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Published on: June 12, 2018
Characterization of neuronal death induced by focally evoked limbic seizures in the C57BL/6 mouse
Tomohiro Araki1, Roger P Simon, Waro Taki
1Robert S. Dow Neurobiology Laboratories, Legacy Research, Portland, Oregon 97232, USA.
Abstract:
Research into the molecular mechanisms of epileptic brain injury is hampered by the resistance of key mouse strains to seizure-induced neuronal death evoked by systemically administered excitotoxins such as kainic acid. Because C57BL/6 mice are extensively employed as the genetic background for transgenic/knockout modeling in cell death research but are seizure resistant, we sought to develop a seizure model in this strain characterized by injury to the hippocampal CA subfields. Adult male C57BL/6 mice underwent focally evoked seizures induced by intraamygdala microinjection of kainic acid. Kainic acid (KA) effectively elicited ipsilateral CA3 pyramidal neuronal death within a narrow dose range of 0.1-0.3 microg, with mortality < 10%. With employment of the most consistent (0.3 microg) dose, seizures were terminated 15, 30, 60, or 90 min after KA by diazepam. Damage was largely restricted to the ipsilateral CA3 subfield of the hippocampus, but injury was also consistent within CA1, suggesting that this mouse model better reflects the hippocampal neuropathology of human temporal lobe epilepsy than does the rat, in which CA1 is typically spared. Confirming this CA1 injury as seizure specific and not a consequence of ischemia, we used laser-Doppler flowmetry to determine that cerebral perfusion did not significantly change (97% to 118%) over control. Degenerating cells were > 95% neuronal as determined by neuron-specific nuclear protein (NeuN) counterstaining of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeled (TUNEL) brain sections. Furthermore, TUNEL-positive cells often exhibited the morphological features of apoptosis, and small numbers were positive for cleaved caspase-3. These data establish a mouse model of focally evoked seizures in the C57BL/6 strain associated with a restricted pattern of apoptotic neurodegeneration within the hippocampal subfields that may be applied to research into the molecular basis of neuronal death after seizures.
Insights
Researchers developed a new kainic acid-induced seizure model in C57BL/6 mice, showing apoptotic neuronal death in the hippocampus. This model aids epilepsy research by mimicking human temporal lobe epilepsy neuropathology.
Area of Science:
- Neuroscience
- Molecular Biology
- Epilepsy Research
Background:
- Standard mouse models often resist seizure-induced neuronal death, hindering research.
- C57BL/6 mice are crucial for genetic research but lack robust seizure models.
- Existing models may not accurately reflect human temporal lobe epilepsy neuropathology.
Purpose of the Study:
- To establish a kainic acid-induced seizure model in C57BL/6 mice.
- To characterize seizure-induced neuronal injury in the hippocampal CA subfields.
- To provide a model that better reflects human temporal lobe epilepsy.
Main Methods:
- Intraamygdala microinjection of kainic acid (KA) in adult male C57BL/6 mice.
- Seizure termination using diazepam at various time points.
- Assessment of neuronal death using TUNEL and NeuN staining, and cleaved caspase-3.
- Cerebral perfusion monitoring via laser-Doppler flowmetry.
Main Results:
- KA induced dose-dependent, ipsilateral CA3 pyramidal neuronal death (0.1-0.3 microg).
- Injury was also observed in CA1, mirroring human temporal lobe epilepsy.
- Neuronal death showed apoptotic features, confirmed by TUNEL and caspase-3 staining.
- Cerebral perfusion remained stable, indicating injury was seizure-specific, not ischemic.
Conclusions:
- A reproducible mouse model of focally evoked seizures in C57BL/6 mice was established.
- The model demonstrates apoptotic neurodegeneration in hippocampal CA1 and CA3 subfields.
- This model offers a valuable tool for investigating the molecular mechanisms of seizure-induced brain injury.
