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Lymphocyte infiltration of neocortex and hippocampus after a single brief seizure in mice
J Silverberg1, D Ginsburg, R Orman
1School of Graduate Studies, State University of New York Downstate Medical Center, Brooklyn, NY 11203, United States. JonathanISilverberg@gmail.com
Insights
A single seizure triggers immune cell entry into the brain, specifically T cells and B cells, primarily in the neocortex. These lymphocytes appear within 24 hours and resolve by 7 days post-seizure.
Area of Science:
- Neuroimmunology
- Epilepsy Research
- Cellular Neuroscience
Background:
- Immune responses in epilepsy are known, but brain immune activity after a single seizure remains unclear.
- Understanding post-seizure immune dynamics is crucial for epilepsy research.
Purpose of the Study:
- To investigate immune cell responses in the brain following a single generalized tonic-clonic seizure in a mouse model.
- To characterize the types and locations of immune cells infiltrating the brain after a seizure.
Main Methods:
- Induction of single generalized tonic-clonic seizures in C57bl/6 mice via electrical stimulation.
- Analysis of brain tissue (neocortex, hippocampus) at various time points (1h-7 days) post-seizure.
- Flow cytometry to quantify CD4+ T cells, CD8+ T cells, and CD45R+ B cells.
Main Results:
- Maximal seizures led to the appearance of CD4+ T cells, CD8+ T cells, and CD45R+ B cells in the brain by 24 hours, peaking at 48 hours.
- Lymphocytes were primarily detected in the neocortex (CD4+ T cells, B cells) and hippocampus (CD8+ T cells) 24 hours post-seizure.
- No significant lymphocyte infiltration was observed in unstimulated, sham-stimulated, or sub-seizure groups, nor was blood-brain barrier permeability increased.
Conclusions:
- A single brief seizure selectively recruits lymphocytes, including T cells and B cells, into the brain.
- This immune cell recruitment is a transient process, with cells resolving by 7 days post-seizure.
- The findings highlight a specific pattern of immune cell trafficking to cortical regions following a seizure.
Abstract:
Various immune responses have been described in epileptic patients and animal models of epilepsy, but immune responses in brain after a single seizure are poorly understood. We studied immune responses in brain after a single brief generalized tonic-clonic seizure in mice. C57bl/6 mice, either unanesthetized or anesthetized (pentobarbital, ethyl chloride) received either electrical (15-30 mA, 100 Hz, 1s) or sham stimulation (subcutaneous electrodes over frontal lobe, no current). Electrical stimulation of unanesthetized mice resulted in tonic-clonic convulsions with hind-limb extension (maximal seizure), tonic-clonic convulsions without hind-limb extension (submaximal seizure), or no seizure. In contrast, such stimulation of anesthetized mice did not result in seizure. Mice were killed at 1h-7 days after seizure. Brains or regions dissected from brain (neocortex, hippocampus, midbrain, cerebellum) of each group were pooled, single cell suspensions prepared, and cells separated according to density. CD4(+) (CD3(+)CD45(Hi)) and CD8(+) (CD3(+)CD45(Hi)) T cell and CD45R(+) (CD45(Hi)) B cell numbers were determined by flow cytometry. At 24h after a maximal seizure, CD4(+) and CD8(+) T cells and CD45R(+) B cells appeared in brain, reaching peak numbers at 48 h, but were no longer detected at 7days. CD4(+) T cells and CD45R(+) B cells were preferentially found in neocortex compared with hippocampus, whereas CD8(+) T cells were preferentially found in hippocampus at 24h after a maximal seizure. In contrast, virtually no lymphocytes were detected in brains of unstimulated or sham stimulated mice, unanesthetized stimulated mice after submaximal or no seizure, and anesthetized stimulated mice at 1 h-7 day. Neither Ly6-G+ neutrophils nor erythrocytes were detected in brains of any animals, nor was there any detectable increase of blood-brain barrier permeability by uptake of Evans Blue dye. The results indicate that lymphocyte entry into brain after a single brief seizure is due to a selective process of recruitment into cortical regions.
