AMPA Receptor antagonist NBQX attenuates later‐life epileptic seizures and autistic‐like social deficits following neonatal seizures

Abstract

Summary Purpose To determine whether AMPA receptor (AMPAR) antagonist NBQX can prevent early mTOR pathway activation and long-term sequelae following neonatal seizures in rats, including later-life spontaneous recurrent seizures, CA3 mossy fiber sprouting, and autistic-like social deficits. Methods Long-Evans rats experienced hypoxia-induced neonatal seizures (HS) at postnatal day (P)10. NBQX (20 mg/kg) was administered immediately following HS (every 12h x 4 doses). 12h post-HS, we assessed mTOR activation marker phosphorylated p70-S6 kinase (p-p70S6K) in hippocampus and cortex of vehicle (HS+V) or NBQX-treated post-HS rats (HS+N) versus littermate controls (C+V). Spontaneous seizure activity was compared between groups by epidural cortical electroencephalography (EEG) at P70-100. Aberrant mossy fiber sprouting was measured using Timm staining. Finally, we assessed behavior between P30-38. Key findings Post-seizure NBQX treatment significantly attenuated seizure-induced increases in p-P70S6K in the hippocampus (p<0.01) and cortex (p<0.001). While spontaneous recurrent seizures increased in adulthood in HS+V rats compared to controls (3.22±1seizures/hour; p=0.03), NBQX significantly attenuated later-life seizures (0.14±0.1 seizures/hour; p=0.046). HS+N rats showed less aberrant mossy fiber sprouting (115±8.0%) than vehicle-treated post-HS rats (174±10%, p=0.004), compared to controls (normalized to 100%). Finally, NBQX treatment prevented alterations in later-life social behavior; post-HS rats showed significantly decreased preference for a novel over a familiar rat (71.0±12 sec) compared to controls (99.0±15.6 sec; p<0.01), while HS+N rats showed social novelty preference similar to controls (114.3±14.1 sec). Significance Brief NBQX administration during the 48 hours post-seizure in P10 Long-Evans rats suppresses transient mTOR pathway activation and attenuates spontaneous recurrent seizures, social preference deficits and mossy fiber sprouting observed in vehicle-treated adult rats after early-life seizures. These results suggest that acute AMPAR antagonist treatment during the latent period immediately following neonatal HS can modify seizure-induced activation of mTOR, reduce the frequency of later-life seizures, and protect against CA3 mossy fiber sprouting and autistic-like social deficits.

The effects of carbamazepine in the intrahippocampal kainate model of temporal lobe epilepsy depend on seizure definition and mouse strain

“…This, however, does not argue against the possibility that they represent electrographic seizures. Monomorphic focal EEG seizures are not uncommon in patients with different types of epilepsy30, 31, 32 and have also been described in other animal models of acquired epilepsy, such as the perinatal hypoxia model of epilepsy 33, 34. Furthermore, the fact that HVSWs can be suppressed by rapidly acting ASDs such as DZP as shown by Klein et al10 in FVB/N mice and here for NMRI mice would be consistent with a nonconvulsive seizure definition as shown in Table 4.…”

“…However, such EEG events in sham controls were only observed in rats at 7–8 months of age and not in younger rats 40. Similarly, intermittent low‐frequency epileptiform discharges were recorded via hippocampal depth electrodes in control rats 33, 34. However, as in the studies in mice, these SLEs in rats were clearly different in several aspects, including morphology, incidence, and frequency, from those in models of acquired epilepsy in rats 33, 34, 40.…”

“…Similarly, intermittent low‐frequency epileptiform discharges were recorded via hippocampal depth electrodes in control rats 33, 34. However, as in the studies in mice, these SLEs in rats were clearly different in several aspects, including morphology, incidence, and frequency, from those in models of acquired epilepsy in rats 33, 34, 40. In addition to the possibility that such SLEs in sham controls are a consequence of depth‐electrode‐induced lesions, inherent 8‐ to 11‐Hz spike‐wave discharges (SWDs) are commonly recorded in both inbred and outbred rat strains, but these SWDs are easily distinguished from lesion‐induced ictal discharges in models of traumatic brain injury 41.…”

Models of hypoxia and ischemia-induced seizures

“…In a follow-up study, Rakhade et al (2011) stained the Fluoro-Jade B, a high affinity fluorescent marker for neuronal degeneration and confirmed the absence of neuronal death and degeneration at 24-48 h following hypoxic seizures at P10. Hippocampal mossy fiber sprouting has been known as a common feature of human temporal lobe epilepsy and observed in numerous neonatal seizure models (Anderson et al, 1999;Babb, 1991;Holmes et al, 1999;Lippman-Bell et al, 2013;Mathern et al, 1996;Rakhade et al, 2011;Sogawa et al, 2001). Furthermore, it has been suggested to play an important role in hippocampal neuronal hyperexcitability and epileptogenesis (Wuarin and Dudek, 1996).…”

“…Furthermore, it has been suggested to play an important role in hippocampal neuronal hyperexcitability and epileptogenesis (Wuarin and Dudek, 1996). Timm staining is usually used to evaluate hippocampal mossy fibers Holmes et al, 1999;Huang et al, 1999;Lippman-Bell et al, 2013;Rakhade and Jensen, 2009;Rakhade et al, 2011). Using neonatal hypoxic seizure model in rats, we have recently shown that hypoxia-induced seizures in the immature brain lead to significant increases in CA3 mossy fiber sprouting later in life as evidenced by increased Timm staining (Lippman-Bell et al, 2013;Rakhade et al, 2011).…”