Cellular interactions in the rat somatosensory thalamocortical system during normal and epileptic 5–9 Hz oscillations

Authors

  • Didier Pinault

    Corresponding author
    1. Laboratoire D'anatomo-électrophysiologie Cellulaire et Intégrée, INSERM U398, Neurobiologie et Neuropharmacologie des Épilepsies Généralisées, Faculté de Médecine, 11 rue Humann, F-67085 Strasbourg, France
    • Correspondence
      D. Pinault: INSERM U405, Faculté de Médecine, 11, rue Humann, F-67085 Strasbourg Cedex, France. Email: pinault@neurochem.u-strasbg.fr

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Abstract

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.

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