Afferent input-associated reduction of muscle activity in microgravity environment

Area of Science:

• Neuroscience
• Physiology
• Gravitational Biology

Background:

• Muscle activity and neural responses are influenced by gravitational forces.
• Understanding these adaptations is crucial for space travel and rehabilitation.

Purpose of the Study:

• To investigate the effects of altered gravity on electromyogram (EMG) activity in rat hindlimb muscles.
• To examine neural responses (afferent and efferent neurograms) at the spinal cord level during parabolic flight.

Main Methods:

• Adult rats were subjected to altered gravity levels (1-G, 1.5-G, 2-G, and microgravity) using parabolic flight.
• Electromyogram (EMG) activity of soleus, gastrocnemius (LG), and tibialis anterior (TA) muscles was recorded.
• Afferent and efferent neurograms at the L(5) spinal cord level were measured.

Main Results:

• Soleus muscle EMG increased with elevated gravity and significantly decreased (approx. 72%) in microgravity.
• Lateral gastrocnemius (LG) EMG showed similar trends, while tibialis anterior (TA) EMG increased slightly in microgravity.
• Afferent neurogram responses mirrored soleus EMG, with a smaller reduction (approx. 26%) in microgravity.
• Efferent neurogram showed a minimal decrease (approx. 9%) during microgravity.

Conclusions:

• Gravity significantly influences the electromyogram activity of antigravity muscles like the soleus.
• Afferent neural input appears closely associated with gravity-dependent muscular activity.
• Spinal cord neural activity adapts to altered gravitational conditions, with afferent pathways showing greater modulation than efferent ones.