[Demyelination and remyelination after multiple intramedullary injections of ethidium bromide in Wistar rats]

Targeted Oligodendrocyte Apoptosis in Optic Nerve Leads to Persistent Demyelination

The optic nerve represents one of the simplest regions of the CNS and has been useful in developing an understanding of glial development and myelination. While the visual system is frequently affected in demyelinating conditions, utilizing the optic nerve to model demyelination/remyelination studies has been difficult due to its accessibility, relatively small size, and dense nature that makes direct injections challenging. Taking advantage of the lack of oligodendrocytes and myelination in the mouse retina, we have developed a model in which the induction of apoptosis in mature oligodendrocytes allows for the selective, non-invasive generation of demyelinating lesions in optic nerve. Delivery of an inducer of oligodendrocyte apoptosis by intravitreous injection minimizes trauma to the optic nerve and allows for the assessment of oligodendrocyte death in the absence of injury related factors. Here we show that following induction of apoptosis, oligodendrocytes are lost within 3 days. The loss of oligodendrocytes is associated with limited microglial and astrocyte response, is patchy along the nerve, and results in localized myelin loss. Unlike in other regions of the murine CNS, where local demyelination stimulates activation of local oligodendrocyte precursors and remyelination, optic nerve demyelination induced by oligodendrocyte apoptosis fails to recover and results in persistent areas of myelin loss. Over time these chronic lesions change cellular composition and ultimately become devoid of GFAP+ astrocytes and OPCs. Why the optic nerve lesions fail to repair may reflect the lack of early immune responsiveness and provide a novel model of chronic demyelination.

Consistent induction of chronic experimental autoimmune encephalomyelitis in C57BL/6 mice for the longitudinal study of pathology and repair

BACKGROUND

While many groups use experimental autoimmune encephalomyelitis (EAE) as a model to uncover therapeutic targets and understand the pathology underlying multiple sclerosis (MS), EAE protocol variability introduces discrepancies in central nervous system (CNS) pathogenesis and clinical disease, limiting the comparability between studies and slowing much-needed translational research.

OPTIMIZED METHOD

Here we describe a detailed, reliable protocol for chronic EAE induction in C57BL/6 mice utilizing two injections of myelin oligodendrocyte glycoprotein (35-55) peptide mixed with complete Freund's adjuvant and paired with pertussis toxin.

RESULTS

The active MOG_35-55-EAE protocol presented here induces ascending paralysis in 80-100% of immunized mice. We observe: (1) consistent T cell immune activation, (2) robust CNS infiltration by peripheral immune cells, and (3) perivascular demyelinating lesions concurrent with axon damage in the spinal cord and various brain regions, including the optic nerve, cortex, hippocampus, internal capsule, and cerebellum.

COMPARISON WITH EXISTING METHOD(S)

Lack of detailed protocols, combined with variability between laboratories, make EAE results difficult to compare and hinder the use of this model for therapeutic development. We provide the most detailed active MOG_35-55-EAE protocol to date. With this protocol, we observe high disease incidence and a consistent, reliable disease course. The resulting pathology is MS-like and includes optic neuritis, perivascular mononuclear infiltration, CNS axon demyelination, and axon damage in both infiltrating lesions and otherwise normal-appearing white matter.

CONCLUSIONS

By providing a detailed active MOG_35-55-EAE protocol that yields consistent and robust pathology, we aim to foster comparability between pre-clinical studies and facilitate the discovery of MS therapeutics.

Effects of aquatic exercises in a rat model of brainstem demyelination with ethidium bromide on the beam walking test

Multiple sclerosis is a demyelinating disease of the central nervous system associated with varied levels of disability. The impact of early physiotherapeutic interventions in the disease progression is unknown. We used an experimental model of demyelination with the gliotoxic agent ethidium bromide and early aquatic exercises to evaluate the motor performance of the animals. We quantified the number of footsteps and errors during the beam walking test. The demyelinated animals walked fewer steps with a greater number of errors than the control group. The demyelinated animals that performed aquatic exercises presented a better motor performance than those that did not exercise. Therefore aquatic exercising was beneficial to the motor performance of rats in this experimental model of demyelination.

Remyelination in experimentally demyelinated connexin 32 knockout mice

The aim of this study was to evaluate the role of connexin 32 (Cx 32) during remyelination of the peripheral nervous system, through a local injection of either 0,1% ethidium bromide solution or saline in the sciatic nerve of Cx 32 knockout mice. Euthanasia was performed ranging from 1, 2, 3, 7, 15, 21 to 30 days after injection. Histochemical, immunohistochemical, immunofluorescence and transmission electron microscopical techniques were used to analyze the development of the lesions. Within the sciatic nerves, Schwann cells initially showed signs of intoxication and rejected their sheaths; after seven days, some thin newly formed myelin sheaths with uneven compactness and redundant loops (tomacula) were conspicuous. We concluded that the regeneration of lost myelin sheaths within the PNS followed the pattern already reported for this model in other laboratory species. Therefore, these results suggest that absence of Cx 32 did not interfere with the normal pattern of remyelination in this model in young mice.

Ethidium bromide-induced demyelination of the sciatic nerve of adult Wistar rats

Peripheral nerve ultrastructure was assessed after single or multiple local injections of the intercalating dye ethidium bromide. Thirty-four adult Wistar rats of both sexes were divided into five groups and maintained in a controlled environment with rat chow and water ad libitum throughout the experiment. The experimental animals were injected with 1 microl of 0.1% ethidium bromide in 0.9% saline into the central third of the left sciatic nerve 1 (group 1), 2 (group 2), 4 (group 3), 6 (group 4) or 8 (group 5) times. In groups 2 to 5 the injections were made at 28-day intervals. Control animals received the same amount of 0.9% saline. The animals were killed at different times after injection: group 1 at 7 days (2 rats) and 15 days (2 rats); for groups 2, 3, 4 and 5, all rats were killed 10 days after the last injection and the lesions were investigated by light and transmission electron microscopy. In the acute lesions, intoxicated Schwann cells showed a vacuolated cytoplasm and separation of the sheaths from the axon. Myelin sheaths underwent progressive vesiculation and subsequent segmental demyelination. Myelin debris were withdrawn by macrophages and remyelination by Schwann cells was prominent. With the increase in the number of injections collagen fibers also increased in number and progressively enveloped smaller numbers of remyelinated axons composing new fascicles. Wallerian degeneration of fibers apparently not affected by ethidium bromide was more intense in the nerves from groups 4 and 5. The peripheral nerve repairs itself after demyelinating challenges with a profusion of collagen fibers and new fasciculations. This experimental model is valid to mimic recurrent demyelinating neuropathies.

Behaviour of oligodendrocytes and Schwann cells in an experimental model of toxic demyelination of the central nervous system

Oligodendrocytes and Schwann cells are engaged in myelin production, maintenance and repairing respectively in the central nervous system (CNS) and the peripheral nervous system (PNS). Whereas oligodendrocytes act only within the CNS, Schwann cells are able to invade the CNS in order to make new myelin sheaths around demyelinated axons. Both cells have some limitations in their activities, i.e. oligodendrocytes are post-mitotic cells and Schwann cells only get into the CNS in the absence of astrocytes. Ethidium bromide (EB) is a gliotoxic chemical that when injected locally within the CNS, induce demyelination. In the EB model of demyelination, glial cells are destroyed early after intoxication and Schwann cells are free to approach the naked central axons. In normal Wistar rats, regeneration of lost myelin sheaths can be achieved as early as thirteen days after intoxication; in Wistar rats immunosuppressed with cyclophosphamide the process is delayed and in rats administered cyclosporine it may be accelerated. Aiming the enlightening of those complex processes, all events concerning the myelinating cells in an experimental model are herein presented and discussed.