Presynaptic But Not Postsynaptic GABA Signaling at Unitary Mossy Fiber Synapses
- Carolina Cabezas1,2,3,
- Theano Irinopoulou1,2,3,
- Grégory Gauvain1,2,3, and
- Jean Christophe Poncer1,2,3
- 1INSERM, UMR 839, F75005, Paris, France,
- 2Université Pierre et Marie Curie, F75005, Paris, France, and
- 3Institut du Fer à Moulin, F75005, Paris, France
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Author contributions: C.C. and J.C.P. designed research; C.C. and T.I. performed research; G.G. contributed unpublished reagents/analytic tools; C.C., T.I., and J.C.P. analyzed data; C.C. and J.C.P. wrote the paper.
Abstract
Dentate gyrus granule cells have been suggested to corelease GABA and glutamate both in juvenile animals and under pathological conditions in adults. Although mossy fiber terminals (MFTs) are known to express glutamic acid decarboxylase (GAD) in early postnatal development, the functional role of GABA synthesis in MFTs remains controversial, and direct evidence for synaptic GABA release from MFTs is missing. Here, using GAD67-GFP transgenic mice, we show that GAD67 is expressed only in a population of immature granule cells in juvenile animals. We demonstrate that GABA can be released from these cells and modulate mossy fiber excitability through activation of GABAB autoreceptors. However, unitary postsynaptic currents generated by individual, GAD67-expressing granule cells are purely glutamatergic in all postsynaptic cell types tested. Thus GAD67 expression does not endow dentate gyrus granule cells with a full GABAergic phenotype and GABA primarily instructs the pre- rather than the postsynaptic element.
- Received October 27, 2011.
- Revision received June 30, 2012.
- Accepted July 11, 2012.
- Copyright © 2012 the authors 0270-6474/12/3211835-06$15.00/0
