Innate immunity is the first line of defense against invading pathogens and plays an essential role in defending the brain against infection, injury, and disease. It is currently well recognized that central nervous system (CNS) infections can result in long-lasting neurological sequelae and that innate immune and inflammatory reactions are highly implicated in the pathogenesis of neurodegeneration. Due to the conservation of the mechanisms that govern neural development and innate immune activation from flies to mammals, the lack of a classical adaptive immune system and the availability of numerous genetic and genomic tools, the fruit fly Drosophila melanogaster presents opportunities to investigate the cellular and molecular mechanisms associated with immune function in brain tissue and how they relate to infection, injury and neurodegenerative diseases. Here, we present an overview of currently identified innate immune mechanisms specific to the adult Drosophila brain.

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Background: Increasing evidence links epileptic seizures to neurodegenerative disorders such as Alzheimer's disease (AD) although the mechanisms underlying this relationship are not fully understood. Ion channels are crucial to the maintenance of intracellular calcium (Ca 2+ ) signaling in the nervous system, and a perturbation in their structure and function could result in both neuropathology and seizures. Moreover, perturbed cellular Ca 2+ homeostasis is known to be implicated in AD pathogenesis. Previous studies in the model organism Drosophila have established a connection between mutations linked to temperature-sensitive (TS) paralysis, which is reminiscent of vertebrate epileptiform behavior, and neurodegeneration. Thus, Drosophila could serve as an excellent model to investigate the molecular mechanisms relating these two conditions. Method:We performed an unbiased genetic screen to identify mutants that exhibit paralytic behavior at 38 • C. We used gene mapping, and DNA sequencing to locate the mutation in the Nckx30C gene. We carried out TS paralysis assays, lifespan analysis, climbing assay and brain histology to look for neurodegeneration, as well as immunohistochemistry to examine synaptic morphology at the larval neuromuscular junction (NMJ). Knockdown using RNAi established the cell-type specific basis of the TSparalytic and neurodegenerative phenotypes. Result: Mutant line 426 exhibited TS paralysis and progressive neurodegeneration in comparison to controls. We mapped the mutation to the Nckx30C locus, in the region encoding the predicted ion-binding domain. In comparison to wild type, 426 flies showed reduced lifespan, impaired climbing and changes in NMJ morphology, indicative of synaptic dysfunction. We found lifespan reduction and early-onset neurodegeneration in flies carrying two other Nckx30C alleles. Neuron-but not glia-specific knockdown of Nckx30C recapitulates the TS-paralytic phenotype of 426 flies. Knockdown of Nckx30C in glia and neurons led to early onset climbing defects. Conclusion:The Drosophila Nckx30C gene encodes for a K + -dependent Na + /Ca 2+ exchanger with enriched expression in brain tissue. Nckx30C is homologous to mammalian Solute Carrier Family 24 (SLC24) proteins of which pathophysiological involve-