Abstracts

Tuberous Sclerosis Complex (TSC) represents an autosomal dominant disorder characterized by the presence of hamartomas in multiple organs, including the brain. The cortical hamartomas, called tubers, are highly epileptogenic lesions, containing abnormal large cells with neuronal or glial characteristics. We showed previously that the dysplastic neurons express selective alterations of glutamate receptor (GluR) subunits, which may enhance network excitability, contributing to the highly epileptogenicity of the tubers [Epilepsia, 2003; 44(S9):36]. As the GluRs critically regulate gap junction-mediated glia-glia signaling, we hypothesized that abnormal astrocytes in the tuber also express GluRs with altered subunit composition. Cortical tubers from 6 patients ages 4-8 years were obtained during epilepsy surgery, in accordance with the Clinical Research Committee at Children[rsquo]s Hospital, Boston. All patients met clinical criteria for TSC with neuropathologic confirmation of the diagnosis. Tissue was fixed in 4% paraformaldehyde, cut at 50 [mu]m and immunocytochemically double labeled with neuronal and glial cell markers, in combination with the TSC mutation marker pS6 and antibodies against AMPAR subunits GluR1-4, NMDAR subunits NR2A and NR2B, as well as the gap junction protein connexin 43 (Cx43). Two types of abnormal glial cells were identified within the tuber, based on their immunoreactivity for cell specific markers and the mutation marker pS6. Dysplastic astrocytes, localized predominantly around the blood vessels, were consistently immunopositive for vimentin and pS6, but only occasionally for GFAP. They showed intense GluR4 and GluR3 immunoreactivity, while GluR2, GluR1, NR2A and NR2B subunits were expressed only at low levels. In contrast, reactive astrocytes were distributed more uniformly throughout the cortex and labeled with both vimentin and GFAP, but not with pS6. Reactive astrocytes were strongly immunopositive for GluR1-4, as well as NR2A subunits. Both cell types showed intense Cx43 immunoreactivity, suggesting capacity for intercellular coupling. Dysplastic astrocytes appear to express AMPA receptor subunits consistent with a pattern of calcium permeability (low GluR2 expression) and Cx43, which may augment cell-cell signaling in this abnormal cell population. Reactive astrocytes display GluR and Cx expression patterns, similar to that reported in other pathologic states. Taken together, these results suggest that dysplastic astrocytes in TSC lesions may be unique in their properties and future studies are necessary to examine their potential role in epileptogenesis of TSC lesions. (Supported by Boston Neurosurgical Fdn (DMT, PMB) and NS31718 (FEJ))