N-methyl-D-aspartate (NMDA)-induced seizures in developing rats.

Intraperitoneal administration of N-methyl-D-aspartate (NMDA) elicited epileptic motor seizures in developing rats aged from 7 to 25 days as well as in young adults. The very first sign of NMDA action is locomotor hyperactivity which is followed by clonic and tonic seizures. In rat pups during the first 3 postnatal weeks flexion seizures (emprosthotonus) appeared as the first pattern of motor seizures; later they were replaced by generalized tonic clonic seizures. Only regular tonic-clonic seizures were observed in 25-day-old and adult rats. The youngest animals are the most sensitive to NMDA. CD50 for tonic-colonic seizures is 6.7 mg/kg in 7-day-old rat pups and it increases up to 86.6 mg/kg in 25-day-old animals. Similar changes could also be demonstrated for LD50, a lethal outcome being very frequent. EEG recordings demonstrated mainly suppressed activity, thus exhibiting a lack of correlation with motor phenomena.