Figure 1: Developmental change in dendritic morphology and PSD distribution in interneurons.

(a) Upper right panel: a hippocampal-dissociated neuron expressing PSD-95-GFP with the typical morphology of an interneuron. The GABAergic phenotype of this neuron was confirmed by anti-GAD67 immunostaining. Upper left panel: a GAD67-negative neuron extending branched dendrites in a dissociated culture. This neuron exhibits the typical morphology of hippocampal pyramidal neurons in culture. Lower right panel: RFP expression in layer II–III non-pyramidal neurons in cortical slices prepared from GAD67-GFP knockin mice. The RFP-positive non-pyramidal neuron (arrows) was also GFP-positive, indicating its GABAergic transmitter phenotype. Lower left panel: RFP-expressing pyramidal-shaped neuron (arrowheads) was GFP-negative. Scale bars, 50 μm. (b) Distribution of PSD-95-GFP puncta and dendritic protrusions in non-pyramidal neurons in a dissociated hippocampal culture at 12 and 19 DIV and a cortical slice culture at 7 and 14 DIV. Dendritic protrusions (arrows) were specifically enriched in immature dendrites and were positive for PSD-95-GFP puncta. Scale bar, 10 μm. (c) Distribution of protrusion lengths in cortical slices at 7 and 14 DIV. At both time points, 2–4 dendritic segments of 12 neurons from 4 slices were imaged and the same number of dendritic protrusions was randomly selected for quantification. (d) The mean lengths of dendritic protrusions at 7 and 14 DIV with or without PSD-95-GFP puncta (PSD+ or PSD−; n=12 neurons from 4 slices at both time points). Significant differences (one-way analysis of variance followed by Tukey–Kramer multiple comparison tests): *P<0.05; **P<0.01. All numeric data are mean±s.e.m.