DISTRIBUTION OF FOS-POSITIVE NEURONS IN CORTICAL AND SUBCORTICAL STRUCTURES AFTER PICROTOXIN-INDUCED CONVULSIONS VARIES WITH SEIZURE TYPE

The distribution of Fos protein was mapped in rat brain following a si ngle non-focal convulsive seizure. Single seizures were induced with i ntravenous picrotoxin in unhandled animals housed in isolation. Differ ent convulsive behaviours occurred unpredictably. The least severe sei zures were predominantly localised to the face, head and forelimbs, wi thout loss of posture control (restricted seizures). The most extensiv e seizures affected all limbs and trunk, sometimes with falling (gener alised seizures). There was a correlation between seizure behaviour an d distribution of Fos induction. After restricted seizures, Fos was in duced at highest levels in neocortex and piriform cortex and was promi nent in entorhinal cortex, caudal-ventral caudate-putamen and amygdala . Regions of thalamus were consistently and lightly labelled, but Fos induction did not occur in hippocampus. After generalised seizures, th ere was Fos induction in cortex but less than after restricted seizure s and, in three of four animals, also in dentate gyrus, hippocampus an d subiculum. There was occasional or variable labelling of thalamus, b asolateral amygdala and caudate-putamen. One animal with generalised s eizures showed no hippocampal Fos induction. The findings indicate tha t picrotoxin induces seizures with at least two different patterns of neuronal involvement. The cortex, part of the caudate-putamen, amygdal a and thalamus are involved in restricted seizures while the hippocamp us, cortex and thalamus are involved in generalised seizures. The resu lts do not support the view that generalised seizures are a progressio n from restricted forms. Cortical Fos involvement is entirely consiste nt with the participation of cortex in non-focal epilepsy. In these no n-focal seizures, the dentate-hippocampus may be a source of excitatio n to cortex in the generalised group while the cortex appears to be th e predominant site of excitation in the restricted group.