Abstract

Altered GABAergic inhibitory tone has been observed in association with a number of both acute and chronic models of epilepsy and is believed to be the result, in part, of a decrease in function of the postsynaptic GABA_A receptor (GABA_AR). This study was carried out to investigate if alterations in receptor internalization contribute to the decrease in GABA_AR function observed with epilepsy, utilizing the hippocampal neuronal culture model of low-Mg²⁺-induced spontaneous recurrent epileptiform discharges (SREDs). Analysis of GABA_AR function in “epileptic” cultures showed a 62% reduction in [³H]flunitrazepam binding to the GABA_A α receptor subunit and a 50% decrease in GABA currents when compared with controls. Confocal microscopy analysis of immunohistochemical staining of GABA_AR β2/β3 subunit expression revealed approximately a 30% decrease of membrane staining in hippocampal cultures displaying SREDs immediately after low-Mg²⁺ treatment and in the chronic epileptic state. Low-Mg²⁺-treated cultures internalized antibody labeled GABA_A receptor with an increase in rate of 68% from control. Inhibition of GABA_AR endocytosis in epileptic cultures resulted in both a recovery to control levels of membrane GABA_A β2/β3 immunostaining and a total blockade of SREDs. These results indicate that altered GABA_AR endocytosis contributes to the decrease in GABA_AR expression and function observed in this in vitro model of epilepsy and plays a role in causing and maintaining SREDs. Understanding the mechanisms underlying altered GABA_A R recycling may offer new insights into the pathophysiology of epilepsy and provide novel therapeutic strategies to treat this major neurological condition.