Which of the following neuronal cell type is involved in the formation of blood brain barrier?

Astrocytes are of two types fibrous and protoplasmic. Both of these types send processes to blood vessels, where they induce capillaries to form the tight junctions making up the blood-brain barrier. Fibrous astrocytes, contain many intermediate filaments and are found primarily in white matter. Protoplasmic astrocytes are found in gray matter and have a granular cytoplasm. Microglia acts as scavenger cells that resemble tissue macrophages and remove debris resulting from injury, infection, and disease. Oligodendrocytes are involved in the formation of myelin in the CNS. Schwann cells are involved in the formation of myelin in the peripheral nervous system. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 4. Excitable Tissue: Nerve. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.