Abstracts

Rationale: Spike-wave discharges have been reported in rodents without epilepsy and also in animal models of epilepsy. To determine whether the discharges in normal animals are similar or different from those in epileptic animals, we examined animals with spike-wave discharges before and after induction of epilepsy. Methods: Female Sprague-Dawley rats were administered pilocarpine (380 mg/kg, s.c.) or kainic acid (12 mg/kg, s.c.) at 2-3 months of age to induce status epilepticus (SE). Pentobarbital (20 mg/kg, i.p.) was administered to decrease the severity of SE. After 4 weeks, animals were implanted with 4 subdural frontal and occipital screws and 2 twisted bipolar depth electrodes in each dorsal hippocampus. A subdural screw over the cerebellum at the midline served as reference and a screw over the left olfactory bulb was ground. After 1-2 weeks they were recorded in their home cage using digital telemetry (Pinnacle Technologies) with a commutator to permit free movement. Animals were recorded during periods of spontaneous exploration, grooming, feeding, behavioral arrest, and sleep. Animals that had SE were also recorded during spontaneous seizures, which were typically convulsive. Females were also studied during pregnancy, because pilot studies showed that spike-wave discharges often increase in duration at this time. Results: Spike-wave discharges were observed in a subset of control female rats as previously described. The discharges were similar in behavioral associations (frozen behavior) and other characteristics (e.g., frequency) before and after SE. Animals that had SE and exhibited convulsive seizures did not show spike-wave discharges during the seizure. However, when interictal spikes occurred, they often initiated spike-wave discharge. During pregnancy, spike-wave discharges fluctuated greatly in duration, sometimes occuring for minutes. During this time, animals exhibited the typical frozen stance that accompanies spike-wave discharges under other conditions. Conclusions: Spike-wave discharges in female rats are present before and after induction of SE. Convulsive seizures were readily distinguished from spike-wave discharges in their EEG characteristics. However, interictal epileptiform discharges were sometimes associated with spike-wave discharges. In pregnancy, spike-wave discharges lengthened, suggesting that a long duration of spike-wave discharge is not necessarily a characteristic of epilepsy. The results provide additional insight to guide investigators interested in animal models that simulate temporal lobe epilepsy and absence epilepsy..