Motor and electrocorticographic epileptic activity induced by bicuculline in developing rats

Motor seizures were induced by intraperitoneally (i.p.) injected bicuculline in 270 rats aged 7, 12, 18, 25, or 90 days. Bicuculline was able to elicit both minimal (clonic) and major (tonic-clonic) seizures in all age groups, but in 7-day-old rats minimal seizures were only noted exceptionally. CD50s (for major seizures) ranged from 2.48 to 2.85 mg/kg in the three younger groups and increased to approximately 7 mg/kg in 25- and 90-day-old rats. An intravenous (i.v.) administration of bicuculline in 67 rats, 18 and 25 days old, caused identical CD50s in these groups, indicating that the difference that occurs with an i.p. administration is due to pharmacokinetic reasons. Electrocorticographic (ECoG) studies in acute experiments as well as in young rats with implanted electrodes demonstrated general principles of the development of EEG: an increase in frequency of individual elements, in generalization of the epileptic activity, in synchronization of activity among various cortical regions, and in the correlation between ECoG and motor phenomena. An exception occurred as an age-related phenomenon: rhythmic activity of the spike-and-wave type. This activity appeared in 18-day-old and older rats and was invariably accompanied by "freezing" of the animals.