Persistent Na+ current modifies burst discharge by regulating conditional backpropagation of dendritic spikes

Area of Science:

• Neuroscience
• Computational Neuroscience
• Electrophysiology

Background:

• Sensory neuron stimulus detection relies on firing mode transitions (tonic to burst).
• Pyramidal cells in electric fish electrosensory lobes use spike bursts for stimulus detection.
• Burst generation involves dendritic spike broadening, potentiating somatic depolarizing afterpotentials (DAPs).

Purpose of the Study:

• Investigate the mechanisms controlling the transition from tonic to burst firing in sensory neurons.
• Determine the factors regulating spike burst frequency in pyramidal cells.
• Explain the physiological basis for variable bursting dynamics.

Main Methods:

• In vitro electrophysiological recordings from weakly electric fish.
• Compartmental modeling of neuronal activity.
• Dynamical systems analysis to understand discharge thresholds.

Main Results:

• Burst frequency is regulated by the rate of DAP potentiation, influencing spike doublet discharge.
• Persistent sodium current (I(NaP)) magnifies DAP potentiation via positive feedback.
• A shift from tonic to burst discharge is induced by I(NaP)-mediated slow depolarization.

Conclusions:

• Conditional backpropagation, a rhythmic dendritic spike failure, converts tonic to burst discharge.
• The interaction between dendritic K+ current and I(NaP) explains variable bursting timescales.
• Neuronal firing mode transitions are explained by saddle-node bifurcations and underlying ionic mechanisms.