Electron microscopic studies of bovine progressive degenerative myeloencephalopathy in brown Swiss cattle.

Selected peripheral nerves from animals affected with Bovine Progressive Degenerative Myeloencephalopathy (BPDME) were examined by transmission electron microscopy. Changes in axons were both degenerative and reactive in nature and included axonal swelling in conjunction with accumulation of altered organelles and various forms of vesicles. Affected axoplasm was often vacuolated and shrunken, with loss of microtubules and microfilaments and separation of the axoplasmic membrane from the myelin sheath. Segmental disorganization of the normal lamellar pattern of myelin sheaths was observed. Affected myelin sheaths exhibited intramyelinic vacuoles or myelin bubbles often in association with concurrent axonal changes. Schwann cells occasionally contained swellen and vacuolated mitochondria and membrane-bound vesicles. Axonal and myelin changes were considered similar, if not identical, to those described in the central nervous system of affected animals reported in the literature. Collectively, the changes described in the axons and myelin sheaths of the peripheral nerves studied were considered to be compatible with the "dying back" process described in various distal axonopathies. A metabolic defect in the enzyme systems associated with axonal transport was postulated to explain these peripheral nerve lesions.