Cellular interactions in the rat somatosensory thalamocortical system during normal and epileptic 5-9 Hz oscillations.
In Genetic Absence Epilepsy Rats from Strasbourg (GAERS), generalized spike-and-wave (SW) discharges (5-9 SW s(-1)) develop during quiet immobile wakefulness from a natural, medium-voltage, 5-9 Hz rhythm. This study examines the spatio-temporal dynamics of cellular interactions in the somatosensory thalamocortical system underlying the generation of normal and epileptic 5-9 Hz oscillations. Paired single-unit and multi-unit recordings between the principal elements of this circuit and intracellular recordings of thalamic, relay and reticular, neurones were conducted in neuroleptanalgesied GAERS and control, non-epileptic, rats. The identity of the recorded neurones was established following juxtacellular or intracellular marking. At least six major findings have emerged from this study. (1) In GAERS, generalized spike-and-wave discharges were correlated with synchronous rhythmic firings in related thalamic relay and reticular neurones. (2) Usually, corticothalamic discharges phase-led related relay and reticular firings. (3) A depolarizing wave emerging from a barrage of EPSPs was the cause of both relay and reticular discharges. (4) In some relay cells, which had a relatively high membrane input resistance, the depolarizing wave had the shape of a ramp, which could trigger a low-threshold Ca2+ spike. (5) In reticular cells, the EPSP barrage could further trigger voltage-dependent depolarizations. (6) The epilepsy-related thalamic, relay and reticular, intracellular activities were similar to the normal-related thalamic activities. Overall, these findings strongly suggest that, during absence seizures, corticothalamic neurones play a primary role in the synchronized excitation of thalamic relay and reticular neurones. The present study further suggests that absence-related spike-and-wave discharges correspond to hypersynchronous wake-related physiological oscillations.
Pinault
Didier
D
Laboratoire D'anatomo-électrophysiologie Cellulaire et Intégrée, INSERM U398, Neurobiologie et Neuropharmacologie des Epilepsies Généralisées, Faculté de Médecine, 11 rue Humann, F-67085 Strasbourg, France. pinault@neurochem.u-strasbg.fr
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002450:Cell Communication; D004569:Electroencephalography; D004832:Epilepsy, Absence / Q000473:pathology / Q000503:physiopathology*; D019706:Excitatory Postsynaptic Potentials; D008297:Male; D009991:Oscillometry; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time; D013003:Somatosensory Cortex / Q000473:pathology / Q000503:physiopathology*; D013787:Thalamic Nuclei / Q000503:physiopathology; D013788:Thalamus / Q000473:pathology / Q000503:physiopathology*
D002118:Calcium