QUANTITATIVE-ANALYSIS OF THE SPINAL-CORD MOTONEURON UNDER CHRONIC COMPRESSION - AN EXPERIMENTAL-OBSERVATION IN THE MOUSE

We investigated quantitative changes in spinal cord motoneurons follow ing chronic compression using a mouse model of cervical cord compressi on. Twenty-five tiptoe-walking Yoshimura (twy) mice with calcified mas s lesions compressing the spinal cord posterolaterally at the C1-C2 ve rtebral levels were compared with five Institute of Cancer Research (I CR) mice that served as controls. Spinal cord motoneurons in the anter ior grey horn between the C1 and C3 spinal cord segments were Nissl-st ained 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 correlatio n with the transverse area of the spinal cord when the cord was compre ssed to 50-70% of control values. A significant reduction in the numbe r 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 pro portion to the magnitude of compression. The current study demonstrate s that a number of neurons, morphologically consistent with anterior h orn cells, were observed at a rostral site absolutely free of external compression where no such cells normally exist.