Abstracts

Rationale: Hypoxia is the most common cause of neonatal seizures and can lead to epilepsy, but the epileptogenic mechanisms are not well understood. Early neuro-inflammatory responses to prolonged or repeated seizures are thought to have a role in neurodegeneration and associated epileptogenesis. In postnatal day (P) 10 rat, a single episode of hypoxia causes repeated brief seizures and promotes long-term hippocampal hyper-excitability and epileptogenesis, but without apparent hippocampal cell loss. Whether inflammatory responses may contribute to these long-term changes has not been examined. In the current study, we asked if neonatal seizure-inducing hypoxia is sufficient to evoke an inflammatory response to determine if this could contribute to epileptogenesis in this setting. Methods: Seizures were induced in P10 Long-Evans rats by 14-16 min exposure to 5-7% O2. Astrocyte morphology and number in dentate gyrus were analyzed at 3 days post-hypoxia using immunohistochemical labeling of glial fibrillary acidic protein (GFAP). Astrocyte numbers were quantified using double-labeling for the nuclear stain DAPI. Experimental animals were compared to age-matched littermate controls. Results: Analysis of GFAP-labeled astrocytes in the hilar region of the dentate gyrus showed astrocyte activation at 3 days after hypoxia-induced seizures. This was exemplified by hypertrophied astrocytes with thickened and dysmorphic processes. Quantitative analysis of the number of GFAP-labeled astrocytes showed a trend toward a greater number of GFAP-labeled astrocytes in the hypoxia group compared to the control. However, significant differences were not found between the control and hypoxia-treated groups (p = 0.07, n = 5 control, 3 hypoxia). Conclusions: The results suggest that neonatal hypoxia-induced seizures result in an inflammatory response in the the dentate gyrus. Although a significant difference between groups was not found in the number of GFAP-expressing astrocytes, the trend towards an increased number in the hypoxia group also suggests increased astrocyte proliferation in response to the hypoxia and/or seizures. It is possible that astrocyte proliferation is delayed, similar to adult rodent seizure models, where an increased number of astrocytes is seen later after seizures, and thus, the observed trend could indicate the initiation of increased proliferation. However, the small number of experimental animals used in this initial study (n = 3) could also account for the lack of statistical significance. A third possibility is that, given the young age of these rats, immature vimentin-expressing astrocytes might be altered, as opposed to the mature S100B- or GFAP-expressing astrocyte populations that are altered in adult seizure-models. Nonetheless, the observation of astrocyte hypertrophy after neonatal hypoxia-induced seizures suggests that even at a young age, there is a neuro-inflammatory response to neonatal hypoxia-induced seizures. The functional significance of this inflammatory response thus needs to be explored in future studies. Supported by NS047385 (RMS) & Scott & White Plummer Fund (LAS, RMS).