This article describes a method for recording electrical signals from neural tissue using a penetrating microelectrode array (PMEA) in a hippocampal preparation. The procedure involves acclimatizing the tissue with aCSF solutions, including one with 4-aminopyridine (4-AP), to enhance neuronal firing.
Take a recording chamber containing the penetrating microelectrode array or PMEA, which records electrical signals from neural tissue.
Connect the inlet to bottles containing oxygenated aCSF and oxygenated aCSF with 4-aminopyridine or 4-AP using a trivalve connector.
Attach the outlet to a vacuum tube.
Heat the pipeline between the inlet and trivalve to physiological temperature.
With the inlet and outlet closed, transfer the unfolded hippocampus into the chamber.
Under a microscope, position the hippocampus on the PMEA.
Remove the solution from the chamber.
Place a tissue anchor to hold the tissue onto the PMEA electrodes.
Open the inlet and outlet to start the aCSF flow.
Incubate the tissue with aCSF to allow neuronal acclimatization.
Then, flow in aCSF with 4-AP. The 4-AP blocks the neuronal potassium channels, extending the action potential duration.
The PMEA captures the electrical signals proportional to the enhanced neural firing from hippocampal neurons.
In this procedure, fill one bottle with normal aCSF and another bottle with 4-AP aCSF. Bubble the solutions with 95% oxygen, 5% carbon dioxide from the beginning of the experiments. Use a trivalve connector to control which solution will be selected during an experiment.
Next, connect a vacuum tube to the outlet of the chamber to remove the solution into a dust container. Heat the pipeline before delivering the solution into the recording chamber and keep it at 35 degrees Celsius controlled temperature. After closing the inlet and outlet of the recording chamber, use a custom-made glass pipette dropper to transfer the unfolded hippocampus to the recording chamber.
Under the microscope, position the unfolded hippocampus with its obvious side facing down, CA3 area pointing away, and CA1 field pointing towards the researcher. Carefully aspirate away the solution in the chamber using a vacuum pipette from the edge of the recording chamber until the chamber is dried and the tissue lies on the array.
Then, carefully place a custom-made tissue anchor on top of the tissue to hold the unfolded hippocampus onto the array. Refill the recording chamber with a few drops of solution. Gradually open the inlet and outlet to adjust the flow rate to about two drops per second in the IV drip chamber.
Incubate the tissue in the recording chamber with normal aCSF for about one minute. Then, switch the solution supply to 4-AP dissolved aCSF, and adjust the flow rate properly. Incubate the tissue in 4-AP dissolved aCSF for about 5 to 10 minutes before recording.
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