Dendritic L-type calcium currents in mouse spinal motoneurons: implications for bistability

Area of Science:

• Neuroscience
• Cellular Physiology

Background:

• Mammalian spinal motoneurons possess intrinsic properties enabling sustained firing (bistability) in response to transient inputs.
• A persistent dendritic calcium current has been hypothesized to underlie this depolarizing drive but lacked direct demonstration.

Purpose of the Study:

• To investigate and demonstrate the presence of a persistent dendritic calcium current in mature mammalian spinal motoneurons.
• To elucidate the role of this current in motoneuron bistability.

Main Methods:

• Somatic whole-cell patch-clamp recordings from mature mouse spinal motoneurons.
• Analysis of calcium currents under step and ramp voltage commands.
• Neuromorphic motoneuron modeling, pharmacological studies (dihydropyridines, FPL-64176), and immunohistochemistry (alpha1D subunits).

Main Results:

• Recorded calcium currents exhibited kinetics suggestive of a somatally segregated origin, appearing as late-onset, low-amplitude persistent currents and low-voltage hysteresis.
• Simulations required dendritic non-inactivating calcium conductance to replicate these currents.
• Pharmacological sensitivity to dihydropyridines and FPL-64176, along with dendritic localization of alpha1D L-type calcium channel subunits, was confirmed.

Conclusions:

• Dendritically located L-type calcium channels in mammalian motoneurons mediate a persistent depolarizing drive to the soma.
• These channels are likely responsible for the bistable firing behavior observed in these neurons.