At glutamatergic synapses of the central nervous system, AMPA-type glutamate receptors provide the major fast, excitatory currents that stimulate action potentials, while NMDA receptors conduct Ca2+ currents that induce plastic changes in synaptic transmission. The GluR1 AMPA receptor subunit trafficks to synapses in response to NMDA receptor activation, increasing AMPA receptor currents and contributing to the mechanism of long-term potentiation (LTP). The C-terminal domain of GluR1 binds the scaffolding protein, SAP97, which in turn binds the AKAP79-PKA complex (Oh et al. (2006)). NMDA receptor-induced cAMP transients activate the GluR1-associated PKA, which phosphorylates GluR1 on S845 in the subunit C-terminal domain, leading to an increase in GluR1 plasma membrane levels. The NMDA receptor also activates neuronal nitric oxide synthase (nNOS), which produces NO that activates the production of cGMP by soluble guanylate cyclase (sGC). We have shown that cGMP activates the cyclic GMP-dependent protein kinase II (cGKII), whereupon cGKII binds directly to the GuR1 CTD and phosphorylates S845 (Serulle et al (2007); please see this reference for these and other experimental details). Residues of GluR1 required for formation of this the complex flank the phosphorylation site (S845) and share sequence homologies with other kinase binding peptides. For biochemical experiments, rats were anesthetized with a lethal dose of sodium pentobarbital (120mg/kg) prior to sacrifice by decapitation. The cGKII-GluR1 complex was detected in rat brain extracts after cGMP stimulation. In dissociated embryonic hippocampal neurons (21 DIV), provision of exogenous NO or cGMP activates cGKII and the phosphorylation of S845, which increases the plasma membrane levels of GluR1 at extrasynaptic sites. Stimulation of the NMDA receptor via chemical LTP (200 micromolar glycine; chemLTP) induces these steps in dissociated hippocampal neurons, but leads to synaptic incorporation of GluR1, as reflected by increases in mini EPSC amplitude and colocalization of GluR1 with synaptic markers. These increases are sensitive to inhibitors of nNOS, sGC and cGKII, indicating that the described pathway of activation of cGKII contributes to chemLTP. In hippocampal slices, LTP induced by stimulation of the CA3/Schaffer collateral-CA1 pathway is sensitive to nNOS, sGC and cGKII inhibitors, indicating that this pathway contributes to LTP in slices. To confirm the direct involvement of cGKII in LTP, we expressed a peptide corresponding to the cGKII autoinhibitory domain fused to GFP, in hippocampus of mice following anesthetization with 20 mg/kg Avertin and prepared slices. This peptide, GFP-cGKII-i, is a very highly selective inhibitor of cGKII and does not inhibit the related cGKI or PKA or other kinases. The peptide, GFP-cGKII-i, blocked LTP induction while a control, GFP, had no effect, confirming the role of cGKII. These experiment establish a postsynaptic role for nitric oxide in the mechanism of LTP that involves the NMDA receptor-nNOS-NO-sGC-cGKII pathway. This pathway appears to complement the previously described NMDA receptor-PKA pathway. Both pathways lead to elevation of GluR1 at extrasynaptic sites and additional steps are required for synaptic insertion and function of GluR1. We will discuss the possible functional relationships of the cGMP and cAMP-dependent mechanisms of GluR1 trafficking.