Abstracts

Rationale: Repeated administration of caffeine to immature rats led to changes in sensitivity to convulsant drugs. These changes were different according to the mechanism of convulsant action. To answer the question if seizure pattern is also important we induced a model of absence seizures and minimal clonic seizures by different doses of pentylenetetrazol (PTZ). Methods: Caffeine (10 or 20 mg/kg s.c.) was administered daily at postnatal days (PD) 7 to 11. Rats were implanted with cortical recording electrodes at PD18 and/or 25 and after a control EEG recording PTZ was injected intraperitoneally at doses of 20 or 40 mg/kg. Because the 40-mg/kg dose was not sufficient to elicit minimal seizures, groups with two injections (20 and 40 mg/kg separated by a 20-min interval) were added. Latency of spike-and-wave (SW) episodes and their incidence and duration were measured in the intervals from 10 to 15 min and from 20 to 25 min after PTZ injection. Incidence and duration of convulsions were evaluated in the groups with two PTZ doses. Results: Generally, 25-day-old rats exhibited shorter latency to the first SW episode than 18-day-old ones. Both caffeine groups exhibited lower number and decreased duration of SW episodes induced by the 20-mg/kg dose of PTZ in 18-day-old rats whereas the higher PTZ dose led to shorter latency and increased duration of SW episodes in the 10-15-min interval in this age group. No significant changes were found at the age of 25 days. Minimal clonic seizures were not significantly changed in any age and dose group. Surprisingly generalized tonic-clonic seizures appeared in nearly half of the control animals but they were never observed in caffeine-treated 25-day-old rats. Conclusions: Different seizure patterns induced by PTZ were influenced in a different way by postnatal caffeine treatment. Both anti- and proconvulsant changes were observed and these changes varied with age. Supported by a grant No.NR/9184-3 of the Ministry of Health of the Czech Republic