[MOS] March 27, 2007

[Zina Queen]

Seminar on
Modern Optics and Spectroscopy


Mriganka Sur, MIT

Imaging cells, synapses and molecules in the live brain

March 27, 2007

12:00 - 1:00 p.m.
Grier Room 34-401

Neuroscience is being transformed by optical tools, particularly 
those that combine high resolution cellular imaging with novel 
reporters of cell structure and function. Recent studies from our 
laboratory demonstrate the power of these approaches for revealing 
mechanisms of function and plasticity in neurons and networks of the 
mammalian cerebral cortex. Cortical neurons receive excitatory 
synapses at trillions of tiny protrusions, termed spines. Spines 
change their structure dynamically. By combining structural 
two-photon imaging of GFP-labeled neurons and functional intrinsic 
signal optical imaging in visual cortex in vivo, we have shown that 
functional plasticity in cortical networks is anchored by structural 
changes in precisely located spines. To examine the role of CaMKII_ 
in mediating such plasticity, we have used a virally packaged CFP/YFP 
FRET probe to reveal real-time changes in CaMKII_ autophosphorylation 
within spines and dendrites in vivo. Synaptic plasticity is known to 
require precise spatial and temporal expression in cells of molecules 
such as Arc. By using mice genetically engineered to express GFP in 
response to Arc activation, we have demonstrated the physiological 
role of Arc in network development and cortical information 
processing.  Finally, using functional two-photon imaging of calcium 
signals in vivo combined with cell-specific markers, we have revealed 
the function of astrocytes - which constitute half of all cortical 
cells but whose function was hitherto unknown. Individual neurons and 
their adjacent astrocytes in visual cortex have matched spatial 
receptive fields and similarly sharp tuning to stimulus features. 
Astrocytes mediate structural plasticity at spines as well as a key 
component of the brain's hemodynamic response, which couples neuronal 
activity to vascular signals critical for noninvasive brain imaging.
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