Brain slice electrophysiology video protocol

Brain slice electrophysiology allows the study of a synapse or neural circuit in isolation from the rest of the brain, in controlled physiological conditions. This protocol describes the preparation of hippocampal slice and electrophysiology recording (12:04 minutes).

  For other video protocols please visit our video protocols library here. 

Solutions and reagents

2 L of aCSF (artificial cerebrospinal fluid) solution

127 mM NaCl
1.0 mM KCl
1.2 mM KH₂PO₄
26 mM NaHCO₃
10 mM D-glucose

Weigh out salts using a fine balance to make up 2 L of artificial cerebrospinal fluid (aCSF) solution. Top it up to with deionised H₂0 to around 1.9 L, leaving enough room to add other components later. Shake well and make sure all salts have dissolved. Bubble aCSF with carbogen 95% O₂/5% CO₂ for 15-20 minutes to stabilize the pH to 7.3-7.4. Afterwards add 4.8 ml of 1M CaCl₂ and 2.6 ml of 1M MgCl₂ using a suitable pipette to give a final concentration of:

2.4 mM CaCl₂
1.3 mM MgCl₂

Top it up with deionised H₂0 to 2 L. Bubble for a further 15 minutes with carbogen.

Intracellular recording solution

140 mM Potassium gluconate
10 mM KCl
1 mM EGTA-Na
10 mM HEPES
4 mM Na₂ATP
0.3 mM Na₂GTP

pH adjusted to 7.3 with 0.5M KOH and the osmolarity adjusted with 1M sucrose.

Test compounds

CGP 55845 hydrochloride
Tetrodotoxin citrate

Brain slice preparation

1. Chill 1 L of aCSF over dry ice until < 4^oC and add 250 ml of aCSF to slice holding chamber.
2. Setup vibratome by filling the buffer chamber wtih cold aCSF solution, setting the desired thickness (2-500 µM for brain slices) and adjust the cutting speed to the desired setting (in the video protocol we used number 0.15 mm/min).
3. Place the brain into pre-chilled aCSF solution. For hippocampal sections, trim the brain by cutting off the cerebellum, which provides a flat surface to mount the brain with, and a small part of the prefrontal cortex.
4. Mount the brain (cerebellum side) onto the vibrotome specimen disc using superglue, orienting the sample such that the cortex faces the razor blade. Add a supporting piece of agar behind the brain, away from the side of the vibratome, to provide structural support during the slicing.
5. Set the limit stop positions of the microtome to define the start and stop positions of the slicing. Set the frequency of the vibrotome to maximum (100 Hz).
6. Use the Up-rocker button to move the buffer tray and brain to a position where the exposed surface is just below the razor blade edge and press start to begin the brain slicing.
7. Using a transfer pipette (transfer each individual brain slice containing the region of interest from the buffer tray to a clean petri-dish prefilled with chilled aCSF.
8. Carefully hemisect the brain down the midline and transfer the individual slices to a holding chamber pre-filled with aCSF.
9. Store the slices for at least 1 hour at room temperature to allow the brain tissue to recover from the mechanical shock of slicing.

Tips: It is important to continually top up the chamber with cold aCSF solution to keep the brain tissue cool whilst slicing.

If unfamiliar with brain anatomy, use a reference such as Paxinos and Watson, The Rat Brain Atlas to ensure slicing of the correct brain area.

Image: Figure 35 from the Rat Brain Atlas

Electrophysiology recording preparation

1. Prepare intracellular recording solution into a 1 ml microcentrifuge tube from pre-prepared stock solutions.
2. Optional: Add Alexa Fluor® 633 to a final concentration of 50 µM to allow for further IHC experiments of the recorded brain neurones. See IHC protocol.
3. Make an electrode filler by melting a 1 ml plastic Pasteur pipette over a Bunsen burner flame. Once the Pasteur pipette has turned opaque within the flame, pull each end apart to stretch the plastic and once cooled down, cut allowing enough length to reach the bottom of the recording pipette.
4. Fill the electrode filler with the intracellular solution.
5. Fabricate a glass recording pipette by using appropriate glass capillaries and pipette puller.
6. Prepare test compounds and add it to aCSF to acheive the final working concentration that will be used in the experiment.

Tip: It is important to ensure the batch specific molecular weight is used to determine an accurate concentration of test compounds. Check out our FAQ on small molecules for more information.

Electrophysiology recording

1. Fill up a bottle with aCSF solution and testing compound solution. Bubble both with carbogen and adjust the flow rate of the aCSF solution to approximately 5 ml/min using metal Hoffman clamps.
2. Place brain slice into recording chamber using a small brush and secure the slice with reference electrode.
3. Fill the glass recording pipettes with intracellular solution using the pipette filler, making sure the solution is all the way down at the tip of the pipette.
4. Attach the pipettes to the electrode holders of the patch-clamp amplifier headstages and turn into position.
5. Using fine control micromanipulators, descend the recording pipettes to the region of interest within the brain slice. In the video, the CA1 region of the hippocampus.
6. If required, use a coarse-manipulator to position an appropriate stimulating electrode again to the appropriate region of the brain slice to stimulate inputs to recorded neurones.
7. Once pipette is in contact with a neurone within the brain slice, apply negative pressure to pipette via 1 ml syringe. Monitor resistance of seal formation on oscilloscope or computer.
8. Once seal resistance has exceeded 1 GΩ, using amplifier and computer software to compensate transients and apply further negative pressure to rupture cell membrane gaining whole-cell access to neurone.
9. Perform current-voltage relationship using computer controlled software to access neuronal health and to assess for presence of active membrane conductances.
10. Once happy with quality of recording, perform set experiment applying test compounds via syringes connected in-line with the aCSF flow.
11. Monitor response of test compound using computer controlled software and perform electrophysiological tests such as current voltage relationships, evoke excitatory or inhibitory post synaptic potentials.
12. Optional: Once experiment has finished, remove brain slice from recording chamber and fix tissue overnight with 4% paraformaldehyde in 0.1 M phosphate buffer pH 7.4. Continue with IHC to identify proteins of interest.

View our IHC protocol.

Acknowledgment

The video protocol was produced by Abcam in partnership with NeuroSolutions.

Reference

• Paxinos, George, and Charles Watson. The rat brain in stereotaxic coordinates: hard cover edition. Access Online via Elsevier, 2006.

Alexa Fluor® is a registered trademark of Life Technologies. Alexa Fluor® dye conjugates contain(s) technology licensed to Abcam by Life Technologies.

Webinar transcript

Weigh out salts using a fine balance to make up two liters of artificial cerebrospinal fluid solution, aCSF. Top it up with deionized water to around 1.9 liters, leaving enough room to add other components later. Shake well and make sure all salts have dissolved.

Bubble aCSF with carbogen, 95% oxygen, 5% carbon dioxide for 15 to 20 minutes to stabilize the pH to 7.3 to 7.4.

Afterwards add 4.8 mLs of one molar calcium chloride, and 2.6 mLs of one molar magnesium chloride, using a suitable pipette to get a final concentration of 2.4 millimolar and 1.3 millimolar.

Top it up with deionized water to two liters. Bubble for a further 15 minutes with carbogen.

Then chill one liter of aCSF over ice until it is cold at or below four degrees C.

Mount a double-edged razor blade onto the knife holder. Screw to tighten into place.

Set the microtome to the desired thickness. Two to 500 microns for brain slices and adjust the cutting speed to the desired setting. In this case, number three or 0.15 millimeters per minute.

Place the brain into pre-chilled aCSF solution.

For hippocampus sections, trim the brain by cutting off the cerebellum, which provides a flat surface to mount the brain with and a small part of the prefrontal cortex.

Mount the brain, cerebellum side onto the microtome specimen disc using super glue.

Orienting the sample such that the cortex faces the razor blade.

Add a supporting piece of agar behind the brain away from the slide of the viva tome to provide structural support during the slicing.

Set the limit stop positions of the microtome to define the start and stop positions of the slicing.

Set the frequency of the microtome to maximum, 100 hertz.

Use the up-rocker button to move the buffer tray and brain to a position where the exposed surface is just below the razor blade edge and press start to begin the brain slicing.

It is important to continually top up the chamber with cold aCSF solution to keep the brain tissue cool while slicing. If unfamiliar with brain anatomy, use a reference such as Paxinos Watson, the rat brain atlas to ensure correct slicing of a brain area.

Using a transfer pipette, transfer each individual brain slice containing the region of interest from the buffer tray to a clean Petri dish prefilled with chilled aCSF.

Carefully hemisect the brain down the midline and transfer the individual slices to a holding chamber prefilled with aCSF.

Store the slices for at least one hour at room temperature to allow the brain tissue to recover from the mechanical shock of slicing.

Prepare intracellular recording solution into a one mL Eppendorf tube from pre-prepared stock solutions.

Here, we added Alexa-633 dye to a final concentration of 50 micromolar to allow for further IHC experiments of the recorded brain neurons.

Make an electrode filler by melting a one mL plastic Pasteur pipette over a Bunsen burner flame. Once the Pasteur pipette has turned opaque within the flame, pull each end apart to stretch the plastic, and once cooled down, cut allowing enough length to reach the bottom of the recording pipette.

Fill the electrode filler with the intracellular solution.

Fabricate a glass recording for PET by using appropriate glass capillaries and pipette puller.

It is essential to ensure that the batch-specific molecular weight is used to determine an accurate concentration of test compounds.

On all Abcam compounds, the batch-specific molecular weight is clearly displayed on the vial.

Prepare the test compound and make the stock solution by weighing out the compound by using a fine balance.

Stabilization instructions can be found on the certificate of authenticity accompanying your product or on the website.

Some products may be difficult to solubilize, and you may find that rapid stirring, warming in a water bath, or sonication of the solution may help.

Solubility is temperature-dependent. As such, cooling or freezing solutions may lead to precipitation of a product after solution. It is therefore important to ensure that your product is completely redissolved before use. After making up the stock solution, aliquot at the desired volume and freeze until use.

On the day of experimentation, defrost a single tube and add it to the aCSF to achieve the final working concentration that will be used in the experiment.

Now, the solutions have all been produced, the recording can start. Fill up a bottle with aCSF solution and testing compound solution.

Bubble both with carbogen and adjust the flow rate of the aCSF solution to approximately five mLs per minute using metal Hoffman clamps.

After one-hour incubation at room temperature, carefully place the brain slice into the recording chamber using a transfer pipette or small brush. Top up the chamber with aCSF solution. Move the slice into place using a small brush and secure the slice with reference electrode.

Fill the glass recording pipette with intracellular solution using the pipette filler, making sure the solution is all the way down at the tip of the pipette. Flick to get rid of any air bubbles. Attach the pipettes to the electrode holders with a patch-clamp amplifier head stages and turn into position.

Using fine control micromanipulators, descend the recording pipette to the region of interest within the brain slice. Here, the CA1 region of the hippocampus.

If required, use a course manipulator top position an appropriate stimulating electrode again to the appropriate region of the brain slice to stimulate inputs to recorded neurons. Here, this is within the Schaffer collaterals of the hippocampus.

Use the control dials of the micromanipulator to descend the recording pipette into the aCSF solution covering the brain slice. Open the seal test function of the computer-controlled acquisition software and monitor the resistance of the recording pipette.

The ideal resistance when filled with intracellular recording solution is between five and eight mega ohms.

Using the pipette offset or track functions of the recording amplifier, set the offset current to zero prior to advancing the electrode into the brain slices with the micromanipulator.

At the same time, apply pressure to the recording electrode via a syringe connected to the electrode holder. When a neuron is encountered, the conductivity through the recording electrode is increasingly reduced as the tip of the recording pipette gets closer to the neuronal membrane.

Gentle positive pressure is applied via the syringe to clear the tip of the recording pipette of any debris that may have occluded as the recording electrode is lowered through the brain slice.

Once close to a neuron, the height of the injected current step will have fallen to approximately 20% of its starting value.

Negative pressure is then applied then via the syringe to obtain a giga ohm seal and negative current applied to the electrode via the acquisition software.

After allowing the giga ohm seal to improve over time, we apply further negative pressure via the syringe to rupture the membrane and gain direct access to the cytoplasm of the neuron whilst maintaining a tight seal to prevent current leakage. We now have wholesale access to the recorded neuron as defined by the increased capacitance transience visible in our current step.

Using the patch-clamp amplifier, the capacitance transience is progressively canceled and electrophysiological experiments can begin on the recorded neuron. Using the computer-controlled acquisition software, the health and electrophysiological properties of the recorded neuron are assessed. A current-voltage relationship is constructed by injecting square wave negative and positive rectangular current injection of constant increment into the neuron.

This smooth membrane trace, an action potential firing on the positive current steps, indicates the health of the recorded neuron. In the current clamp recording mode of the wholesale patch-clamp technique, the neuronal membrane responses to apply test compounds can be assessed.

In order to test the effects of test compounds, switch the recording solution from aCSF in the main aCSF bottle to the pre-prepared test compound contained within 50 mil syringes connected to the recording chamber by three-way taps.

In this example, we are applying a one micromolar Tetrodotoxin a potent sodium channel blocker to a recorded neuron in the current clamp recording mode of the wholesale patch-clamp technique. The cessation of spontaneous action potential firing can clearly be observed.

Using the stimulating electrode placed within the Schaffer collateral pathway of the hippocampus, the responses to electrically evoke postsynaptic potentials can also be monitored. Here, a mixed excitatory glutamatergic EPSP, an inhibitory gabaergic IPSP can be seen in response to electrical stimulation.

Once the experiment has finished, the brain slice is removed from the recording chamber using a paintbrush and carefully placed within a suitable glass container.

A pipette is used to fill the container with 4% paraformaldehyde in 0.1 molar phosphate buffer, pH 7.4, and stored in the fridge until used for immunized to chemical processing.

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