Gephyrin cluster sizes were measured in reconstructed 2D images through cluster segmentation and by counting the pixels above the segmentation threshold forming a single cluster (Figures 1B and 5C). Alternatively, cluster areas were measured directly from superresolution localizations based on relative localization densities (ViSP software, El Beheiry and Dahan, 2013; Figure 5F). 3D PALM/STORM imaging was performed using adaptive optics (AO) to induce 2D astigmatism to the PSF of single molecules (Izeddin et al., 2012). With PSF shaping, the

axial symmetry of the signal was broken, giving access CP-673451 research buy to the z position of individual fluorophores in addition to the x/y coordinates. The experimental set-up was as described earlier, with the addition of a MicAO system (Imagine Optic) in the emission pathway. The AO system was used to correct aberrations of the PSF and to induce

a controlled degree of astigmatism (amplitude, 0.06 μm). For z axis check details calibration, 100 nm TetraSpeck beads were imaged with the help of a nanopositioning piezo stage (Nano-Z500, Mad City Labs) over a range of 1 μm, with a step size of 6 nm. Calibration curves were taken for the 593/40 nm and 684/24 emission wavelengths for each experiment. We then proceeded with the STORM and PALM acquisitions. Astigmatic PSFs were analyzed using an asymmetric 2D Gaussian fit. The center position of the fit represented the x/y coordinates of the fluorophores, whereas the difference of the length and width of the fitted PSFs (Δw = wx − wy) was mapped against the calibration curves in order to

retrieve the z positions of single fluorophores. Localized molecules were rendered as a point cloud in a 3D scatterplot for both color channels (ViSP software, El Beheiry and Dahan, 2013). Point cloud densities were calculated to illustrate the relative molecular concentrations of gephyrin and GlyRs, whereas surface rendering served to further depict the morphology and orientation of the synaptic clusters. To quantify the number of photoconverted fluorophores (Dendra2-gephyrin), 100 ms many pulses of 405 nm laser were applied every 30 s, during continuous imaging with the 561 nm laser (≤4 × 104 frames at 50 ms). Dendra2 bleaching steps were identified in the decay traces of the conversion pulses of individual gephyrin clusters to measure the mean intensity of single fluorophores above the background offset. The sum of the pulse peak intensities, ni, was then used to calculate the total number of molecules in the same cluster: N = Σni. Gephyrin clusters were photobleached with laser illumination (mRFP-gephyrin with 561 nm and the nonconverted form of Dendra2 with 491 nm; ≤104 frames at 20–50 ms).