Reduced barrel segregation in Syngap^+/− mice. Propidium iodide staining showing neuronal distribution in flattened sections from WT (a, c) and Syngap^+/− (b, d) mice showing a clear reduction in the ratio of cells in the barrel wall to barrel hollow in Syngap^+/− mice. Cell counts revealed a significant decrease (p < 0.01) in the density of barrel wall neurons and a significant increase (p < 0.01) in the density of barrel hollow neurons in Syngap^+/− (gray bars) compared with Syngap^+/+ (black bars) animals (e). The barrel wall to hollow ratio is significantly reduced (p < 0.01) from 1.8 in WT mice to 1.2 in Syngap^+/− mice (f). The reduction in this ratio appears to be caused by a change in the distribution of cells rather than an overall change in the number of cells (f). Scale bar (in d): a, b, 250 μm; c, d, 70 μm. Error bars represent SE. het, Heterozygotes.