Subthreshold membrane depolarization powerfully engages intracellular calcium dynamics in the brain

Area of Science:

• Neuroscience
• Cellular Signaling
• Electrophysiology

Background:

• Membrane voltage (Vm) dynamics are critical for neuronal function, regulating spike timing and intracellular signaling pathways.
• How subthreshold Vm dynamics engage intracellular signaling in the awake mammalian brain remains poorly understood.
• Calcium ions (Ca ²⁺ ) are crucial second messengers involved in numerous cellular processes.

Purpose of the Study:

• To investigate the relationship between subthreshold membrane voltage dynamics and intracellular calcium signaling in awake mammalian neurons.
• To simultaneously record membrane voltage and calcium dynamics in the same neuron in vivo.
• To elucidate how different patterns of Vm activity, including prolonged depolarization and individual spikes, influence intracellular Ca ²⁺ levels.

Main Methods:

• Development of a bicistronic viral vector for co-expression of genetically encoded voltage and calcium indicators in single neurons.
• Simultaneous in vivo recording of cellular Vm and Ca ²⁺ dynamics in awake mice.
• Application of brief and prolonged intracranial electrical stimulation to modulate Vm and assess Ca ²⁺ responses.

Main Results:

• Prolonged subthreshold Vm depolarization is tightly correlated with significant elevations in intracellular Ca ²⁺.
• Individual action potentials are associated with smaller Ca ²⁺ transients compared to prolonged depolarization.
• Post-spiking Vm depolarization influences the engagement of intracellular Ca ²⁺ dynamics, highlighting the role of slow Vm changes.
• While brief electrical stimulation enhances Vm-Ca ²⁺ coupling, prolonged stimulation disrupts this relationship, indicating regulated cellular mechanisms.

Conclusions:

• Slow, subthreshold membrane voltage depolarization plays a dominant role in regulating intracellular calcium signaling in awake neurons.
• The brain employs tightly regulated cellular mechanisms to relay slow Vm depolarization to intracellular signaling pathways.
• Understanding Vm-Ca ²⁺ coupling dynamics is essential for comprehending neuronal computation and signaling in physiological and pathological states.