Dendritic spine viscoelasticity and soft-glassy nature: balancing dynamic remodeling with structural stability
Benjamin A. Smith 1, Hugo Roy 2, Paul De Koninck 2, Peter Grütter 3 and Yves De Koninck 2*
1 University of British Columbia
2 Centre de recherche Université Laval Robert-Giffard
3 McGill University
* To whom correspondence should be addressed. E-mail: yves.dekoninck{at}crulrg.ulaval.ca.
Submitted on July 3, 2006
Revised on August 24, 2006
Accepted on 27 October 2006
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Abstract |
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Neuronal dendritic spines are a key component of brain circuitry, implicated in many mechanisms for plasticity and long-term stability of synaptic communication. They can undergo rapid actin-based activity-dependent shape fluctuations, an intriguing biophysical property which is believed to alter synaptic transmission. Yet, due to their small size (~1µm or less) and metastable behavior, spines are inaccessible to most physical measurement techniques. Here we employ atomic force microscopy elasticity mapping and novel dynamic indentation methods to probe the biomechanics of dendritic spines in living neurons. We find that spines exhibit i) a wide range of rigidities, correlated with morphological characteristics, axonal association, and glutamatergic stimulation, ii) a uniquely large viscosity, 4-5 times that of other cell types, consistent with a high density of solubilized proteins, and iii) weak power-law rheology, described by the soft-glassy model for cellular mechanics. Our findings provide a new perspective on spine functionality and identify key mechanical properties that govern the ability of spines to rapidly remodel and regulate internal protein trafficking yet also maintain structural stability.
Key Words:
actin, atomic force microscopy, diffusion, glutamate, rheology, synapse
