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Postfusional regulation of cleft glutamate concentration during LTP at ‘silent synapses’

Nature Neuroscience volume 3, pages 330–336 (2000)Cite this article

Abstract

‘Silent synapses’ show responses from high-affinity NMDA receptors (NMDARs) but not low-affinity AMPA receptors (AMPARs), but gain AMPAR responses upon long-term potentiation (LTP). Using the rapidly reversible NMDAR antagonist l-AP5 to assess cleft glutamate concentration ([glu]cleft), we found that it peaked at ≪170 μM at silent neonatal synapses, but greatly increased after potentiation. Cyclothiazide (CTZ), a potentiator of AMPAR, revealed slowly rising AMPA EPSCs at silent synapses; LTP shortened their rise times. Thus, LTP at silent synapses increased rate-of-rise and peak amplitude of [glu]cleft. Release probability reported by NMDARs remained unchanged during LTP, implying that [glu]cleft increases arose from immediately presynaptic terminals. Our data suggest that changes in the dynamics of fusion-pore opening contribute to LTP.

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Figure 1: Binding and unbinding kinetics of l-AP5 on NMDA receptors in outside-out patches.
Figure 2: l-AP5 (250 μM) completely inhibited NMDAR-mediated synaptic responses at silent synapses but lost effectiveness after pairing.
Figure 3: CTZ does not alter glutamate transporter currents recorded from astrocytes in stratum radiatum of area CA1, but enhances AMPA receptor function.
Figure 4: Potentiation of receptor function by CTZ revealed small, often slowly rising AMPAR-mediated synaptic responses from silent synapses.
Figure 5: In the presence of CTZ, pairing-induced potentiation altered EPSC kinetics.

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Acknowledgements

This work was supported by the Silvio Conte-NIMH Center for Neuroscience Research at Stanford (R.W.T.), a Dean's Fellowship (S.C.) and a fellowship of the Boehringer Ingelheim Fonds (J.K.). We thank D.V. Madison and P. Mermelstein for comments on the manuscript, N. C. Harata and E. T. Kavalali for discussions and D. Wheeler and D. Profitt for technical support. We are grateful to other members of the Tsien lab for their support.

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  1. Jürgen Klingauf

    Present address: Dept. Membrane Biophysics, Max-Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany

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  1. Department of Molecular Cellular Physiology, Beckman Center, Stanford University School of Medicine, Stanford, 94305-5345, California, USA

    Sukwoo Choi, Jürgen Klingauf & Richard W. Tsien

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Correspondence to Richard W. Tsien.

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Choi, S., Klingauf, J. & Tsien, R. Postfusional regulation of cleft glutamate concentration during LTP at ‘silent synapses’. Nat Neurosci 3, 330–336 (2000). https://doi.org/10.1038/73895

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