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The Journal of Neuroscience, May 17, 2006, 26(20):5370-5382; doi:10.1523/JNEUROSCI.5255-05.2006
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Cellular/Molecular
GABAergic Network Activation of Glial Cells Underlies Hippocampal Heterosynaptic Depression
Alexandre Serrano,
Nasser Haddjeri,
Jean-Claude Lacaille, and
Richard Robitaille
Centre de Recherche en Sciences Neurologiques et Département de Physiologie, Université de Montréal, Succursale Centre-Ville, Montréal, Québec, Canada H3C 3J7
Correspondence should be addressed to Dr. Richard Robitaille, Département de Physiologie, Faculté de Médecine, Université de Montréal, C.P. 6128 Succursale Centre-ville, Montréal, Québec, Canada H3C 3J7. Email: richard.robitaille{at}umontreal.ca
Tetanus-induced heterosynaptic depression in the hippocampus is a key cellular mechanism in neural networks implicated in learning and memory. A growing body of evidence indicates that glial cells are important modulators of synaptic functions, but very little is known about their role in heterosynaptic plasticity. We examined the role of glial cells in heterosynaptic depression, knowing that tetanization and NMDA application caused depression of synaptic field responses (fEPSPs) and induced Ca2+ rise in glial cells. Here we report that chelating Ca2+ in a glial syncytium interfered with heterosynaptic depression and NMDA-induced fEPSP depression, suggesting that Ca2+ activation of glial cells is necessary for heterosynaptic depression. The NMDA-induced Ca2+ rise in glial cells was sensitive to tetrodotoxin and reduced by the GABAB antagonist CGP55845. Both heterosynaptic depression and simultaneous Ca2+ activation of glial cells were prevented by CGP55845, suggesting an involvement of the GABAergic network in glial activation and heterosynaptic depression. Also, the GABAB agonist baclofen caused both a Ca2+ rise in glial cells and fEPSP depression. Heterosynaptic depression, as well as NMDA- and baclofen-induced depression, were attenuated by an A1 antagonist, cyclopentyl-theophylline, whereas glial cell activation was not, indicating a role of adenosine downstream of glial activation. Finally, heterosynaptic depression requires ATP degradation because ectonucleotidase inhibitors reduced this plasticity. Our work indicates that Ca2+ activation of glial cells is necessary for heterosynaptic depression, which involves the sequential interaction of Schaffer collaterals, the GABAergic network, and glia. Thus, glial and neuronal networks are functionally associated during the genesis of heterosynaptic plasticity at mammalian central excitatory synapses.
Key words: neuronglia interactions; heterosynaptic depression; GABA; GABAB receptors; NMDA; adenosine
Received June 30, 2005;
revised April 10, 2006;
accepted April 11, 2006.
Correspondence should be addressed to Dr. Richard Robitaille, Département de Physiologie, Faculté de Médecine, Université de Montréal, C.P. 6128 Succursale Centre-ville, Montréal, Québec, Canada H3C 3J7. Email: richard.robitaille{at}umontreal.ca
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