Depolarizing afterpotentials and burst production in molluscan pacemaker neurons

Area of Science:

• Neuroscience
• Cellular Electrophysiology

Background:

• Molluscan bursting neurons exhibit unique electrical properties, including depolarizing afterpotentials (DAPs).
• DAPs are distinct from those in non-bursting cells and play a role in sustained neuronal firing.

Purpose of the Study:

• To investigate the ionic mechanisms underlying depolarizing afterpotentials (DAPs) in molluscan bursting neurons.
• To determine the contribution of specific ions (Ca++, Na+, K+) to DAP generation and summation.

Main Methods:

• Electrophysiological recordings from bursting and non-bursting molluscan neurons.
• Manipulation of extracellular ion concentrations (Ca++-free, Na+-free saline) and intracellular iontophoresis (TEA-Cl).
• Analysis of DAP amplitude during hyperpolarization and repetitive stimulation.

Main Results:

• DAPs were observed in bursting cells but not non-bursting cells, and they sum to sustain discharge.
• Subthreshold depolarization activated a DAP-like process in bursters.
• DAP amplitude was dependent on extracellular Ca++ and Na+ concentrations, decreasing significantly in their absence.
• DAP amplitude was unaffected by K+-free saline or intracellular TEA-Cl, and declined during repetitive stimulation.

Conclusions:

• Depolarizing afterpotentials (DAPs) in bursting neurons result from a slowly decaying component of Ca++ and Na+ permeability.
• These DAPs are critical for generating and sustaining the bursting activity observed in these neurons.