axonal region, via oligodendrocyte N-methyl-D-aspartate (NMDA) receptors. The retina and optic nerve, as approachable regions of the brain, provide a unique anatomical substrate to investigate the "downstream" effect of isolated excitotoxic perikaryal injury on central nervous system (CNS) axons, potentially providing information about the pathogenesis of the axonopathy in clinical neurological disorders.

Herein, we provide ultrastructural information about the retinal ganglion cell (RGC) somata and their axons, both unmyelinated and myelinated, after NMDA-induced retinal injury. Male Sprague-Dawley rats were killed at 0 h, 24 h, 72 h and 7 days after injecting 20 nM NMDA into the vitreous chamber of the left eye (n = 8 in each group). Saline-injected right eyes served as controls. After perfusion fixation, dissection, resin-embedding and staining, ultrathin sections of eyes and proximal (intraorbital) and distal (intracranial) optic nerve segments were evaluated by transmission electron tomography (TEM).

Results

TEM demonstrated features of necrosis in RGCs: mitochondrial and endoplasmic reticulum swelling, disintegration of polyribosomes, rupture of membranous organelle and formation of myelin bodies. Ultrastructural damage in the optic nerve mimicked the changes of Wallerian degeneration; early nodal/paranodal disturbances were followed by the appearance of three major morphological variants: dark degeneration, watery degeneration and demyelination.

Conclusion

NMDA-induced excitotoxic retinal injury causes mainly necrotic RGC somal death with Wallerian-like degeneration of the optic nerve. Since axonal degeneration associated with perikaryal excitotoxic injury is an active, regulated process, it may be amenable to therapeutic intervention.

Multi-channel visual evoked potential as an ancillary tool to diagnose intraorbital optic nerve lesions

Multi-channel visual evoked potential (MVEP) recording method was used to assist in diagnosing a 4-month-old Chinese Albino rabbit with an intraorbital mass. Subcutaneous MVEP of its both eyes were recorded simultaneously using 16 electrodes (4 x 4) multi-channel array. Analysis of the cortical potential landscapes (CPL) showed that the conduction function of right eye was remarkably impaired in terms of decreased amplitudes and prolonged latencies. Specific side-dominant distribution asymmetry of the decreased MVEP amplitudes indicated that the temporal side of the optic nerve (ON) was severely involved. Overall prolonged latencies of the CPL without side differences suggested that the functional impairment could have been caused by the mechanical compression exerted by an intraorbital mass. Surgical removal procedures confirmed that the mass was located temporally to the ON. Pathological examination provided a final diagnosis of a giant polycystic mucocele. Beyond its significance as a standard tool to assess functional changes of the visual pathway, MVEP recordings might assist locating intraorbital lesions that involve the ON by careful analysis of abnormal CPLs.

Efficacy of niosomal formulation of diallyl sulfide against experimental candidiasis in Swiss albino mice

Aim: We developed a niosomal formulation of diallyl sulfide (DAS), a garlic oil component, and evaluated its efficacy against experimental candidiasis in mice. Methods: DAS-bearing niosomes prepared from sorbitan monoester surfactants were evaluated for drug entrapment efficiency, release kinetics, toxicity, size, ζ-potential and others. Mice challenged with Candida albicans were treated with various DAS formulations. The efficacy of the formulations was assessed on the basis of reduction in mortality and decrease in residual fungal load in vital organs, such as liver and spleen, of treated mice. Results: Niosomal DAS (12 mg/kg body weight) significantly reduced fungal load and mortality in treated animals compared with the free form of DAS. Niosomal DAS was also found to be free of toxic manifestations, as revealed by histopathological studies, as well as liver/kidney function tests. Conclusion: Incorporation of DAS in niosomes enhances its antifungal efficacy. Further studies are needed to optimize the current findings to develop an efficient nature-derived alternative antifungal therapeutic strategy.

Expression of neurotrophin-3 promotes axonal plasticity in the acute but not chronic injured spinal cord

Previously, we reported that over-expression of neurotrophin-3 (NT-3) promoted sprouting of axons in the injured but not uninjured spinal cord, suggesting that processes associated with the injury such as Wallerian degeneration (WD) participated to induce the neuroplasticity. To determine whether NT-3-induced axonal sprouting depends upon processes associated with an acute injury, we uncoupled the injury and NT-3 over-expression in time. Rats were treated with a replicationdefective adenoviral vector carrying the NT-3 gene (Adv.NT-3) 2 weeks or 4 months after receiving a unilateral lesion of their corticospinal tract (CST). Adv.LacZ was used as a control vector. Morphometric analysis of axonal sprouting was performed to measure the number of CST axons that arise from the intact CST, traverse the midline, and grow into the gray matter of the lesioned side of the spinal cord where the NT-3 was over-expressed. The number of axons sprouting across the midline was greater in the rats treated with Adv.NT-3 than in the control groups when the Adv.NT-3 was delivered 2 weeks after injury. These axons persisted for at least 6 months after Adv.NT-3 delivery. In contrast, when Adv.NT-3 was delivered 4 months after lesion, there was no significant difference in the number of CST axons that crossed the midline compared to controls. Since the processes of WD would have resolved within 4 months after injury, these data demonstrate that products of WD are a potential source of the co-inducing signals that support neuroplasticity in the presence of NT-3.

Oxidative stress in glaucomatous neurodegeneration: mechanisms and consequences

Reactive oxygen species (ROS) are generated as by-products of cellular metabolism, primarily in the mitochondria. Although ROS are essential participants in cell signaling and regulation, when their cellular production overwhelms the intrinsic antioxidant capacity, damage to cellular macromolecules such as DNA, proteins, and lipids ensues. Such a state of "oxidative stress" is thought to contribute to the pathogenesis of a number of neurodegenerative diseases. Growing evidence supports the involvement of oxidative stress as a common component of glaucomatous neurodegeneration in different subcellular compartments of retinal ganglion cells (RGCs). Besides the evidence of direct cytotoxic consequences leading to RGC death, it also seems highly possible that ROS are involved in signaling RGC death by acting as a second messenger and/or modulating protein function by redox modifications of downstream effectors through enzymatic oxidation of specific amino acid residues. Different studies provide cumulating evidence, which supports the association of ROS with different aspects of the neurodegenerative process. Oxidative protein modifications during glaucomatous neurodegeneration increase neuronal susceptibility to damage and also lead to glial dysfunction. Oxidative stress-induced dysfunction of glial cells may contribute to spreading neuronal damage by secondary degeneration. Oxidative stress also promotes the accumulation of advanced glycation end products in glaucomatous tissues. In addition, oxidative stress takes part in the activation of immune response during glaucomatous neurodegeneration, as ROS stimulate the antigen presenting ability of glial cells and also function as co-stimulatory molecules during antigen presentation. By discussing current evidence, this review provides a broad perspective on cellular mechanisms and potential consequences of oxidative stress in glaucoma.