Fine structural study of the spinal cord and spinal ganglia in mice afflicted with a hereditary sensory neuropathy, dystonia musculorum

Dystonia musculorum in mice is a hereditary autosomal recessive disorder, characterized by a progressive neuromuscular incoordination. This paper describes the ultrastructural changes in the spinal cord and compares and correlates the results with changes in the spinal ganglia in dystonic mice. Ganglion cells exhibited various stages of degeneration and pyknosis. The dorsal roots of the spinal nerves showed severe degeneration and loss of myelinated fibres accompanied by fibrosis, whilst the ventral roots appeared normal. Nerve cells within the dorsal and intermediate grey matter (laminae I to VII) of the spinal cord showed chromatolysis, atrophy, and necrosis. Boutons exhibited glycogen accumulation or an increase in their electron density. Axonal changes consisted of focal swellings, marked accumulation of neurofilaments, membranous and dense bodies, and disintegration of axoplasm. Myelin sheath degeneration of Wallerian type and degenerating axons were prominent in the dorsal, lateral and ventral white columns of the spinal cord. Glial reactions in the spinal cord were limited to mild hypertrophy and hyperplasia of astrocytic processes. The process of phagocytic activity was not intense in spite of the presence of an abundance of degenerating myelin and cell debris. This study showed that the ultrastructural changes in the spinal cord are more severe than those seen with routine light microscopy. The detection of definite neuronal degeneration of the dorsal root ganglia and spinal cord suggests that the defect apparently operates at the level of cell bodies, as well as axons, of the primary and second order sensory neurons.