Neuroinflammation and its role in seizure initiation and epilepsy disease development is being investigated, specifically the role of innate immune complement activation through the C5a receptor, C5ar1.C5ar1 expression was found to be significantly upregulated during epilepsy disease progression in several experimental mouse models, in addition to other complement components such as C3, the precursor to C5a. Building upon existing studies supporting the role of inflammation and other complement components in epilepsy, this finding indicates a contribution of C5a and complement activation in this disease. This lead to creation of the primary hypothesis of this thesis; inhibition of C5ar1 activation is potentially neuroprotective and anticonvulsant in epilepsy.To test this hypothesis a small peptide antagonist of C5ar1, PMX53, was used. It was shown to be anticonvulsant in two acute and two chronic seizure models. PMX53 increased the seizure threshold significantly in both the 6Hz test and the corneal kindling model, as well as reduced EEG seizure power in the pilocarpine-induced SE model, indicating anticonvulsant actions. Studies using the chronic intrahippocampal kainate model combined with EEG, showed that PMX53 was acutely anticonvulsant after a single peripheral administration, significantly reducing total time in seizure by >50% as well as EEG seizure power. In addition, treatment of mice with PMX53 during pilocarpine-SE lead to a vast reduction in EEG seizure power highlighting further anticonvulsant effects. These results suggest inhibition of C5ar1 is beneficial in increasing seizure thresholds in several mouse models of epilepsy.Further studies using inert structural analogues of PMX53 and C5ar1-deficient mice in the 6Hz model showed that PMX53's anticonvulsant effect is C5ar1-dependent. This confirms my hypothesis that antagonism of C5ar1 is anticonvulsant. To determine if C5ar1-mediated anticonvulsant effects lead to changes in subsequent cellular damage, neuronal cell death in the hippocampal formation was evaluated acutely after pilocarpine-induced SE. In both PMX53-treated animals and mice lacking the C5ar1 receptor, significant reductions in neuronal degeneration and loss were evident in key hippocampal areas including CA1 and CA3 pyramidal cell layers.iii In addition, the explicit role of C5ar1 expression on microglial cells was investigated, given that consistent upregulation of the receptor was shown at varying stages post-epileptic insult in mice. Specifically microglial activation phenotypes were assessed, based on expression patterns of inflammatory and activation markers. M1 phenotype is considered to be more inflammatory in nature and is detected through expression of pro-inflammatory cytokines, i.e. IL-1β, TNFα, IL-6 and classical activation markers, i.e. CD16, CD86. M2 phenotype is defined as being more reparative in nature, with markers such as Arginase1 (Arg1) and Chitinase-like-3 (Ym1) being associated with this phenotype, all linked to different aspects of cell repair, as wel...