Specific ion channels contribute to key elements of pathology during secondary degeneration following neurotrauma

Background: Following partial injury to the central nervous system, cells beyond the initial injury site undergo secondary degeneration, exacerbating loss of neurons, compact myelin and function. Changes in Ca 2+ flux are associated with metabolic and structural changes, but it is not yet clear how flux through specific ion channels contributes to the various pathologies. Here, partial optic nerve transection in adult female rats was used to model secondary degeneration. Treatment with combinations of three ion channel inhibitors was used as a tool to investigate which elements of oxidative and structural damage related to long term functional outcomes. The inhibitors employed were the voltage gated Ca 2+ channel inhibitor Lomerizine (Lom), the Ca 2+ permeable AMPA receptor inhibitor YM872 and the P2X 7 receptor inhibitor oxATP. Results: Following partial optic nerve transection, hyper-phosphorylation of Tau and acetylated tubulin immunoreactivity were increased, and Nogo-A immunoreactivity was decreased, indicating that axonal changes occurred acutely. All combinations of ion channel inhibitors reduced hyper-phosphorylation of Tau and increased Nogo-A immunoreactivity at day 3 after injury. However, only Lom/oxATP or all three inhibitors in combination significantly reduced acetylated tubulin immunoreactivity. Most combinations of ion channel inhibitors were effective in restoring the lengths of the paranode and the paranodal gap, indicative of the length of the node of Ranvier, following injury. However, only all three inhibitors in combination restored to normal Ankyrin G length at the node of Ranvier. Similarly, HNE immunoreactivity and loss of oligodendrocyte precursor cells were only limited by treatment with all three ion channel inhibitors in combination. Conclusions: Data indicate that inhibiting any of a range of ion channels preserves certain elements of axon and node structure and limits some oxidative damage following injury, whereas ionic flux through all three channels must be inhibited to prevent lipid peroxidation and preserve Ankyrin G distribution and OPCs

Oligodendrocytes: biology and pathology

Oligodendrocytes are the myelinating cells of the central nervous system (CNS). They are the end product of a cell lineage which has to undergo a complex and precisely timed program of proliferation, migration, differentiation, and myelination to finally produce the insulating sheath of axons. Due to this complex differentiation program, and due to their unique metabolism/physiology, oligodendrocytes count among the most vulnerable cells of the CNS. In this review, we first describe the different steps eventually culminating in the formation of mature oligodendrocytes and myelin sheaths, as they were revealed by studies in rodents. We will then show differences and similarities of human oligodendrocyte development. Finally, we will lay out the different pathways leading to oligodendrocyte and myelin loss in human CNS diseases, and we will reveal the different principles leading to the restoration of myelin sheaths or to a failure to do so

Lame ducks or fierce creatures? : The role of oligodendrocytes in multiple sclerosis

In the pathogenesis of multiple sclerosis (MS), oligodendrocytes and its myelin sheaths are thought to be the primary target of destruction. The mechanism leading to oligodendrocyte injury and demyelination is still elusive. Oligodendrocytes are maintaining up to 50 internodes of myelin, which is an extraordinary metabolic demand. This makes them one of the most vulnerable cell types in the central nervous system (CNS), and even small insults can lead to oligodendrocyte impairment, demyelination, and axonal dysfunction. For this reason, oligodendrocytes are viewed as more or less the "lame ducks" of the CNS who can easily become victims. However, recent data demonstrate that this perception possibly needs to be revised. The latest data suggest that oligodendrocytes may also act as "fierce creatures," influencing the surrounding cells in many ways to preserve its own, as well as their function, allowing sustained functionality of the CNS upon an attack. In this review, the concept of "reactive or activated oligodendrocyte" is introduced, describing alterations in oligodendrocytes which are either protective mechanisms allowing survival in otherwise lethal environment or influence and possibly modulate the ongoing inflammation. Although "harnessed", oligodendrocytes might actively modulate and shape their environment and be part of the immune privilege of the brain