This article details a method for recording local field potentials (LFPs) from mouse hippocampal slices. The procedure involves the use of stimulation and recording pipettes to investigate synaptic activity between CA3 and CA1 neurons.
Secure a mouse hippocampal-entorhinal cortex slice in a submerged recording chamber.
Continuously flow oxygenated ACSF at a constant temperature to maintain tissue viability.
Position a stimulation pipette filled with an electrolyte solution within the stratum radiatum of the hippocampal CA3 region, containing neurons that receive information from the entorhinal cortex.
Insert an ACSF-filled recording pipette into the stratum pyramidale of the CA1 region, consisting of neurons that form synapses with axonal projections from the CA3.
Using the stimulation pipette, apply an electric pulse to trigger action potentials in the presynaptic CA3 neurons.
The action potential induces the release of neurotransmitters, which bind to receptors on the postsynaptic CA1 neurons. The binding induces ion influx, leading to a change in the membrane potential.
The combined changes in the membrane potential of multiple postsynaptic CA1 neurons, termed the local field potential or LFP, are recorded extracellularly by the recording pipette.
To record local field potentials, fill a 400-milliliter beaker with carbogen-bubbled ACSF, and place one end of the pump tubing into the beaker. Turn on a peristaltic pump at eight to 10 milliliters per minute, to direct ACSF from the 400-milliliter beaker to a heated reservoir and from the reservoir to the recording chamber at 32 degrees Celsius.
Next, briefly clamp the tubing, and turn off the pump to pause the flow. Using fine forceps, transfer a brain tissue slice to the recording chamber by the corner of the lens paper the tissue is resting on, slice down. Peel away the lens paper, leaving the slice submerged in the recording chamber, and use a harp to secure the slice.
Using a manual micromanipulator, slowly advance the tip of a sodium chloride-filled stimulation pipette into the surface of the slice at a 30- to 45-degree angle. Then, use a second micromanipulator to slowly advance the tip of an ACSF-filled local field potential pipette into the region of interest at a 30- to 45-degree angle, and record the local field potential of the sample according to standard protocols.
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