Abstracts

Rationale:
Terminal apnea is a critical factor in sudden unexpected death in epilepsy (SUDEP), and in DBA/1 mice. Audiogenic seizure (AGSz) priming is required for consistent susceptibility to S-IRA in DBA/1 mice (Faingold et al., 2010). The mechanisms mediating priming are unclear, but excitotoxity and neuroinflammation are proposed (Faingold and Feng, 2023). Since the effects of NMDA antagonists on DBA/1 mice were unknown, we first evaluated their actions on AGSz in primed DBA/1 mice. We then evaluated the effects of sub-anticonvulsant doses of these agents or an ARB (losartan), which exerts anti-inflammatory effects, to see if these treatments affected priming.

Methods:
DBA/1 mice (22-28 days old) were subjected to priming (4 AGSz at daily intervals), using an electric bell (122 dB SPL for 60 sec) and resuscitated. Next, NMDA antagonists (memantine or MK-801) were given i.p., and changes in AGSz (wild running, clonus, tonus and S-IRA) were evaluated. Effective anticonvulsant doses of these agents were evaluated, and ineffective doses were determined.  These ineffective doses or an ARB with anti-inflammatory effects (losartan, 40 mg/kg) were given to un-primed mice immediately after each priming stimulation to evaluate changes in priming.

Results:
Memantine (5 mg/kg) did not affect wild running but significantly reduced other AGSz behaviors in primed mice 90 min after injection with recovery by 24h, while 2.5 mg/kg was ineffective. In un-primed mice memantine (2.5 mg/kg) induced a significant delay in the development of S-IRA, when drug and testing were performed in the AM vs. PM, although there was no difference in the incidence of priming-induced S-IRA incidence (80%) at day 4, which was reduced compared to the usual 100% incidence of S-IRA. MK-801 (0.025 and 0.05 mg/kg) did not affect wild running but significantly reduced the other AGSz behaviors in primed mice 30 min after administration with recovery at 48h, while 0.0125 mg/kg did not block any seizure behavior. MK-801 (0.0125 mg/kg) given to un-primed mice immediately after AGSz did not block priming. Losartan (40 mg/kg) in un-primed mice, did not block priming, using the standard protocol but did induce a significant delay in the onset of S-IRA. However, when the stimulus duration was reduced to 20 sec, priming was blocked by losartan, but priming still occurred in vehicle treated mice with 20 sec stimulation.

Conclusions:
NMDA antagonists (memantine and MK-801) were effective in blocking S-IRA in primed DBA/1 mice at doses that didn’t block AGSz. Sub-anticonvulsant doses of these drugs produced a slight reduction in priming efficacy. Losartan did not block priming with the standard protocol, but this agent did block priming when the stimulus duration was decreased, suggesting that priming may involve an initial neuroinflammatory mechanism.  Additional experiments are needed to explore these effects further.

Funding:
NIH NS126870