Abstracts

Rationale: Despite much work on the alterations in ion and neurotransmitter content following seizures, changes in tissue water content have never been directly studied following seizures. Water content can be indirectly estimated by sensitive and accurate measurements of tissue specific gravity using bromobenzene-kerosene gravimetry. This technique has been applied to characterize traumatic brain injury-induced changes in tissue water content, but has not been applied to an animal model of epilepsy. To characterize tissue water content changes following seizures, we applied this method in a mouse model of status epilepticus. To determine the role of glial water transport in seizure-induced water content changes, we also performed these measurements in mice lacking the glial water channel aquaporin-4 (AQP4). Methods: Kainic acid was injected subcutaneously into AQP4+/+ and AQP4-/- adult male mice to induce status epilepticus (SE). At 6 hours, 1 day, 4 days and 7 days after the initial SE, mice were sacrificed and bilateral hippocampal and cortical microdissections were performed. Specific gravities (SG) of the hippocampal and cortical biopsies were obtained using an organic (bromobenzene-kerosene) gradient column. Hippocampal and cortical SGs were compared with saline controls, and also compared between AQP4+/+ and AQP4-/- mice. Results: Baseline hippocampal and cortical biopsies demonstrated that AQP4+/+ mouse brains had a slightly higher SG than AQP4-/- brains (as previously published). At 6 hours after the initial SE, there was a trend towards reduced hippocampal SG in both AQP4+/+ and AQP4-/ mice relative to their respective controls. While AQP4+/+ mice demonstrated a reduction in hippocampal SG at 1 day after SE, AQP4-/- mice had a significantly greater reduction in hippocampal SG than AQP4+/+ mice (p<0.01). By day 4 after SE, AQP4+/+ hippocampal SG had already recovered to baseline and was significantly higher than saline controls. By contrast, AQP4-/- hippocampal SG was no different than baseline. On day 7 after SE, AQP4+/+ hippocampal SG had returned to baseline; however, AQP4-/- hippocampal SG was significantly higher than controls (p<0.001). Interestingly, no significant change was observed in cortical SG at any time point in either genotype compared to controls.