THALAMIC MULTIPLE-UNIT ACTIVITY UNDERLYING SPIKE-WAVE DISCHARGES IN ANESTHETIZED RATS

In epilept WAG/Rij rats, multiple unit activity coinciding with the oc currence of spike-wave discharges was recorded under neurolept anesthe sia. Recordings were made in the frontal cortex and in various nuclei of the thalamus, in specific nuclei such as the ventroposterolateral, the ventroposteromedial and the ventrolateral nuclei, as well as in no n-specific nuclei such as the mediodorsal nucleus, the reticular thala mic nucleus, the interanteromedial nucleus and the intralaminar nuclei (the central medial nucleus, the centrolateral nucleus and the parace ntral nucleus). Rhythmic unit firing concurrent with the spike compone nt of the cortical spike-wave discharge was observed in deep layers of the cortex and in the following thalamic nuclei: in specific nuclei, the mediodorsal and the reticular thalamic nucleus. The activity in th e specific nuclei and the mediodorsal nucleus shortly preceded the pea k of the spike component. The burst in the reticular thalamic nucleus occurred later than in the specific nuclei. A wave-concurrent firing p attern was observed in the centrolateral nucleus and the paracentral n ucleus. Cells in the central medial nucleus and interanteromedial nucl eus did not fire in a phase-locked manner. Neurons in the latter nucle us, however, were generally tonically activated during the occurrence of spike-wave discharges. It is suggested that those thalamic nuclei t hought to be involved in the production of cortical spindles, and that also fire concurrently with the spike component of the spike-wave dis charges, are mediated in the genesis of the latter activity. The findi ngs in the centrolateral and the paracentral nucleus and, furthermore, in the interanteromedial nucleus, indicate that these nuclei may play a differential role in the production of spike-wave discharges, as in the expression or maintenance of this activity.