Authors :
Presenting Author: Lauren Lau, PhD – Massachusetts General Hospital
Paige O'Gorman, BS,MS – Massachusetts General Hospital
Monique Krummradt, - – Massachusetts General Hospital
Kevin Staley, MD – Massachusetts General Hospital
Kyle Lillis, PhD – Massachusetts General Hospital
Rationale:
Epilepsy affects 1% of the population, with one third of patients experiencing drug-resistant seizures. To develop new therapeutic options for these patients, we need a more detailed understanding of seizure generating mechanisms, which will require well characterized animal models of epilepsy. The murine intrahippocampal kainate (IHK) model reproduces key features of mesial temporal lobe epilepsy, including hippocampal sclerosis, granule cell dispersion, and spontaneous convulsive seizures. Despite the tremendous potential of the IHK model to advance our understanding of intractable epilepsy, progress has been slowed by model variability. One source of variability lies in the form of kainic acid used. The IHK model relies on a focal injection of the neuroexcitatory compound kainic acid to the hippocampus. Kainic acid injection induces status epilepticus, which provokes the neuronal cell death and circuit reorganization that leads to chronic epilepsy. Historically, kainic acid was obtained by purification from naturally occurring sources, most commonly the seaweed Digenea simplex. In recent years, most major vendors have switched to supplying only synthetic kainic acid. However, it appears that synthetic kainic acid differs from naturally derived kainic acid in receptor selectivity and/or potency.
Methods:
We aimed to develop a protocol of intrahippocampal injection of synthetic kainic acid, which would result in low mortality and the robust emergence of spontaneous seizures and characteristic hippocampal sclerosis. Spontaneous seizure frequency was assessed by blinded behavioral screenings and chronic EEG recordings. Hippocampal sclerosis was assessed by immunohistochemistry with the neuronal marker NeuN, to quantify neuronal cell loss and granule cell layer dispersion.
Results:
We found that intrahippocampal injection of synthetic kainic acid (Tocris) greatly increased acute mortality, compared to reported mortality with natural sources of kainic acid at the same dose and volume (100 or 50 nL of 20 mM kainic acid). Acute mortality was reduced by delivering the same micrograms dose, as an injection of 200nL of 5mM kainic acid which lowered acute mortality from ~40% to 0%. This injection protocol resulted in several hours of status epilepticus, with the robust development of spontaneous seizures and hippocampal sclerosis.
Conclusions:
In conclusion, we have developed a modified protocol for the robust induction of epilepsy with low mortality using synthetic sources of kainic acid. This work will help advance the standardization of the widely used intrahippocampal kainate mouse model of temporal lobe epilepsy.
Funding: NIH NINDS R01NS112538 (Lillis)
CURE Taking Flight (Lau)