Inflammation enhances epileptogenesis in the developing rat brain

Abstract

In many experimental systems, proinflammatory stimuli exhibit proconvulsant properties. There are also accumulating data suggesting that inflammation may contribute to epileptogenesis in experimental models as well as in humans. Using two different models (Lithium-pilocarpine induced-status epilepticus (SE) and rapid kindling), we address this issue in the developing brain. Using P14 Wistar rat pups, we showed that inflammation induced by LPS results, after SE, into a more severe disease in adulthood. The main histological feature was an active gliosis that was observed only when inflammation and SE was combined. The use of a kindling model at P14, a model where seizure progress without any neurodegeneration, permits to show that systemic inflammation is responsible of an enhancement of epileptogenesis. The role of inflammation should be further explored in immature brain to identify therapeutic targets that may be relevant to clinical practice where the association of inflammation and epileptic events is common.

Figure 1

A: Table with the number of epileptic rats and the various type of seizures (Stage 1–2, Stage 3–4, reflex seizure) that were observed in the studied groups. B: example of a stage 1 seizure in a rat from the LiPC group. C: Example of a stage 4 reflex seizure in a rat from the 3LPS-LiPC group.

Figure 2

Histograms of the number (mean ± SEM) of pyramidal cell in CA-1 counted using a grid. A: pyramidal cell counts in CA-1 in the three studied groups. B: pyramidal cell counts in CA-1 comparing epileptic animals versus non-epileptic animals. C: pyramidal cell counts in CA-1 comparing LPS-treated versus non-LPS-treated animals. D: Hematoxylin & Eosin stained brain section taken at the level of the hippocampus representing the areas where the cell counts were performed.

Figure 3

GFAP-Immunostaining in the hippocampus. A: CA-1 of a rat from control group. B: CA-1 of a rat from LiPC group at higher magnification showing a moderate gliosis. C: CA-1 of a rat from LPS+LiPC group at higher magnification showing strong reactive gliosis. D: CA-1 of a rat from 3LPS+LiPC group at higher magnification showing strong reactive gliosis. Note in both C and D panel the aspect of the glial cells that are hypertrophic with thick processes.

Figure 4

A: H&E showing damage of CA-1 in a rat from LPS+LiPC group. A small cell with acidophilic cytoplasm is surrounded by a fibrillar structure. B: Double immunostaining NeuN-GFAP in CA-1 area from LiPC group showing a mild gliosis within CA-1; C: Double immunostaining NeuN-GFAP in CA-1 with strong gliosis in a rat from LPS+LiPC. The gliosis surounds the neurons. Note the decrease of the size of the NeuN staining in the area of gliosis. D: Fluorojade-B staining in CA-1 area that was observed only in LPS treated animals that exhibit spontaneous recurrent seizures. E: Representation in a stereotaxic atlas of the location of the positive Fluorojade-B staining.