The influence of temperature on neuromuscular performance

Area of Science:

• Neuroscience
• Muscle Physiology
• Biochemistry

Background:

• Temperature significantly influences physiological processes, including muscle function and neurotransmission.
• Understanding temperature effects on neuromuscular junctions is crucial for various clinical and research applications.

Purpose of the Study:

• To investigate the impact of controlled temperature reduction on rat phrenic nerve-hemidiaphragm function.
• To elucidate the effects of cooling on muscle tension, acetylcholine release, and enzyme activity.

Main Methods:

• In vitro study on rat phrenic-nerve-hemidiaphragm preparation.
• Temperature varied in 10°C increments from 37°C to 17°C.
• Measurements included twitch (Pt) and tetanic (Po) tension, acetylcholine (ACh) release, and acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activity.

Main Results:

• Cooling progressively increased isometric twitch tension (Pt) and prolonged twitch duration.
• The tetanic tension (Po)/twitch tension (Pt) ratio decreased significantly at lower temperatures.
• Presynaptic ACh release and muscle AChE/BuChE activities decreased with cooling.
• Cooling facilitated post-tetanic facilitation at higher temperatures but exacerbated exhaustion at 37°C.

Conclusions:

• The primary site of cooling's facilitating effect on twitch tension is the muscle fiber, due to delayed relaxation.
• Reduced nerve conduction velocity and ACh release negatively impact neuromuscular transmission.
• Decreased muscle cholinesterase activity and increased postjunctional membrane sensitivity partially counteract transmission deficits.