Ndel1 CKO mice show reduced number of synapses, decreased frequency of mIPSCs, and lower number of synaptic vesicles at inhibitory (symmetric) synapses in CA1 hippocampus. A, Approximately 35% decrease in the number of dendritic spines on CA1 pyramidal neurons of 9-week-old Ndel1 CKO mice (−/−) compared with WT littermates (+/+), and representative Golgi-stained CA1 pyramidal neurons. WT: 9.53 ± 1.18 versus Ndel1 CKO: 6.33 ± 0.17; mean ± SD (n = 5 animals). ***p < 0.0005. B, A ∼50% decrease in the total number of synapses in CA1 of 9-week-old Ndel1 CKO mice as detected by electron microscopy, and representative electron microscopic photographs of CA1 hippocampus. WT: 41.0 ± 4.4% versus Ndel1 CKO: 20.6 ± 2.7%; mean ± SD (n = 4 animals). ***p < 0.001. Arrows indicate synapses. C, A ∼50% decrease in the number of asymmetric (AS) and symmetric synapses (SS) in CA1 of 9-week-old Ndel1 CKO mice as counted under electron microscopy. AS: WT: 33.3 ± 5.3% versus Ndel1 CKO: 17.1 ± 4.0%; mean ± SD (n = 4). **p < 0.01. SS: WT: 7.8 ± 3.3% versus Ndel1 CKO: 3.5 ± 1.5%; mean ± SD (n = 4 animals). *p < 0.05. D, Representative traces of mIPSCs recorded in the presence of AP5, DNQX, and TTX on CA1 pyramidal neurons in 7-week-old Ndel1 CKO mice (red trace, n = 14) and WT littermates (green trace, n = 5). Note the decreased mIPSCs frequency (from 2.7 ± 0.5 Hz in control to 1.6 ± 0.1 Hz CKO; *p = 0.01) but no significant change in amplitude (34.0 ± 3.3 pA in control vs 32.9 ± 1.0 pA CKO; p = 0.69). E, A ∼50% decrease in the number of synaptic vesicles at inhibitory (symmetric) synapses per μm2 of CA1 in 9-week-old Ndel1 CKO mice (−/−) compared with WT littermates (+/+), and representative electron microscopic photographs of flattened, ellipsoidal, or pleomorphic vesicles found in symmetric synapses of CA1. WT: 215.6 ± 18.7 versus Ndel1 CKO: 98.5 ± 9.8; mean ± SD (n = 4 animals). ***p < 0.0001. Student's t test was used for all statistical analyses in this figure. Two blinded independent investigators completed all counts in these experiments.