NO regulates spine and synapse formation under control conditions. (A) 3D reconstruction of a dendritic segment from a control pyramidal neuron treated for 2 d with 200 μM L-NAME. Note the decrease in spine density. (B) Quantitative analysis of the spine density measured in control (ctrl; n = 8 cells; total length = 134 μm; 145 spines) and L-NAME–treated slice cultures (n = 8 cells; total length = 99 μm; 59 spines; *, P < 0.05). (C) Same as in B but for the synapse density measured by analyzing all PSDs per micrometer of length on dendritic segments of control and L-NAME–treated slice cultures (n = 8 cells; *, P < 0.05). Data are mean ± SEM (error bars). Bar, 1 μm.