Jessica Madison
Marquette University Biology Apprenticeship Program
Abstract

In order for space research to progress, the length of space missions will need to be increased.  Muscle atrophy is one of the most debilitating consequences of weightlessness during to space travel negatively effecting work capacity of the astronauts during flight missions.  The results of the atrophy are even more devastating when returning to a gravitational environment.  To understand and thus prevent muscle atrophy, researchers first studied the dynamics of the soleus muscle in weight bearing (VirB) rats.  A ground based model of space flight, hindlimb unloading, was developed to simulate weightlessness in rats to study the atrophy process in hindlimb muscles. 14d hindlimb unloading (HU) resulted in a decrease in the force per muscle weight of soleus twitch and tetanic contractions.  Furthermore, 14d HU resulted in faster soleus muscle contractions and significantly greater fatigue than the controls.  For this project the model developed for the rats was adapted for research in mice. 14d HU resulted in soleus atrophy in the mice; 9.43±0.54g (n=4) for V%TB, and 6.88±1.08g (n=4) for HU.  However, in contrast to rats, force per soleus muscle weight of twitch and tetanic contraction was not significantly reduced by HU.  Furthermore, HU in mice did not result in great velocity contractions like the HU rats.  Similar to the findings in rats, the HU mouse soleus muscle was more easily fatigued than control mice.

More research needs to be done in order to determine if the rate of atrophy of the soleus muscle and effects on muscle contraction velocity are different in mice.  Because the atrophy was less severe and the contraction velocity was not effected, the mice may need to be HU for a greater amount of time in order to produce similar results found in rats.  For research to be continued on mice several improvements are needed; most importantly the HU harness needs to be refined since it did not prevent loaded contractions.  More mice will need to be studied to fully understand the effect of 14d HU on mice.