Abstracts

Rationale: Astrocyte dysfunction may contribute to epileptogenesis and other neurological deficits in Tuberous Sclerosis Complex (TSC). In particular, decreased expression and function of astrocyte glutamate transporters have been implicated in causing elevated extracellular glutamate levels, neuronal death, and epilepsy in a mouse model of TSC (Tsc1^GFAPCKO mice), involving inactivation of the Tsc1 gene primarily in astrocytes. In this study, we tested whether pharmacological induction of astrocyte glutamate transporter expression can prevent or reverse the neurological phenotype of Tsc1^GFAPCKO mice. Methods: Tsc1^GFAPCKO and control mice were treated with vehicle or ceftriaxone (200 mg/kg, i.p, daily), which has previously been shown to increase expression of the astrocyte glutamate transporter, Glt-1. Early ceftriaxone treatment was initiated at 3 weeks of age, prior to typical seizure onset in Tsc1^GFAPCKO mice. Late ceftriaxone treatment was started at 6 weeks of age, after seizure onset in most Tsc1^GFAPCKO mice. Glt-1 expression was assayed by Western blotting. Hippocampal glutamate levels were measured by in vivo microdialysis. Neuronal death was assayed by Fluoro-Jade B and TUNEL staining. Seizures were monitored by video-EEG. Results: Compared to vehicle-treated Tsc1^GFAPCKO mice, early treatment with ceftriaxone prior to the onset of epilepsy increased expression of astrocyte glutamate transporters and decreased extracellular glutamate levels and neuronal death in hippocampus of Tsc1^GFAPCKO mice. Early ceftriaxone treatment also significantly reduced seizure frequency and improved survival of Tsc1^GFAPCKO mice, although all treated KO mice still had some seizures and died by 6 months of age. In contrast, late treatment with ceftriaxone after the onset of epilepsy increased astrocyte glutamate transporter expression, but had no effect on seizures or survival. Conclusions: Modulation of astrocyte glutamate transporter at an early, but not late, age can decrease seizure frequency and moderately improve survival of Tsc1^GFAPCKO mice. These results indicate that astrocyte glutamate transporters contribute to epileptogenesis in Tsc1^GFAPCKO mice and suggest novel therapeutic strategies for epilepsy in TSC directed at astrocytes. Supported by NINDS and Tuberous Sclerosis Alliance