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The Journal of Neuroscience, April 15, 2002, 22(8):3108-3116
Remodeling of Hippocampal Synaptic Networks by a Brief
Anoxia-Hypoglycemia
Pascal
Jourdain*,
Irina
Nikonenko*,
Stefano
Alberi, and
Dominique
Muller
Neuropharmacology, University Medical Center, 1211 Geneva 4, Switzerland
Cerebral ischemia is a major cause of brain dysfunction. Using a
model of delayed death induced by a brief, transient oxygen and glucose
deprivation, we studied here how this affected the structural
organization of hippocampal synaptic networks. We report that brief
anoxic-hypoglycemic episodes rapidly modified the structure of
synapses. This was characterized, at the electron microscopic level, by
a transient increase in the proportion of perforated synapses, followed
after 2 hr by an increase in images of multiple synapse boutons.
These changes were considerable because 10-20% of all synapses were
affected. This structural remodeling was correlated by three kinds of
modifications observed using two-photon confocal microscopy: the growth
of filopodia, occurring shortly (5-20 min) after anoxia-hypoglycemia,
enlargements of existing spines, and formation of new spines, both seen
mainly 20-60 min after the insult. All of these structural changes
were calcium and NMDA receptor dependent and thus reproduced, to a
larger scale, those associated with synaptic plasticity. Concomitantly
and related to the severity of anoxia-hypoglycemia, we could also
observe spine loss and images of spine, dendrite, or presynaptic
terminal swellings that evolved up to membrane disruption. These
changes were also calcium dependent and reduced by NMDA receptor
antagonists. Thus, short anoxic-hypoglycemic episodes, through NMDA
receptor activation and calcium influx, resulted in a profound
structural remodeling of synaptic networks, through growth, formation,
and elimination of spines and synapses.
Key words:
ischemia; synaptic plasticity; spines; morphology; synaptogenesis; anoxic LTP
*
P.J. and I.N. contributed equally to this work.
Copyright © 2002 Society for Neuroscience 0270-6474/02/2283108-09$05.00/0
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