Ferret brain blocking

Why block the brain

We block (that is, cut down and/or remove unnecessary parts of) the brain for 3 primary reasons: 1) chunks of brain will freeze more evenly if they are as small as possible; 2) we want to reduce the amount of time we spend slicing the brain so it is focused on the parts in which we are interested, and 3) we want to present specific surfaces of the brain to the blade edge of our cutting instrument.

The planes of section:

From: Kelly JB, Rooney BJ, Phillips DP. Effects of bilateral auditory cortical lesions on gap-detection thresholds in the ferret (Mustela putorius), Behav Neurosci. 1996 Jun;110(3):542-50.

1. Blocking the parasagittal plane (instructions from Len White @ Duke)

This is generally a good choice for electrode reconstructions in areas 17/18; as Len White writes "the plane is more-or-less orthogonal to the visual cortex at all extreme convexities, except for the midline and the far lateral aspect, where I seldom sample anyway. I always want to see the track as it penetrates all the cortical layers and if your track is far caudal or superficial, you just might have difficulty interpreting a coronal or horizontal section."

How to do it:

  1. Make a mid-sagittal cut through the posterior portion of the corpus callosum

  2. Make a coronal cut at approximately the caudal tip of the suprasylvian sulcus (depending on how much extrastriate cortex you need to capture) (see "SS" above for the suprasylvian sulcus)

  3. Decide whether you want subcortical structures are not; if you do want subcortical structures, make sure cut #1 goes all the way through the diencephalon and brainstem so that you completely separate the posterior forebrain and hindbrain. If you don't have an interest in subcortical structures, then you can make one final cut (#3) that is in the horizontal plane or an oblique plane that undercuts the visual cortex. This cut can be about in the middle of the posterior hemisphere so that what you end up with is a small block that contained the posterior cortex of interest, but not all the subcortical (and far lateral/medial cortex) that you need not process for the purpose of reconstructing the electrode track.

2. Tangential plane

This is a good choice for looking at the different areas of visual cortex from above.

How to do it:

  1. Block the brain similarly to the parasagittal plane instructions.

  2. Flatten the brain for freezing, from Len White: "This is done by using two glass slides that are covered in standard Home Depot plumbers Teflon tape. The piece of brain to be flattened is then laid on one Teflon coated glass slide. It is flattened to a specified depth by compressing against the brain the second Teflon coated glass slide. The slides are separated by small (1" X 0.25") sections of glass slide that I use as spacers (these I made by scoring and breaking glass slides into 0.25" sections). Then, this glass/brain "sandwich" is held together with standard (black) paper binding clips (you know, what we typically use to hold a manuscript worth of paper together)."

  3. Freeze the block, again from Len White: "this entire sandwich is then immersed for 5 minutes in isopentane (2-methylbutane) that has been chilled on dry ice to a temperature of at least -40 degrees C. After 5 minutes, remove the binder clips and the flattened brain should pop off easily and it is then ready to freeze onto mounting medium on a microtome stage. If you have any trouble "popping" the flattened brain off the Teflon, just chill a small lab spatula in dry ice and use the cold end to gentle pop the brain off the Teflon."

3. Coronal plane (instructions will be here in the future)

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How to do it:

  1. Method1

  2. Method2

  3. Method3

4. Horizontal plane (instructions will be here in the future)

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How to do it:

  1. Method1

  2. Method2

  3. Method3