Ictal heterogeneity in the awake cortex
Péter Sere1, Tibor Guba2, Francois David3, Nikolett Zsigri2, Vincenzo Crunelli4, 5, and Magor L. Lőrincz1, 2, 4
1 Department of Physiology, Anatomy and Neuroscience, Faculty of Sciences University of Szeged, Szeged, Hungary; 2Department of Physiology, Faculty of Medicine, University of Szeged, Szeged, Hungary; 3Integrative Neuroscience and Cognition Center, University Paris-Descartes; 4Neuroscience Division, School of Bioscience, Cardiff University, Museum Avenue, Cardiff, UK; 5Department of Physiology and Biochemistry, University of Malta, Msida, Malta
Absence seizures consist of a sudden and brief impairment of consciousness accompanied by a lack of voluntary movements and generalized, bilaterally synchronous ‘spike and wave discharges’ (SWDs) at 2.5-4 Hz in the EEG. Similar SWDs are exhibited by diverse genetic rodent models including the behaviorally, physiologically and pharmacologically fully validated GAERS (Genetically Epileptic Rats from Strasbourg) providing direct evidence for the crucial involvement of cortico-thalamo-cortical networks in SWD generation. Previous studies performed in anesthetized rodents found that neurons in the infragranular layers of the peri-oral region of the primary somatosensory cortex are important for iniciating SWDs, this region is therefore termed the cortical initiation network (CIN). By performing intra- and extracellular recordings from various neurons in the CIN of awake head restrained GAERS rats we show that in contrast to previous findings in anesthetized preparations the activity of various types of cortical neurons shows a marked heterogeneity and correlates with SWDs on various timescales and the entrainment of individual neurons to the SWDs varies considerably. Neurons exhibiting low action potential output during the SWDs show rhythmic oscillations of their membrane potential coupled to the proxymally recorded SWDs. The pre-ictal LFP oscillations are accompanied by rhythmic fluctuations of the membrane potential of most CIN neurons. In addition, a rearrangement of peri-ictal rhythmicity characterizes a subset of neurons in the CIN. These results highlight the role of pronounced ictal neuronal heterogeneity revealed by performing membrane potential recordings in awake rodents.