Ultrastructural, morphometric, and immunocytochemical study of anterior horn cells in mice with "wasted" mutation

Mice with the autosomal recessive gene "wasted" (wst/wst) manifest hindlimb paralysis and tremulousness, develop reduced secretory immune responses, and have abnormal DNA repair mechanisms. There is prominent vacuolar degeneration of neurons within anterior horns of the spinal cord and motor nuclei of the brainstem. A morphometric analysis of motor neurons in the spinal cord was performed on 2-hydroxyethyl methacrylate-embedded tissue from ten wst/wst mice, ten littermates (wst/+, +/+) without clinical deficits, and ten parental (+/+) control mice. Vacuolated neurons were present only in wst/wst mice (p = 0.0008). Fibrillary neurons were more numerous in the wst/wst mice than in littermates (p = 0.01) or controls (p = 0.007). The number of total or normal neurons did not differ significantly among the three groups. Volume measurements for normal, fibrillary, vacuolated, and total neurons were greater in wst/wst mice (p less than 0.008). Electron microscopic studies revealed vacuolar degeneration exclusively within neurons of wst/wst mice with the prominent accumulation of neurofilaments. Immunocytochemical staining of Araldite-embedded sections with monoclonal antibodies (MAb) to 68 kDa, 160 kDa, and 200 kDa neurofilament proteins showed prominent staining of vacuolated and fibrillary neurons in wst/wst mice exclusively with the MAb to 200 kDa neurofilaments. Dephosphorylation of tissue reduced the staining of 200 kDa neurofilaments in wst/wst mice. These studies suggest that phosphorylated neurofilaments may be important in events producing neuronal dysfunction. Therefore the "wasted" mutation may be an excellent model for the study of motor neuron disease.