This new technique is just too cool not to blog about.
|Novak et al. 2013 Figure 1A pre-synaptic patch clamp|
The synapse is the connection between two neurons. The pre-synaptic part is from the neuron sending a signal and the post-synaptic part is from the neuron receiving the signal.
If you want to learn about the connection between the two neurons, you want to know what is happening on both sides of the synapse. It's relatively easy to record signals from the post-synaptic side using patch clamp or sharp electrode recording, but it is much much harder (basically impossible until now) to record from the pre-synaptic side.
There is a gigantic synapse called the Calyx of Held where the pre-synaptic side is huge and envelops the post-synaptic side like a baseball glove holding a baseball.
|Calyx of Held (a schematic diagram) source|
But Novak et al. have published a paper using this 'electrode hopping' technique to find and patch normal sized pre-synaptic terminals.
A computer controlled nanopipette (which is essentially a micropipette) goes up comes back down across a layer of cells. It 'senses' cell membrane by an increase in resistance and stops before it hits the cell. Then it raises up again and moves over a little bit and comes back down. After a bazillion hops, the whole surface of an area of cell can be mapped. You can see a video of this in their very nice video abstract.
After they have mapped an area, they find a pre-synaptic terminal (called a bouton) and they use the same pipette that was just used to map the area to patch the bouton (They have to make the opening of the pipette bigger first, so they just smash it into the glass near the tissue until it breaks...!!.. .but apparently that works).
They patch the pre-synaptic bouton and record the calcium channels that help the pre-syanptic cell send its signal to the post-synaptic cell.
Novak P, Gorelik J, Vivekananda U, Shevchuk AI, Ermolyuk YS, Bailey RJ, Bushby AJ, Moss GW, Rusakov DA, Klenerman D, Kullmann DM, Volynski KE, & Korchev YE (2013). Nanoscale-targeted patch-clamp recordings of functional presynaptic ion channels. Neuron, 79 (6), 1067-77 PMID: 24050398