Caesium blocks depolarizing after-potentials and phasic firing in rat supraoptic neurones

Area of Science:

• Neuroscience
• Cell Physiology
• Ion Channel Function

Background:

• Magnocellular neurosecretory cells (MNCs) in the hypothalamus regulate vital physiological processes.
• Action potential properties, including after-potentials, are critical for neuronal firing patterns.
• Understanding ion channel contributions to MNC function is essential for comprehending neuroendocrine regulation.

Purpose of the Study:

• To investigate the effects of cesium ions (Cs+) on action potential characteristics, after-potentials, and firing patterns in rat MNCs.
• To determine the role of Cs+-sensitive currents in generating depolarizing after-potentials (DAPs) and phasic firing in MNCs.

Main Methods:

• Intracellular recordings were performed on MNCs in superfused rat hypothalamic explants.
• Extracellular application of Cs+ was used to assess its effects on membrane potential and firing properties.
• Voltage-clamp techniques were employed to isolate specific ionic currents.

Main Results:

• Extracellular Cs+ reversibly inhibited DAPs and associated after-discharges in MNCs.
• Cs+ did not significantly affect action potential duration, spike broadening, or hyperpolarizing after-potentials (AHPs).
• Cs+ abolished phasic firing in MNCs, indicating the necessity of the DAP current for plateau potentials and sustained firing.

Conclusions:

• The current underlying the DAP is likely directly blocked by Cs+, rather than indirectly through reduced Ca2+ influx.
• The DAP current plays a critical role in the generation of plateau potentials and phasic firing in MNCs.
• The interplay between DAP and AHP currents influences post-train after-potential dynamics in MNCs.