IL-1β induction and IL-6 suppression are associated with aggravated neuronal damage in a lipopolysaccharide-pretreated kainic acid-induced rat pup seizure model

Expression of Cytokines and Neurodegeneration in the Rat Hippocampus and Cortex in the Lithium-Pilocarpine Model of Status Epilepticus and the Role of Modulation of Endocannabinoid System

A significant body of evidence shows that neuroinflammation is one of the key processes in the development of brain pathology in trauma, neurodegenerative disorders, and epilepsy. Various brain insults, including severe and prolonged seizure activity during status epilepticus (SE), trigger proinflammatory cytokine release. We investigated the expression of the proinflammatory cytokines interleukin-1β (Il1b) and interleukin-6 (Il6), and anti-inflammatory fractalkine (Cx3cl1) in the hippocampus, entorhinal cortex, and neocortex of rats 24 h, 7 days, and 5 months after lithium-pilocarpine SE. We studied the relationship between cytokine expression and neuronal death in the hippocampus and evaluated the effect of modulation of endocannabinoid receptors on neuroinflammation and neurodegeneration after SE. The results of the present study showed that inhibition of endocannabinoid CB1 receptors with AM251 early after SE had a transient neuroprotective effect that was absent in the chronic period and did not affect the development of spontaneous seizures after SE. At the same time, AM251 reduced the expression of Il6 in the chronic period after SE. Higher Cx3cl1 levels were found in rats with more prominent hippocampal neurodegeneration.

Pre- and Neonatal Exposure to Lead (Pb) Induces Neuroinflammation in the Forebrain Cortex, Hippocampus and Cerebellum of Rat Pups

Lead (Pb) is a heavy metal with a proven neurotoxic effect. Exposure is particularly dangerous to the developing brain in the pre- and neonatal periods. One postulated mechanism of its neurotoxicity is induction of inflammation. This study analyzed the effect of exposure of rat pups to Pb during periods of brain development on the concentrations of selected cytokines and prostanoids in the forebrain cortex, hippocampus and cerebellum. Methods: Administration of 0.1% lead acetate (PbAc) in drinking water ad libitum, from the first day of gestation to postnatal day 21, resulted in blood Pb in rat pups reaching levels below the threshold considered safe for humans by the Centers for Disease Control and Prevention (10 µg/dL). Enzyme-linked immunosorbent assay (ELISA) method was used to determine the levels of interleukins IL-1β, IL-6, transforming growth factor-β (TGF-β), prostaglandin E2 (PGE2) and thromboxane B2 (TXB2). Western blot and quantitative real-time PCR were used to determine the expression levels of cyclooxygenases COX-1 and COX-2. Finally, Western blot was used to determine the level of nuclear factor kappa B (NF-κB). Results: In all studied brain structures (forebrain cortex, hippocampus and cerebellum), the administration of Pb caused a significant increase in all studied cytokines and prostanoids (IL-1β, IL-6, TGF-β, PGE2 and TXB2). The protein and mRNA expression of COX-1 and COX-2 increased in all studied brain structures, as did NF-κB expression. Conclusions: Chronic pre- and neonatal exposure to Pb induces neuroinflammation in the forebrain cortex, hippocampus and cerebellum of rat pups.

The role of IL-1β and glutamate in the effects of lipopolysaccharide on the hippocampal electrical kindling of seizures

In our study, we used rapid electrical hippocampal kindling and in vivo microdialysis methods to assess the involvement of inflammatory mediators: lipopolysaccharide (LPS) and proinflammatory interleukin-1β (IL-1β) in mechanisms of epileptogenesis. We observed, that both, LPS and IL-1β, administered into stimulated hippocampus, accelerated kindling process. LPS also increased the expression of IL-1β in stimulated hippocampus in kindled rats. In vivo acute LPS perfusion, via a microdialysis cannula implanted into the naïve rat's hippocampus, produced an increase in extracellular glutamate release. We suppose, that particularly IL-1β action and increased glutamate concentration may significantly contribute to LPS effects on kindling development.

Role of the Toll‑like receptor 3 signaling pathway in the neuroprotective effect of sevoflurane pre‑conditioning during cardiopulmonary bypass in rats

The aim of the present study was to explore the roles and possible molecular mechanism of the alleviating effect of sevoflurane pre‑treatment on the extracorporeal circulation and to investigate the possible involvement of the Toll‑like receptor (TLR3) signaling pathway. A total of 64 male Sprague Dawley rats were randomly divided into three groups: The sham operation group (H group; n=8), cardiopulmonary bypass (CPB) group (C group; n=24) and sevoflurane pre‑conditioning group (S group; n=32). The C group was subjected to tracheal intubation and mechanical ventilation, vessel puncture and catheter placement in the right femoral artery and right internal jugular vein, while no CPB was performed in the H group. The S group was pre‑treated with 2.4% sevoflurane for 1 h prior to establishing the CPB model. The CPB in the C and S groups was performed for 1 h. Blood of the rats was analyzed and clinical parameters were detected prior to, during and at various time‑points after CPB. In addition, eight rats from the C and S groups each were sacrificed at these time‑points and brain tissue samples were analyzed. The levels of the brain damage‑specific protein S100‑β as well as IL‑6 and IFN‑β in the serum were detected by ELISA; furthermore, the expression levels of TLR3 and TIR‑domain‑containing adapter‑inducing interferon‑β (TRIF) in the left hippocampus were assessed by ELISA and/or western blot analysis. The right hippocampus was assessed for neuronal apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling assay. The mean arterial pressure, heart rate and hematocrit were significantly decreased following CPB (P<0.05), while there was no significant changes in any other clinical parameters. The serum levels of S100‑β and IL‑6 in the C group were significantly increased compared with those in the H group (P<0.05), which was attenuated by sevoflurane‑pre‑treatment. Compared with the H group, the serum levels of IFN‑β as well as hippocampal protein levels of TLR3 and TRIF were significantly increased in the C group during and after CPB (P<0.05), which was markedly aggravated in the S group (P<0.05). The number of apoptotic hippocampal neurons, although being generally low, was significantly increased in the C group compared with that in the H group (P<0.05), while apoptosis was significantly attenuated by sevoflurane‑pre‑treatment (P<0.05). The present study therefore concluded that 2.4% sevoflurane pre‑treatment has a protective effect on the rat brain against CPB‑induced injury, which may be mediated via the TLR3 signaling pathway through upregulating the expression levels of anti‑inflammatory and downregulating pro‑inflammatory proteins.

Postnatal interleukin-1β administration after experimental prolonged febrile seizures enhances epileptogenesis in adulthood

It remains unclear whether prolonged febrile seizures (pFS) in childhood facilitate mesial temporal lobe epilepsy (MTLE) in adulthood. Interleukin (IL)-1β is associated with seizures in children and immature animal models. Here, we use a rat model of pFS to study the effects of IL-1β on adult epileptogenesis, hippocampal damage, and cognition. We produced prolonged hyperthermia-induced seizures on postnatal days (P) 10-11 and administered IL-1β or saline intranasally immediately after the seizures. Motor and cognitive functions were assessed at P85 using rotarod and passive avoidance tests. Electroencephalogram recordings were conducted at P90 and P120. Hippocampal CA1 and CA3 neurons and gliosis were quantified at the end of the experiment. Spontaneous seizure incidence was significantly greater in rats that had received IL-1β than in those that had received saline or those without hyperthermia-induced seizures (p < 0.05). Seizure frequency did not differ significantly between the three groups and no motor deficits were observed. Passive avoidance learning was impaired in rats that received IL-1β compared with controls (p < 0.05), but was not different from that in rats that received saline. Hippocampal cell numbers and gliosis did not differ between the three groups. These results indicate that neuronal loss and gliosis are not prerequisites for the epileptogenic process that follows pFS. Our results suggest that infantile pFS combined with IL-1β overproduction can enhance adulthood epileptogenesis, and might contribute to the development of MTLE.

Postnatal interleukin-1β enhances adulthood seizure susceptibility and neuronal cell death after prolonged experimental febrile seizures in infantile rats

Febrile seizures (FS) are recognized as an antecedent to the development of temporal lobe epilepsy with hippocampal sclerosis (TLE-HS), but it is unclear whether prolonged FS are a direct cause of TLE-HS. Here, we used a rat model of infantile FS to study the effects of inflammatory cytokines on seizure susceptibility and neuronal death in adults. Prolonged hyperthermia-induced seizures (pHS) were induced in male Lewis rats at post natal day (P) 10. Cytokines were administered twice intranasally, once immediately after pHS and once the following day. The effects of intranasal interleukin (IL)-1β or tumor necrosis factor (TNF) α were tested in rats undergoing a single episode of pHS (P10) and in rats undergoing repeated pHS (P10 and P12). Seizure susceptibility was tested at P70-73 by quantifying the seizure onset time (SOT) after kainic acid administration, and neuronal cell injury and gliosis in adulthood. SOT significantly reduced in rats receiving IL-1β together with repeated pHS, whereas no significant effects were seen in rats receiving IL-1β after a single pHS episode, or in rats receiving TNFα. Hippocampal neuronal cell loss was observed in the CA3 region of rats receiving IL-1β together with repeated pHS; however, there was no significant change in gliosis among each group. Our results are consistent with the hypothesis that excessive production of IL-1β after repeated prolonged FS can enhance adult seizure susceptibility and neuronal cell death, and might contribute to the development of TLE-HS.

Dynamic Change in Cells Expressing IL-1β in Rat Hippocampus after Status Epilepticus

BACKGROUND

The time course of cytokine dynamics after seizure remains controversial. Here we evaluated the changes in the levels and sites of interleukin (IL)-1β expression over time in the hippocampus after seizure.

METHODS

Status epilepticus (SE) was induced in adult Wistar rats by means of intraperitoneal injection of kainic acid (KA). Subsequently, the time courses of cellular localization and IL-1β concentration in the hippocampus were evaluated by means of immunohistochemical and quantitative assays.

RESULTS

On day 1 after SE, CA3 pyramidal cells showed degeneration and increased IL-1β expression. In the chronic phase (>7 days after SE), glial fibrillary acidic protein (GFAP)—positive reactive astrocytes—appeared in CA1 and became IL-1β immunoreactive. Their IL-1β immunoreactivity increased in proportion to the progressive hypertrophy of astrocytes that led to gliosis. Quantitative analysis showed that hippocampal IL-1β concentration progressively increased during the acute and chronic phases.

CONCLUSION

IL-1β affects the hippocampus after SE. In the acute phase, the main cells expressing IL-1β were CA3 pyramidal cells. In the chronic phase, the main cells expressing IL-1β were reactive astrocytes in CA1.