Theiler's virus infection chronically alters seizure susceptibility

Purpose: Central nervous system infections greatly increase the risk for the development of seizures and epilepsy (recurrent unprovoked seizures). We have previously shown that Theiler's murine encephalomyelitis virus (Theiler's virus or TMEV) infection causes acute symptomatic seizures in C57BL6 (B6) mice. The objective of the present study was threefold: (1) to assess pathologic changes associated with acute TMEV infection and infection-induced seizures, (2) to determine whether Theiler's virus infection and associated acute seizures lead to chronically altered seizure susceptibility, and (3) to determine whether genetic background influences seizure susceptibility following Theiler's virus infection. Methods: Immunohistochemical techniques were used to assess Theiler's virus antigen localization in the brain and associated neuronal cell death. A battery of electroconvulsive threshold (ECT) tests and corneal kindling studies were conducted to assess whether there were chronic alterations in seizure susceptibility and kindling development. Studies were conducted in both B6 and SJLJ mice to assess strain-dependent effects. Results: Histopathologic analyses indicate that TMEV has specific tropism for limbic structures and causes widespread cell death in these regions. Results from ECT studies demonstrate that B6 mice that displayed acute symptomatic seizures have significantly reduced seizure thresholds and kindle faster than either control mice or infected mice without acute seizures. Furthermore, these effects were mouse-strain dependent, since SJLJ mice displayed a different seizure threshold spectrum. Discussion: These findings indicate that Theiler's virus infection leads to chronically altered seizure susceptibility in mice. It is important to note that Theiler's virus infection of B6 mice represents a novel model to study postinfection hyperexcitability.