ASYMMETRICAL ELECTROPHYSIOLOGICAL PROPERTIES IN ASTROCYTE SOMA AND PERISYNAPTIC PROCESSES

The electrophysiological properties of brain cells are the foundation of information transfer within the brain. Although neurons have been the primary focus of many electrophysiological studies, substantial progress in glial electrophysiology has revealed heterogeneous glial responses. Astrocytes, which account for more than half of glial cells in the human brain, have generally shown passive responses to classical electrophysiological techniques. As astrocyte conductances are mainly dominated by potassium channels, experiments have also revealed that astrocyte membrane potentials often reflect changes in extracellular potassium. On the other hand, many culture studies observe astrocyte depolarization independent of potassium Nernst potential in response to various neurotransmitters. Interestingly, somatic recordings from brain slices or in vivo show strong discrepancies, often showing minimal or undetectable amplitudes of synaptic receptor currents.
In this study, we aimed to investigate whether such properties can coexist within the same astrocyte, with a specific focus on comparing the electrophysiological dynamics of the soma and perisynaptic astrocytic processes (PAP). Unfortunately, the sites where neurons and PAPs interact are below the diffraction limit of light, hindering observation and research. Therefore, we constructed an empirical conductance-based NEURON model with a realistic morphology to simultaneously capture both astrocyte processes and soma dynamics, and to simulate realistic extracellular dynamics in vivo. Our results predict a breakdown of the 'potassium electrode'-like behavior of astrocytes when potassium stimuli are isolated to perisynaptic extracellular spaces. We also observe strong capabilities for isolating neurotransmitter responses to specific synaptic inputs, with minimal effect on the astrocyte soma.