Glutamate receptors regulate actin-based plasticity in dendritic spines

Dendritic spines at excitatory synapses undergo rapid, actin-dependent shap e changes which may contribute to plasticity in brain circuits. Here we sho w that actin dynamics in spines are potently inhibited by activation of eit her AMPA or NMDA subtype glutamate receptors. Activation of either receptor type inhibited actin-based protrusive activity from the spine head. This b lockade of motility caused spines to round up so that spine morphology beca me both more stable and more regular. Inhibition of spine motility by AMPA receptors was dependent on postsynaptic membrane depolarization and influx of Ca2+ through voltage-activated channels. In combination with previous st udies, our results suggest a two-step process in which spines initially for med in response to NMDA receptor activation are subsequently stabilized by AMPA receptors.