Seizures induced by homocysteic acid in immature rats are prevented by group III metabotropic glutamate receptoragonist (R,S)-4-phosphonophenylglycine

The potential anticonvulsant effect of group III metabotropic glutamate receptor (mGluR) agonist (R,S)-4-phosphonophenylglycine ((R,S)-PPG) against seizures induced in immature 12-day-old rats by bilateral intracerebroventricular (icv) infusion of DL-homocysteic acid (DL-HCA, 600 nmol/side) was examined in the present study. Rat pups were sacrificed during generalized clonic-tonic seizures, approximately 45 to 50 min after infusion. Comparable time intervals were used for sacrificing the pups which had received (R,S)-PPG. Low doses of (R,S)-PPG (10 nmol, icv) provided a pronounced anticonvulsant effect which was abolished by pretreatment with a selective group III mGluR antagonist (R,S)-alpha-methylserine-O-phosphate. Generalized clonic-tonic seizures were completely suppressed and cortical energy metabolite changes which normally accompany these seizures were either normalized (glucose and glycogen decreases) or markedly ameliorated (an accumulation of lactate). Despite the absence of obvious motor phenomena, EEG recordings revealed sporadic ictal activity, mostly in the dorsal hippocampus. Spreading of this activity into the frontal cortex was rather exceptional. The latency of ictal EEG in pretreated rats was significantly prolonged. Our data suggest that the predominant effect of (R,S)-PPG might concern seizure spread. The administration of (R,S)-PPG alone did not cause any overt behavioral side effects; it did not change the EEG pattern and did not influence cortical metabolite levels, with the exception of increased concentrations of glucose. The present findings suggest that group III mGlu receptor agonists may be of therapeutic significance for treating childhood epilepsies.     

Attenuation of seizures induced by homocysteic acid in immature rats by metabotropic glutamate group II and group III receptor agonists

Previous studies demonstrated that selected agonists for metabotropic glutamate group II and group III receptors can provide protection against seizures in adult animals. The present study has examined the potential effect of some of these compounds on seizures induced in immature rats by intracerebroventricular infusion of DL-homocysteic acid (DL-HCA, 600 nmol/side). Rat pups were sacrificed during generalised clonic-tonic seizures, 50--60 min after infusion. Comparable time intervals were used for sacrificing the pups which had received the protective drugs. The anticonvulsant effect was evaluated according to the suppression of behavioural manifestations of seizures and the protection of energy metabolite changes which normally accompany these seizures (large decreases of glucose and glycogen, and approximately 7- to 10-fold accumulation of lactate). Partial protection was exhibited by group II mGluR agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG IV, 0.6 nmol) and this effect was abolished after pretreatment with an antagonist for group II mGluRs (RS)-alpha-methyl-4-tetrazolylphenylglycine (MTPG, 100 nmol). In high doses (5--100 nmol), however, DCG IV evoked seizures which were prevented by AP7, suggesting that the convulsant effect was mediated by interaction with NMDA receptors. A pronounced anticonvulsant effect against DL-HCA-induced seizures was achieved with low doses of a highly selective group II mGluR agonist (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (2R,4R-APDC, 0.6 nmol), group II agonist and group I mGluR antagonist (S)-4-carboxy-3-hydroxyphenylglycine ((S)-4-C3HPG, 0.6 nmol) and group III mGluR agonist (RS)-1-amino-3-(phosphonomethylene) cyclobutane-carboxylic acid (32 nmol). Generalised clonic--tonic seizures were completely suppressed and the metabolic changes were markedly ameliorated, there being only a 1.5-, 2- and 2.5-fold rise of lactate, respectively. Higher doses of (S)-4-C3HPG (1--100 nmol) were, however, less anticonvulsant than low doses. The present results have confirmed that mGluRs may be considered a potential target for treatment of epilepsy.     

Effect of free radical spin trap N-tert-butyl-alpha-phenylnitrone (PBN) on seizures induced in immature rats by homocysteic acid

The present study has examined the effect of free radical spin trap N-tert-butyl-alpha-phenylnitrone (PBN) in the model of seizures induced in immature 12-day-old rats by bilateral intracerebroventricular infusion of dl-homocysteic acid (dl-HCA, 600 nmol/side). PBN was given i.p. in two doses (100 mg/kg each), 30 min prior and 30 min after dl-HCA infusion. PBN did not significantly influence the severity of seizures, evident both from the behavioral symptoms and EEG recordings. PBN normalized decreased ATP levels in the hippocampus, occurring during the acute phase of seizures ( approximately 45-50 min after infusion) and persisting until the end of the 24-h recovery period. PBN also led to normalization of decreased glucose levels and to a significant reduction of lactate accumulation in the cerebral cortex and hippocampus. The neuroprotective effect of PBN was evaluated after 24 h and 6 days of survival following dl-HCA-induced seizures (Nissl and Fluoro-Jade B staining). The administration of PBN resulted in a partial amelioration of severe damage observed in many brain regions following infusion of dl-HCA alone. The data suggest that increased free radical production is apparently occurring during seizures induced in immature rats by homocysteic acid. Free radical scavenger PBN had a clear-cut protective effect, evident as the improved recovery of brain energy status and as a partial, but significant, attenuation of neuronal degeneration associated with this model of seizures.