Selective alterations in glutamate and GABA receptor subunit mRNA expression in dysplastic neurons and giant cells of cortical tubers

The molecular pharmacologic basis of epileptogenesis in cortical tubers in the tuberous sclerosis complex is unknown. Altered transcription of genes e ncoding glutamatergic and gamma -aminobutyric acid (GABA)-ergic receptors a nd uptake sites may contribute to seizure initiation and may occur selectiv ely in dysplastic neurons and giant cells. Arrays containing GABA A (GABAAR ), GluR, NMDA receptor (NR) subunits, GAD65, the vesicular GABA transporter (VGAT), and the neuronal glutamate transporter (EAAC1) cDNAs were probed w ith amplified poly (A) mRNA from tubers or normal neocortex to identify cha nges in gene expression. Increased levels of EAAC1, and NR2B and 2D subunit mRNAs and diminished levels of GAD65, VGAT, GluR1, and GABAAR alphal and a lpha2 were observed in tubers. Ligand-binding experiments in frozen tuber h omogenates demonstrated an increase in functional NR2B-containing receptors . Arrays were then probed with poly (A) mRNA from single, microdissected dy splastic neurons, giant cells, or normal neurons (n = 30 each). Enhanced ex pression of GluR 3, 4, and 6 and NR2B and 2C subunit mRNAs was noted in the dysplastic neurons, whereas only the NR2D mRNA was upregulated in giant ce lls. GABAAR alpha1 and alpha2 mRNA levels were reduced in both dysplastic n eurons and giant cells compared to control neurons. Differential expression of GluR, NR, and GABAAR mRNAs in tubers reflects cell-specific changes in gene transcription that argue for a distinct molecular phenotype of dysplas tic neurons and giant cells and suggests that dysplastic neurons and giant cells make differential contributions to epileptogenesis in the tuberous sc lerosis complex.