Overwork weakness in rats with acrylamide neuropathy

Exercised rats have larger myelinated nerve fibers than sedentary rats and exercised rats with acrylamide neuropathy have smaller fibers than acrylamide-treated sedentary rats. These nerve fiber changes were the result of work hypertrophy and overwork atrophy, respectively. This study was designed to reassess morphologic changes in nerves after overwork was induced in rats with acrylamide neuropathy and to test the effects of rest before and after an overwork period in rats with acrylamide neuropathy. The 4-week-old rats divided into four groups of eight rats. Acrylamide was administered to three groups (Groups 2, 3, and 4) to induce subacute paralysis followed by gradual ameriolation. Group 3 was exercised for the first 5 weeks and was rested for the last 5 weeks. Group 4 was exercised for the last 5 weeks. The diameter distribution of myelinated fibers of the tibial and sural nerves was analyzed. The percentage of larger myelinated fibers was decreased in all acrylamide-treated groups. The average values of fiber diameters in Group 4 were significantly smaller than injected sedentary animals (Group 2) or those with rest (Group 3), whereas no significant difference was found between the latter groups. Axonal degeneration of teased fibers was assessed in the tibial and sural nerves. The percentage of axonal degenerated fibers in exercised animals (Group 4) was significantly higher than in the other acrylamide-injected groups (Groups 2 and 3). This study supports the concept that acrylamide neuropathy worsens with moderate intensity of running activities for a prolonged period and that recovery may occur if vigorous exercise is avoided.