Maintenance of Thalamic Epileptiform Activity Depends on the Astrocytic Glutamate-Glutamine Cycle

Bryant AS, Li B, Beenhakker MP, Huguenard JR. Maintenance of thalamic epileptiform activity depends on the astrocytic glutamate-glutamine cycle. J Neurophysiol 102: 2880-2888, 2009. First published September 9, 2009; doi:10.1152/jn.00476.2009. The generation of prolonged neuronal activity depends on the maintenance of synaptic neurotransmitter pools. The astrocytic glutamate-glutamine cycle is a major mechanism for recycling the neurotransmitters GABA and glutamate. Here we tested the effect of disrupting the glutamate-glutamine cycle on two types of neuronal activity patterns in the thalamus: sleep-related spindles and epileptiform oscillations. In recording conditions believed to induce glutamine scarcity, epileptiform oscillations showed a progressive reduction in duration that was partially reversible by the application of exogenous glutamine (300 mu M). Blocking uptake of glutamine into neurons with alpha-(methylamino) isobutyric acid (5 mM) caused a similar reduction in oscillation duration, as did blocking neuronal GABA synthesis with 3-mercaptoproprionic acid (10 mu M). However, comparable manipulations did not affect sleep spindles. Together, these results support a crucial role for the glutamate-glutamine cycle in providing the neurotransmitters necessary for the generation of epileptiform activity and suggest potential therapeutic approaches that selectively reduce seizure activity but maintain normal neuronal activity.