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ROLES OF THE NO - cGMP - PKG PATHWAY AND RHO GTPASES IN THE INCREASE IN SYNAPTOPHYSIN PUNCTA DURING LONG - LASTING POTENTIATION


, : ROLES OF THE NO - cGMP - PKG PATHWAY AND RHO GTPASES IN THE INCREASE IN SYNAPTOPHYSIN PUNCTA DURING LONG - LASTING POTENTIATION. Society for Neuroscience Abstract Viewer & Itinerary Planner : Abstract No 149 17

Brief application of glutamate (200 uM in 0 Mg++ saline for 1 min) to cultured hippocampal neurons produces a rapid and long-lasting increase in the number of synaptophysin puncta that is blocked by D-APV, suggesting the involvement of retrograde signaling (Antonova et al., 2001). Because the NO-cGMP-PKG pathway is thought to contribute to retrograde signaling during synaptic potentiation in culture (Hawkins et al., 1998; Wang and Hawkins, 2001), we investigated the role of that pathway. The increase in synaptophysin puncta was blocked by either the NO synthase inhibitor N-nitro-L-arginine (100 uM for 1 hr) or the PKG inhibitor Rp-8-Br-cGMPS (100 uM for 1 hr), and was mimicked by NO (20 nM for 1 min) or the membrane permeable analog 8-Br-cGMP (500 uM for 5 min). Moreover, glutamate produced increases in colocalization of synaptophysin with cGMP, PKG1, and phospho-VASP (a substrate of PKG), further supporting a role for the NO-cGMP-PKG pathway. Because the increase in synaptophysin puncta by glutamate is blocked by an inhibitor of actin polymerization (Antonova et al., 2001), we also investigated the role of Rho GTPases, which regulate actin. A general inhibitor of Rho GTPases, toxin B (5 ng/ml for 2 hrs) blocked the increase in synaptophysin puncta by glutamate but in preliminary experiments it did not block the increase by 8-Br-cGMP, suggesting that Rho GTPases are involved but may not act downstream of cGMP. These results are consistent with results on mEPSC frequency (Wang and Hawkins, 2002), and suggest that both the NO-cGMP-PKG pathway and Rho GTPases play important roles in the increase in synaptophysin puncta.

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