Proto-oncogene tyrosine-protein kinase SRC is a hydrophobic protein belonging to the SRC family kinase including nine members that is a family of non-receptor tyrosine kinases. SRC protein may exist in different forms: C-SRC and V-SRC. C-SRC is only activated under certain circumstances where it is required such as growth factor signaling, while V-SRC is a constitutively active as opposed to normal SRC (C-SRC). Thus, V-SRC is an instructive example of an oncogene protein kinase whereas C-SRC is a proto-oncogene protein kinase. Inhibition of SRC with NR2A tyrosine phosphorylation mediated by PSD-95 may contribute to the lithium-induced downregulation of NMDA receptor function and provide neuroprotection against excitotoxicity.