Basic Science

Gautam Ullal, Margaret Fahnestock, and Ronald Racine

Neurons communicate with each other via chemical neurotransmitters that react with protein receptors. The most common of the excitatory neurotransmitters is glutamate, which reacts with a variety of different receptor subtypes. One of these subtypes (called the kainate receptor, because it responds to the excitatory drug, kainate), itself comes in at least three different forms [referred to as glutamate receptors (or GluR) 5, 6, and 7). It has been suggested that GluR 5 and GluR 6 play an important role in human epilepsy. The role of GluR7 in epilepsy is not yet understood. In this experiment, we monitored the messenger ribonucleic acid (mRNA) and protein expression of GluR5, GluR6, and GluR7 in rat hippocampus, a structure often implicated in epileptic activity, 72 h, 90 days, and 180 days after a strong and prolonged seizure induced by kainate injections. An increase in GluR5 expression, which may render the system more excitable, was seen at 72 h and remained elevated until 180 days, so the change is very long lasting. The GluR7 measures showed only a decrease at 90 days after seizures. No change was found in the GluR6 measures at any of the times after the seizure. These results suggest a rather complex array of seizure-induced changes in these receptor subtypes, but the increase in GluR5 expression may be related to a long-lasting increase in seizure susceptibility that develops after an initial, prolonged seizure. Epilepsia 2005;46(5).