Synaptic activity and F-actin coordinately regulate CaMKII alpha localization to dendritic postsynaptic sites in developing hippocampal slices

We examined the timing and mechanisms of CaMKII alpha recruitment to nascent synapses of developing rat hippocampal pyramidal neurons in slice culture. Time-lapse confocal imaging shows that GFP-CaMKII alpha in transfected neurons accumulates in spines as they are forming, and loss of CaMKII alpha coincides with spine destabilization. Immunolabeling shows that endogenous CaMKII alpha is concentrated at postsynaptic sites in spines under ambient slice culture conditions, and this is not disrupted by short-term (3 h) synaptic activity blockade or Latrunculin-induced F-actin depolymerization. However, the combination of activity blockade and F-actin depolymerization significantly reduces synaptic CaMKII alpha. Conversely, postsynaptic activation induces synaptic recruitment of CaMKII alpha even in the presence of F-actin depolymerizing drugs. Thus, synaptic-activity-dependent mechanisms and (synaptic activity-independent) F-actin-based mechanisms are individually sufficient and act in parallel to localize CaMKII alpha to the dendritic spine compartment. Moreover, the timing of CaMKII alpha recruitment to developing spines suggests a role for CaMKII alpha in spine assembly and maintenance. (C) 2005 Elsevier Inc. All rights reserved.