Neuronal interactions mediated by neurally evoked changes in the extracellular potassium concentration

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Neurophysiology

Background:

• Neuronal communication relies on ion concentration changes, particularly extracellular potassium ([K+]o).
• Interactions mediated by [K+]o vary in efficacy and can occur between neuronal populations or single neurons.
• These K+-mediated interactions share characteristics with postsynaptic potentials (PSPs) from chemical or electrotonic synapses.

Purpose of the Study:

• To review experimental evidence demonstrating diverse levels of neuronal interactions mediated by extracellular potassium.
• To investigate the role of extracellular space geometry in modulating K+-mediated neuronal communication.
• To explore the potential for K+-mediated interactions to be misidentified as synaptic events.

Main Methods:

• Experiments utilized giant axons (Gax) and non-giant axons from the cockroach central nervous system (CNS).
• Studies involved inducing neuronal activity and observing effects of altered extracellular potassium concentrations.
• Analysis included examining pathological, restricted, and local K+-mediated interactions.

Main Results:

• Extracellular spaces in the CNS act as pathways for K+-mediated neuronal communication.
• The geometry of giant axons, combined with elevated [K+]o, facilitates restricted interactions.
• Highly efficient, local K+-mediated interactions among giant axons were observed.
• K+-mediated interactions in narrow extracellular spaces resemble synaptic PSPs.

Conclusions:

• Extracellular potassium is a significant mediator of neuronal communication within the CNS.
• The physical constraints of extracellular spaces can shape the nature and detection of K+-mediated interactions.
• The similarity between K+-mediated events and synaptic potentials may lead to under-recognition of K+ signaling in the CNS.