The pineal gland is part of the endocrine system located near the center of the mammalian brain (the gland is closer to the surface of the brains of some lower vertebrates). The first known description of the pineal gland was written by Greek physician Galen, who suggested that its name stems from its appearance, which resembles that of a pine nut. Later the seventeenth century mathematician and philosopher René Descartes famously described the pineal gland as the seat of the soul and the site where all thought originates, basing his view in large part on the belief that it was the only part of the brain that was not double. Modern studies suggest that the gland, which is an outgrowth of the posterior wall of the third ventricle, may be an evolutionary predecessor of the eye. This view is supported by the fact that in some animals it plays a regulatory role in the response to light and dark.

Immunofluorescence was utilized to label neurofilaments and astrocytes in a section of rat brain tissue (presented above). First, the specimen was fixed, permeabilized, blocked with 10-percent normal goat serum, and treated with a cocktail of mouse anti-NF-P (phosphorylated neurofilaments) and rabbit anti-GFAP (glial fibrillary acidic protein) primary antibodies. Then, to visualize the primary targets, the tissue section was treated with goat anti-mouse and anti-rabbit secondary antibodies (IgG) conjugated to Alexa Fluor 488 and Alexa Fluor 568, respectively. Finally, 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.