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Selective acquisition of AMPA receptors over postnatal development suggests a molecular basis for silent synapses


Early in postnatal development, glutamatergic synapses transmit primarily through NMDA receptors. As development progresses, synapses acquire AMPA receptor function. The molecular basis of these physiological observations is not known. Here we examined single excitatory synapses with immunogold electron–microscopic analysis of AMPA and NMDA receptors along with electrophysiological measurements. Early in postnatal development, a significant fraction of excitatory synapses had NMDA receptors and lacked AMPA receptors. As development progressed, synapses acquired AMPA receptors with little change in NMDA receptor number. Thus, synapses with NMDA receptors but no AMPA receptors can account for the electrophysiologically observed 'silent synapse'.

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Figure 1: Immunogold labeling of NMDA receptors in the CA1 stratum radiatum of the hippocampus.
Figure 4: Frequency distribution of AMPA and NMDA–R immunogold labeling, observed and fit by the low–detection model.
Figure 2: Immunogold labeling of AMPA receptors in the CA1 stratum radiatum of the hippocampus.
Figure 3: AMPA–R immunolabeling in high–sensitivity conditions.
Figure 5: Frequency distributions of AMPA–R immunogold particles with high–sensitivity immunolabeling conditions.
Figure 6: Amplitude of focally evoked miniature excitatory postsynaptic currents does not change with development.


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We thank A. Allen and N. Dawkins–Pisani for technical support, and J. Lisman and members of the Malinow and Wenthold laboratories for comments.

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Correspondence to R. Malinow.

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Supplementary Figure

Low-detection analysis of theoretical receptor frequency distributions. (a) Comparison of goodness-of-fit with Poisson or gamma distributions. Theoretical distributions were composed of 500 synapses. For half of the synapses (250), the number of receptors in each synapse was determined randomly according to a gamma distribution with mean of 30 receptors/synapse and different coefficients of variation (c.v.) as indicated. (Similar conclusions were obtained with other theoretical distributions: binomial, bimodal and uniform.) The remaining 50% of the synapses were considered to have no receptor, that is, FLR = 0.5. These distributions were randomly sampled with a detection efficiency of 0.1 (Methods). Then, the resulting distributions were fitted to a model comprised of a Poisson distribution plus a fraction of zeroes (filled bars) or a gamma distribution plus a fraction of zeroes (open bars). The goodness-of-fit was evaluated by comparing the corresponding cumulative distributions according to the Kolmogorov-Smirnov test. Significance levels obtained for each model are plotted as a function of the c.v. of the original, non-zero, distribution. Notice that the model composed of a Poisson distribution plus a fraction of zeroes fails to describe accurately (has low goodness of fit) low-detection distributions that originated from broad receptor distributions (c.v. = 0.6). Nevertheless, a good fit can be obtained even for very broad distributions (c.v. = 0.9) with a model composed of a gamma distribution plus a fraction of zeroes. (b) Effect of detection level and c.v. on the estimated fraction of synapses lacking receptors (FLR) and the goodness of fit. Two groups of theoretical distributions with the indicated c.v. were generated as described above. One group included 50% of synapses lacking receptors (FLR = 0.5, filled symbols), whereas in the other group all synapses contained receptors (FLR = 0, open symbols). Each theoretical distribution was randomly sampled with different detection efficiencies (Methods). Then, the resulting distributions were fitted to a Poisson distribution plus a fraction of zeroes (FLR). Average values of FLR are plotted as a function of the detection level, error bars representing one standard deviation. The correct values for FLR (either 0 or 0.5) are indicated with dashed lines. The goodness-of-fit was evaluated by comparing the corresponding cumulative distributions according to the Kolmogorov-Smirnov test. The significance levels (p) obtained for each distribution sampled at 0.1 detection are indicated (p = 1.00 for lower detection values). Notice how the estimated value for FLR increases above its real value (either 0 or 0.5) when detection becomes smaller and c.v. is large. This effect is more pronounced when the starting distribution has a low FLR value (0 versus 0.5). Nevertheless, the estimations were always accurate (close to the actual value of FLR) when they showed no dependence on the detection level. Therefore, a plot of FLR estimation versus detection can be used as a diagnostic method for the accuracy of the estimated values. (GIF 25 kb)

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Petralia, R., Esteban, J., Wang, Y. et al. Selective acquisition of AMPA receptors over postnatal development suggests a molecular basis for silent synapses. Nat Neurosci 2, 31–36 (1999).

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