Convulsant action of systemically administered glutamate and bicuculline methiodide in immature rats

Developmental changes of transport of drugs into the brain play an important role in ontogenetic neuropharmacology. Two convulsant drugs with different mechanisms of action (glutamate and bicuculline methiodide) were chosen to demonstrate these changes in developing rats. High dose of glutamate (4 g/kg i.p.) induced both minimal (predominantly clonic) and generalized tonic-clonic seizures in rat pups 7, 12, and 18 days old. In contrast, seizures were only exceptionally observed in 25 and 90 days old animals. Bicuculline methiodide was administered in a dose of 2 or 20 mg/kg i.p. The first sign of bicuculline methiodide action in all age groups was represented by automatisms, a symptomatology never seen after bicuculline hydrochloride administration. Minimal seizures were induced in 12-day-old and in a few 18-day-old and adult rats. Generalized seizures were common after the higher dose of bicuculline methiodide in 7- and 12-day-old rat pups, seldom in 18-day-old ones and never seen in 25-day-old and adult animals. Both glutamate and bicuculline methiodide enter the brain in immature rats but the mechanisms are probably different - glutamate is transported actively through the blood-brain barrier whereas no similar system is known for bicuculline methiodide.