Changes in motoneuron excitability during postnatal life in the mouse

Area of Science:

• Neuroscience
• Developmental Biology
• Motor Control

Background:

• Motoneuron excitability is crucial for motor function.
• Understanding developmental changes in motoneuron excitability is key to motor development.
• The H-reflex is a valuable tool for assessing spinal cord excitability.

Purpose of the Study:

• To investigate motoneuron excitability and its developmental changes in mice.
• To analyze H-reflex recovery, H-amplitude, and H/M ratio across different developmental stages (3-12 weeks).

Main Methods:

• Electrophysiological recordings of H-reflex recovery, H-amplitude, and H/M ratio.
• Study conducted on 54 mice aged 3 to 12 weeks.
• Analysis of H-reflex patterns at specific time intervals (e.g., 10 ms, 40-100 ms).

Main Results:

• H-reflex recovery showed a significant increase in excitability between 3 and 6 weeks.
• H-reflex amplitude increased significantly from 3 to 6 weeks, likely due to muscle mass.
• The H/M ratio did not show significant changes, suggesting development in presynaptic/polysynaptic mechanisms rather than direct motoneuron output.
• The 12-week-old mice displayed an H-reflex recovery pattern lacking late inhibition, indicating reduced supra-spinal control compared to humans.

Conclusions:

• Early hypoexcitability at 3 weeks suggests motoneuron immaturity.
• Development of presynaptic and polysynaptic mechanisms occurs between 3-6 weeks.
• Reduced supra-spinal modulation in adult mice (12 weeks) compared to humans.