Abstracts

RATIONALE: Abnormal thalamocortical oscillations, such as those seen during the generation of generalized epileptic seizures, have been proposed to depend upon the generation of rhythmic bursts of action potentials in thalamic neurons. This theory has been challenged with the report that many thalamic neurons may not burst during some forms of seizure activity, and that cortical networks by themselves are capable of sustaining spike-wave discharges. METHODS:_ We sought to investigate the possible generation of burst discharges in thalamic neurons in an animal model of absence seizures: spike-wave discharge in the fentanyl/haloperidol anesthetized WAG/Rij rat. Single unit recordings were thus performed with stereotactic guidance under neurolept anesthesia. RESULTS:_ In this system, both spindle waves and spike-wave seizures were recorded. These discharges were associated with bursts of 5-10 action potentials with an intraburst frequency of approximately 350-700 Hz recorded in single thalamic neurons. CONCLUSIONS: _ Burst firing of this kind in thalamic neurons is likely to result from rhythmical activation of a low threshold calcium current giving rise to Ca2+ spikes with superimposed bursts of action potentials. Our data support the suggestion that at least some forms of spike-wave seizures depend critically upon the generation of rhythmic low threshold Ca2+ spikes in thalamocortical neurons. Supported by a Pfizer Postdoctoral Fellowship and NIH NS02060.