Excitatory amino acid transporter 2 downregulation correlates with thalamic neuronal death following kainic acid‐induced status epilepticus in rat

Abstract

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.

Inhibiting HIF-1α Decreases Expression of TNF-α and Caspase-3 in Specific Brain Regions Exposed Kainic Acid-Induced Status Epilepticus

“…A rat model of cerebral KA injection-induced SE was employed to further investigate the mechanisms responsible for epileptic disease and antiepileptic drugs in the previous studies [18][19][20]. In the current study, using the same rat model our data showed that HIF-1α was significantly increased in the specific brain regions such as the parietal cortex, hippocampus and amygdala 1-7 days after induction of SE by cerebral KA injection (Fig.…”

“…In this report, a rat model of cerebral KA injection-induced SE [18][19][20] was employed and we also determined the effects of inhibiting HIF-1α on the levels of PICs in the parietal cortex, hippocampus and amygdala. Moreover, we examined the effects of inhibiting of HIF-1α and TNF-α receptor on protein expression of an indicator of cell apoptosis Caspase-3 in those specific brain regions of epileptic rats.…”

Regulation of astrocyte glutamate transporter-1 (GLT1) and aquaporin-4 (AQP4) expression in a model of epilepsy

“…The use of animal models, on the other hand, has so far demonstrated equivocal results on the regulation of GLT1 expression in epilepsy. Downregulation (Samuelsson et al 2000; Ueda et al 2001; Lopes et al 2013; Sakurai et al, 2015), upregulation (Simantov et al 1999), or no change (Miller et al 1997) in GLT1 have all been reported in a variety of epilepsy models. These differences, however, can be accounted for by several factors, including mRNA vs .…”

“…Recently, Sakurai et al (2015) demonstrated that neuronal cell death was associated with a focal loss of GLT1 immunoreactivity and stronger immunoreactivity for glutamate (Sakurai et al, 2015). In addition, Murphy-Royal et al (2015) found that although GLT1 is anchored to the membrane at synapses, it can be untethered after glutamate release and can undergo rapid, activity-regulated surface diffusion between synaptic and non-synaptic sites to ensure effective glutamate clearance (Murphy-Royal et al, 2015).…”

Enhanced neurogenesis and possible synaptic reorganization in the piriform cortex of adult rat following kainic acid‐induced status epilepticus

“…Thirty‐six rats were subjected to intraperitoneal injection of KA (5 mg/mL in saline, 10 mg/kg; Sigma‐Aldrich, St. Louis, MO, USA) to induce status epilepticus (SE), and 15 animals were treated with the same volume of normal saline solution (Otsuka Seiyaku, Tokyo, Japan) as controls. According to our previous report, we judged behavioral scale stage 4 (proposed by Zhang and colleagues) as induction of generalized seizure, and SE was considered as a condition with recurrent generalized seizure that lasts at least 30 min based on the International League Against Epilepsy task force report . The rats having SE were kept for 0 day (5 h after KA injection; n = 5), 7 (n = 8) and 14 days ( n = 8).…”