Functional changes of the sciatic nerve in mice chronically infected with Trypanosoma cruzi

Early histological studies carried out in the sciatic nerve of mice chronically infected with Trypanosoma cruzi showed demyelination and scanty axonal degeneration. The experiments reported in this paper were designed to assess the functional state of the sciatic nerve and of some of the muscles it supplies. For these purposes 14 mice were infected with trypomastigotes (clon K-98, CA-I strain) 12 months before the investigation. Results were compared with 13 normal mice matched by age and weight. Hamstring muscles were studied electromyographically by means of a fine coaxial needle electrode and the sciatic nerve action potential characteristics were recorded with surface electrodes. All the experiments were carried out in vivo. In the infected mice the electromyogram 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 collateral sproutings and reinnervation of muscle fibers previously relinquished by their original innervation. The sciatic nerve action potential of the infected animals showed diminished amplitude and prolonged latency. 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 involvement of the peripheral nervous system in Chagas disease and give additional information about the functional state of the peripheral nerves in the experimental model.