Assessment of Blood-brain Barrier Permeability by Intravenous Infusion of FITC-labeled Albumin in a Mouse Model of Neurodegenerative Disease

The overall goal of this procedure is to assess the brain-blood barrier permeability in a mouse model of degenerative disorder by intrajugular injection of FITC-labeled albumin. This method can help answer the key questions in the study of brain homeostasis. It can be particularly useful to investigate any possible link between blood-brain barrier damage and neurodegeneration.

The main advantage of this technique is that it is fast and easy to perform and can be applied, also, to larger animal models and to other neuro-pathological settings. Demonstrating the surgical procedure of intrajugular injection of FITC-albumen will be Luca Capocci. Salvatore Castaldo will demonstrate the histological sectioning of a brains.

And Enrico Amico will demonstrate the procedure for micrograph acquisition. Begin by preparing FITC-albumen solution by dissolving FITC-albumen powder in phosphate buffered saline at 10 milligrams per milliliter. Lay out the autoclaved surgical instruments.

Clean the surgical bench with 70%ethanol and place a surgical sterile disposable drape. Then set up the operating stereo microscope. After anesthetizing the mouse with an intraperitoneal injection of an appropriate does of ketamine xylazine solution, monitor animal sedation by giving a gentle toe pinch and ensuring the absence of the withdrawal reflex.

Place the anesthetized mouse in a face-up supine position and fix the four legs and the tail on the surgical workbench with adhesive tape. After the mouse is secured, carefully shave the appropriate surgical margin on the neck and disinfect it with povidone-iodine solution in 70%ethanol. Dry the exposed shaved surface with cotton swabs.

Next, after making a 1.5 centimeter long longitudinal incision in the mid-clavicular line, starting midway on the thorax and extending to just below the neck, carefully stretch apart connective tissue with forceps under microscopic observation to expose the external jugular vein. Ensure sufficient space on the right and on the left of the jugular vein to facilitate the insertion of the 30 and a half gauge needle for the infusion of the FITC-albumen solution. Inject 100 microliters of 10 milligrams per milliliter FITC-albumen in the right jugular vein over three minutes.

This is the most critical step during the procedure. Incorrect insertion of the needle can cause irreversible damage of the vein wall and compromise the entire experiment. Fifteen minutes after injection, after euthanizing the mouse by decapitation, rapidly remove the brain from the skull and immerse it in a volume of pre-chilled isopentane, that is ten times that of the brain, for 15 minutes.

Move the isopentane frozen brain into a pre-chilled tube and store it in a 80 degrees Celsius freezer until histological sectioning. Embed frozen brain in optimal cutting temperature compound prior to cryostat sectioning. Cut the brain into 20 micron thick sections with a cryostat and mount them onto microscope glass slides.

Perform the FITC-albumin laminin co-staining by using a specific anti-laminin antibody, as previously described. Cover slip slides with mounting medium containing DAPI and leave the slide to dry overnight at four degrees Celsius in the dark. The next day, observe the fluorescence staining under a fluorescence microscope at 20 times magnification, equipped with both FITC and Cy3 filters.

Turn on the fluorescence lamp about 10 minutes before use. Turn on the microscope, the connected computer and the digital camera. Run the image analysis software.

Use the appropriate objective for optimal signal collection and spatial resolution and select appropriate filters. Acquire a minimum of four, 24-bit color exposures per brain slice. Analyze the fluorescence intensity for each single channel, using the freely available ImageJ software.

The following representative fluorescence micrographs of brain cryosections show differential distribution of green fluorescent albumin under both physiological and pathological conditions. The red staining, shown here, represents the vascular marker, laminin, under physiological conditions and under conditions of blood-brain barrier compromise. These merged images show co-localization of green fluorescent albumin and laminin, along with DAPI staining of nuclei in the intact and compromised blood-brain barriers.

This graph displays the quantification of the green fluorescence emitted by FITC-albumin, which is reported as the green fluorescence intensity in both healthy and compromised conditions. While attempting this procedure, it's important to remember to freshly prepare each single reagent and predispose the surgical bench. After watching this video, you may have a good understanding of how to assess the permeability of the blood-brain barrier in an animal model of neurodegenerative disease, by measuring the affixation of the green fluorescent albumin into brain parenchyma.