The sciatic and saphenous nerves were sectioned in the upper leg in rats and mice. Regeneration to the foot was prevented. All such animals have a permanently anesthetic foot. After about one week, the animals begin autotomy, an attack on the anesthetic foot. The autotomy usually begins with the toe nails and proceeds proximally. Numbers were assigned as an autotomy score to measure the extent of the attack. The animals were observed regularly during the first 5 weeks after the nerves had been sectioned. The most rapid rise of the autotomy score occurred 1–3 weeks after the operation in mice and 2–4 weeks after section in the rats. Little further autotomy occurs after 5 weeks.
Knowing that fibers sprouting in a neuroma become sensitive to noradrenaline, we investigated the effect of an antisympathetic drug on autotomy. From 4 to 9 days after nerve section, mice and rats were given 30 mg/kg/day intraperitoneal guanethidine in order to inactivate sympathetic nerve terminals before autotomy was expected to begin. All the treated animals showed a nearly complete absence of the autotomy. Reasons are given to suggest that the untreated animals have a type of anesthesia dolorosa caused by the generation of nerve impulses in the cut and sprouting peripheral nerve fibers. It is further suggested that the local release of norepinephrine by sympathetic fibers in the neuroma may be one of the factors producing sufficient peripheral afferent discharge to cause autotomy.