Differential Regulation of Cytokine Expression Following Pilocarpine-Induced Seizure

While the pathological changes that occur in the brain following seizure have been well characterized, the molecular mechanisms underlying these events are poorly understood. Cell death, reactive gliosis, and axonal sprouting are among the best studied alterations in the epileptic brain. Previous work in both the peripheral and the central nervous systems suggests that cytokines are capable of affecting each of these processes. To better understand the role of cytokines in seizures and their sequelae, we have characterized cytokine expression in an animal model of epilepsy. Using pilocarpine to chemically induce seizures, and RNase protection assays to assess mRNA levels, we have quantified changes in expression of several members of the neuropoietic cytokine family following a single, prolonged seizure. Levels of oncostatin M (OSM), leukemia inhibitory factor (LIF), cardiotrophin-1, and ciliary neurotrophic factor were all increased in the hippocampus after seizure, though to differing extents and with markedly different time courses. Cells expressing the most dramatically up-regulated cytokines, LIF and OSM, were identified by combined in situ hybridization and immunohistochemistry. The majority of LIF(+) cells in the hippocampus were glial fibrillary acidic protein(+) astrocytes, while the majority of OSM(+) cells had the morphology of interneurons and were occasionally colabeled with neurofilament markers. Both the time course and the localization of cytokine up-regulation following seizure suggest possible roles for these intercellular signaling molecules in epilepsy.