The brain is often considered to be composed of two basic types of material: gray matter and white matter. Gray matter chiefly consists of cell bodies and dendrites, whereas white matter is primarily made up of myelinated axons. Thus, the white matter of the brain can be considered responsible for the transmission of signals, while gray matter mainly functions in the production of those signals. White matter is most prevalent deep within the brain, though regions of gray matter known as nuclei are scattered throughout the white matter. Gray matter also is found along the outer portions of the organ.

In order to visualize components of the blood brain barrier and astroglia in a rat brain sagittal tissue section (shown above), the specimen was immunofluorescently labeled with mouse anti-BBB and rabbit anti-GFAP primary antibodies followed by goat anti-mouse and anti-rabbit secondary antibodies conjugated to Alexa Fluor 568 and Alexa Fluor 488, respectively. Hoechst 33342 was employed to counterstain cell nuclei. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.