Morphological study on the hereditary neurogenic amyotrophic dogs: accumulation of lipid compound-like structures in the lower motor neuron

A morphological study was performed on hereditary neurogenic amyotrophic dogs, the clinical features of which especially resembled spinal progressive muscular atrophy (SPMA), a human motor neuron disease. The skeletal muscles showed obvious neurogenic atrophy with endomysial fibrosis. The peripheral nerves revealed axonal degeneration mainly limited to the motor nerve. In the spinal cord, the number of anterior horn cells seemed normal but, interestingly enough, numerous accumulated granules were detected in these anterior horn cells. Histochemically, these granules were interpreted as a lipid compound. Under the electron microscope, the granules were disclosed as multi-lamellar structures, arranged concentrically or in parallel, resembling membranous cytoplasmic bodies (MCBs) or zebra bodies. This finding strongly suggests that hereditary abnormality of lipid metabolism may underlie SPMA in these dogs. However, unlike other metabolic disorders where accumulations of granules are diffusely distributed, in the dogs we examined accumulations were found only in the anterior horn cells of the spinal cord and in the hypoglossal and spinal accessory nuclei. We are unable to explain this occurrence at the present time. Further investigations should be made on dogs because they serve as an important animal model of human motor neuron disease.