Different patterns of neuronal activation and neurodegeneration in the thalamus and cortex of epilepsy-resistant Proechimys rats versus Wistar rats after pilocarpine-induced protracted seizures

Gastrodin Attenuates Neuroinflammation and Injury in Young Rats with LiCl/Pilocarpine-Induced Status Epilepticus

Status epilepticus is a severe neurological emergency that often leads to long-term neuronal damage and functional impairment. Gastrodin is a compound widely used in traditional Chinese medicine with potential neuroprotective effects. This study aims to investigate the effects of GAS on neuroinflammation and injury caused by LiCl/pilocarpine-induced SE in young rats. SE in rats was induced using the LiCl/pilocarpine model. Morris water maze and Y-maze experiments were used for the behavioral test of rats. Enzyme-linked immunosorbent assay was utilized to quantify the levels of interleukin (IL)-1β, IL-6, and IL-8 levels, and biochemical kits assessed the levels of malondialdehyde, superoxide dismutase and glutathione peroxidase (GSH-px) in hippocampus tissues. Additionally, Western blot analysis was performed to evaluate the protein expression levels of p-p65, p65, p-IκBα and IκBα, which are key factors of the nuclear factor kappa B (NF-κB) signaling pathway. Compared to the control group, the SE group rats exhibited reduced learning and memory abilities. Markedly elevated levels of inflammatory factors (IL-1β, IL-6, and IL-8). The expression levels of p-p65 and p-IκBα were significantly upregulated, while IκBα levels were notably decreased. Following GAS treatment, the latency of seizure onset was significantly shortened, the incidence of SE was significantly reduced and the severity of nerve injury was alleviated. Additionally, both the inflammation levels and the oxidative stress were significantly decreased, primarily through inhibition NF-κB signaling pathway. These findings suggest that GAS may be a potential therapeutic agent for treating SE.

Downregulation of the Astroglial Connexin Expression and Neurodegeneration after Pilocarpine-Induced Status Epilepticus

Astrocytic networks and gap junctional communication mediated by connexins (Cxs) have been repeatedly implicated in seizures, epileptogenesis, and epilepsy. However, the effect of seizures on Cx expression is controversial. The present study focused on the response of Cxs to status epilepticus (SE), which is in turn an epileptogenic insult. The expression of neuronal Cx36 and astrocytic Cx30 and Cx43 mRNAs was investigated in the brain of rats in the first day after pilocarpine-induced SE. In situ hybridization revealed a progressive decrease in Cx43 and Cx30 mRNA levels, significantly marked 24 h after SE onset in neocortical areas and the hippocampus, and in most thalamic domains, whereas Cx36 mRNA did not exhibit obvious changes. Regional evaluation with quantitative real-time-RT-PCR confirmed Cx43 and Cx30 mRNA downregulation 24 h after SE, when ongoing neuronal cell death was found in the same brain regions. Immunolabeling showed at the same time point marked a decrease in Cx43, microglia activation, and interleukin-1β induction in some microglial cells. The data showed a transient downregulation of astroglial Cxs in the cortical and thalamic areas in which SE triggers neurodegenerative events in concomitance with microglia activation and cytokine expression. This could potentially represent a protective response of neuroglial networks to SE-induced acute damage.

Differences in activation of ERK1/2 and p38 kinase in Jnk3 null mice following KA treatment

The MAPK family is formed by extracellular signal-regulated kinases p38 kinase and stress-activated protein kinases (SAPK/JNK). There are three genes that encode for three JNK proteins. JNK3 is mainly expressed in the central nervous system and has been related to various processes in that tissue. Specifically, JNK3 plays a crucial role in neuronal death in several neurodegenerative diseases. The activation of this kinase has been described in epilepsy, Alzheimer's disease, Parkinson's disease and Huntington's disease. Different studies have shown that the lack of the Jnk3 gene confers neuroprotection. However, the specific mechanism involved in such neuroprotection has not yet been elucidated. Therefore, in the present study, we analyzed the neuroprotection in mice lacking Jnk3 against neuronal death induced by kainic acid. Moreover, we analyzed the activation of different MAPKs. The results revealed that neuronal death was attenuated and different activation/inactivation of p38 and extracellular signal-regulated kinases 1/2 was reported with respect to control. Therefore, the data indicate that the lack of the JNK3 protein modulates other MAPKs and these changes could also have a pivotal role in neuroprotection.

Hippocampal expression and distribution of CB1 receptors in the Amazonian rodent Proechimys: an animal model of resistance to epilepsy

Proechimys, a rodent living in the Amazon region, has shown resistance to developing chronic epilepsy when submitted to different experimental models. Recently, many studies have attributed a potent anticonvulsant action to cannabinoid receptor CB1. This study investigated the distribution and expression of the CB1 receptor in the hippocampal formation of Proechimys using immunohistochemistry and Western blotting techniques. Results were compared with values obtained from adult Wistar rats. The immunoreactivity for CB1 was evident throughout the Ammon's horn and in the hilar region of both animal species. However, the distribution of these receptors was higher in the stratum lucidum of CA3 and in the hilar region of Proechimys. In addition, higher expression of CB1 receptors was observed in the Proechimys hippocampus. These data could explain, at least partially, the natural resistance of this animal species to developing spontaneous seizures following epileptogenic precipitating events.

Kainic acid-induced early genes activation and neuronal death in the medial extended amygdala of rats

The medial extended amygdala modulates pheromonal perception, influencing emotional and social behavior. As the amygdala is part of neuronal circuits that are very sensitive to excitability, its neurons are targets of seizures in temporal lobe epilepsy. It has been suggested that the hippocampus is strongly involved this pathology. There is less consistent information, however, on the effects of this disease in the amygdala. The effects of status epilepticus on the medial extended amygdala were analyzed by immunohistochemistry for neural stress and by the amino-cupric-silver technique for neuronal death in rats after kainic acid (KA) administration. Sixty adult Wistar male rats were used. Thirty animals received an injection of KA, and 30 were injected with saline. After 2, 4, 12, 24 and 48 h survival the brains were stained for Fos and FosB and for neuronal death. In the present study we show that KA induces Fos and FosB expression in neurons of the medial extended amygdala after 2, 4-48 h, with time courses that are different between them and from control animals. While Fos-IR peaks at 2-4 h post KA and then decreases, FosB-IR increases in the same period reaching its highest expression at 24-48 h. Moreover, KA injection produced massive neuronal death with a peak at 24 h. This neurodegeneration paralleled FosB-IR protein expression. These findings show that KA produces neuronal stress and activation of early genes and neuronal death in the medial extended amygdala, demonstrating the vulnerability of its neurons to the epileptogenic effects of KA.

Cellular injury and neuroinflammation in children with chronic intractable epilepsy

Objective

To elucidate the presence and potential involvement of brain inflammation and cell death in neurological morbidity and intractable seizures in childhood epilepsy, we quantified cell death, astrocyte proliferation, microglial activation and cytokine release in brain tissue from patients who underwent epilepsy surgery.

Methods

Cortical tissue was collected from thirteen patients with intractable epilepsy due to focal cortical dysplasia (6), encephalomalacia (5), Rasmussen's encephalitis (1) or mesial temporal lobe epilepsy (1). Sections were processed for immunohistochemistry using markers for neuron, astrocyte, microglia or cellular injury. Cytokine assay was performed on frozen cortices. Controls were autopsy brains from eight patients without history of neurological diseases.

Results

Marked activation of microglia and astrocytes and diffuse cell death were observed in epileptogenic tissue. Numerous fibrillary astrocytes and their processes covered the entire cortex and converged on to blood vessels, neurons and microglia. An overwhelming number of neurons and astrocytes showed DNA fragmentation and its magnitude significantly correlated with seizure frequency. Majority of our patients with abundant cell death in the cortex have mental retardation. IL-1beta, IL-8, IL-12p70 and MIP-1beta were significantly increased in the epileptogenic cortex; IL-6 and MCP-1 were significantly higher in patients with family history of epilepsy.

Conclusions

Our results suggest that active neuroinflammation and marked cellular injury occur in pediatric epilepsy and may play a common pathogenic role or consequences in childhood epilepsy of diverse etiologies. Our findings support the concept that immunomodulation targeting activated microglia and astrocytes may be a novel therapeutic strategy to reduce neurological morbidity and prevent intractable epilepsy.