Hub GABA neurons are revealed as the maestros of Gamma Frequency Oscillation mediation in new study of seizure onset

An epileptic seizure or fit can manifest with a range of physical or mental symptoms, ranging from out of control motor-activity to altered mental states. In order to develop preventative treatments or means to manage these events it is necessary to understand how brain activity changes during periods of seizure.

Gamma-Frequency Oscillations (GFOs) are synchronised patterns of activity within populations of neurons; at frequencies greater than 40Hz they are indicative of epileptic seizure onset and are a marker for chronic epileptic conditions. These GFOs have been identified in diverse regions of the brain and suggesting the presence of long-range mechanisms for synchronisation.

A recent study that graced the cover of Neuron last month, explores the underlying mechanisms controlling GFO activity during seizure-like events in the immature brain. Bernard et al used a range of electrophysiology techniques to untangle the complicated relationship between neuronal subtypes and GFO genesis. They worked in vitro first using various stimuli to induce epileptic-type events and recorded extracellularly to confirm GFO activity throughout the CA1 area. They then explored the activity of subtypes of neurons in the CA1 region, making cell-attached recordings to identify firing patterns of different classes of cells. Hippocamposeptal (HS) cells were identified as having a leading role - firing before GFO's and other subtypes of interneurons.

They were finally able to reveal that HS cell firing was crucial to illiciting GFO activity, via the depolarizing action of GABA, but not necessary for seizure-like activity. This importantly highlights that there is not a causal link between GFO's and seizure genesis, but GFO's in fact precede the transition to a seizure-type event.

Hub GABA Neurons Mediate Gamma-Frequency Oscillations at Ictal-like Event Onset in the Immature Hippocampus

Pscale P. Quilichini, Michel Le Van Quyen, Anton Ivanov, Dennis A. Turner, Aure lie Carabalona, Henri Gozlan, Monique Esclapez, and Christophe Bernard

Neuron 74, 57–64, April 12, 2012