Kainate receptors and rhythmic activity in neuronal networks: hippocampal gamma oscillations as a tool.

Rhythmic electrical activity is ubiquitous in neuronal networks of the brain and is implicated in a multitude of different processes. A prominent example in the healthy brain is electrical oscillations in the gamma-frequency band (20-80 Hz) in hippocampal and neocortical networks, which play an important role in learning, memory and cognition. An example in the pathological brain is electrographic seizures observed in certain types of epilepsy. Interestingly the activation of kainate receptors (KARs) plays an important role in synaptic physiology and plasticity, and can generate both gamma oscillations and electrographic seizures. Electrophysiological recordings of extracellular gamma oscillations and intracellular currents in a hippocampal slice combined with computer modelling can shed light on the expression loci of KAR subunits on single neurones and the distinct roles subunits play in rhythmic activity in the healthy and the pathological brain. Using this approach in wild-type (WT) and KAR knockout mice it has been shown that KAR subunits GluR5 and GluR6 have similar functions during gamma oscillations and epileptiform bursts and that small changes in the overall activity in the hippocampal area CA3 can tilt the balance between excitation and inhibition and cause the neuronal network to switch from gamma oscillations to epileptiform bursts.