Abstracts

Rationale: Low frequency (6 Hz) transcorneal stimulation elicits a generally accepted model of temporal lobe seizures. This model is common in mice, there are only a few studies in rats (e.g. Metcalf et al. Epilepsia 2017; 58(6):1073-1084). There are no data on this model in developing rodents, therefore we started to study it in immature rats to have basic data for future drug experiments. Methods: Male Wistar rats 15 to 60 days old were used. Stimulation (biphasic 0.2 ms pulses, 6 Hz for 3 s) with stepwise increasing intensity from 10 to 90 mA was applied in 20-min intervals. Before each stimulation a drop of 0.5% mesocaine was applied to each eye. Seizure pattern was formed by clonic convulsions of head and forelimb muscles, sometimes with rearing and falling, for quantification of intensity of seizures Racine’s scale was used. The lowest intensity eliciting seizures was taken as a threshold, mean thresholds were calculated for each age group, average seizure intensity was counted for each stimulation intensity. Results: Mean seizure threshold was highest in 15-day-old rats (48.75±2.95 mA, mean±S.E.M.). It decreased up to postnatal day 25 (34.17±2.6 mA) and stayed at this level up to postnatal day 45. The threshold tended to increase in the group of young adult animals (60 days old). Results were regular in younger groups (up to postnatal day 21), each stimulation intensity higher than the threshold elicited seizures. On the other hand, such a regularity was absent in older animals, some intensities higher than threshold did not elicit seizures. Pilot experiments with longer interstimulation intervals also did not result in constant appearance of seizures in rats 25 and more days old. Mean intensity of seizures was 3.0 or a little higher in all age groups. Conclusions: The 6 Hz model can be used for pharmacological studies in developing rats. It is reliable in younger age groups, results of stimulations in rats older than 21 days should be taken cautiously. Funding: This study was supported by European Regional Development Fund-Project PharmaBrain No. CZ.CZ.02.1.01/0.0/0.0/16_025/0007444 and project No.67985823 of the Czech Academy of Sciences.