Progressive axonopathy: an inherited neuropathy of boxer dogs. An immunocytochemical study of the axonal cytoskeleton.

The distribution of the major axonal cytoskeletal proteins has been determined in lumbar ventral roots and spinal cord of dogs with progressive axonopathy, an inherited neuropathy of boxer dogs. The three neurofilament proteins, and beta-tubulin, actin and fodrin were localized using immunocytochemistry. The majority of swollen axons in the nerve roots contained excessive, disorientated neurofilaments. In about 5% of such fibres the peripheral filaments in the axoplasm were orientated circumferentially and such zones were deficient in tubulin. Many, but not all, spheroids contained increased amounts of actin, often with internal areas of more intense staining. Similar findings were present in axonal swellings in the CNS, although their contents were more variable. The distribution of axonal fodrin in CNS and PNS appeared unaltered. The perikarya of many motor neurons in the spinal cord and brain stem contained phosphorylated neurofilaments. The results support previous suggestions that defects in slow axonal transport are involved in the pathogenesis of this disease.