Retrograde transneuronal transfer of the C-fragment of tetanus toxin

The transport of the C-fragment of tetanus toxin after intramuscular injection was studied with immunohistochemical techniques. Brainstems and spinal cords of mice were examined after injections of C-fragment into the tongue or forearm. Labelled motorneurons were observed within 6 h. By two days after injection, the bulk of detectable C-fragment had passed out of motorneurons into the surrounding neuropil. C-fragment, like native tetanus toxin, appears to be transferred from motorneurons to presynaptic structures to an extent not observed with other proteins. It is useful in the study of retrograde transneuronal transfer since it lacks the toxicity of tetanus toxin.