Histology

Staining of brain section for the visualization of cell structures

Method

Histology is the study of organ tissues on a cellular level and an important discipline of anatomy and pathology. For the histological examination of brain tissue, very thin sections are prepared and stained with various dyes which possess specific affinities towards the different cell structures. For example, Nissl staining with cresyl violet recognizes the nucleolus within the cell nucleus and the Nissl bodies within the cytoplasma where cellular protein synthesis takes place.

 

Cresyl violet stained brain sections. Left; healthy neurons with intact nucleolus and predominant Nissl bodies. Right: following experimental stroke deep-blue neurons (so-called „dark neurons“) indicate irreversible neuron injury.

 

 

With other dyes like hematoxylin-eosin (HE), cytoplasma and the intercellular space can be differentiated. HE staining in intact brain sections results in a deep-red nucleus and nucleolus. The cytoplasma of healthy neuron, e.g, collagen proteins and other cytoplasmatic proteins are stained pink to red. Such characteristics are lost in ischemia-affected brain cells.

 

Hematoxylin-eosin (HE) stained brain sections: Left; typical staining pattern of healthy neurons with reddish appearance of the cell body and processes. Right: Neurons following experimental stroke with irreversible cell damage. Note shrinkage of the nucleus and vacuolization of the cytoplasm, collagen fibers and other protein rich structures.

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Technical Equipment

One of the most important technical devices of histology is the light microscope. It allows the examination of very thin tissue slices at a magnification up to 1000 times.
In addition, we use transmission electron microscopy (TEM). Due to the enormous resolution of TEM up to 100.000 times, it is possible to visualize in detail the various intracellular structures of brain cells. TEM, for example, allows the differentiation between the most common forms of irreversible neuron injury, namely necrosis (cell death by structural failure of intracellular components) and apoptosis (programmed cell death under genetic control). Disturbances of vital cell functions, e.g. energy production via respiratory chain, can be identified by the appearance of mitochondria.
 
See also Microscopy

 

Electron microscopic images of a necrotic (upper left) and an apoptotic (upper right) neuron. As is clearly evident, necrosis caused a diffuse damage of the nucleus whereas apoptosis induced the fragmentation of the nuclear components suggesting the “programmed” decomposition of cell functionality. A similar fate to mitochondria, the power stations of a cell: in necrotic neurons, the mitochondrial structure is irreversibly damaged, but appears functional in apoptotic cells. This makes sense, because apoptosis needs energy for it’s own cellular destruction.

Working at an electron microscope
 

See also Microscopy