Klc1−/− brains display enlarged caliber but reduced axon number in striatal fascicles. (A) Transmission electron microscopy (TEM) images from caudal striatum of Klc1+/+ and Klc1−/− mice at P0. Klc1−/− mice display enlarged axon fascicles (area enclosed in red dashed line). (A′) Higher magnifications of TEM images of panel A showing reduced axon density but enlarged calibers in Klc1−/− mice. (B,C) Quantification of axon fascicle area (B) and axon number (C) per 30 µm2 area. (D) Quantification of axon diameter distribution. Data in B and C are mean±s.e.m. Klc1+/+, n=11-12; Klc1−/−, n=12-14 fascicles. *P<0.03, **P<0.01; Student's t-test. Data in D show probability density function analysis of pooled axon diameters; dashed lines indicate median. Klc1+/+, n=1536; Klc1−/−, n=750 axons. ***P<0.001; Kolmogorov–Smirnov test. Scale bars: 2 µm (A); 0.5 µm (A′).