Silent synapses

NMDA and AMPA receptors are spread across the post-synaptic density (PSD), whereas metabotropic glutamate receptors (except mGluR7) are located along the periphery of the PSD (Fig. 15-2). NMDA receptors appear to be present at most or all glutamatergic synapses whereas the content of AMPA receptors is variable - from zero to about 50 receptors per PSD [33]. Some synapses are silent , meaning that activation of them does not elicit AMPA receptor currents when the plasma membrane is hyperpolarized and Mg2+ blocks NMDA receptors. Such silent synapses contain only NMDA receptors. However, AMPA receptors are recruited from the cytosol to the PSD to activate such silent synapses in LTP. 

Lerma J, Morales M, Vicente MA, Herreras O (1997) Glutamate receptors of the kainate type and synaptic transmission. Trends Neurosci 20 9-12 Liao DZ, Hessler NA, Malinow R (1995) Activation of postsynaptically silent synapses during pairing-induced LTP in CAl region of hippocampal slice. Nature 375 400-404... 

Another possible postsynaptic mechanism could involve a rapid switching of silent synapses to a functional state (e.g., by a translocation of AMPA receptors) (36,37). The resulting increase in spEPSC frequency would then be the... 

Liao D, Hessler NA, Malinow R (1995) Activation of postsynaptically silent synapses during pairing-induced LTP in CAl region of hippocampal slice. Nature 375 400-404. 

Petralia RS, Esteban JA, Wang YX, Partridge JG, Zhao HM, Wenthold RJ, Malinow R (1999) Selective acquisition of AMPA receptors over postnatal development suggests a molecular basis for silent synapses. Nat Neurosci 2 31-36. 

In addition, some synapses in the hippocampus and other regions may have NMDA receptors but lack AMPA receptors, while most synapses on the same neurons have both NMDA and AMPA receptors. The former synapses are called silent synapses and can acquire AMPA receptors following adequate activation (e.g., review by Malenka and Nicoll, 1997 Nusser et al., 1998 Petralia et al., 1999a Shi et al., 1999) (see Section 3.1.2). 

Malenka RC, Nicoll RA (1997) Silent synapses speak up. Neuron I9 4Ti-416. 

Liao D, Zhang X, O Brien R, Ehlers MD, Huganir RL (1999) Regulation of morphological postsynaptic silent synapses in developing hippocampal neurons. Nat Neurosci 2 37-43. 

Isaac JTR, Crair MC, Nicoll RA, Malenka RC (1997) Silent synapses during development of thalamocortical inputs. Neuron 18 269-280. 

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