Abstract: Since the identification of Thy-1 (CD-90) in 1964 by Reif and Allen, the precise functions of this glycosyl phosphatidylinositol-anchored surface protein within the central nervous system have been difficult to characterize. Thy-1 is a 110-amino acid cellular adhesion molecule that plays a role in cell-cell communication by interacting with other  cellular adhesion molecules, including integrins (Leyton et al., 2001). While found on a diverse array of cells within the body, Thy-1 is present on the surface of almost every neuron in the brain (Morris and Grosveld, 1989). In Reif and Allen’s 1964 study, they found that Thy-1 levels increased in the brain nearly 100-fold during post-natal development (Reif and Allen, 1964). Later, Xue et al. (1990) elaborated on this discovery and found that Thy-1 protein levels increased following the cessation of axonal and dendritic growth in the olfactory system. It was subsequently shown that neuronal Thy-1 inhibited neurite outgrowth on astrocytes in vitro, but not Schwann cells or embryonic glia, and anti-Thy-1 antibody is able to counteract the inhibition (Tiveron et al., 1992). Moreover, Thy-1 is localized to the ends of axon terminals, which may account for the ability of Thy-1 to block axon growth (Herrera-Molina et al., 2012).