The actin cytoskeleton is involved in key neuronal functions such as synaptic transmission and morphogenesis. However, the roles and regulation of actin cytoskeleton in memory formation remain to be clarified. In this study we unveil the mechanism whereby actin cytoskeleton is regulated to form memory by exploring the roles of the major actin- regulatory proteins Arp2/3, VASP and formins in long-term memory formation. Inhibition of Arp2/3, involved in actin filaments branching and neuronal morphogenesis, in lateral amygdala (LA) with the specific inhibitor CK-666 during fear conditioning impaired long-term, but not short-term, fear memory. The inactive isomer CK-689 had no effect on memory formation. We observed that Arp2/3 is co-localized with the actin-regulatory protein profilin in LA neurons of fear conditioned rats. VASP binding to profilin is needed for profilin-mediated stabilization of actin cytoskeleton and dendritic spine morphology. Microinjection of poly-proline peptide (G(GP5)3) into LA, to interfere with VASP binding to profilin, impaired long-term but not short-term fear memory formation. Control peptide (G(GA5)3) had no effect. Inhibiting formins, that regulate linear actin elongation, in LA during fear conditioning by microinjecting the formins specific inhibitor SMIFH2 into LA had no effect on long-term fear memory formation. We conclude that Arp2/3 and VASP, through its profilin binding site, are essential for the formation of LTM in LA and propose a model whereby these proteins subserve cellular events leading to memory consolidation.
Significance Statement: The actin cytoskeleton is involved in synaptic transmission and morphogenesis. However, little is known about how learning may regulate actin cytoskeleton and the putative mechanistic participation of actin cytoskeleton in memory formation. Here we show that Arp2/3, required for actin filaments branching and neuronal morphogenesis, and VASP profilin-binding domain, needed for stabilization of actin cytoskeleton and neuronal morphology, are essential for the formation of long- but not short-term fear memory in lateral amygdala. The current results provide critical evidence of how memory can be formed through controlling actin cytoskeleton structure and dynamics. Moreover, Arp2/3 and VASP profilin-binding domain may serve as targets for pharmacological treatment of fear and anxiety disorders.
The authors declare no competing financial interests.