Abstracts

There is currently no effective postnatal intervention for newborn infants with hypoxic encephalopathy to prevent brain injury and long-term neurologic sequelae. Using a rat model of perinatal hypoxia-induced seizures, we have previously shown that perinatal hypoxia increases long-term susceptibility to seizure-induced neuronal injury, and that AMPA receptor blockade [italic]prior [/italic]to hypoxia effectively suppressed acute seizures and attenuated chronic epileptogenic effect of hypoxia. In the present study, we evaluated the efficacy of two drugs, NBQX (AMPA receptor antagonist) and topiramate (a FDA approved AED with multiple mechanisms of action including attenuation of AMPA mediated currents), in preventing the delayed effect of hypoxia on subsequent susceptibility to seizures and neuronal injury when given [italic]after[/italic] hypoxia-induced seizures.
A total of 18 litters of male Long Evans rats were used. Each litter was divided into four groups: control/PBS([italic]n[/italic]=36), hypoxia/PBS([italic]n[/italic]=31), hypoxia/NBQX([italic]n[/italic]=21), or hypoxia/topiramate([italic]n[/italic]=26). Hypoxia seizures were induced by subjecting postnatal (P) 10 animals to global hypoxia (7-14%) for 15 min in an airtight chamber into which N[sub][sup2][/sub] was rapidly infused. Littermates served as controls. NBQX or topiramate was dissolved in PBS at 5mg/ml and injected [italic]i.p[/italic]. at a dose volume of 0.1-0.2 ml. First dose of NBQX (20 mg/kg), topiramate (30mg/kg) or the vehicle (PBS) was administered immediately after hypoxia-induced seizures and three more doses were given 12 hours apart over the next 48 h. At P30, kainate (KA, 10mg/kg, [italic]i.p.[/italic]) were administered and seizure activity was recorded over a 3-hour period. Neuronal injury was quantified by DNA fragmentation by [italic]in situ[/italic] end labeling nick translation histochemistry. A total of 582 hippocampi from 97 animals were analyzed.
Although the mean latency of vehicle-treated hypoxia group was the shortest, there was no significant difference in the latency to KA seizure at P30 (control : 1231.6[plusmn]60.2; Hypoxia/PBS : 1033.6[plusmn]47.8; Hypoxia/NBQX 1213.3[plusmn]51.8; Hypoxia/topiramate 1193.6 [plusmn]93.7, One- Way ANOVA, [italic]p[/italic]=0.10. No difference in seizure severity was noted among the four groups (mean maximal seizure severity = 3). Compared to hypoxia alone, neuronal injury was significantly less in the Hypoxia/NBQX, Hypoxia/topiramate and control groups (p[lt]0.001, one way ANOVA).
The heightened susceptibility to KA-induced DNA fragmentation within the hippocampus by perinatal hypoxic seizures was effectively prevented by either NBQX or topiramate posttreatment. Our results demonstrate that AMPA receptor blockade post-hypoxia prevents the priming effect of perinatal hypoxia-induced seizures and that this protective effect occurs independent of its anticonvulsant action. These results may indicate a potential for treatment in the newborn, as AES is often initiated after seizure onset in the clinical setting.
[Supported by: K08NS02068 (SK), R01NS31718(FEJ), and R.W.Johnson Pharmaceutical Research Institute(SK, FEJ).]