CaMKII and PSD-95 colocalization studies The spatial and temporal localization of signaling molecules are crucial for the form and endurance of synaptic plasticity [1] [2] [3] . Though the postsynaptic density acts as an integrated macromolecular machine, the spatial and temporal dynamics of individual PSD proteins are integral to the nature and strength of a postsynaptic response to impinging signals. Ca 2+ / calmodulin-dependent protein kinase II (CaMKII) is a major component of the PSD and

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... a crucial regulator of neuronal and behavioral plasticity [4-8]. Ca 2+ signaling at the postsynaptic membrane occurs upon stimulation of the NMDA receptor and the subsequent activation of CaMKII. Consequently, the location of CaMKII relative to activated NMDA receptors is crucial to its subsequent signal transduction. Numerous proteins of the PSD are known to bind and interact with CaMKII [9]. However, strategic interactions that specifically position CaMKII for optimal activation by Ca 2+ influx and the subsequent phosphorylation of proteins important for LTP are particularly crucial. The binding of CaMKII with NR2A and NR2B subunits of the NMDA receptor is one such strategic interaction [1, [10] [11] [12] [13] . We have hypothesized that Densin is another [14, 15] . Both the NR1 and NR2 subunits are required to form functional NMDA receptors at the synapse [16] [17] [18] . Deletion of synaptic NMDA receptors can thus be achieved by deletion of the c-terminal tails of the NR2 subunits [19, 20] or by deletion of the NR1 subunit [21] . I have shown that in NR2A x NR2B double tailless mutant animals,