MOTOR AND ELECTROCORTICOGRAPHIC EPILEPTIC ACTIVITY-INDUCED BY 3-MERCAPTOPROPIONIC ACID IN IMMATURE RATS

The convulsant action of 3-mercaptopropionic acid (3-MPA), a known inh ibitor of glutamate decarboxylase activity, was studied in 7-, 12-, 18 - and 25-day-old rats and in adult animals. 3-MPA elicited predominant ly clonic, minimal seizures as well as generalized tonic clonic (major ) seizures at all developmental stages studied. The CD50 for major sei zures did not change during development; CD50 for minimal seizures was significantly lower in 18-day-old rats than in older animals. Latency to the onset of seizures was shortest in 18-day-old rats and extremel y long in 12- and, especially, in 7-day-old rats. This long latency mi ght signify either changing molecular properties of glutamate decarbox ylase during development or slow turnover of GABA at early postnatal s tages. Electrocorticographic recordings demonstrated sharp EEG compone nts in the frontal region as a first sign of 3-MPA action, and seizure patterns exhibited similar developmental changes as found with other seizure models (a decrease in duration of individual graphoelements an d an increase in synchronization among various cortical regions). This indicates the primary importance of brain maturation in the expressio n of epileptic EEG phenomena. The correlation between EEG and motor ph enomena was poor in the youngest animals and it ameliorated with age, but it never became perfectly coincidental.