A number of interconnected cavities known as ventricles are located in the brain. A clear, watery substance called cerebrospinal fluid flows through this ventricular system. Primarily secreted by the choroid plexus, cerebrospinal fluid is absorbed into the bloodstream through arachnoid villi if the pressure in the ventricles is greater than venous pressure. The reverse, however, does not occur; blood does not flow into the ventricular system if venous pressure is higher than ventricular pressure. The function of cerebrospinal fluid is multifold. In addition to providing buffer-like protection to the brain, the substance makes the brain buoyant, which reduces its net weight, and serves as a means of metabolic waste removal and hormone transport.

A sagittal section of rat brain (presented above) was immunofluorescently labeled for the blood brain barrier with mouse anti-BBB antibodies followed by goat anti-mouse secondary antibodies conjugated to Alexa Fluor 568. In addition, glial fibrillary acidic protein (GFAP), which is strongly and specifically expressed in various astroglia and neural stem cells, was targeted in the specimen with rabbit anti-GFAP monoclonal antibodies visualized with goat anti-rabbit antibodies conjugated to Alexa Fluor 488. Nuclear DNA was counterstained with Hoechst 33342. 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.