Motor learning changes the axon initial segment of the spinal motoneuron.

Area of Science:

• Neuroscience
• Motor Learning
• Cellular Biology

Background:

• The axon initial segment (AIS) is crucial for neuronal excitability, initiating action potentials.
• Previous studies suggested AIS changes might underlie H-reflex conditioning, a simple learning model.
• The role of AIS plasticity in motor learning remained largely unexplored.

Purpose of the Study:

• To investigate the impact of H-reflex operant conditioning on the AIS of spinal motoneurons in adult rats.
• To determine if specific changes in AIS structure and molecular composition correlate with successful H-reflex conditioning (up- and down-conditioning).

Main Methods:

• Utilized blinded, quantitative histological and immunohistochemical techniques in adult rats.
• Examined AIS dimensions (length, distance from soma), ankyrin G (AnkG) immunoreactivity, p-p38 protein kinase, and GABAergic terminals.
• Correlated observed AIS changes with the degree of H-reflex conditioning.

Main Results:

• Successful H-reflex up-conditioning correlated with increased AIS length and greater distance from the soma.
• Successful H-reflex down-conditioning was associated with more GABAergic terminals on the AIS, reduced AnkG immunoreactivity, and increased p-p38 protein kinase.
• Unsuccessful conditioning attempts did not yield significant AIS changes.

Conclusions:

• AIS plasticity in spinal motoneurons is associated with and potentially contributes to H-reflex operant conditioning.
• These findings support the hypothesis that motor learning involves both spinal and brain plasticity, encompassing neuronal and synaptic changes.
• AIS properties in spinal motoneurons likely integrate the influences of all motor behaviors utilizing them.