Tracer-toxins: cholera toxin B-saporin as a model

We have shown previously that retrogradely-transported cholera toxin B (CTB )-saporin has eliminated sympathetic preganglionic neurons by 7 days after injection (Llewellyn-Smith, I.J., Martin, C.L., Arnolda, L.F., Minson, J.B. , 1999. NeuroReport 10, 307). To ascertain whether this tracer-toxin can ki ll other types of neurons that transport CTB retrogradely with a similar ti me course, we injected CTB-saporin into the facial nerves of rats and allow ed them to survive for 7 days. Facial motoneurons were counted ipsilateral and contralateral to the injected nerves in sections of perfused medulla pr ocessed to reveal immunoreactivity for choline acetyltransferase (ChAT). Th ere was a statistically significant decrease in the number of ChAT-immunore active neurons ipsilateral to the injected nerve in three out of nine rats. Inadequate injections were probably the reason that most rats showed no de crease in motoneurons numbers after treatment with CTB-saporin, since the s taining intensity and numbers of facial motoneurons that showed CTB-immunor eactivity varied markedly between rats after retrograde tracing with unconj ugated CTB. These results show that CTB-saporin can eliminate motoneurons a s well as sympathetic preganglionic neurons, indicate that protocols for th e injection of tracer-toxins should be optimized to ensure maximum neuronal death and support our contention that CTB-saporin should kill any central neuron that expresses GM1 ganglioside, the membrane component to which CTB binds. (C) 2000 Elsevier Science B.V. All rights reserved.