Noninvasive detection of cuprizone induced axonal damage and demyelination in the mouse corpus callosum

Abstract

Previously, we tested the prediction that axonal damage results in decreased axial diffusivity ( ʈ ) while demyelination leads to increased radial diffusivity ( Ќ ). Cuprizone treatment of C57BL/6 mice was a highly reproducible model of CNS white matter demyelination and remyelination affecting the corpus callosum (CC). In the present study, six C57BL/6 male mice were fed 0.2% cuprizone for 12 weeks followed by 12 weeks of recovery on normal chow. The control mice were fed normal chow and imaged in parallel. Biweekly in vivo DTI examinations showed transient decrease of ʈ in CC at 2-6 weeks of cuprizone treatment. Immunostaining for nonphosphorylated neurofilaments demonstrated corresponding axonal damage at 4 weeks of treatment. Significant demyelination was evident from loss of Luxol fast blue staining at 6 -12 weeks of cuprizone ingestion and was paralleled by increased Ќ values, followed by partial normalization during the remyelination phase Diverse central nervous system (CNS) disorders involve white matter pathology leading to myelin and axon dysfunction (1-6). However, current neurologic examinations are not capable of differentiating the underlying axon and myelin pathologies causing the deficits (7,8). Recently, an analytical approach interpreting magnetic resonance diffusion tensor imaging (DTI) data in light of white matter pathology has been proposed (9 -11). Briefly, directional diffusivities of water molecules in white matter derived from DTI are separated into two components, i.e., axial ( ʈ ) and radial ( Ќ ) diffusivities describing water diffusion along and across axonal tracts, respectively. It has been demonstrated that axonal injury, such as axonal swelling and Wallerian degeneration (10), results in reduced ʈ , while dysmyelination increases Ќ without changing ʈ (11).The development of an effective therapy targeted at repairing axons and the protective myelin sheath may benefit from improved diagnostic tools that are capable of detecting and differentiating axonal damage and demyelination in various CNS disorders. To validate the aforementioned DTI parameters as surrogate markers of axon and myelin injury, the well-characterized CNS demyelination and remyelination mouse model of cuprizone (bis-cyclohexanone oxaldihydrazone) ingestion has been examined serially in living mice in the present study. Cuprizone, 0.2% by weight, was mixed in ground rodent chow and fed to a group of male C57BL/6 mice. The corpus callosum (CC) is the only tract in this mouse model that has been consistently documented to undergo massive and unequivocal demyelination as a result of cuprizone toxicity and remyelination after removal of cuprizone from the feed (12-16). The myelin and axonal pathology of the CC in the cuprizone-treated mice was demonstrated by histopathology and correlated with ex vivo DTI (9). Thus, the CC is the target white matter tract of the current study to test the in vivo DTI sensitivity and specificity of Ќ to demyelination and remyelination along with ʈ to axonal damage associated with cupri...

Differentiation and quantification of inflammation, demyelination and axon injury or loss in multiple sclerosis

“…However, inflammation can interfere with measuring myelin and axons because inflammation-induced tissue swelling falsely reduces the measured myelin water and NAA content (oedema water contains no NAA and dilutes myelin water fraction), MTR (oedema water exhibits no transfer effect while contributing to the total signal), and PET marker intensity (diluting marker density) (Schmierer et al, 2004;Stanisz et al, 2004;McCreary et al, 2009;Vavasour et al, 2011). Despite that DTI-derived axial diffusivity and radial diffusivity can concurrently quantify coexisting axonal injury and demyelination in some settings (Song et al, 2002(Song et al, , 2003(Song et al, , 2005, DTI becomes inaccurate in the presence of inflammation (Sun et al, 2006b;Lodygensky et al, 2010;Xie et al, 2010), tissue loss (Kim et al, 2007), crossing fibres (Wheeler-Kingshott and Cercignani, 2009), and CSF contamination (Karampinos et al, 2008;Cheng et al, 2011) and cannot measure the inflammatory components. We thus developed DBSI and have previously accurately captured the severity of axonal injury, demyelination, and inflammation in white matter tracts from mouse models of CNS inflammatory demyelination (Wang et al, 2011bChiang et al, 2014).…”

Quantitative fiber tracking of lateral and interhemispheric white matter systems in normal aging: Relations to timed performance

“…This pattern differs from acute animal models of axonal injury and demyelination. For instance, 12 weeks of cuprizone treatment in a mouse resulted in demyelination and produced a decrease in λL followed by an increase in λT in the corpus callosum (Sun et al, 2006). The decrease in λL was transient and almost fully recovered at the time the increase in λT occurred.…”

Age-related differences in white matter microstructure: Region-specific patterns of diffusivity

“…The first eigenvalue is referred to as axial diffusivity (AD, diffusion parallel to the axon fibers; Basser, 1995;Song et al, 2002), whereas the average of the second and third eigenvalues is termed radial diffusivity (RD, diffusivity perpendicular to the axonal fibers; Basser, 1995;Song et al, 2002). Lowered AD reflects axon injury both in ischemic (Song et al, 2003(Song et al, , 2005 and chemically induced (Sun et al, 2006) WM lesions. Increases in RD have been linked to incomplete myelination in shiverer mice (Song et al, 2002), drug-induced demyelination (Song et al, 2005), and loss of myelin following axon injury (Song et al, 2003(Song et al, , 2005.…”