ro-25-6981 and Seizures

Ro 25-6981 maleate is a highly selective and activity-dependent antagonist of NMDA ionotropic glutamate receptors containing NR2B subunit (NR2B/NMDARs). The aim of our study was to investigate the influence of Ro 25-6981 administration in developing rats on physiological (single and paired pulse cortical interhemispheric evoked potentials) and epileptic brain activity (cortical afterdischarges (ADs)). Electrophysiological experiments were performed in animals with epidurally implanted electrodes at postnatal days (P) P12, P18, and P25. The drug was injected intraperitoneally at a dose of 1 or 3mg/kg. Control animals were injected with saline (1ml/kg). Single interhemispheric responses were evoked with 0.5-ms biphasic pulses with intensities increasing from 0.4 to 5mA, paired-pulse responses were elicited by twofold threshold intensity. The ADs were elicited by series of 15-s of 1-ms pulses at 8-Hz frequency. Firstly, six stimulations with stable suprathreshold intensity repeated at 30-min intervals were used to determine the time course of Ro 25-6981 effects against ADs in P12 animals. Secondly, similar experiment was performed in all age groups of animals but with 20-min intervals as well as a further experiment using stimulations with stepwise intensities increasing at 10-min intervals from 0.2 to 15 mA. Pretreatment with the 3-mg/kg (but not the lower) dose of Ro 25-9681 decreased significantly the amplitude of single responses evoked with higher stimulation intensities in P12 and P18 animals. Both doses affected responses in P25 animals, only the 1-mg/kg dose was more efficacious than the 3-mg/kg one. Paired pulse responses were not affected by either dose of Ro 25-6981 in any age group. Ro 25-9681 clearly influenced the duration of ADs only in P12 animals. The 1-mg/kg dose did not change the duration of ADs whereas the 3-mg/kg dose suppressed progressive prolongation of ADs with repeated stimulations. This effect was seen even 110-min after the drug injection. The modification of ADs, i.e. stimulations with stepwise increasing intensities (10 min intervals) was used to demonstrate possible dependence on activity. The Ro 25-6981 was administered immediately after the 4-mA stimulation (i.e. when rats experienced six ADs on the average). The 3-mg/kg dose resulted in shorter ADs after high stimulation intensities in P12. There were no significant effects in older animals, only a tendency to ADs shortening was observed in P25 rats. In conclusion, our resu

Topics: Age Factors; Animals; Anticonvulsants; Electric Stimulation; Male; Membrane Potentials; Phenols; Piperidines; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Seizures; Sensorimotor Cortex

NR2B-subtype-selective antagonists differ from MK-801, a nonselective NMDA receptor antagonist. MK-801 antagonizes electrical seizures at doses as low as 0.1 to 0.18mg/kg and elicits popping at doses as low as 0.5mg/kg, whereas ifenprodil and Ro 8-4304 were unable to do so at the doses tested. Ro 25-6981, however, was able to antagonize electrically-precipitated tonic hindlimb extension at 100mg/kg, but was not able to elicit popping behavior at this dose.

Topics: Animals; Dose-Response Relationship, Drug; Electroshock; Male; Mice; Phenols; Piperidines; Receptors, N-Methyl-D-Aspartate; Seizures

We showed previously that electrographic seizures involving dentate granule cells in organotypic hippocampal slice cultures were dramatically reduced following chronic treatment with the NR2B-selective antagonist, Ro25,6981, but were increased following chronic treatment with the high-affinity competitive antagonist, D(-)-2-amino-5-phosphonopentanoic acid (D-APV). To begin to investigate the potential mechanisms underlying the differential effects of N-methyl-D-aspartate receptor (NMDAR) antagonists on seizures, electrophysiologic experiments were conducted in dentate granule cells in hippocampal slice cultures treated for the entire 17-21 day culture period with vehicle, Ro25,6981 or D-APV. Initial experiments revealed a lack of an association between miniature excitatory postsynaptic current (mEPSC) measures and seizures suggesting that shifts in mEPSC were unlikely to account for the differential effects of D-APV and Ro25,6981 on seizures. However, the amplitude of tonic NMDAR-mediated currents was reduced in cultures treated chronically with D-APV and dramatically enhanced in cultures treated chronically with Ro25,6981. Because tonic NMDAR currents are mediated primarily by extrasynaptic NMDAR, these data show an inverse relationship between changes in extrasynaptic NMDAR function and alterations in seizure expression.

Topics: Animals; Dentate Gyrus; Disease Models, Animal; GABA-A Receptor Antagonists; Hippocampus; Phenols; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Seizures; Synaptic Transmission

Freeze-lesion-induced focal cortical dysplasia in rats closely resembles human microgyria, a neuronal migration disorder associated with drug-resistant epilepsy. Alterations in expression of N-methyl-D-aspartate receptors (NMDARs) containing NR2B subunits have been suggested to play a role in the hyperexcitability seen in this model. We examined the effect of NMDAR antagonists selective for NR2B subunits (Ro 25-6981 and ifenprodil) on activity evoked by intracortical stimulation in brain slices from freeze-lesioned rat neocortex. Whole-cell voltage-clamp recordings showed that Ro 25-6981 (1 microM) significantly reduced the response area of evoked postsynaptic currents in pyramidal cells from the paramicrogyral area whereas responses were unaffected in slices from control (sham operated) animals. Voltage-sensitive dye imaging was used to examine spatiotemporal spread of evoked activity in lesioned and control cortices. The imaging experiments revealed that peak amplitude, duration, and lateral spread of evoked activity in the paramicrogyral area was reduced by bath application of Ro 25-6981 (1 microM) and ifenprodil (10 microM). Ro 25-6981 had no effect on evoked activity in neocortical slices from control animals. The non-selective NMDAR antagonist d-2-amino-5-phosphonvaleric acid (APV, 20 microM) reduced activity evoked in presence of 50 microM 4-aminopyridine (known to increase excitability by enhancing neurotransmitter release) in neocortical slices from control animals whereas Ro 25-6981 (1 microM) did not. These results suggest that NR2B subunit-containing NMDARs contribute significantly to the enhanced spatiotemporal spread of paroxysmal activity observed in vitro in the rat freeze-lesion model of focal cortical dysplasia.

Topics: Adrenergic alpha-Antagonists; Animals; Disease Models, Animal; Evoked Potentials; Neocortex; Patch-Clamp Techniques; Peptide Fragments; Phenols; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Seizures

Recently, we disclosed 4-aminoquinolines as structurally novel NR1/2B subtype selective NMDA receptor antagonists. We would now like to report our findings on structurally related pyridine analogues. The SAR developed in this series resulted in the discovery of high affinity antagonists which are selective (vs alpha1 and M1 receptors) and active in vivo.

Topics: Acoustic Stimulation; Animals; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Hydrogen-Ion Concentration; Isoquinolines; Mice; Mice, Inbred DBA; Pyridines; Receptors, N-Methyl-D-Aspartate; Seizures; Structure-Activity Relationship

Excitotoxic neuronal injury by action of the glutamate receptors of the N-methyl-d-aspartate (NMDA) subtype have been implicated in the pathogenesis of brain damage as a consequence of bacterial meningitis. The most potent and selective blocker of NMDA receptors containing the NR2B subunit is (R,S)-alpha-(4-hydroxyphenyl)-beta-methyl-4-(phenylmethyl)-1-piperid inepropanol (RO 25-6981). Here we evaluated the effect of RO 25-6981 on hippocampal neuronal apoptosis in an infant rat model of meningitis due to Streptococcus pneumoniae. Animals were randomized for treatment with RO 25-6981 at a dosage of either 0.375 mg (15 mg/kg; n = 28) or 3.75 mg (150 mg/kg; n = 15) every 3 h or an equal volume of sterile saline (250 microl; n = 40) starting at 12 h after infection. Eighteen hours after infection, animals were assessed clinically and seizures were observed for a period of 2 h. At 24 h after infection animals were sacrificed and brains were examined for apoptotic injury to the dentate granule cell layer of the hippocampus.. Treatment with RO 25-6981 had no effect on clinical scores, but the incidence of seizures was reduced (P < 0.05 for all RO 25-6981 treated animals combined). The extent of apoptosis was not affected by low or high doses of RO 25-6981. Number of apoptotic cells (median [range]) was 12.76 [3.16-25.3] in animals treated with low dose RO 25-6981 (control animals 13.8 [2.60-31.8]; (P = NS) and 9.8 [1.7-27.3] (controls: 10.5 [2.4-21.75]) in animals treated with high dose RO 25-6981 (P = NS).. Treatment with a highly selective blocker of NMDA receptors containing the NR2B subunit failed to protect hippocampal neurons from injury in this model of pneumococcal meningitis, while it had some beneficial effect on the incidence of seizures.

Topics: Animals; Animals, Suckling; Apoptosis; Cell Count; Cerebrospinal Fluid; Dentate Gyrus; Disease Models, Animal; Disease Progression; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Excitatory Amino Acid Antagonists; Meningitis, Pneumococcal; Neurons; Phenols; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Seizures; Survival Rate; Treatment Outcome