Quantitative measurement of postural sway in mouse models of human neurodegenerative disease.

Detection of motor dysfunction in genetic mouse models of neurodegenerative disease requires reproducible, standardized and sensitive behavioral assays. We have utilized a center of pressure (CoP) assay in mice to quantify postural sway produced by genetic mutations that affect motor control centers of the brain. As a positive control for postural instability, wild type mice were injected with harmaline, a tremorigenic agent, and the average areas of the 95% confidence ellipse, which measures 95% of the CoP trajectory values recorded in a single trial, were measured. Ellipse area significantly increased in mice treated with increasing doses of harmaline and returned to control values after recovery. We also examined postural sway in mice expressing mutations that mimic frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17) (T-279, P301L or P301L-nitric oxide synthase 2 (NOS2)(-/-) mice) and that demonstrate motor symptoms. These mice were then compared with a mouse model of Alzheimer's disease (APPSwDI mice) that demonstrates cognitive, but not motor deficits. T-279 and P301L-NOS2(-/-) mice demonstrated a significant increase in CoP ellipse area compared with appropriate wild type control mice or to mice expressing the P301L mutation alone. In contrast, postural instability was significantly reduced in APPSwDI mice that have cognitive deficits but do not have associated motor deficits. The CoP assay provides a simple, sensitive and quantitative tool to detect motor deficits resulting from postural abnormalities in mice and may be useful in understanding the underlying mechanisms of disease.