C5aRKO mice are more susceptible to KA excitotoxicity and apoptosis than wild type littermates. KA or vehicle (Veh) was administered intraventricularly in C5aRKO mice and age matched wild type litermates (WT) (n = 4). A. KA treatment in C5aRKO mice resulted in greater number of TUNEL positive neurons than in KA injected WT littermates (100×). The arrow points to the region in the inset showing the apoptotic neurons. B. Both Hematoxylin and eosin (H&E) staining as well as Apoptag (TUNEL) staining methods of assessing apoptosis showed that there were a significantly greater number of apoptotic neurons in C5aRKO mice treated with KA than in WT mice treated with KA in the CA3 hippocampal region. Significance in the number of neurons was assessed using one way ANOVA with Bonferroni's multiple testing correction. All results are expressed as mean ± SD. Hematoxylin/eosin WT and C5aRKO – KA induced: *p < 0.01; TUNEL WT and C5aRKO – KA induced: *p < 0.006. SO = stratum oriens; SR = stratum radiatum.