Synaptophysin immunoreactive axonal swelling in p-bromophenylacetylurea-induced neuropathy

A single intraperitoneal dose of 300 mg/kg of p-bromophenylacetylurea (BPAU) induced progressive distal neuropathy in rats, prominently involving peripheral nerves and long central nervous system myelinated tracts such as the fasciculus gracilis and spinocerebellar pathways. Clinical signs assessed using a Functional Observational Battery (FOB) and in-cage observation included weakness and deficits in motor and sensory integration, definitively noted on post-dosing day 7. The signs were more pronounced upon repetition of the FOB on post-dosing day 12. The neuropathological substrate of these signs was a progressive axonopathy with regional swelling, leading to Wallerian-like degeneration of affected myelinated fibers. Immunocytochemical staining for synaptophysin revealed often striking increase in immunoreactivity for this synaptic vesicle glycoprotein in swollen and otherwise injured axons. Such accumulations were considered consistent with interruption of anterograde (and possibly retrograde) fast axonal transport systems secondary to toxicant-induced nerve fiber breakdown.