Recording Neuronal Field Excitatory Postsynaptic Potentials in Acute Hippocampal Slices

Place a mouse hippocampal slice into a submersion chamber filled with artificial cerebrospinal fluid, or aCSF.

Secure the slice with a holding mesh to prevent movement.

Continuously circulate oxygenated aCSF to maintain neuronal viability.

Install reference electrodes to provide a stable voltage reference.

Position the stimulation and recording electrodes in line with and parallel to the hippocampal CA1 stratum pyramidale.

Apply electrical pulses.

These pulses stimulate the neurons, causing voltage-gated ion channels to open, allowing positive ions to flow in, and triggering action potentials.

These action potentials propagate along the neurons and induce the release of excitatory neurotransmitters into the synaptic cleft.

The neurotransmitters bind to specific receptors on the postsynaptic neurons, allowing positive ion influx and resulting in a change in membrane potential — the excitatory postsynaptic potential, or EPSP.

The recording electrode measures the EPSP from a population of neurons within the recording region — the field EPSP.

Pre-soak a small piece of lens cleaning paper and a nylon mesh fixed on a U-shaped platinum wire in the submersion slice chamber for a few minutes. After that, remove the U-shaped platinum wire. Switch off the recycling and place a slice on the lens cleaning paper. Then, immediately place the slice-holding mesh on top of the slice.

Switch on the pump, and let the slice equilibrate for 30 minutes without dipping the objective into ACSF. In the meantime, fill the recording electrode with ACSF, and mount it into the pipette holder.

Next, place the tested epoxy-insulated tungsten stimulation electrode in the manipulator holder, and the reference wire in the slice chamber. Add a second reference electrode to the chamber and connect it to the reference socket of the head stage of the recording electrode.

In the amplifier control software, click on the Zero-clamp Mode box, then double-click the Output Gain List box. Choose a gain of 100. Double-click the High-Pass Filter Box bessel. Choose 3 kilohertz and double-click the Low-Pass Filter List Box AC to choose 0.1 hertz.

In the recording software, click on Acquire Open Protocol. Choose a protocol that has the settings allowing for episodic stimulations and the digitalization of amplified potentials at 10 to 20 kilohertz for 50 to 100 milliseconds, and that automatically triggers a stimulus isolator 10 milliseconds after the start of an episodic recording.

Place the stimulation and recording electrodes in line and parallel to the stratum pyramidale. Subsequently, click Acquire Edit Protocol and choose the Trigger tab in the pop-up window. Click on the Trigger Source box and choose Spacebar as the trigger source. Then, click the OK button and click the Record button to start the acquisition.

In the stimulus isolator software, click on the Voltage Control Box and enter zero. Click the Download button. Following that, click on the Recording Software window and press the space bar. Repeat this cycle by sequentially entering values from 1,000 to 8,000. Correlate the stimulation strength with FEPSP slope values and determine the stimulation strength required to get 40% of the FEPSP slope maximum. Click the Voltage Control box and enter the determined value. Then, click the Download button.

In the recording software, click the Stop button and then the Acquire menu. Click on Edit Protocol and choose the Trigger tab in the pop-up window. Afterward, click on the Trigger Source box and choose the Internal Timer as the trigger source. Click the OK button, followed by the Record button that starts the automatic recording of field potentials every 60 seconds. Click the Stop button after 30 to 60 minutes.

In the recording software, click Acquire Open Protocol and choose the same protocol as the baseline recording. Click the OK button and then click Record. Keep automatically running the field potential recordings for two to four hours. When it is finished, click the Stop button to terminate the recording.