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<div><font face="Arial" color="#000000">Seminar on<br>
<b>Modern Optics and Spectroscopy<br>
<br>
<br>
Mriganka Sur</b>, MIT<br>
<br>
<i><b>Imaging cells, synapses and molecules in the live brain<br>
<br>
</b></i>March 27, 2007<br>
<br>
12:00 - 1:00 p.m.</font></div>
<div><font face="Arial" color="#000000">Grier Room 34-401</font><br>
<font face="Arial" color="#000000"></font></div>
<div><font face="Times New Roman" color="#000000">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<i> in
vivo</i>, 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</font><font
face="Times New Roman" color="#660066"> reveal real-time changes
in</font><font face="Times New Roman" color="#000000"> CaMKII_
autophosphorylation within spines and dendrites<i> in vivo</i>.
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<i> Arc</i>
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<i> in
vivo</i> 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.</font></div>
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