Ng lowers LTP threshold in CA1 hippocampal pyramidal neurons.

<p>(<b>A</b>) LTP was induced by pairing 3-Hz presynaptic stimulation (300 pulses) with −20 mV postsynaptic depolarization (indicated with an arrow) in uninfected neurons (open squares, <i>n</i> = 8) and neurons expressing GFP-Ng (black squares, <i>n</i> = 7). Inserts: sample traces of evoked AMPAR-mediated synaptic responses recorded at −60 mV before pairing (gray line) and 20 min after pairing (black line) from control or infected cells as indicated. Scale bars: 20 pA, 20 ms. (<b>B</b>) Normalized average steady-state AMPAR-mediated responses in paired (LTP pathway) and unpaired (control pathways) for uninfected neurons and those expressing GFP-Ng. Pairing significantly increased AMPAR-mediated responses in both groups. Neurons expressing GFP-Ng showed higher level of LTP than control neurons (<i>p</i><0.05).</p

Ng targets and relocates dendritic CaM closer to plasma membrane of the postsynaptic compartment.

<p>(<b>A</b>) Representative images of immunogold-EM for CaM in control and Ng-overexpressing neurons. Scale bar, 100 nm. (<b>B</b>) Frequency histograms of CaM (n = 214) in control neurons and Ng-inf (n = 319) neurons. Normalized radial distance was measured the same way as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041275#pone-0041275-g001" target="_blank">Figure 1</a>. Note the increased fraction of CaM at 0.1 interval in Ng-expressed condition. (<b>C</b>) Cumulative probabilities of normalized radial distance of CaM particles located within 0.2 of the normalized radial distance, where Ng was found to be concentrated in our previous study. Ng targeted CaM closer to the plasma membrane (<i>p</i> = 0.05). (<b>D</b>) Ng did not change the global distribution of CaM in the spine (PSD: postsynaptic density; E: extrasynaptic membrane; I: intraspine). The <i>p-</i>value for comparing cumulative distribution was calculated using Kolmogorov-Smirnov test. The <i>p-</i>value for comparing global CaM distribution in different sub-compartments was calculated using Chi-squared test.</p

CaM is not randomly distributed within the synapse.

<p>(<b>A</b>) Representative images of immunogold-EM for endogenous CaM in dendritic spines of CA1 hippocampal neurons. The postsynaptic compartment (<i>s</i>) is recognized by the appearance of the prominent postsynaptic density (black arrowhead) and well-defined plasma membrane. <i>t</i>, presynaptic terminal. Arrows indicate anti-CaM immunogold particles. Scale bar, 100 nm. (<b>B</b>) Cumulative probabilities of normalized radial distance. The distance of each gold particle from the plasma membrane (within the spine) was normalized (x axis) to the corresponding radius of the spine measured through that particle. The distribution of CaM within the spine is significantly different from a theoretical random distribution (n = 214, <i>p</i><0.001).</p