A rat model of Urtica ferox neuropathy

A species of stinging nettle, Urtica ferox, is indigenous to New Zealand and has caused deaths in animals and humans. We previously reported a human case of acute polyneuropathy due to U. ferox stings. We developed an experimental animal model of U. ferox toxin neuropathy to determine its neurophysiological and pathological characteristics. Male Wistar rats received either normal saline or fluid from U. ferox trichomes by injection into the epineurium of the left sciatic nerve. Neurophysiological and histological studies were carried out 5, 14 and 28 days after administration. Toxin-injected rats developed paresis of the left leg by 14 days with recovery by 28 days. Compound muscle action potentials amplitudes on the left side of toxin-administered rats at day 14 were significantly reduced compared to the right uninjected side. Toxin-injected nerves at days 5 and 14 showed a reduction in the number of myelinated fibres compared to the saline-injected nerves and frequency distributions of myelinated fibres showed a shift to smaller fibres. U. ferox neurotoxin thus produced a transient neuropathy in rat peripheral nerves with neurophysiological and pathological features suggestive of axonopathy. The identity and mechanism of action of the toxin responsible for neuropathy are uncertain.