Quantitative analysis of the spinal cord motoneuron under chronic compression: an experimental observation in the mouse.

We investigated quantitative changes in spinal cord motoneurons following chronic compression using a mouse model of cervical cord compression. Twenty-five tip-toe-walking Yoshimura (twy) mice with calcified mass lesions compressing the spinal cord posterolaterally at the C1-C2 vertebral levels were compared with five Institute of Cancer Research (ICR) mice that served as controls. Spinal cord motoneurons in the anterior grey horn between the C1 and C3 spinal cord segments were Nissl-stained and counted topographically and then analysed in relation to the extent of spinal cord compression. The number of motoneurons in C1-C3 spinal cord segments decreased significantly with a linear correlation with the transverse area of the spinal cord when the cord was compressed to 50-70% of control values. A significant reduction in the number of motoneurons occurred at the C2-C3 spinal cord segment compressed at the C1-C2 vertebral level. In contrast, at the level rostral to the C1 vertebra, the number of motoneurons increased significantly in proportion to the magnitude of compression. The current study demonstrates that a number of neurons, morphologically consistent with anterior horn cells, were observed at a rostral site absolutely free of external compression where no such cells normally exist.