2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline and Status-Epilepticus

The AMPA receptor subtype of glutamate receptors, which mediates fast synaptic excitation, is of primary importance in initiating epileptiform discharges, so that AMPA receptor antagonists exert anti-seizure activity in diverse animal models of partial and generalized seizures. Recently, the first AMPA receptor antagonist, perampanel, was approved for use as adjunctive therapy for the treatment of resistant partial seizures in patients. Interestingly, the competitive AMPA receptor antagonist NBQX has recently been reported to prevent development of spontaneous recurrent seizures (SRS) in a neonatal seizure model in rats, indicating the AMPA antagonists may exert also antiepileptogenic effects. This prompted us to evaluate competitive (NBQX) and noncompetitive (perampanel) AMPA receptor antagonists in an adult mouse model of mesial temporal lobe epilepsy. In this model, SRS develop after status epilepticus (SE) induced by intrahippocampal injection of kainate. Focal electrographic seizures in this model are resistant to several major antiepileptic drugs. In line with previous studies, phenytoin was not capable of blocking such seizures in the present experiments, while they were markedly suppressed by NBQX and perampanel. However, perampanel was less tolerable than NBQX in epileptic mice, so that only NBQX was subsequently tested for antiepileptogenic potential. When mice were treated over three days after kainate-induced SE with NBQX (20 mg/kg t.i.d.), no effect on development or frequency of seizures was found in comparison to vehicle controls. These results suggest that AMPA receptor antagonists, while being effective in suppressing resistant focal seizures, are not exerting antiepileptogenic effects in an adult mouse model of partial epilepsy.

Topics: Animals; Anticonvulsants; Chronic Disease; Disease Models, Animal; Electroencephalography; Epilepsy, Temporal Lobe; Female; Hippocampus; Kainic Acid; Mice; Nitriles; Phenytoin; Pyridones; Quinoxalines; Receptors, AMPA; Seizures; Status Epilepticus

Glutamatergic mossy fibers of the hippocampus sprout in temporal lobe epilepsy and establish aberrant synapses on granule cells from which they originate. There is currently no evidence for the activation of kainate receptors (KARs) at recurrent mossy fiber synapses in epileptic animals, despite their important role at control mossy fiber synapses. We report that KARs are involved in ongoing glutamatergic transmission in granule cells from chronic epileptic but not control animals. KARs provide a substantial component of glutamatergic activity, because they support half of the non-NMDA receptor-mediated excitatory drive in these cells. KAR-mediated EPSC(KA)s are selectively generated by recurrent mossy fiber inputs and have a slower kinetics than EPSC(AMPA). Therefore, in addition to axonal rewiring, sprouting of mossy fibers induces a shift in the nature of glutamatergic transmission in granule cells that may contribute to the physiopathology of the dentate gyrus in epileptic animals.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Disease Models, Animal; Electric Stimulation; Epilepsy; Excitatory Postsynaptic Potentials; Hippocampus; In Vitro Techniques; Male; Mossy Fibers, Hippocampal; Patch-Clamp Techniques; Quinoxalines; Rats; Rats, Wistar; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Status Epilepticus; Synapses

Various studies demonstrated that the neurotransmitter norepinephrine (NE) plays a relevant role in modulating seizures; in particular, a powerful effect consists in delaying the kindling of limbic areas such as the amygdala and hippocampus. Given the rich NE innervation of limbic regions, we selected a sensitive trigger area, the anterior piriform cortex, to test whether previous loss of noradrenergic terminals modifies sporadic seizures in rats. The damage to locus coeruleus terminals was produced by using the selective neurotoxin N-(-2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4, 60 mg/kg i.p.). In intact rats, bicuculline (a GABA-A antagonist, 118 pmol) microinfused into this area produced sporadic seizures, while in rats previously injected with DSP-4, bicuculline determined long-lasting self-sustaining status epilepticus. In intact rats, sporadic seizures were accompanied by a marked increase in norepinephrine release in the contralateral piriform cortex, while in locus coeruleus-lesioned rats this phenomenon was attenuated. While bicuculline-induced sporadic seizures were prevented by the focal infusion of amino-7-phosphonoheptanoic acid (AP-7, a selective NMDA antagonist), or 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulphonamide (NBQX, a selective non-NMDA antagonist), status epilepticus obtained in norepinephrine-lesioned rats was insensitive to AP-7 but was still inhibited by NBQX. By using fluorescent staining for damaged (Fluoro-Jade B) and intact (DAPI) neurons, as well as cresyl violet, we found that rats undergoing status epilepticus developed neuronal loss in various limbic regions. This study demonstrates a powerful effect of noradrenergic terminals in regulating the onset of limbic status epilepticus and its sensitivity to specific glutamate antagonists.

Topics: Animals; Benzylamines; Bicuculline; Biogenic Monoamines; Cerebellum; Dopamine beta-Hydroxylase; Drug Interactions; Electroencephalography; Excitatory Amino Acid Antagonists; Extracellular Space; Frontal Lobe; GABA Antagonists; Hippocampus; Immunohistochemistry; Kindling, Neurologic; Locus Coeruleus; Male; Neurons; Neurotoxins; Norepinephrine; Olfactory Pathways; Quinoxalines; Rats; Rats, Sprague-Dawley; Seizures; Staining and Labeling; Status Epilepticus; Time Factors

To investigate if AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor activation contributes to acute manifestations and long term consequences of status epilepticus (SE), we administered the AMPA receptor antagonist NBQX to P35 rats undergoing kainic acid (KA)-induced SE. NBQX (30 mg/kg/dose) given intraperitoneally (i.p.) at 30, 60 and 90 min after i.p. KA injection (12 mg/kg) reduced severity of SE. When tested as adults, rats that had received KA and NBQX were similar to controls with no long term impairment in visuospatial memory (assessed by the water maze test), or histologic damage in the CA1 or CA3 hippocampal subfields. However, both P35 groups, those receiving KA alone and those receiving KA and NBQX, had similar rates of spontaneous recurrent seizures (SRS). In P15 rats, NBQX resulted in increased acute mortality from KA associated SE. These results indicate that the effects of NBQX on KA-induced SE are age dependent, and that non-NMDA receptor activation contributes to the acute manifestations and to the long term sequelae seen after KA-induced SE in the prepubescent rat brain.

Topics: Animals; Brain; Brain Chemistry; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Kainic Acid; Maze Learning; Quinoxalines; Rats; Receptors, AMPA; Status Epilepticus

The present study investigates the role of pharmacologic blockade of NMDA (N-methyl-D-aspartate) and non-NMDA receptors at deep prepiriform cortex (area tempestas, AT) in neuronal injury during prolonged seizures in rat. Status epilepticus was induced by intravenous kainate (15 mg/kg) and neuronal death was assessed in hippocampal CA3 sector 72 h following status epilepticus. Unilateral equimolar microinjections of 2-amino-7-phosphonoheptanoic acid (AP-7), an NMDA receptor antagonist, or 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX), a non-NMDA receptor antagonist, into AT were given prior to kainate administration. Counts of surviving cells in CA3 ipsilateral to NBQX-injected AT were significantly greater than on the contralateral control-side, but no significant difference between the AP-7-injected and saline-injected side was found. These results indicate that neurotransmission via non-NMDA receptors is more important than that via NMDA receptors at AT in the genesis of neuronal injury in hippocampus during kainate-induced status epilepticus.

Topics: 2-Amino-5-phosphonovalerate; Animals; Anticonvulsants; Cell Death; Drug Evaluation, Preclinical; Excitatory Amino Acid Antagonists; Hippocampus; Kainic Acid; Male; Neuroprotective Agents; Olfactory Pathways; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Reproducibility of Results; Status Epilepticus

MUSCARINIC, NMDA and metabotropic glutamate receptor antagonists were tested for anticonvulsant effects in a continuous hippocampal stimulation model in rats in order to identify the receptors involved in the initiation of electrically induced status epilepticus (SE). Whereas the muscarinic receptor antagonists scopolamine and atropine and the metabotropic receptor antagonist L(+)-2-amino-3-phosphonopropionic acid (AP3) did not affect SE initiation, the N-methyl-D-aspartate (NMDA) antagonist dizocilpine (MK-801) (1 mg kg-1 i.p.) and the non-NMDA ionotropic receptor antagonist 2,3-dihydroxy-6-nitro-7-sulphamoylbenzo(F)-quinoxaline (NBQX) (two doses of 50 micrograms i.c.v.) prevented the induction of SE. It has been shown in a previous study that non-NMDA ionotropic receptors are involved in SE maintenance and it is now suggested that activation of NMDA receptors may principally initiate electrically induced SE, although non-NMDA ionotropic receptors may also be involved.

Topics: Animals; Atropine; Cerebral Ventricles; Dizocilpine Maleate; Electric Stimulation; Hippocampus; Injections, Intraperitoneal; Injections, Intraventricular; Male; Quinoxalines; Rats; Rats, Wistar; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Scopolamine; Status Epilepticus

We used a 24 h perforant path stimulation model of status epilepticus to study the role of non-NMDA receptors in the loss of hilar interneurons and paired pulse inhibition associated with the model. In one experiment, NBQX administered i.v. at 1.0 mg/kg/h significantly reduced the loss of hematoxylin and eosin-stained hilar neurons from 360.2 to 125.3 but failed to protect against the loss of paired pulse inhibition. In a second experiment, i.v. NBQX at 1.5 mg/kg/h significantly protected against loss of SS- and NPY-positive hilar interneurons but also failed to protect against loss of paired pulse inhibition. These results demonstrate that the neuronal loss associated with sustained stimulation of this excitatory pathway is mediated in part through non-NMDA receptors. The lack of protection against loss of paired pulse inhibition suggests that SS- and NPY-immunoreactive interneurons may not be responsible for frequency-dependent paired-pulse inhibition of dentate granule cells.

Topics: Animals; Cell Survival; Hippocampus; Interneurons; Male; Neuropeptides; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Amino Acid; Status Epilepticus

The role of N-methyl-D-aspartate (NMDA), non-NMDA glutamate, metabotropic and muscarinic receptors in the maintenance of status epilepticus (SE) was investigated. SE induced in rat brain by continuous electrical stimulation to the hippocampus was terminated by intracerebroventricular (i.c.v.) injection of the non-NMDA antagonists DNQX and NBQX, but not by the muscarinic antagonists scopolamine or atropine, or the metabotropic antagonist AP3. The NMDA antagonist, MK-801 suppressed motor seizure activity but did not terminate electrographic seizures when generalized SE was induced, suggesting that both non-NMDA and NMDA receptors maintain generalized convulsive SE. However, when limbic SE was induced, MK-801 also had an anticonvulsant effect suggesting differences in the mechanisms maintaining limbic SE and generalized SE.

Topics: Animals; Anticonvulsants; Atropine; Brain; Cerebral Ventricles; Dizocilpine Maleate; Electric Stimulation; Electroencephalography; Hippocampus; Injections, Intraventricular; Male; Quinoxalines; Rats; Rats, Wistar; Receptors, Glutamate; Receptors, Muscarinic; Scopolamine; Status Epilepticus