Abstracts

Rationale: Rodent models of temporal lobe epilepsy (TLE) typically initiate epileptogenesis using a convulsant or electrical stimulation to induce status epilepticus (SE). Ultimately the animals develop lifelong seizures, so these models have been extremely valuable to ask questions about epilepsy. However, they have been criticized because widespread neuronal loss typically follows SE, and it has been pointed out that the extensive damage does not characterize TLE well. We hypothesized that decreasing neuronal damage would lead to a model that offered new opportunities to investigate TLE. Therefore, we modified the methods that are commonly used in SE models and evaluated the outcome. Methods: Adult male and female Sprague-Dawley rats (2-3 months old) were treated with pilocarpine or kainic acid (i.p. or s.c.) to elicit status epilepticus (SE), and after 1 hr they were treated with pentobarbital (10 mg/kg, i.p.). Comparisons were made to animals treated with pentobarbital at other times (5-60 min) or diazepam (10 mg/kg, i.p.). Three days after SE, animals were perfused with 4% paraformaldehyde and sectioned to evaluate neuronal death using fluorojade-B histochemistry. In other animals, EEG (2-6 months after SE; Bio-Signal Group) was conducted using 2 dorsal hippocampal electrodes and 4 epidural cortical electrodes. After these animals were perfused (>2 months after SE), antibodies to neuronal and glial markers were used (NeuN, GFAP, calbindin D28K, neuropeptide Y) to quantify pathology (Image J; StereoInvestigator) using a brightfield microscope (Olympus BX51). Results: Animals that were treated with kainic acid (12 mg/kg, s.c.) and pentobarbital (10 mg/kg, i.p.) after 1 hr of SE provided the most reproducible approach, with all animals exhibiting SE (100%; 23/23), no mortality, and decreased morbidity with respect to food intake in the days after SE. Female reproductive function persisted as indicated by regular estrous cycles. Interestingly, spontaneous stage 5 convulsions were rare after SE (<1/week by 24 hr video recording 3 months after SE; n=4). However, stress (induced by restraint) initiated stage 5 convulsions readily. EEG recordings revealed non-convulsive seizures and interictal spikes that increased in frequency over the first 6 months after SE. Anatomical evaluation demonstrated limited neuronal damage, with preserved hippocampus, neocortex, and minimal enlargement of the ventricles. Neuronal loss primarily occurred in entorhinal cortex, amygdala, and piriform cortex. Conclusions: The relative preservation of the brain and ease of use of the modified model, relative to previous methods where SE is more severe, provides opportunities to evaluate aspects of TLE such as progression and the effects of stress, variables that are important clinically. This model also preserves reproductive function, allowing opportunities to investigate the relationship between reproductive hormones and TLE. Finally, an animal model of TLE with primarily extrahippocampal pathology provides a complement to pre-existing models where the hippocampus exhibits extensive neuronal loss.