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J Physiol Volume 586, Number 6, 1519-1527, March 15, 2008 DOI: 10.1113/jphysiol.2007.149336
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SYMPOSIUM SECTION: RELATED PAPERS

Developmental presence and disappearance of postsynaptically silent synapses on dendritic spines of rat layer 2/3 pyramidal neurons

 Giuseppe Busetto1,2, Michael J. Higley1 and Bernardo L. Sabatini1

1 Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, MA 02115, USA
2 Dipartimento di Scienze Neurologiche e della Visione, Sezione di Fisiologia, Universita' di Verona, Strada le Grazie 8, 37134 Verona, Italy

Silent synapses are synapses whose activation evokes NMDA-type glutamate receptor (NMDAR) but not AMPA-type glutamate receptor (AMPAR) mediated currents. Silent synapses are prominent early in postnatal development and are thought to play a role in the activity- and sensory-dependent refinement of neuronal circuits. The mechanisms that account for their silent nature have been controversial, and both presynaptic and postsynaptic mechanisms have been proposed. Here, we use two-photon laser uncaging of glutamate to directly activate glutamate receptors and measure AMPAR- and NMDAR-dependent currents on individual dendritic spines of rat somatosensory cortical layer 2/3 pyramidal neurons. We find that dendritic spines lacking functional surface AMPARs are commonly found before postnatal day 12 (P12) but are absent in older animals. Furthermore, AMPAR-lacking spines are contacted by release-competent presynaptic terminals. After P12, the AMPAR/NMDAR current ratio at individual spines continues to increase, consistent with continued addition of AMPARs to postsynaptic terminals. Our results confirm the existence of postsynaptically silent synapses and demonstrate that the morphology of the spine is not strongly predictive of its AMPAR content.

(Received 4 December 2007; accepted after revision 15 January 2008; first published online 17 January 2008)
Corresponding author B. L. Sabatini: Department of Neurobiology, Harvard Medical School, 220 Longwood Ave., Boston, MA 02115, USA. Email: bsabatini{at}hms.harvard.edu

This paper has online supplemental material.






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