Spatial and temporal parameters of cortical inactivation by GABA

Area of Science:

• Neuroscience
• Electrophysiology
• Computational Neuroscience

Background:

• Gamma-aminobutyric acid (GABA) is crucial for studying specific cortical region functions.
• GABA's reversible inactivation is valuable in electrophysiology for precise control.
• Iontophoresis inactivates neurons up to 300 microm; pressure injection's characteristics are less understood.

Purpose of the Study:

• To investigate the spatial and temporal characteristics of GABA pressure injection for cortical inactivation.
• To develop methods for more homogeneous and predictable GABA-induced neuronal inactivation.
• To create a mathematical model for estimating the extent of GABA inactivation zones.

Main Methods:

• Constructed devices combining micropipettes and microelectrodes at varying distances.
• Administered repeated small injections versus bolus injections of 100 mM GABA.
• Developed a mathematical model to fit experimental inactivation data around the pipette tip.

Main Results:

• Repeated small GABA injections resulted in more homogeneous cortical inactivation than bolus injections.
• GABA diffusion after pressure injection appears to follow an ellipsoidal form, not point spread.
• The mathematical model accurately estimated inactivation zones for volumes < 60 nl, with limits 250-500 microm laterally.
• Predicting inactivation geometry beyond 60 nl is difficult; inactivation >800 microm is hazardous.

Conclusions:

• Repeated small pressure injections of GABA offer a more controlled method for cortical inactivation.
• A mathematical model can predict GABA inactivation extent for smaller volumes, aiding experimental design.
• Careful control of GABA volume is necessary to avoid unpredictable inactivation zones in electrophysiological studies.