Spike threshold dynamics in spinal motoneurons during scratching and swimming

Area of Science:

• Neuroscience
• Motor Control
• Computational Neuroscience

Background:

• Action potential threshold is crucial for neuronal excitability and firing patterns.
• Motor behaviors involve complex neural network activity with intense synaptic inputs to motoneurons.
• Understanding motoneuron excitability dynamics is key to deciphering motor command generation.

Purpose of the Study:

• To investigate the dynamics of action potential threshold in spinal motoneurons during fictive scratching and fictive swimming.
• To identify the factors influencing spike threshold changes during functional motor behaviors.
• To elucidate the role of threshold dynamics in regulating motoneuron excitability and muscle activation.

Main Methods:

• Used an ex vivo turtle carapace-spinal cord preparation.
• Performed intracellular recordings from spinal motoneurons.
• Analyzed action potential threshold during fictive scratching and fictive swimming network activity.

Main Results:

• The action potential threshold depolarized by approximately 10 mV within each spike burst during both fictive scratching and swimming.
• The threshold potential recovered to a slightly depolarized level between bursts.
• Slow synaptic integration, not fast synaptic events or interspike intervals, was identified as the primary factor influencing threshold dynamics within bursts.
• Synaptic inputs did not modulate the threshold of the first action potential in these motor behaviors.

Conclusions:

• Spike threshold in motoneurons dynamically changes during functional motor behaviors.
• This depolarization of threshold potential decreases motoneuron excitability.
• Threshold dynamics may serve as a mechanism to stabilize motoneuron responses to intense synaptic inputs, optimizing muscle activation.