The hippocampal formation is an assembly that is deeply seated within the brain in the temporal lobe. It is composed of three main structures: the hippocampus, the dentate gyrus, and the subiculum. Together these components form part of the limbic system, which plays an important role in emotions and memory formation. The limbic system was one of the first parts of the brain to evolve, and is found in fish, reptiles, and amphibians, as well as mammals. It was first described in 1878 by Paul Broca, a French physician, but its association with emotion was not outlined until the 1930s.

Glial fibrillary acidic protein and cyclic nucleotide phosphodiesterase were immunofluorescently labeled in a rat brain tissue section (illustrated above) by treating the specimen with a cocktail of rabbit anti-GFAP and mouse anti-myelin CNPase primary antibodies followed by goat anti-rabbit and anti-mouse secondary antibodies conjugated to Alexa Fluor 568 and Alexa Fluor 488, respectively. Hoechst 33342, a DNA-interactive agent, was utilized to visualize 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.