A 30-year-old technique to record the
electrical activity of neurons gets a robotic makeover.
THE DEVICE: Whole-cell patch clamping, a Nobel
Prize-winning technique to record the electrical activity of neurons, has never
looked so good. A shoebox-sized robot lowers a thin glass pipette, its tip
sharpened to 1 micrometer in diameter, into the brain of an anesthetized mouse.
The robot moves the pipette around inside the brain, almost imperceptibly,
hunting for neurons. When the glass tip bumps into a neuron, the robot arm
instantly halts and applies suction through the pipette to form a seal with the
cell membrane. Once attached, the pipette tears a small hole in the membrane
and records the cell’s internal electrical activity.
The
automated process performs in vivo patch clamping faster and more accurately
than manual patch clamping, which involves the physical manipulation of a glass
pipette by a researcher, according to the robot’s inventors, who published
their design earlier this month (May 6) in Nature Methods.
“By
adding in a robot, this will make [in vivo patch-clamping] much more accessible
to someone who might not have considered it before,” said Derek Bowie, who
studies neuronal receptors at McGill University in Montreal, Canada, and was
not involved in the research.
WHAT’S
NEW: The
idea is simple: record the electrical activity of a single neuron in a living
brain. The execution is not: it takes researchers months to learn the
technique, and even an experienced patch clamper records only 2-4 successful
readings per day. The process is so laborious, in fact, that only
around 30 labs in the world perform whole-cell patch clamping in vivo (though
others do it in a dish). But researchers have continued to use the technique
for over 30 years because of its value. “This is a really powerful technique
for identifying the type of neuron you’re looking for, determining the
electrophysiology of a diseased neuron, or figuring out how a drug affects the
firing of a neuron,” said coauthor Craig
Forest, director of the Precision Biosystems Laboratory at the Georgia
Institute of Technology. “But it’s really, really hard.”
The new
patch-clamping robot makes an in vivo recording in just 3 to 5 minutes, detects
cells with 90 percent accuracy, and achieves a successful seal with the cell
membrane about 40 percent of the time. Overall, the machine, produced in
collaboration with researchers at the Massachusetts Institute of Technology, is
about 50 percent more successful than an individual manually attempting to make
a recording, said Forest.
IMPORTANCE: Robotics has made a
major impact on many fields of biology, but it has rarely been applied in
neuroscience, said Forest. “We’re excited to bring robotics into the living
brain,” he said. The team has already begun to use the robot in collaboration
with the Seattle-based Allen Institute for a 10-year
project to catalog all the types of neurons in the mouse brain.
The
robot design is freely available at autopatcher.org, or an assembled robot can
be purchased through a spin-off company, Neuromatic Devices. The robot can be
set-up and used in a single day, said Forest—a dramatic difference from the 6
months typically required to train a graduate student or postdoc how to do the
technique by hand. “I guess postdocs can now just sit at home or on a beach
somewhere,” said Bowie with a laugh.
NEEDS
IMPROVEMENT: The
technique could be made even more useful if combined with another new tool
called shadow
patching, said Bowie. Shadow patching, developed in 2008 by Michael Häusser
and colleagues at University College London, involves spraying the
extracellular space around a neuron with a fluorescent dye in order to
visualize the shape of the cell.
The
MIT/Georgia Tech team has already modified the robot to perform a similar
technique: rather than injecting dye into the extracellular space, the robot
injects the die into the neuron itself to visualize its shape, said Forest. The
set-up can also be tweaked to extract DNA to sequence a cell’s genome. Now, the
researchers are working on increasing the number of electrodes operated by a
single robot so as to record from multiple neurons at the same time, and trying
to streamline the process so that a single operator can control multiple robots
simultaneously. “We’re open to collaborating with folks who want to take this
in new directions,” said Forest.
S. B. Kodandaramaiah, et al., “Automated whole-cell
patch-clamp electrophysiology of neuronsin vivo,” Nature
Methods, doi:10.1038/nmeth.1993, 2012.
Megan
Scudellari
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