Abstract

Excitatory synaptic transmission and plasticity are critically modulated by N-methyl-D-aspartate receptors (NMDARs). Activation of NMDARs elevates intracellular Ca²⁺ affecting several downstream signaling pathways that involve Ca²⁺/calmodulin-dependent protein kinase II (CaMKII). Importantly, NMDAR activation triggers CaMKII translocation to synaptic sites. NMDAR activation failed to induce Ca²⁺ responses in hippocampal neurons lacking the mandatory NMDAR subunit NR1, and no EGFP-CaMKII translocation was observed. In cells solely expressing Ca²⁺-impermeable NMDARs containing NR1^N598R-mutant subunits, prolonged NMDA application elevated internal Ca²⁺ to the same degree as in wild-type controls, yet failed to translocate CaMKII. Brief local NMDA application evoked smaller Ca²⁺ transients in dendritic spines of mutant compared to wild-type cells. CaMKII mutants that increase binding to synaptic sites, namely CaMKII-T286D and CaMKII-TT305/306VA, rescued the translocation in NR1^N598R cells in a glutamate receptor-subtype-specific manner. We conclude that CaMKII translocation requires Ca²⁺ entry directly through NMDARs, rather than other Ca²⁺ sources activated by NMDARs. Together with the requirement for activated, possibly ligand-bound, NMDARs as CaMKII binding partners, this suggests that synaptic CaMKII accumulation is an input-specific signaling event.