Abstract
Dendritic spines are micron-sized protrusions that harbor the majority of excitatory synapses in the central nervous system. The head of the spine is connected to the dendritic shaft by a 50–400 nm thin membrane tube, called the spine neck, which has been hypothesized to confine biochemical and electric signals within the spine compartment. Such compartmentalization could minimize interspinal crosstalk and thereby support spine-specific synapse plasticity. However, to what extent compartmentalization is governed by spine morphology, and in particular the diameter of the spine neck, has remained unresolved. Here, we review recent advances in tool development – both experimental and theoretical – that facilitate studying the role of the spine neck in compartmentalization. Special emphasis is given to recent advances in microscopy methods and quantitative modeling applications as we discuss compartmentalization of biochemical signals, membrane receptors and electrical signals in spines. Multidisciplinary approaches should help to answer how dendritic spine architecture affects the cellular and molecular processes required for synapse maintenance and modulation.
Highlights
DENDRITIC SPINES The dendritic compartment of a neuron receives input from thousands of upstream neurons via synapses
SPINE MORPHOLOGY AS COMPARTMENTALIZATION MECHANISM We have summarized the evidence for spine-based compartmentalization on three levels: biochemical signaling, membranebound receptor dynamics and electrical signaling
Mushroom shaped spines were found to retain AMPA receptors in the vicinity of the synapse for an increased period of time (Ashby et al, 2006; Ehlers et al, 2007; Opazo and Choquet, 2011, see Figure 3A). These observations have been rationalized by several modeling studies, which showed that the typical mushroom-like morphology of dendritic spines strongly alters the lateral diffusion of AMPA receptors, demonstrating a pronounced suppression of the receptor exit rate out of spines with decreasing neck radius as well as increasing neck length (Holcman and Schuss, 2011; Kusters et al, 2013; Kusters and Storm, 2014)
Summary
DENDRITIC SPINES The dendritic compartment of a neuron receives input from thousands of upstream neurons via synapses. The diffusional coupling of CaMKII with the dendrite was significantly slower, in the range of several minutes (Lee et al, 2009), and additional modeling studies have shown that the effective CaMKII diffusion constant depends heavily on binding to synaptic scaffolds and the actin cytoskeleton in spine necks (Byrne et al, 2011).
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