Complement and glutamate neurotoxicity. Genotypic influences of C5 in a mouse model of hippocampal neurodegeneration.

Using mice genetically deficient in the complement (C)-system component C5, this study explored a potential novel role of the C-system in Ca(2+)-mediated control of glutamate AMPA receptor functions. We found that Ca2+ preincubation of frozen brain tissue sections enhances AMPA binding capacity more dynamically in C5 deficient (C5-) than congenic C5 sufficient (C5+) mice. The Ca(2+)-mediated response was mostly localized to the CA3 and CA1 subdivisions of the pyramidal layers of the hippocampal formation. In C5- mice, kainic acid (KA) excitotoxicity that models hippocampal neurodegeneration abolished the Ca(2+)-mediated induction of hippocampal AMPA binding. The changes in AMPA binding preceded temporally and overlapped anatomically the appearance of apoptotic features in the same hippocampal neuron layers. C5- mice showed greater hippocampal neurodegeneration then C5+ mice. NMDA binding controlled for specificity of glutamate-mediated changes and found no C5 genotypic influences. The study gives further credence to the role of the C-system in modifying the intensity and outcome during response to conditions leading to hippocampal neurodegeneration.