Although
hippocampal sclerosis is frequently identified as a possible epileptic focus in patients with
temporal lobe epilepsy, neuronal loss has also been observed in additional structures, including areas outside the temporal lobe. The claim from several researchers using animal models of acquired
epilepsy that the immature brain can develop
epilepsy without evidence of hippocampal neuronal death raises the possibility that neuronal death in some of these other regions may also be important for epileptogenesis. The present study used the
lithium pilocarpine model of acquired
epilepsy in immature animals to assess which structures outside the hippocampus are injured acutely after
status epilepticus. Sprague-Dawley rat pups were implanted with surface EEG
electrodes, and
status epilepticus was induced at 20 days of age with
lithium pilocarpine. After 72 h, brain tissue from 12 animals was examined with
Fluoro-Jade B, a histochemical marker for degenerating neurons. All animals that had confirmed
status epilepticus demonstrated
Fluoro-Jade B staining in areas outside the hippocampus. The most prominent staining was seen in the thalamus (mediodorsal, paratenial, reuniens, and ventral lateral geniculate nuclei), amygdala (ventral lateral, posteromedial, and basomedial nuclei), ventral premammillary nuclei of hypothalamus, and paralimbic cortices (perirhinal, entorhinal, and piriform) as well as parasubiculum and dorsal endopiriform nuclei. These results demonstrate that
lithium pilocarpine-induced
status epilepticus in the immature rat brain consistently results in neuronal injury in several distinct areas outside of the hippocampus. Many of these regions are similar to areas damaged in patients with
temporal lobe epilepsy, thus suggesting a possible role in epileptogenesis.