Sensing the electrical activity of individual neurons within the brain is a job for a steady hand and a focused mind, especially if the technique used in the study is whole-cell patch-clamp electrophysiology. It is extremely difficult to control a hollow glass micropipette, guide it to a very narrowly defined location, attach to the cell(s) membrane, and to read the potentials. So all this limits our ability to study the brain with patch-clamp EP.
Now researchers have built a robot that automates this process and greatly increases the number of cells that can be monitored. The technology, reported in the latest Nature Methods, should make whole-cell patch-clamp EP available to more laboratories that don’t have a solid team of lab techs able to do precision work.
Some details of how the system works:
Kodandaramaiah [Georgia Tech grad student Suhasa Kodandaramaiah] and his colleagues built a robotic arm that lowers a glass pipette into the brain of an anesthetized mouse with micrometer accuracy. As it moves, the pipette monitors a property called electrical impedance — a measure of how difficult it is for electricity to flow out of the pipette. If there are no cells around, electricity flows and impedance is low. When the tip hits a cell, electricity can’t flow as well and impedance goes up.
The pipette takes two-micrometer steps, measuring impedance 10 times per second. Once it detects a cell, it can stop instantly, preventing it from poking through the membrane.
Once the pipette finds a cell, it applies suction to form a seal with the cell’s membrane. Then, the electrode can break through the membrane to record the cell’s internal electrical activity. The robotic system can detect cells with 90 percent accuracy, and establish a connection with the detected cells about 40 percent of the time.
The researchers also showed that their method can be used to determine the shape of the cell by injecting a dye; they are now working on extracting a cell’s contents to read its genetic profile.
Abstract in Nature Methods: Automated whole-cell patch-clamp electrophysiology of neurons in vivo