Distribution of ¹²⁵I-tetanus toxin and ¹²⁵I-toxoid in rats with local tetanus, as influenced by antitoxin

Summary

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• 1. Local tetanus was produced in rats by application of sublethal doses of ¹²⁵I-tetanus toxin into the right m. gastrocnemius. Radioactivity was found in the lumbar part of the spinal cord for at least 24 days which is indicative of a long-lasting binding of toxin to its target organ. Radioactivity appears in the lumbar region before local tetanus becomes manifest.

• 2. The influence of antitoxin on both local tetanus and radioactivity of the lumbar cord heavily depends on the time of its application. When it is injected simultaneously into a foreleg, it prevents the symptoms and the spinal concentration process. When given ten hours after toxin, it does not change appreciably the severity of local tetanus; it diminishes, however, the radioactivity accumulating in the spinal cord. Antitoxin, given 48 hours after toxin, is ineffective in both respects.

• 3. 22 hours after application, about 9% of the initial radioactivity still persists in the injected leg; 50 hours after application, only 1–2% are still present.

• 4. Plasma radioactivity is measurable for between 50 and 96 hours in animals given ¹²⁵I-toxin i.m. It is higher in animals having received antitoxin 10 hours after the toxin or simultaneously with toxin.

• 5. Labelled toxoid was prepared by formol treatment of labelled toxin. Following i.m. injection, toxoid was bound to a lesser degree and for a shorter time by the lumbar cord than was toxin. Like toxin, toxoid was found in the ipsilateral sciatic nerve, and simultaneous application of antitoxin prevented its appearance there as wells as in the lumbar cord. As with toxin, plasma radioactivity after injection of labelled toxoid was increased by simultaneous application of antitoxin into another leg.

• 6. It is concluded that antitoxin prevents the entrance of toxin into the spinal cord, but does neither remove nor detoxify appreciable amounts of radioactive material once fixed.