Excitatory aminoacids and epileptic seizures in immature brain

Data on convulsant and anticonvulsant action of drugs influencing excitatory amino acid receptors in developing rats are reviewed. Agonists of NMDA type of receptors NMDA and homocysteic acid, elicited an age-related seizure pattern--flexion, emprosthotonic seizures--in the first three postnatal weeks of rats. Generalized clonic-tonic seizures appeared only after a longer latency. Kainic acid administration resulted in epileptic automatisms and later in minimal, clonic seizures followed by generalized tonic-clonic seizures. A decrease of sensitivity to convulsant action with age is a general rule for all agonists tested. Different anticonvulsant action of NMDA and nonNMDA antagonists was demonstrated in a model of generalized tonic-clonic seizures induced by pentetrazol, whereas their action against epileptic afterdischarges elicited by electrical stimulation of cerebral cortex was similar. Again, higher efficacy in younger animals was a rule. As far as metabotropic glutamate receptors are concerned, agonists of groups II and III were shown to protect against convulsant action of homocysteic acid in immature rats and an antagonist of group I receptors MPEP suppressed the tonic phase of generalized tonic-clonic seizures induced by pentetrazol more efficiently in younger than in more mature rat pups. Unfortunately, a higher sensitivity to the action of antagonists of ionotropic glutamate receptors was demonstrated also for unwanted side effects (motor functions were compromized). In contrast, glutamate metabotropic receptor antagonist MPEP did not exhibit any serious side effects in rat pups.