Here we used mice lacking tumor necrosis factor-alpha (TNF alpha) and its associated receptors to study a model of demyelination and remyelination in which these events could be carefully controlled using a toxin, cuprizone. Unexpectedly, the lack of TNF alpha led to a significant delay in remyelination as assessed by histology, immunohistochemistry for myelin proteins and electron microscopy coupled with morphometric analysis. Failure of repair correlated with a reduction in the pool of proliferating oligodendrocyte progenitors (bromodeoxyuridine-labeled NG2(+) cells) followed by a reduction in the number of mature oligodendrocytes. Analysis of mice lacking TNF receptor 1 (TNFR1) or TNFR2 indicated that TNFR2, not TNFR1, is critical to oligodendrocyte regeneration. This unexpected reparative role for TNF alpha in the CNS is important for understanding oligodendrocyte regeneration/proliferation, nerve remyelination and the design of new therapeutics for demyelinating diseases.

Interleukin-1beta (IL-1beta) is a proinflammatory cytokine associated with the pathophysiology of demyelinating disorders such as multiple sclerosis and viral infections of the CNS. However, we demonstrate here that IL-1beta appears to promote remyelination in the adult CNS. In IL-1beta(-/-) mice, acute demyelination progressed similarly to wild-type mice and showed parallel mature oligodendrocyte depletion, microglia-macrophage accumulation, and the appearance of oligodendrocyte precursors. In contrast, IL-1beta(-/-) mice failed to remyelinate properly, and this appeared to correlate with a lack of insulin-like growth factor-1 (IGF-1) production by microglia-macrophages and astrocytes and to a profound delay of precursors to differentiate into mature oligodendrocytes. Thus, IL-1beta may be crucial to the repair of the CNS, presumably through the induction of astrocyte and microglia-macrophage-derived IGF-1.

We have documented changes in the oligodendrocyte population during demyelinating insult to the adult CNS. Feeding of cuprizone to adult mice led to apoptotic death of mature oligodendrocytes followed by profound demyelination of the corpus callosum. A regenerative response was initiated even during active demyelination. Oligodendrocyte progenitors have begun to proliferate and then accumulate within the lesion. Many of these cells may have migrated from the sub‐ventricular zone and fornix before their accumulation in the demyelinating corpus callosum. The accumulation of differentiating oligodendrocyte progenitors was followed closely by the reappearance of mature oligodendrocytes and remyelination. Interestingly, an increase in IGF‐1 mRNA was detected at Week 3 through Week 7, suggesting potential involvement in remyelination. Other factors, however, such as PDGF, NT3, FGF, jagged, and notch remained unchanged. These results suggest that the mature oligodendroglial population depleted by apoptosis is replaced by a newly formed oligodendroglial population derived from progenitors; these accumulate and seem to differentiate during remyelination. J. Neurosci. Res. 61:251–262, 2000. © 2000 Wiley‐Liss, Inc.

Our studies demonstrate that LINGO-1 antagonism promotes OPC differentiation and remyelination, and suggest LINGO-1 functions as an inhibitor of OPC differentiation to retard central nervous system remyelination.

Exposure of young adult C57BL/6 mice to cuprizone in the diet initiated profound and synchronous demyelination of the corpus callosum, which was virtually complete by 4 weeks of exposure. Interestingly, even in the face of a continued exposure to cuprizone, there was spontaneous remyelination 2 weeks later. This remyelination preferentially involved smaller calibre axons. There was a suggestion of yet another cycle of demyelination (at 10 weeks) and remyelination (at 12 weeks), but by 16 weeks of exposure, the regenerative capacity was exhausted and the animals were near death. The relapsing-remitting pattern suggests this may be a useful model for certain human demyelinating disorders. In contrast to the above chronic model, the corpus callosum from mice exposed to cuprizone for only 6 weeks continued to remyelinate, with 67% of the axons being myelinated or remyelinated at 10 weeks. Interestingly, a significant reduction in the mean value for axonal diameter was observed during acute demyelination. Upon remyelination, however, the axonal calibre distribution returned to near-normal. In contrast, when mice were maintained on a cuprizone diet for 16 weeks, the mean value for axonal diameter was reduced to 60% of normal. These results provide further evidence that the interactions between oligodendrocytes and axons alter axonal calibre.

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Much attention has been given to the pelvic nerve afferent innervation of the urinary bladder; however, reports differ considerably in descriptions of afferent receptor types, their conduction velocities, and their potential roles in bladder reflexes and sensation. The present study was undertaken to do a relatively unbiased sampling of bladder afferent fibers of the pelvic nerve in adult female rats. The search stimulus for units to be studied was electrical stimulation of both the bladder nerves and the pelvic nerve. Single-unit activity of 100 L(6) dorsal root fibers, activated by both pelvic and bladder nerve stimulation, was analyzed. Sixty-five units had C-fiber and 35 units had Adelta-fiber conduction velocities. Receptive characteristics were established by direct mechanical stimulation, filling of the bladder with 0.9% NaCl at a physiological speed and by filling the bladder with solutions containing capsaicin, potassium, or turpentine oil. The majority (61) of these fibers were unambiguously excited by bladder filling with 0.9% NaCl and were classified as mechanoreceptors. All mechanoreceptors with receptive fields on the body of the bladder had low pressure thresholds (

To understand mechanisms that may underlie the progression of a demyelinated lesion to a chronic state, we have used the cuprizone model of chronic demyelination. In this study, we investigated the fate of oligodendrocytes during the progression of a demyelinating lesion to a chronic state and determined whether transplanted adult oligodendrocyte progenitors could remyelinate the chronically demyelinated axons. Although there is rapid regeneration of the oligodendrocyte population following an acute lesion, most of these newly regenerated cells undergo apoptosis if mice remain on a cuprizone diet. Furthermore, the oligodendrocyte progenitors also become progressively depleted within the lesion, which appears to contribute to the chronic demyelination. Interestingly, even if the mice are returned to a normal diet following 12 weeks of exposure to cuprizone, remyelination and oligodendrocyte regeneration does not occur. However, if adult O4 ؉ progenitors are transplanted into the chronically demyelinated lesion of mice treated with cuprizone for 12 weeks, mature oligodendrocyte regeneration and remyelination occurs after the mice are returned to a normal diet. Thus, the formation of chronically demyelinated lesions induced by cuprizone appears to be the result of oligodendrocyte depletion within the lesion and not due to the inability of the chronically demyelinated axons to be remyelinated. Although most acutely demyelinated lesions in multiple sclerosis (MS) are remyelinated, 1 the lesions eventually progress to a state of chronic demyelination, characterized by sparse remyelination, few oligodendrocytes, and axon degeneration.2-5 Although the central nervous system (CNS) has the ability to regenerate new oligodendrocytes that remyelinate demyelinated axons following acute demyelination, 6 -9 it has been suggested that mature oligodendrocytes are not regenerated within chronically demyelinated lesions due to: 1) the depletion of the oligodendrocyte progenitors; 4 2) the inability of the progenitors to proliferate and differentiate within the lesion due to aging 10 or a non-conducive environment; [11][12][13][14] and/or 3) axon damage 3,15,16 or the inability of chronically demyelinated axons to be remyelinated.