Increased spontaneous activity of a network of hippocampal neurons in culture caused by suppression of inhibitory potentials mediated by anti-gad antibodies

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Abstract
Anti-glutamic acid decarboxylase autoantibodies (GAD-Ab) are commonly considered the marker of autoimmune diabetes; they were first described in patients affected by stiff-person syndrome and recently, in ataxic or epileptic patients. The pathogenetic role of GAD-Ab remains unclear but inhibition of GABA synthesis or interference with GABA exocytosis are hypothesized. The aim of the study was to assess whether GAD-Ab interfere with neuronal transmission. Serum from a GAD-Ab positive epileptic patient (by IHC and RIA), serum from a GAD-positive (only by RIA) diabetic case, sera from two epileptic GAD-Ab negative patients and a normal control were selected. Post-synaptic inhibitory potentials (IPSPs) were registered on hippocampal neurons in culture before and after the application of diluted sera in a patch clamp study. A significant increase in the frequency of IPSPs was observed after application of GAD-positive epileptic serum, while no effect was noted using sera from negative controls. The inhibition in neuronal transmission only after application of GAD-positive epileptic serum, suggests an interference with GABA function and consequently with neuronal inhibition supporting a pathogenetic role of GAD-Ab in the development of epilepsy.