PSD-95 is a very prominent component of the postsynaptic densities of synapses. It contains three PDZ domains which play key roles in its interactions with other proteins in the synapse. It has been proposed that these PDZ domains organize glutamate receptors and their associated signaling proteins and determine the size and strength of synapses (Kim and Sheng, 2004). Recent work suggests that interaction of the NMDAR with PSD-95 via these PDZ domains can be regulated by phosphorylation (Chung et al., 2004). Anti-PSD-95 Western blot of rat hippocampal (Hipp) lysate showing specific immunolabeling of the ~95k PSD-95 protein.