Effects of Viral Infection on Contraction of the Diaphragm in Mice

Abstract

Isometric contractile properties of isolated phrenic nerve-diaphragm muscle preparations were used to study the effects of picornavirus infections on diaphragm muscle function. Properties of muscles from virus-inoculated and control mice were similar during brief contractions. However, when subjected to a series of fatiguing contractions by indirect or direct stimulation, muscles of mice inoculated with a paralytic variant of encephalomyocarditis (EMC) virus showed a greater rate of fatigue and a reduced capacity to recover from fatigue than did muscles from uninoculated control mice or muscles from mice inoculated with a nonparalytic coxsackievirus B3 (CVB3). Mice paralyzed by EMC virus infection had high titers of virus in the brain and similar titers of virus in diaphragm muscle as found in diaphragm muscles of CVB3-inoculated mice. The results indicate that EMC virus infection of mice leads to increased fatigability of the diaphragm muscle and that there are both neural and muscular components of this enhanced fatigue.