Cerebellar Mild Iron Accumulation in a Subset of FMR1 Premutation Carriers with FXTAS.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder associated with premutation alleles of the FMR1 gene. Iron is essential for many facets of cell metabolism in the brain but when altered is likely to contribute to the development of neurodegenerative diseases. We previously reported that iron accumulates in the choroid plexus and the putamen in FXTAS and that the level and distribution of key iron-binding proteins are also altered, suggesting a potential alteration of iron metabolism in the brain. Here, we hypothesize that iron metabolism is also altered in the FXTAS cerebellum. To test this hypothesis, we used cerebellum samples collected from FXTAS and control subjects and measured the amount of iron contained within the cerebellar cortex and dentate nucleus. We found that the number of iron deposits increased in the cerebellum only in a subset of cases of FXTAS. This accumulation is likely to be mediated by factors other than or in addition to CGG-repeat coupled pathology. Thus, iron deposition in the cerebellum cannot be used as a hallmark of FXTAS pathogenesis.

A Majority of FXTAS Cases Present with Intranuclear Inclusions Within Purkinje Cells.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive neurodegenerative disorder that affects carriers of a FMR1 premutation. Symptoms include cerebellar ataxia, tremor, and cognitive deficits. The most characteristic pathology of FXTAS is the presence of eosinophilic ubiquitin-positive intranuclear inclusions in neurons and astrocytes throughout the nervous system and non-nervous tissues. Inclusions are present in neurons throughout the brain but are widely believed not to be present in the Purkinje cells (PCs) of the cerebellum. However, we analyzed 26 postmortem cases of FXTAS and demonstrated that 65 % of cases presented with inclusions within PCs of the cerebellum. We determined that the presence or absence of inclusions in PCs is correlated with age and that those cases with PC inclusions were overall 11 years older than those with no PC inclusions. Half of the cases with PCs with inclusions presented with twin nuclear inclusions. This novel finding demonstrating the presence of inclusions within PCs provides an insight into the understanding of the FXTAS motor symptoms and provides a novel target for the development of therapeutic strategies.

Calibrated forceps model of spinal cord compression injury.

Compression injuries of the murine spinal cord are valuable animal models for the study of spinal cord injury (SCI) and spinal regenerative therapy. The calibrated forceps model of compression injury is a convenient, low cost, and very reproducible animal model for SCI. We used a pair of modified forceps in accordance with the method published by Plemel et al. (2008) to laterally compress the spinal cord to a distance of 0.35 mm. In this video, we will demonstrate a dorsal laminectomy to expose the spinal cord, followed by compression of the spinal cord with the modified forceps. In the video, we will also address issues related to the care of paraplegic laboratory animals. This injury model produces mice that exhibit impairment in sensation, as well as impaired hindlimb locomotor function. Furthermore, this method of injury produces consistent aberrations in the pathology of the SCI, as determined by immunohistochemical methods. After watching this video, viewers should be able to determine the necessary supplies and methods for producing SCI of various severities in the mouse for studies on SCI and/or treatments designed to mitigate impairment after injury.