Significantly increased C1q expression was observed in the hippocampal synaptosomal preparation of the rats injected with amyloid fibrils, which was effectively attenuated by C1q siRNA (a, n = 7 rats in each group, F3,24 = 6.3, P = 0.0026). Significantly increased co-localization of C1q with PSD95 was observed in the hippocampal CA1 of the rats injected with Aβ1–40 fibrils, but not those injected with Aβ40–1 fibrils (b, n = 5 rats in each group, F4,20 = 42.8, P <0.0001, scale bar = 10 μm). Each dot represents the mean value of 4 brain sections of one animal. Significantly increased expression of C1q was observed in hippocampal CA1 synaptosomal preparation in the Tg-APPsw/PSEN1DE9 (APP/PSI) compared to C57BL/6 mice (c, n = 8 mice in each group, unpaired t-test, t = 3.7, DF = 14, two-tailed P = 0.002). Data represent mean ± s.e.m. *P<0.05, **P<0.01, ***P<0.001.