Abstracts

Uptake and metabolism of synaptically released glutamate by astrocytes is critical for brain homeostasis and protection of neurons against overexcitation. To test the hypothesis that glutamate uptake and metabolism are deteriorated in gliotic protoplasmic astrocytes, we carried out immunohistochemical and electrophysiological analysis of surgically resected brain tissue in patients with pharmaco-resistant temporal lobe epilepsy and Tuberous Sclerosis Complex (TSC)., Specimens of neocortex and hippocampi from pharmaco-resistent MTLE (n = 44) and cortical tubers resected from epileptic TSC patients (n = 12) were studied with immunohistochemical and patch-clamp electrophysiological techniques., Areas of severe gliosis/sclerosis typical of cortical tubers in TSC and hippocampal sclerosis in MTLE were composed of [quot]scar[quot] astrocytes characterized by high upregulation of GFAP and S100 beta and less upregulation of CD44 and alphaB-crystallin. These cells revealed dramatic reduction in the expression of glutamine synthetase (GS) and astrocytic glutamate transporters proteins (GT: EAAT1 and EAAT2). In addition, scar astrocytes underwent conspicuous alterations in their [ldquo]gross[rdquo] morphology consisting of transformation into fibrous-like astrocytes accompanied by elongation of cell processes but loss of fine lamellipodial structures. Whole cell patch-clamp recordings of scar astrocytes showed dramatic decrease in inward glutamate transport currents, in comparison to control protoplasmic astrocytes., Downregulation of GS and GT expression proceeds in parallel with progression of gliotic changes in protoplasmic astrocytes. We hypothesize that these glutamate metabolic alterations may not be pathology specific, but rather may constitute a common effect of profound reconstruction of the cellular cytoskeleton during the development of gliosis. Astrocytic lamellipodia may be the main subcellular compartment involved in glutamate uptake by protoplasmic astrocytes. These structures are significantly lost in association with GFAP upregulation in gliosis., (Supported by Parents Against Childhood Epilepsy; R21 NS 42334.)