Abstracts

Rationale: The purpose of our study was to determine if the necroptotic pathway is activated in lithium-pilocarpine-induced status epilepticus (LPCSE), and if inhibition of the first enzyme in this pathway, receptor-interacting protein kinase-1 (RIPK-1), protects hippocampal neurons from SE-induced neuronal necrosis. Methods: Twelve male Wistar rats were implanted with EEG electrodes, intracerebroventricular (ICV) cannulae and telemetric body temperature sensors intraperitoneally. Six d after surgery, two groups of animals underwent LPCSE; Group 1 (SE vehicle control, n=5) received 3 ICV injections of vehicle (20% DMSO 5 uL) at the beginning, middle and the end of 3-h SE period before the seizures were terminated by diazepam and phenobarbital, while Group 2 (SE experimental, n=4) received 3 ICV injections of 5 uL 8 mM 7-Cl-O-Nec-1 at the same times as SE control rats. Rats in Group 3 (control group, n=3) also received ICV vehicle injections and diazepam and phenobarbital. After 3-h SE and a 6-h recovery period, animals were euthanized and transcardially perfused for histology. Sixty-um-thick brain sections were stained with hematoxylin and eosin (H&E). Unbiased stereological cell counting using the optical fractionator was done in the dorsal hippocampal hilus (CA4). EEG power spectrum analysis was performed on the EEG recording of the two SE groups for any potential differences in seizure discharges. Results: The estimated numbers of acidophilic (necrotic) neurons in the hilus in SE vehicle control group and SE experimental group were 10,699 ± 966 and 7,634 ± 760 respectively (mean ± SEM), while the total numbers of neuronal cell counts were the same in all three groups. The RIPK-1 inhibitor reduced the neuronal death by 29% (p < 0.025). There was no significant difference in the EEG power spectrum of epileptiform discharges in the two SE groups. Conclusions: Inhibition of RIPK-1 reduced seizure-induced neuronal necrosis without reducing epileptic seizure discharges. This suggests that in addition to excitotoxicity, the necroptotic pathway is activated in LPCSE and contributes to seizure-induced neuronal necrosis. The degree of cross-talk between these two pathways will be determined by future research. Funding: VA Merit Review grant I01BX001858-01 and the UCLA Department of Neurology Bridge Fund.