FUNCTIONAL-CHANGES OF THE SCIATIC-NERVE IN MICE CHRONICALLY INFECTED WITH TRYPANOSOMA-CRUZI

Early histological studies carried out in the sciatic nerve of mice ch ronically infected with Trypanosoma cruzi showed demyelination and sca nty axonal degeneration. The experiments reported in this paper were d esigned to assess the functional state of the sciatic nerve and of som e of the muscles it supplies. For these purposes 14 mice were infected with trypomastigotes (clon K-98, CA-I strain) 12 months before the in vestigation. Results were compared with 13 normal mice matched by age and weight. Hamstring muscles were studied electromyographycally by me ans of a fine coaxial needle electrode and the sciatic nerve action po tential characteristics were recorded with surface electrodes. All the experiments were carried out in vivo. In the infected mice the electr omyogram showed that some motor unit potentials has enlarged amplitude and duration and increased number of phases, suggesting that the size of their territories had been enlarged, probably through axonal colla teral sproutings and reinnervation of muscle fibers previously relinqu ished by their original innervation. The sciatic nerve action potentia l of the infected animals showed diminished amplitude and prolonged la tency. These features signal reduced number of functional axons within the nerve and demyelination of the remaining conducting fibers. These findings are in line with the histological evidences of the involveme nt of the peripheral nervous system in Chagas disease and give additio nal information about the functional state of the peripheral nerves in the experimental model.