Recurrent
seizures without interictal resumption (
status epilepticus) have been reported to induce neuronal death in the midline thalamic region that has functional roles in memory and decision-making; however, the pathogenesis underlying
status epilepticus-induced thalamic neuronal death is yet to be determined. We performed histological and immunohistochemical studies as well as cerebral blood flow measurement using 4.7 tesla magnetic resonance imaging spectrometer on midline thalamic region in Sprague-Dawley rats (n = 75, male, 7 weeks after birth,
body weight 250-300 g) treated with
intraperitoneal injection of
kainic acid (10 mg/kg) to induce
status epilepticus (n = 55) or
normal saline solution (n = 20). Histological study using
paraffin-embedded specimens revealed neuronal death showing ischemic-like changes and
Fluoro-Jade C positivity with
calcium deposition in the midline thalamic region of epileptic rats. The distribution of neuronal death was associated with focal loss of immunoreactivity for
excitatory amino acid transporter 2 (EAAT2), stronger immunoreaction for
glutamate and increase in number of Iba-1-positive microglial cells showing swollen cytoplasm and long processes. Double immunofluorescence study demonstrated co-expression of
interleukin-1 beta (IL-1β) and
inducible nitric oxide synthase (iNOS) within microglial cells, and loss of EAAT2 immunoreactivity in reactive astrocytes. These microglial alterations and astrocytic EAAT2 downregulation were also observed in tissue without obvious neuronal death in
kainic acid-treated rats. These results suggest the possible role of
glutamate excitotoxicity in neuronal death in the midline thalamic region following
kainic acid-induced
status epilepticus due to astrocytic EAAT2 downregulation following microglial activation showing upregulation of IL-1β and iNOS.