EARLY ACTIVATION OF INHIBITORY NEURONS IN THE THALAMIC RETICULAR NUCLEUS DURING FOCAL NEOCORTICAL SEIZURES

The neurons of the thalamic reticular nucleus are among the main targe ts of corticothalamic projections and their vulnerability in pathologi cal conditions is well established. The present experiments aimed at t he description and immunocytochemical characterization of the neurons of the thalamic reticular nucleus activated in neocortical seizures. F ocal seizures were induced by the topical application of isotonic, iso hydric 4-aminopyridine solution to the sensorimotor neocortex of adult , anesthetized Wistar rats. The animals were perfused with fixative af ter 1 and 2h of recorded seizure activity. Coronal plane vibratome sec tions were incubated with cocktails of polyclonal c-fos and monoclonal parvalbumin antisera. Labeled cells in the thalamic reticular nucleus were counted and related to total cell counts. Neurons and neuropil s howed strong parvalbumin immunoreactivity. Double-stained sections rev ealed that 55.32% of the parvalbumin-positive cell population expresse d c-fos protein in their cell nuclei at the end of the Ih seizure peri od. This ratio decreased to 43.5% following 2h seizure. Labeled cells, although less in number were also observed in the contralateral thala mic reticular nucleus. Since parvalbumin labels GABAergic cells, it is tempting to speculate that this activation of intrathalamic inhibitio n might exert an important anticonvulsant protection on other thalamic nuclei.