Two reciprocating current components underlying slow oscillations in Aplysia bursting neurons

Area of Science:

• Neuroscience
• Cellular Electrophysiology
• Computational Neuroscience

Background:

• Burst firing neurons in Aplysia californica exhibit slow oscillatory potentials.
• Understanding these oscillations is key to deciphering neuronal communication patterns.

Purpose of the Study:

• To elucidate the ionic mechanisms driving slow oscillatory potentials in Aplysia neurons.
• To characterize the interplay of inward and outward currents responsible for burst firing.

Main Methods:

• Utilized voltage clamp techniques, including a novel track and hold method.
• Investigated ionic dependencies by altering external sodium (Na)0 and potassium (K)0 concentrations.
• Employed 'track and store' voltage clamping to analyze reciprocating currents.

Main Results:

• Identified a steady-state negative resistance characteristic attributed to a persistent, inward sodium current (INa).
• Revealed a slow outward potassium current (IS) with an extremely slow decay (tau ~45 sec) during burst phases.
• Demonstrated that INa and IS reciprocally generate slow oscillations and burst firing.

Conclusions:

• Slow oscillations are generated by a cycle of INa-driven depolarization followed by IS-mediated hyperpolarization.
• The slow decay of IS underlies the interburst depolarization ramp.
• A quantitative model explains the observed oscillatory dynamics and graded/all-or-none behaviors.