6-cyano-7-nitroquinoxaline-2-3-dione and Status-Epilepticus

In the present study, we aimed to investigate the effects of immediate and delayed treatment with intracerebroventricular (i.c.v.) gabapentin (GBP), carbamazepine (CBZ) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on learning and memory, anxiety, and locomotor activity in rats with lithium-pilocarpine-induced status epilepticus (SE). SE was induced by intraperitoneal injections of 3mEq/kg LiCl followed by 45mg/kg pilocarpine 24h later. In the first series of experiments, rats were divided into four groups three hours after the onset of SE and received GBP (100μg/10μl, two times a day; i.c.v.), CBZ (200μg/10μl; i.c.v.), CNQX (25nmol/10μl; i.c.v.) or saline (10μl; i.c.v.) for 7days. Six weeks after SE, cognitive and behavioral performances were evaluated by Morris water maze, elevated plus maze, and open field tests. In the second series, rats received no treatment for six weeks following SE. On the seventh week the same treatment with the previous rats was given and six weeks later the cognitive and behavioral tests were applied. SE significantly impaired spatial learning and memory in the Morris water maze. GBP treatment improved the acqusition and memory performance. CNQX worsened the acqusition but improved the memory performance, while CBZ worsened both parameters. In the elevated plus maze, epileptic rats which received saline showed significantly lower anxiety levels with respect to the naive rats. Only CBZ led to further anxiolysis, while the other drugs had no effect. Locomotor activity significantly increased due to SE, which was augmented by GBP and CNQX. The impact of immediate and delayed treatment with these drugs on cognition and behavior seems to be quite similar.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Amines; Animals; Behavior, Animal; Carbamazepine; Cognition; Cyclohexanecarboxylic Acids; Disease Models, Animal; Gabapentin; gamma-Aminobutyric Acid; Lithium; Male; Maze Learning; Motor Activity; Pilocarpine; Rats; Rats, Wistar; Status Epilepticus

γ-Aminobutyric acid (GABA)ergic transmission plays an important role in the initiation of epileptic activity and the generation of ictal discharges. The functional alterations in the epileptiform hippocampus critically depend on GABAergic mechanisms and cation-chloride cotransporters.. To understand the cellular basis of specific functional alterations in the epileptic hippocampus, we studied physiologic characteristics and pharmacologically isolated evoked GABA(A) receptor-mediated inhibitory postsynaptic currents (IPSCs) recorded from principal neurons in hippocampal slices from status epilepticus (SE) and control rats using whole-cell and gramicidin perforated patch-clamp recordings.. Whereas the resting membrane potential and input resistance were not significantly different between control and epileptic tissue, the reversal potential (E(GABA) ) of IPSCs was significantly shifted to more positive values in SE rats with regard to the resting membrane potential. Pharmacologic experiments and quantitative reverse transcriptase polymerase chain reaction (RT-PCR) showed that the observed changes in the epileptic tissue were due to a decreased ratio of the main Cl(-) extrusion transporter (K(+) -Cl(-) cotransporter, KCC2) to the main Cl(-) uptake transporter (Na(+) -K(+) -2Cl(-) cotransporter, NKCC1).. Our results suggest that alterations of cation-chloride cotransporter functions, comprising a higher NKCC1 action, contribute to hyperexcitability within the hippocampus following SE.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Analysis of Variance; Animals; Biophysical Phenomena; Bumetanide; Chlorides; Disease Models, Animal; Drug Interactions; Electric Stimulation; Excitatory Amino Acid Antagonists; Furosemide; Gene Expression Regulation; Hippocampus; Homeostasis; In Vitro Techniques; Inhibitory Postsynaptic Potentials; K Cl- Cotransporters; Male; Membrane Potentials; Neurons; Patch-Clamp Techniques; Pilocarpine; Rats; Rats, Wistar; Receptors, GABA-A; RNA, Messenger; Sodium Potassium Chloride Symporter Inhibitors; Status Epilepticus; Symporters

Glutamine (GLN) is a precursor for synthesis of glutamate and gamma-aminobutyric acid (GABA) and has been found in the cerebrospinal fluid (CSF) at mean concentrations of 0.6 mM. Experiments on slices are usually performed in artificial CSF (aCSF) kept free of amino acids. Therefore, the role of glutamine, particularly in tissue of epileptic animals, remains elusive.. Using extracellular recordings we studied effects of GLN on field potentials and stimulus-evoked field responses in the medial entorhinal cortex (MEC) of combined entorhinal cortex hippocampal slices from pilocarpine-treated chronic epileptic rats and age-matched saline-injected control rats.. In presence of GLN (0.5 and 2 mM) recurrent epileptiform discharges (REDs) were observed in slices from epileptic rats (64% and 80%, respectively), but not in slices from control rats. REDs were restricted to the superficial MEC, suppressed by the alpha-Amino-3-hydroxy-5-methyl-4-isoxazol-propionate (AMPA)/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (30 microM), attenuated by the inhibitor of neuronal glutamine transporters methylamino-isobutyric acid (10 mM), and apparently augmented and prolonged by the GABA(A) receptor antagonist bicuculline-methiodide (5 microM). In contrast, amplitudes of stimulus evoked nonsynaptic and synaptic field responses increased in slices from control rats (+23% and +12% of the reference values) and insignificantly less or not in those of epileptic rats (+6.5% and -0.25%, respectively). Notably, stimulus-evoked slow negative transients confined to slices of epileptic animals were reduced in amplitude (-18%).. In combined entorhinal hippocampal slices from chronic epileptic animals, GLN induces glutamatergic REDs via neuronal uptake in superficial layers of the MEC where inhibitory function seemed to be partially preserved.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Aminoisobutyric Acids; Animals; Bicuculline; Disease Models, Animal; Entorhinal Cortex; Evoked Potentials; Excitatory Amino Acid Antagonists; GABA Antagonists; Glutamine; In Vitro Techniques; Male; Pilocarpine; Rats; Rats, Wistar; Status Epilepticus

We examined the effects of blockers of N-methyl-D-asparate (NMDA) and +/- -alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptors on the maintenance of self-sustaining status epilepticus (SSSE) induced in rats by brief intermittent electrical stimulation of the perforant path (PPS). Blocking of NMDA receptor at the PCP site by MK-801 (0.5 mg/kg, i.p.) or ketamine (10 mg/kg, i.p.) as well as at the glycine allosteric site by intrahippocampal 5,7-dichlorokynurenic acid (5,7-DCK, 10 nmol), rapidly and irreversibly aborted both behavioral and electrographic manifestation of SSS. Intrahippocampal injection of the AMPA/kainate receptor blocker 6-cyano7-nitroquinixaline-3-dione (CNQX, 10 nmol) transiently suppressed seizures, which reappeared 4-5 h later. We suggest that the maintenance phase of SSSE depends on activation of NMDA receptors and that NMDA receptor blockers may be a promising class of compounds for the treatment of status epilepticus.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Anticonvulsants; Disease Models, Animal; Dizocilpine Maleate; Electric Stimulation; Excitatory Amino Acid Antagonists; Hippocampus; Ketamine; Kynurenic Acid; Male; Perforant Pathway; Rats; Rats, Wistar; Receptors, AMPA; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Status Epilepticus

In humans temporal lobe epilepsy (TLE) is characterized by recurrent seizures, neuronal hyperexcitability, and selective loss of certain neuronal populations in the hippocampus. Animal models of the condition indicate that a diminution of inhibition mediated by gamma-aminobutyric acid (GABA) accounts for the altered function, and it has been hypothesized that the diminution arises because GABAergic basket interneurons are "dormant" as a result of their being disconnected from excitatory inputs. In hippocampal slices, inhibitory postsynaptic potentials (IPSPs) were elicited in CA1 pyramidal cells by activation of basket cells; responses from an animal model of TLE were compared to those from control tissue. IPSPs evoked indirectly by activation of terminals that then excited basket cells were reduced in the epileptic tissue, whereas IPSPs evoked by direct activation of basket cells, when excitatory neurotransmission was blocked, were not different from controls. These results provide support for the "dormant basket cell" hypothesis and have implications for the pathophysiology and treatment of human TLE.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Baclofen; Electric Stimulation; Epilepsy, Temporal Lobe; Evoked Potentials; Hippocampus; In Vitro Techniques; Interneurons; Male; Membrane Potentials; Picrotoxin; Pyramidal Tracts; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate; Status Epilepticus