Actin Dynamics within Single Dendritic Spine Investigated by Two Photon Fluorescence Correlation Spectroscopy during Synaptic Plasticity

Abstract

Dendritic spines are the major site of excitatory synaptic input to pyramidal neurons of the hippocampus. The activity-dependent changes in the structure of spine structure have been clearly related to learning and memory processes. Actin is known to regulate cell shape and motility and in mature neurons is highly concentrated within dendritic spines (1). Indeed, the integrity as well as the changes in the spine structure have been shown to depend on the actin cytoskeleton dynamics. However, how actin filament dynamics are regulated during activity-dependent structural changes at synapses is up to now largely unexplored. Our study, by combining fluorescence microscopy (FM) with two-photon fluorescence correlation spectroscopy (2P-FCS)(2), allows us to simultaneously monitor the morphological changes and the dynamic behavior of actin filaments within single dendritic spine of neurons expressing actin-eGFP before and after chemical induction of synaptic plasticity (cLTP). Analyzing the autocorrelation curves from the 2P-FCS measurements and fitting them with two components diffusion model provide us quantitatively results, which show that: (1) actin dynamics within spines are significantly altered upon C-LTP induced morphological changes, (2) the highly dynamic actin filament exhibit a. heterogeneous structural composition, and (3) the regulations of actin filaments in single dendritic spine are precisely controlled individually instead of being a globally homogeneous function.1. Cingolani, L.A. & Goda, Y. Actin in action: the interplay between the actin cytoskeleton and synaptic efficacy. Nat Rev Neurosci 9, 344-56 (2008).2. Bacia, K., Kim, S.A. & Schwille, P. Fluorescence cross-correlation spectroscopy in living cells. Nat Methods 3, 83-9 (2006).