Histology and slicing

Good morning and Happy MLK Day! Unfortunately I did not get to sleep in this morning like many people because I am at work today. Last friday I learned slicing techniques to prepare slides of specimens (rats' brains, specifically the Nucleus Accumbens) for histology. I will be doing more of that today, and so I decided that I would write my post about that. Here are some pictures to get started. 

I'm going to use wikipedia to help me to describe some of the processes here, and since I am giving a broad overview, and not writing a paper, I think that should suffice for now.

We fix tissues via perfusion (I'll tell you more about that another day.) According to wikipedia,  

Perfusion: Fixation via bloodflow. The fixative is injected into the heart with the injection volume matching cardiac output. The fixative spreads through the entire body, and the tissue doesn't die until it is fixed. This has the advantage of preserving perfect morphology, but the disadvantages that the subject dies and the cost is high (because of the volume of fixative needed for larger organisms)

After the tissues have been placed in a formalin solution for an amount of time, and you are ready to actually section the brain, we use a vibratome which is a microtome sectioning machine to cut sections of the brain and place them onto a slide to examine them under the microscope. Here is a machine like the one we use.


Here's what wikipedia has to say about microtome sectioning machines: 

A microtome (from the Greek mikros, meaning "small", and temnein, meaning "to cut") is a sectioning instrument that allows for the cutting of extremely thin slices of material, known as sections. Microtomes are an important device inmicroscopy preparation, allowing for the preparation of samples for observation under transmitted light or electronradiation. Microtomes use steel, glass, or diamond blades depending upon the specimen being sliced and the desired thickness of the sections being cut. Steel blades are used to prepare sections of animal or plant tissues for light microscopy histology. Glass knives are used to slice sections for light microscopy and to slice very thin sections forelectron microscopy. Industrial grade diamond knives are used to slice hard materials such as bone, teeth and plant matter for both light microscopy and for electron microscopy. Gem quality diamond knives are used for slicing thin sections for electron microscopy.

Microtomy is a method for the preparation of thin sections for materials such as bones, minerals and teeth, and an alternative to electropolishing and ion milling. Microtome sections can be made thin enough to section a human hair across its breadth, with section thickness between 0.05 and 100 µm.

After placing the rat brain on a metal piece to place in the formalin mixture, you are ready to turn on the machine and get thin sections of the brain. An ideal slice on this machine is 100 microns, which is is 1/10 of a millimeter. It takes you a while to be able to do this, and so when I was learning I started by sectioning thicker slices. As I got progressively better at it, I was able to do the 100 micron slice without having the specimen tear. While there is a technique to learn before you are able to be good at it, it is not very hard to do quickly and correctly once you master the skill.

If you ignore the part about freezing, then this is a good video to watch to learn more, in case my explanation is unclear.

Have a great Monday!