TY - JOUR T1 - Changes in Synaptic Morphology Accompany Actin Signaling during LTP JF - The Journal of Neuroscience JO - J. Neurosci. SP - 5363 LP - 5372 DO - 10.1523/JNEUROSCI.0164-07.2007 VL - 27 IS - 20 AU - Lulu Y. Chen AU - Christopher S. Rex AU - Malcolm S. Casale AU - Christine M. Gall AU - Gary Lynch Y1 - 2007/05/16 UR - http://www.jneurosci.org/content/27/20/5363.abstract N2 - Stabilization of long-term potentiation (LTP) is commonly proposed to involve changes in synaptic morphology and reorganization of the spine cytoskeleton. Here we tested whether, as predicted from this hypothesis, induction of LTP by theta-burst stimulation activates an actin regulatory pathway and alters synapse morphology within the same dendritic spines. TBS increased severalfold the numbers of spines containing phosphorylated (p) p21-activated kinase (PAK) or its downstream target cofilin; the latter regulates actin filament assembly. The PAK/cofilin phosphoproteins were increased at 2 min but not 30 s post-TBS, peaked at 7 min, and then declined. Double immunostaining for the postsynaptic density protein PSD95 revealed that spines with high pPAK or pCofilin levels had larger synapses (+60–70%) with a more normal size frequency distribution than did neighboring spines. Based on these results and simulations of shape changes to synapse-like objects, we propose that theta stimulation markedly increases the probability that a spine will enter a state characterized by a large, ovoid synapse and that this morphology is important for expression and later stabilization of LTP. ER -