Extraction and Dissection of the Domesticated Pig Brain

This protocol details the technique for removal of the pig brain in its entirety and dissection of several brain regions commonly studied in neuroscience.

Transcript

The following video is a demonstration of removal and dissection of the pig brain. It may be helpful to refer to an atlas, or fiber dissection guide before or during the procedure. A large butcher knife is best for decapitation as it will allow for one clean cut between the atlas and axis.

Ensure the knife is sharp before starting with a new subject. A meat hook is used to remove the skull. A long slender tool such as a scalpel handle is used to remove the brain from the skull.

A vice with screws or protrusions is necessary to secure the head while cutting the skull. Once the animal has been humanely euthanized according to established protocols proceed as follows. Cut just above the nape of the neck, between the shoulders and the top of the head.

Secure the pig and move the years out of the way during decapitation. Use a scalpel to make incisions to separate the skin from the skull. Make an initial cut on the middle of the skull that continues to the posterior of the head.

The second transverse cut should be on the posterior of the head. The third cut also transverse will start at the posterior of this snout, and inline with the eyes to ensure easy access to the skull. Use a bone saw to make to anterior to posterior cuts lateral to the midline.

Start by lightly marking the area for the cut with the saw, and then begin sawing until you meet less resistance from the skull. Slightly bevel the saw toward the midline while cutting as this will ensure that you are cutting the thinnest part of the skull. If the cut is too close to the ear it will be difficult to remove the skull.

But if the cut is too close to the midline the opening will be too small to remove the brain. Repeat this process on the perpendicular sides to create a rectangular window. Ensure that each corner of the window is completely cut, so that part of the skull can be removed to reveal the brain beneath.

Next, use a meat hook or curved instrument to pry the rectangular skull section out of position. Start by placing the hook into one of the corners, and applying pressure to pop the skullcap off. In some cases, the meninges will remain on the brain.

And if this occurs carefully use forceps and blunt scissors, or alternatively a scalpel to remove the meninges without cutting the brain. For reference the brain should look as follows before and after the meningeal layers have been removed. Cut through the muscle and fat on the posterior of the head to prepare for exposure of the cerebellum.

To expose the cerebellum make two transverse cuts along the posterior of the skull. When making these cuts take care to not cut into the exposed brain. Once the cuts have been made place one hand on the snout, and one on the skull, and apply backwards pressure to pull the posterior portion of the skull away from the rest of the head.

As highlighted here, the cerebellum is tucked behind the remaining meningeal layers. Use the end of a blunt instrument like a scalpel handle to carefully separate the brain from the skull, taking care to avoid damaging the brain in the process. Slightly invert the head to help coax the brain out of the skull, and use a gentle scooping motion to sever the cranial nerves and remove the brain.

This process requires patience and practice to eliminate all remaining connections between the brain and cranial cavity. Inverting the pig's head can be helpful during this process. Continue using sweeping motions with the blunt instrument to free the brain.

As highlighted here, the cerebellum and brainstem may be difficult to remove as they are tucked into the skull cavity. Take care when removing the cerebellum and medulla, or brainstem. The brain should fall out on its own when it is completely detached from the skull.

The skull cavity should look as shown after removal of the brain. In preparation for brain region dissection ensure pre-labeled containers are organized, and in close proximity. Example preservation methods include snap freezing samples in liquid nitrogen, or submerging them in a preservative solution.

Once extracted from the cranial cavity the whole brain should look as follows. To remove the medulla or brainstem, make a coronal cut caudal to the cerebellum. To remove the cerebellum, make a coronal cut posterior to the cortex.

To separate the hemispheres make a midsagittal cut along the longitudinal fissure using a continuous motion to prevent damage. For the purposes of this video we will only show dissections from the right hemisphere. To remove the midbrain look for the superior, and inferior colliculi which are two bumps on the posterior portion of the brain.

Remove the desired amount of brain tissue just ventral to these regions. To remove the hippocampus position the scalpel handle on the posterior of the corpus callosum, and gently roll the hippocampus out. The entire hippocampus horn will be bean shaped.

The hippocampus should easily roll out when scooping your finger in a j-motion, starting from the posterior corpus callosum. To remove the striatum or caudate nucleus clear away the anterior portion of the corpus callosum. The caudate nucleus is the striated or striped region that's colored gray and white and located just below the corpus callosum.

With the scalpel handle angled remove this region which predominantly includes the caudate nucleus. After removing this tissue you should be able to see a striated pattern where the brain region had been located. To remove the medial prefrontal cortex dissected tissue from the frontal gyrus to the corpus callosum taking the most medial portion of that section.

The right cortex should remain after removal of the medial prefrontal cortex. To remove the thalamus, remove the bulb like structure at the center of the midsagittal surface. The thalamus has an obvious spherical shape, and it will look slightly darker than the surrounding tissue.

Upon completion of the dissection tissue samples should be preserved properly based on specific experimental outcomes. Shown here are the dissected brain regions, including the relative size and shape expected when working with young pigs. Upon mastering these techniques, the entire brain extraction, and dissection procedure will take less than 15 minutes per subject, and produce consistent results.

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Journal (Neuroscience)

Journal (Neuroscience)

Extraction and Dissection of the Domesticated Pig Brain

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