Anticonvulsant action of a NMDA receptor antagonist CGP 40116 varies only quantitatively during ontogeny in rats

The NMDA receptor complex as a therapeutic target in epilepsy: a review

A substantial amount of research has shown that N-methyl-D-aspartate receptors (NMDARs) may play a key role in the pathophysiology of several neurological diseases, including epilepsy. Animal models of epilepsy and clinical studies demonstrate that NMDAR activity and expression can be altered in association with epilepsy and particularly in some specific seizure types. NMDAR antagonists have been shown to have antiepileptic effects in both clinical and preclinical studies. There is some evidence that conventional antiepileptic drugs may also affect NMDAR function. In this review, we describe the evidence for the involvement of NMDARs in the pathophysiology of epilepsy and provide an overview of NMDAR antagonists that have been investigated in clinical trials and animal models of epilepsy.

AIDA, a class I metabotropic glutamate-receptor antagonist limits kainate-induced hippocampal dysfunction

PURPOSE

In the developing animal, intraperitoneal injections of kainic acid (KA) lead to a prolonged initial seizure followed by chronic recurrent seizures and long-term hippocampal dysfunction. We investigated whether the class I metabotropic glutamate receptor (mGluR) antagonist 1-aminoindan-1,5-dicarboxylic acid (AIDA) is neuroprotective in the KA model of epilepsy.

METHODS

Immature rats aged postnatal day 20 (P20) and P30 were injected with fixed volumes of KA, KA + AIDA, AIDA, or saline. We monitored recurrent seizures. Thirty days later, we tested hippocampal function with the Morris water-maze test or prepared hippocampal slices to record extracellularly evoked and spontaneous potentials from the CA1 area. In a third group, we performed neuronal counts.

RESULTS

In both age groups, acute seizures were similar in KA and KA + AIDA groups. Rare spontaneous recurrent seizures occurred only in KA-injected rats. The KA P20 group performed significantly worse than controls in the water-maze test. The KA + AIDA group showed impaired performance on day 1, but learning improved substantially, reaching control values in the remaining 3 days. The P30 KA rats performed worse than controls on all trial days, whereas the KA + AIDA rats improved by day 3, but did not reach control values. Electrophysiologic recordings showed small but consistent differences between KA and control animals, suggestive of an adaptive modification in the gamma-aminobutyric acid (GABA)ergic system, reversed by AIDA. On histology, we observed a loss of CA1 interneurons in both ages. Cell loss was reversed by the use of AIDA.

CONCLUSIONS

Blockade of the class I mGluR during KA-induced seizures in the developing brain limits seizure-induced hippocampal dysfunction.

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.

Anticonvulsant action of topiramate against motor seizures in developing rats

PURPOSE

To study the anticonvulsant action of topiramate (TPM) in developing rats.

METHODS

Motor seizures were elicited by administering pentylenetetrazol (100 mg/kg subcutaneously) in five age groups of Wistar rats (7, 12, 18, 25, and 90 days old). TPM was administered intraperitoneally in doses from 10 to 640 mg/kg 2 hours before pentylenetetrazol. The time course of TPM action was studied in 12- and 25-day-old rats up to 24 hours after the 160-mg/kg dose, and the incidence and pattern of seizures were evaluated.

RESULTS

TPM did not influence minimal seizures (clonus of forelimb and head muscles with preserved righting ability). Generalized tonic-clonic seizures, however, were reliably changed at all developmental stages studied. The tonic phase was suppressed so that the majority of animals exhibited generalized clonic seizures (with a loss of righting reflexes). In addition, the incidence of generalized seizures was decreased after the 20-, 40-, and 80-mg/kg doses in the 7-day-old rat pups. The specific suppression of the tonic phase of generalized seizures was observed up to 12 hours in the 12-day-old rat pups. The same result was obtained over 6 hours after TPM administration in the 25-day-old animals, and with longer intervals the incidence of generalized seizures decreased in this age group.

CONCLUSIONS

TPM exhibits stable anticonvulsant action against the tonic phase of generalized tonic-clonic seizures throughout development. In addition, it suppresses all phases of generalized seizures in 7-day-old rats. The anticonvulsant action of TPM lasted longer in 25-day-old than in 12-day-old rats. The two actions of TPM might be ascribed to two different mechanisms of action.