Modulation of parallel fiber excitability by postsynaptically mediated changes in extracellular potassium

Area of Science:

• Neuroscience
• Cellular Electrophysiology

Background:

• Extracellular potassium concentration ([K+]o) plays a critical role in neuronal excitability.
• Modulation of presynaptic fiber excitability by postsynaptic activity is a key mechanism in neural circuit function.

Purpose of the Study:

• To investigate the relationship between extracellular potassium ([K+]o) accumulation and parallel fiber excitability in the rat cerebellar cortex.
• To determine if changes in [K+]o associated with synaptic activity can modulate presynaptic afferent fiber excitability.

Main Methods:

• Simultaneous monitoring of field potentials and extracellular potassium concentration ([K+]o) in the cerebellar molecular layer.
• Stimulation of parallel fibers in the rat cerebellum.
• Application of methods to reduce synaptic field potentials.

Main Results:

• Parallel fiber stimulation led to a marked increase in parallel fiber excitability.
• This increase in excitability correlated with the degree of extracellular K+ accumulation.
• Reduction of synaptic field potentials was accompanied by increased parallel fiber excitability.

Conclusions:

• Increases in extracellular potassium ([K+]o) associated with postsynaptic activity can modulate the excitability of presynaptic afferent fibers.
• This provides evidence for a mechanism by which postsynaptic events influence presynaptic function in the cerebellar cortex.