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SUMMARY:Structural synaptic changes in cortical adaptive plasticity - Anth
 ony Holtmaat	  Département des Neurosciences fondamentales CMU\, 1 Rue Mi
 chel-Servet 1211 GENEVE 4
DTSTART:20090401T080000Z
DTEND:20090401T084500Z
UID:TALK17646@talks.cam.ac.uk
CONTACT:Anna Di Pietro
DESCRIPTION:To understand the synaptic\, cellular and network mechanisms o
 f circuit plasticity in relation to learning and memory\, neurons need to 
 be studied in the intact brain over extended periods of time. I will descr
 ibe a procedure to image neurons and their synapses in the mouse neocortex
 \, using long term high-resolution two-photon laser scanning microscopy th
 rough a chronic cranial window\, followed by the ultrastructural reconstru
 ction of imaged neurons\, using serial section EM. Such studies have shown
  that proxies for synapses\, such as dendritic spines and axonal boutons\,
  are dynamic structures\, even in the adult brain. Whereas most spines are
  persistent for months\, a small subset of dendritic spines can appear and
  disappear over days. The generation and loss of persistent spines in the 
 somatosensory barrel cortex is enhanced after trimming of every other whis
 ker (a paradigm known to induce adaptive functional changes in barrel cort
 ex). Most new persistent spines are added on a subclass of L5B neurons loc
 ated at the barrel interfaces\, where adaptive functional changes are larg
 est. Further evidence for a correlation between functional plasticity and 
 new persistent spine formation is provided by studies in αCaMKII-T286A au
 tophosphorylation mutants. Whisker trimming in these mice fails to induce 
 adaptive receptive field changes and also fails to enhance the addition of
  new persistent spines. Ultrastructural analysis of new pines and their as
 sociated boutons shows that new spines often lack synapses shortly after t
 hey appear\, whereas spines that persist for more than a few days always h
 ave synapses. New synapses are predominantly found on large multisynpase b
 outons\, suggesting that spine growth is followed by synapse formation\, p
 referentially on existing boutons. Altogether these data indicate that nov
 el sensory experience drives the stabilization of new spines and promotes 
 the formation of new synapses on subclasses of cortical neurons. These syn
 aptic changes could underlie experience-dependent functional remodelling o
 f specific neocortical circuits.
LOCATION:Cripps Court\, Magdalene College
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