4-aminopyrrolidine-2-4-dicarboxylic-acid and homocysteic-acid

The widely-held assumption was that oxidative stress does not occur during seizures in the immature brain. The major finding of the present study concerns evidence of oxidative stress in the brain of immature rats during seizures induced by DL-homocysteic acid. Seizures were induced in 12-day-old rats by bilateral intracerebroventricular infusion of DL-homocysteic acid (DL-HCA, 600 nmol/side) and oxidative stress was evaluated by in situ detection of superoxide anion (O(2)·(-)). Using hydroethidine (Het) method, the fluorescent signal of the oxidized products of Het (reflecting O(2)·(-) production) significantly increased (by 50%-60%) following 60 min lasting seizures in all the studied structures, namely CA1, CA3 and dentate gyrus of the hippocampus, cerebral cortex and thalamus. The enhanced O(2)·(-) production was substantially attenuated or completely prevented by substances providing an anticonvulsant effect, namely by a competitive NMDA receptor antagonist AP7, a highly selective and potent group II metabotropic glutamate receptor (mGluR) agonist 2R,4R-APDC and highly selective group III mGluR, subtype 8 agonist (S)-3,4-DCPG. Complete protection was achieved by two SOD mimetics Tempol and MnTMPYP which strongly suggest that the increased fluorescent signal reflects O(2)·(-) formation. In addition, both scavengers provided a partial protection against brain damage associated with the present model of seizures. Signs of neuronal degeneration, as evaluated by Fluoro-Jade B staining, were detected at 4h following the onset of seizures. The present findings thus suggest that the increased superoxide generation precedes neuronal degeneration and may thus play a causative role in neuronal injury. Occurrence of oxidative stress in brain of immature rats during seizures, as demonstrated in the present study, can have a clinical relevance for a novel approach to the treatment of epilepsy in children, suggesting that substances with antioxidant properties combined with the conventional therapies might provide a beneficial effect.

Topics: 2-Amino-5-phosphonovalerate; Animals; Animals, Newborn; Anticonvulsants; Brain; Disease Models, Animal; Homocysteine; Infusions, Intraventricular; Male; Metalloporphyrins; Proline; Rats; Rats, Wistar; Seizures; Statistics, Nonparametric; Superoxides; Time Factors

The present study has examined the anticonvulsant and neuroprotective effect of 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate (2R,4R-APDC), a selective agonist for group II metabotropic glutamate receptors (mGluRs) when given 10-15 min after the onset of seizures induced in 12-day-old rats by bilateral icv infusion of DL-homocysteic acid (DL-HCA, 600 nmol/side). For biochemical analyses, rat pups were sacrificed during generalized clonic-tonic seizures, approximately 45-50 min after infusion of DL-HCA. Comparable time intervals were used for sacrificing the animals which received 2R,4R-APDC (0.05 nmol/side) or saline. The severity of seizures was influenced only slightly when the agonist was given after the onset of seizures, as evaluated both from the behavioral symptoms and from EEG recordings. A tendency to lower number and a shorter duration of seizures was outlined in animals posttreated with 2R,4R-APDC, but the differences did not reach the level of statistical significance. Cortical energy metabolite changes which normally accompany seizures in immature rats (large decrease of glucose and glycogen and a marked rise of lactate) were ameliorated only partially. The neuroprotective effect of 2R,4R-APDC was evaluated after 24 h and 6 days of survival following DL-HCA-induced seizures. Massive neuronal degeneration in many brain regions, mainly in the hippocampus and thalamus, following infusion of DL-HCA alone was only partially attenuated after 2R,4R-APDC posttreatment. The present findings clearly indicate that both anticonvulsant and neuroprotective effect of 2R,4R-APDC against DL-HCA-induced seizures is substantially diminished when the agonist is given after the onset of seizures as compared with its efficacy after the pretreatment (Exp. Neurol.192, 420-436, 2005).

Topics: Aging; Animals; Brain; Convulsants; Cytoprotection; Drug Administration Schedule; Drug Interactions; Epilepsy; Excitatory Amino Acid Agonists; Hippocampus; Homocysteine; Male; Nerve Degeneration; Neuroprotective Agents; Proline; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Thalamus; Treatment Outcome

The present study has examined the anticonvulsant and neuroprotective effect of group II metabotropic glutamate receptor (mGluR) agonist (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (2R,4R-APDC) 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). For biochemical analyses, rat pups were sacrificed during generalized clonic-tonic seizures, approximately 45-50 min after infusion. Comparable time intervals were used for sacrificing the pups which had received 2R,4R-APDC. Low doses of 2R,4R-APDC (0.05 nmol/side) provided a pronounced anticonvulsant effect which was abolished by pretreatment with a selective group II mGluR antagonist LY341495. Generalized clonic-tonic seizures were completely suppressed and cortical energy metabolite changes which normally accompany these seizures were either normalized (decrease of glucose and glycogen) or markedly reduced (an accumulation of lactate). EEG recordings support the marked anticonvulsant effect of 2R,4R-APDC, nevertheless, this was only partial. In spite of the absence of obvious motor phenomena, isolated spikes or even short periods of partial ictal activity could be observed. Isolated spikes could also be seen in some animals after application of 2R,4R-APDC alone, reflecting most likely subclinical proconvulsant activity of this agonist. The neuroprotective effect of 2R,4R-APDC was evaluated after 24 h and 6 days of survival following DL-HCA-induced seizures. Massive neuronal degeneration, as revealed by Fluoro-Jade B staining, was observed in a number of brain regions following infusion of DL-HCA alone (seizure group), whereas 2R,4R-APDC pretreatment provided substantial neuroprotection. The present findings support the possibility that group II mGluRs are a promising target for a novel approach to treating epilepsy.

Topics: Amino Acids; Animals; Animals, Newborn; Anticonvulsants; Behavior, Animal; Brain; Brain Chemistry; Brain Injuries; Dose-Response Relationship, Drug; Drug Interactions; Electroencephalography; Excitatory Amino Acid Antagonists; Fluoresceins; Fluorescent Dyes; Functional Laterality; Glucose; Glycogen; Homocysteine; Lactic Acid; Male; Nerve Degeneration; Organic Chemicals; Proline; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Seizures; Time Factors; Xanthenes

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.

Topics: Animals; Animals, Newborn; Anticonvulsants; Brain; Cyclobutanes; Cyclopropanes; Dose-Response Relationship, Drug; Epilepsy; Excitatory Amino Acid Agonists; Glycine; Homocysteine; Male; Neuroprotective Agents; Organophosphorus Compounds; Proline; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Seizures