GABAA receptor function in the gamma-hydroxybutyrate model of generalized absence seizures

gamma-Hydroxybutyric acid (GHB) produces absence-like seizures when given to animals. One of the distinguishing characteristics of experimental generalized absence seizures is that they are exacerbated by GABAA agonists. Therefore, the hypothesis that GHB-induced absence seizures result from an interaction between GHB and the GABAA receptor complex was tested. The effect of GHB on the function of various components of the GABAA receptor complex in the cortex of the rat, was determined in a series of in vitro experiments. Similar studies were carried out at various times following systemic administration of the prodrug of GHB, gamma-butyrolactone (GBL) and changes in the GABAA receptor were correlated with electrographic and behavioral changes. gamma-Hydroxybutyric acid had no effect on the binding of [3H]muscimol, [3H]flunitrazepam and [35S]t-butylbicyclophosphorothionate (TBPS) or on the uptake of 36Cl- into synaptoneurosomes in the in vitro studies. Nor were changes observed after the administration of GBL before the onset of GHB-induced absence seizures. However, at the onset of GHB-induced spike wave discharge, there was a significant (P < 0.04) decrease in the binding of [35S]TBPS, associated with a significant decrease in muscimol-stimulated uptake of 36Cl- with no other biochemical change. One minute after onset of GHB-induced absence seizure, a significant (P < 0.05) increase in the binding of [3H]muscimol was noted. Ten minutes later the decrease in muscimol-stimulated uptake of 36Cl- had normalized, while the changes in binding of [3H]muscimol and [35S]TBPS persisted. Because GABAA function remained unchanged in the in vitro studies, as well as prior to the onset of GHB-induced absence seizures in the in vivo experiments, these studies do not support the hypothesis that GHB interacts directly with the GABAA receptor complex to produce absence-like seizures.