Abstracts

Rationale: The childhood epilepsy syndrome X-linked Infantile Spasms (ISSX) is characterized by motor spasms beginning in the first year of life, seizures and mental retardation. A triplet repeat expansion in Aristaless-related homeobox gene (Arx) is a common cause of ISSX. A mouse with the same mutation ( Arx(GCG)10+7 ) recapitulates most features of ISSX and shows widespread reduction of GABAergic and cholinergic interneurons in the brain (Price et al, 2009). 17?-estradiol (E2) has profound effects in mammalian nervous systems. Acting via both transcriptional and non-transcriptional mechanisms, E2 has both functional and structural effects on the CNS. In vivo and in vitro data suggest that estradiol may also have antiepileptic effects. I will test the hypothesis that E2 can alter epilepsy in the Arx(GCG)10+7 mouse by modulating interneuron development.Methods: Injections: E2 (40ng/g) or oil vehicle was injected s.c. into mice from ages P5-40, P3-10 or P33-40. Video-Electroencephalography: Silver wires were implanted subdurally and secured with superglue and dental cement. Total recording time was 12 hours over 3 weeks. Immunostaining/cell counting: DAB free-floating immunohistochemistry (Chemicon, USA). Cell counts were done with ImageJ.Results: Mutants injected with E2 on days P5-40 had significantly lower interictal spike rates (21.3 6.2, N=9) than controls (393.6 172.3, N=6, p < 0.05). One seizure was detected in the E2 group whereas 23 seizures were detected in the control. Next, E2 was injected either on days P3-10 or P33-40. The early injection group had fewer interictal spikes than the control group and no seizures were detected (8.8 4.0 spikes/hour, N=5 and 60.7 31.5 spikes/hour, N=11, respectively). In contrast, the late injection group (P33-40) had the same interictal spike rate as the vehicle group (65 17.5 spikes/hour, N=9 and 57.8 26.9 spikes/hour, N=7, respectively. Interestingly, mice injected with E2 on days P33-40 had more seizures than the vehicle group (11 and 2, respectively). The number of striatal ChAT-positive neurons was counted and compared between vehicle- and E2-treated mutants (P3-10 only). Vehicle-treated mutants have a 29.4% loss on average of ChAT-positive interneurons in the dorsal striatum relative to wild type (N=6). Mutants treated with E2 from P3-10 had an average increase of 8.0% in ChAT-positive cells relative to wild type (N=5).Conclusions: Early injection of E2 may decrease the frequency of seizures and interictal spike rates. This effect was accompanied by an increase in the number of striatal ChAT-positive interneurons in Arx mutants. In contrast, late injection of E2 may exacerbate epilepsy in Arx mice. These results suggest that 17?-estradiol, when injected early in postnatal development, may decrease cortical hyperexcitability and reverse the pattern of interneuron loss in Arx mutants.