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

Experimental autoimmune encephalomyelitis reproduces in rodents the features of multiple sclerosis, an immune-mediated, disabling disorder of the human nervous system. No adequate therapy is available for multiple sclerosis, despite anti-inflammatory, immunosuppressive, and immunomodulatory measures. Increasingly glutamate is implicated in the pathogenesis of neurodegenerative diseases. Here we (1) review changes in the glutamatergic system in multiple sclerosis and (2) reveal the effects of glutamate AMPA antagonists in acute and chronic rodent models of multiple sclerosis. Administration of structurally diverse competitive and non-competitive AMPA antagonists reduces neurologic disability in rodents subjected to acute experimental autoimmune encephalomyelitis. In addition, AMPA antagonists are active in both the adoptive transfer and in chronic models of experimental autoimmune encephalomyelitis in rats and mice and affect both the acute and chronic relapsing phases. Moreover, short-term therapy with AMPA antagonists leads to sustained benefit well into the progressive phases. These results imply that therapeutic strategies for multiple sclerosis should be complemented by glutamate AMPA antagonists to reduce neurologic disability.

Topics: Animals; Brain Stem; Disease Models, Animal; Encephalomyelitis, Autoimmune, Experimental; Excitatory Amino Acid Antagonists; Glutamic Acid; Humans; Mice; Mice, Inbred Strains; Multiple Sclerosis; Nootropic Agents; Pyrrolidinones; Quinoxalines; Rats; Receptors, AMPA; Spinal Cord

The existence of presynaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-type glutamate autoreceptors on glutamate nerve terminals in vitro has recently been demonstrated using synaptosomal and brain slice preparations. In the present study we have used a modification of a rapid dual-label intracerebral microdialysis method, previously developed by Young and co-workers(80,81) for the study of presynaptic mechanisms of neurotransmitter release, to investigate whether presynaptic AMPA receptors also play a role in the control of striatal glutamate release in vivo. For comparative purposes, the action of locally applied AMPA on striatal GABA release in vivo was also monitored. Local application of AMPA (0.01-100 microM), by reverse dialysis, into the striatum resulted in concentration-dependent increases in the Ca(2+)-dependent efflux of both [3H]L-glutamate and [14C]GABA. Maximum responses reached 142.0+/-6.5% and 166.8+/-7.7% of basal efflux for [3H]L-glutamate and [14C]GABA, respectively. No marked behavioural changes were observed at any dose of the agonist. Unexpectedly, the AMPA-evoked responses were not potentiated by the AMPA receptor desensitization inhibitors cyclothiazide (10-100microM) or aniracetam (1mM). Consistent with this finding, AMPA-stimulated [3H]L-glutamate and [14C]GABA efflux were significantly attenuated by co-perfusion with the selective, competitive AMPA receptor antagonist 6-nitro-7-sulphamoylbenzo(F)quinoxaline-2,3-dione (100microM) but not 1-(aminophenyl)-4-methyl-7,8-methylendioxy-5H-2,3-benzodiazepine (100microM), a non-competitive AMPA receptor antagonist known to interact with the cyclothiazide site to control AMPA receptor function. The broad spectrum ionotropic glutamate receptor antagonist, kynurenic acid (100-1000microM) also markedly inhibited the AMPA-evoked responses in the striatum in vivo. None of the antagonists, when given alone, influenced basal efflux of [3H]L-glutamate suggesting a lack of tonic regulatory control of glutamate release via presynaptic AMPA-type autoreceptors in the rat striatum. These results demonstrate the presence of presynaptic AMPA receptors, of a novel cyclothiazide- and aniracetam-insensitive subtype, on presynaptic nerve terminals in the rat striatum in vivo, acting to enhance glutamate and GABA release. Our data support the concept of AMPA receptor heterogeneity in vivo, a finding which may facilitate the development of novel, more selective drugs for the treatment of a

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Anti-Anxiety Agents; Antihypertensive Agents; Benzodiazepines; Benzothiadiazines; Calcium; Carbon Radioisotopes; Corpus Striatum; Excitatory Amino Acid Antagonists; gamma-Aminobutyric Acid; Glutamic Acid; Kynurenic Acid; Male; Microdialysis; Nootropic Agents; Potassium; Presynaptic Terminals; Pyrrolidinones; Quinoxalines; Rats; Rats, Wistar; Receptors, AMPA; Tritium

The study aimed to ascertain the involvement of central AMPA receptors in impulsive behaviors of aged rats and to examine the effects of aniracetam. Premature response in the two-lever choice reaction task was assessed as an index of impulsivity. Intracerebroventricular injection of 2, 3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX), an AMPA receptor antagonist, dose-dependently (10.1-1009 ng/rat) increased only premature response without altering responding speed and choice accuracy 30 min after the injection. Aniracetam (30 mg/kg p.o.), a positive allosteric modulator of AMPA receptors, or AMPA (55.9 ng/rat, co-injected with NBQX) completely restored the NBQX-induced increase in impulsivity. These results indicate that AMPA receptors are tonically involved in the regulation of impulsivity.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Anxiety; Behavior, Animal; Conditioning, Operant; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Impulsive Behavior; Male; Motor Activity; Nootropic Agents; Pyrrolidinones; Quinoxalines; Rats; Rats, Wistar; Receptors, AMPA

The present study describes the effect of (S)-2,3-dihydro-[3, 4]cyclopentano-1,2,4-benzothiadiazine-1,1-dioxide (S18986-1), a positive allosteric modulator of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors with cognitive-enhancing effects, on (S)-AMPA-induced [3H]noradrenaline release in rat hippocampal and frontal cortex slices. (S)-AMPA significantly increased [3H]noradrenaline release in rat hippocampus and frontal cortex slices, whereas S18986-1 (3-1000 microM) alone, was inactive. However, S18986-1 between 30 and 1000 microM potently enhanced (+200%) (S)-AMPA-mediated [3H]noradrenaline release in both hippocampal and frontal cortex slices. The capacity of S18986-1 to potentiate [3H]noradrenaline release was specific for AMPA receptors as S18986-1 failed to potentiate either kainate and N-methyl-D-aspartate (NMDA)-mediated release of [3H]noradrenaline in rat hippocampal slices. Moreover, 1, 2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX) and 1-(4-aminophenyl)-3-methylcarbamoyl-4-methyl-3, 4-dihydro-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI-53655) but not (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine ((+)-MK-801), inhibited (S)-AMPA and S18986-induced stimulation of (S)-AMPA-mediated [3H]noradrenaline release. In addition, S18986-1-induced stimulation of (S)-AMPA-evoked [3H]noradrenaline release was markedly attenuated in the presence of tetrodotoxin (1 microM) and in Ca(2+)-free buffer. S18986-1 enhanced (S)-AMPA-mediated [3H]noradrenaline release to a greater extent than its corresponding (R)-enantiomer S19024-1 and racemic mixture S17951-1. However, positive allosteric modulators of AMPA receptors such as aniracetam failed to potentiate AMPA-mediated noradrenaline release in hippocampal slices, whereas cyclothiazide potently enhanced (S)-AMPA-mediated [3H]noradrenaline release. These results suggest that the capacity of S18986-1 to enhance AMPA receptor-mediated release of noradrenaline in rat hippocampus and frontal cortex, could contribute to the cognition enhancing mechanisms of S18986-1.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Benzodiazepines; Benzothiadiazines; Calcium; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Synergism; Excitatory Amino Acid Antagonists; Frontal Lobe; Hippocampus; In Vitro Techniques; Male; Norepinephrine; Pyrrolidinones; Quinoxalines; Rats; Rats, Wistar; Receptors, AMPA; Stereoisomerism; Tetrodotoxin; Tritium

Aniracetam, 1-(1,3-benzodioxol-5-yl-carbonyl)piperidine (1-BCP) and cyclothiazide, three compounds considered to enhance cognition through modulation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors, were evaluated in the 'kynurenate test', a biochemical assay in which some nootropics have been shown to prevent the antagonism by kynurenic acid of the N-methyl-D-aspartate (NMDA)-evoked [3H]noradrenaline ([3H]NA) release from rat hippocampal slices. Aniracetam attenuated the kynurenate (100 microM) antagonism of the [3H]NA release elicited by 100 microM NMDA with high potency (EC50< or =0.1 microM). Cyclothiazide and 1-BCP were about 10 and 100 times less potent than aniracetam, respectively. The effect of aniracetam persisted in the presence of the AMPA receptor antagonist 6-nitro-7-sulphamoyl-benzo[f]quinoxaline-2,3-dione (NBQX) added at 5 microM, a concentration that did not affect NMDA receptors; in contrast, NBQX reduced the effect of 1-BCP and abolished that of cyclothiazide. The AMPA-evoked release of [3H]NA from hippocampal slices or synaptosomes was enhanced by cyclothiazide, less potently by 1-BCP and weakly by aniracetam. High concentrations of kynurenate (1 mM) antagonized the AMPA-evoked [3H]NA release in slices; this antagonism was attenuated by 1 microM cyclothiazide and reversed to an enhancement of AMPA-evoked [3H]NA release by 10 microM of the drug, but was insensitive to 1-BCP or aniracetam. It is concluded that aniracetam exerts a dual effect on glutamatergic transmission: modulation of NMDA receptor function at nanomolar concentrations, and modulation of AMPA receptors at high micromolar concentrations. As to cyclothiazide and 1-BCP, our data concur with the idea that both compounds largely act through AMPA receptors, although an NMDA component may be involved in the effect of 1-BCP.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Antihypertensive Agents; Benzothiadiazines; Dioxoles; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Heterocyclic Compounds; Hippocampus; In Vitro Techniques; Kynurenic Acid; Male; N-Methylaspartate; Nootropic Agents; Norepinephrine; Piperidines; Pyrrolidinones; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Tritium

The novel serotonin receptor subtypes, 5-HT6 and 5-HT7, are located in limbic regions and have nanomolar affinities for atypical antipsychotics. These factors have led some to speculate about the involvement of 5-HT6 and 5-HT7 receptors in schizophrenia. However, relatively little is known about these receptor subtypes, including the regulation of their expression in limbic regions. In particular, the regulation of extracellular serotonin levels in the striatum and hippocampal formation by glutamate receptors led us to examine the effects of systemic ionotropic glutamate receptor modulator treatment on 5-HT6 and 5-HT7 receptor expression in these regions. MK-801 treatment induced a dose-dependent decrease in striatal 5-HT6 receptor mRNA levels; similarly, both aniracetam and NBQX treatments also led to decreases in striatal 5-HT6 receptor mRNA levels. Hippocampal 5-HT6 and 5-HT7 receptor expression were not dramatically affected by any of the treatments. To our knowledge, this is the first demonstration of the regulation of striatal 5-HT6 receptor mRNA expression, and provides neurochemical anatomical evidence for the interaction of serotonergic and glutamatergic systems. Furthermore, although these two neurotransmitter systems are separately implicated in schizophrenia, the glutamatergic regulation of the expression of a receptor subtype associated with schizophrenia suggests that alterations in serotonin receptor expression in schizophrenia may result, in part, from altered glutamatergic activity.

Topics: Animals; Corpus Striatum; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Hippocampus; Male; Nootropic Agents; Pyrrolidinones; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, Serotonin; RNA, Messenger; Schizophrenia

Previous studies demonstrated that DBA/2J (DBA) mice performed poorly while C57BL/6J (C57) mice performed normally on a number of complex learning and memory tasks. Chronic oxiracetam treatment dramatically improved the performance of DBA mice but not that of C57 mice on the Morris water task and in contextual fear conditioning. The present study demonstrates that acute treatment with nootropics, oxiracetam (10-1000 mg/kg) or aniracetam (10-100 mg/kg), and N-methyl-D-Aspartate (NMDA) antagonists, (+)-MK-801 (0.1-3 microg/kg), CPP (0.01-0.3 mg/kg), and (+)-HA-966 (0.1-3 mg/kg), administered prior to training and testing, reversed the contextual learning impairment in DBA mice in a dose-dependent manner without affecting auditory cue conditioning. These effects appeared to be independent of testing order (context vs. auditory cue tests) and were not due to state-dependent learning. The inactive stereoisomers, (-)-MK-801 and (-)-HA-966, were incapable of increasing contextual freezing in DBA mice. In DBA mice, the effects of 30 mg/kg oxiracetam and 100 mg/kg aniracetam were inhibited by the (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonists, NBQX, and GYKI-52466. The combined administration of 30 mg/kg oxiracetam and 1 microg/kg (+)-MK-801 produced an additive response. None of the pharmacological treatments altered performance in C57 mice at doses that were effective in DBA mice. These results suggest that DBA mice may be learning impaired due to altered glutamatergic receptor function.

Topics: Acoustic Stimulation; Animals; Anti-Anxiety Agents; Benzodiazepines; Conditioning, Classical; Cues; Excitatory Amino Acid Antagonists; Fear; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Nootropic Agents; Pyrrolidines; Pyrrolidinones; Quinoxalines; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate

Aniracetam (1-p-anisoyl-2-pyrrolidinone) selectively reverses the anticonvulsant activities of the non-NMDA receptor antagonists, GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3- benzodiazepine.HCl) and, to a lesser extent, NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline), without affecting the anticonvulsant activity of the competitive NMDA receptor antagonist, D(-)-CPPene, in DBA/2 mice. Pretreatment with aniracetam (50 nmol i.c.v., 15 min before drugs) increases the ED50 values (mumol/kg i.p., 15 min) for GYKI 52466-induced protection against sound-induced clonic seizures in DBA/2 mice 7 fold, from 20.1 (11.9-33.9) to 142 (91.7-219), and for NBQX-induced protection 2 fold, from 39.7 (33.8-46.7) to 85.6 (63.9-115), respectively. Aniracetam on its own (12.5-100 nmol i.c.v.) has no convulsant activity, but reverses the anticonvulsant effect of GYKI 52466 (60 mumol/kg i.p., 15 min) in a dose-dependent manner.

Topics: Acoustic Stimulation; Animals; Anti-Anxiety Agents; Anticonvulsants; Benzodiazepines; Dose-Response Relationship, Drug; Mice; Mice, Inbred DBA; Piperazines; Pyrrolidinones; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Seizures