2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline and gamma-glutamylaminomethylsulfonic-acid

This study characterizes the receptor subtypes and investigates some of the mechanisms by which glutamate, injected intraplantarly (i.pl.) into the mouse paw, produces nociception and paw oedema. I.pl. injection of glutamate induced a rapid-onset, dose-related pain response associated with oedema formation, with mean ED(50) values of 2.6 (1.6-4.3) and 0.5 (0.4-0.7) micromol/kg, respectively. Pretreatment with Chicago sky blue 6B (100 microg/kg), an inhibitor of glutamate uptake, caused a significant (about sixfold) reduction of the mean ED(50) value for glutamate-induced nociception, but not paw oedema. NMDA receptor antagonist MK 801, given by systemic (i.p.), intracerebroventricular (i.c.v.), i.pl. or intrathecal (i.t.) routes, produced graded inhibition of glutamate-induced nociception. Non-NMDA receptor antagonists NBQX or GAMS, metabotropic antagonist E4CPG, and also the antagonist that acts at the NMDA receptor-associated glycine binding site felbamate, significantly inhibited the nociception induced by glutamate. L(omega)-N-nitro-arginine (given i.p., i.t., i.pl. or i.c.v.) prevented the nociception and paw oedema caused by glutamate, an effect that was reversed by L-arginine but not by D-arginine. S-nitroso-N-acetyl-D,L-penicillamine (SNAP), given i.pl., greatly potentiated glutamate-induced nociception and oedema formation. Finally, the i.pl. injection of glutamate was accompanied by a graded increase in the nitrite levels of the hindpaw exudate. It is concluded that the nociception caused by i.pl. injection of glutamate probably involves the activation of NMDA and non-NMDA receptors by a mechanism which largely depends on the activation of L-arginine-nitric oxide pathway. Glutamate-induced paw oedema seems to be primarily mediated by non-NMDA ionotropic glutamate receptors and release of nitric oxide.

Topics: Animals; Azo Compounds; Coloring Agents; Dizocilpine Maleate; Dose-Response Relationship, Drug; Edema; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Extremities; Glutamic Acid; Glutamine; Male; Mice; Nitric Oxide; Nitric Oxide Donors; Nitrites; Nitroarginine; Nociceptors; Penicillamine; Quinoxalines; Trypan Blue

The behavioural and convulsant effects of imipenem (Imi), a carbapenem derivative, were studied after intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) administration in DBA/2 mice, a strain genetically susceptible to sound-induced seizures. The anticonvulsant effects of some excitatory amino acid antagonists and muscimol (Msc), a GABAA agonist, against seizures induced by i.p. or i.c.v. administration of Imi were also evaluated. The present study demonstrated that the order of anticonvulsant activity in our epileptic model, after i.p. administration, was (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)-cyclohepten-5,10-imine maleate (MK-801) > (+/-)(E)-2-amino-4-methyl-5-phosphono-3-pentenoate ethyl ester (CGP 39551) > 3-((+/-)-2-carboxypiperazin-4-yl)propenyl-1-phosphonic acid (CPPene) > 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CCP) > 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)-quinoxaline (NBQX). Ifenprodil, a compound acting on the polyamine site of NMDA receptor complex was unable to protect against seizures induced by Imi, suggesting that the poliamine site did not exert a principal role in the genesis of seizures induced by Imi. In addition, the order of anticonvulsant potency in our epileptic model, after i.c.v. administration, was CPPene > MK-801 > Msc > (-)-2-amino-7-phosphonic acid (AP7) > gamma-D-glutamylaminomethylsulphonate (gamma-D-GAMS) > NBQX > kynurenic acid (KYNA) > 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX). The relationship between the different site of action and the anticonvulsant activity of these derivatives was discussed. Although the main mechanism of Imi induced seizures cannot be easily determined, potential interactions with the receptors of the excitatory amino acid neurotransmitters exists. In fact, antagonists of excitatory amino acids are able to increase the threshold for the seizures or to prevent the seizures induced by Imi. In addition, Imi acts on the central nervous system by inhibition of GABA neurotransmission and Msc, a selective GABAA agonist, was able to protect against seizures induced by Imi.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Animals; Anticonvulsants; Dizocilpine Maleate; Excitatory Amino Acids; Glutamine; Imipenem; Kynurenic Acid; Mice; Mice, Inbred DBA; Muscimol; Piperazines; Piperidines; Quinoxalines; Seizures

The effects of the glutamate receptor antagonist gamma-D-glutamylaminomethyl sulfonic acid (GAMS) on inward currents induced by bath application of kainic acid (KA) or alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) were studied with single-electrode voltage clamp methods in Xenopus oocytes injected 3-5 days previously with mRNA from the brain of E16-17 chick embryos. Both AMPA and KA induced smooth inward currents, with Hill coefficients of 1.5 (AMPA) and 2.1 (KA). GAMS, at concentrations up to 1 mM, produced no reliable antagonism of AMPA-induced currents but showed a consistent, dose-dependent and reversible antagonism of KA-induced responses; the slope of the Schild plot was 0.76 and the pA2 value 4.32. In the presence of GAMS, however, the Hill coefficient for AMPA is reduced significantly and approaches unity, suggesting that AMPA interacts with both KA and AMPA binding sites on chick brain glutamate receptors. The selectivities of three quinoxalinedione antagonists (6,7-dinitroquinoxaline-2,3-dione [DNQX], 6-cyano-7- nitroquinoxaline-2,3-dione [CNQX] and 6-nitro-7-sulfamoyl-benzo(F)quinoxaline-2,3-dione [NBQX]) were then compared with that shown by GAMS. DNQX, CNQX and NBQX all blocked the effects of both KA and AMPA completely, competitively, reversibly and dose-dependently, with Schild-plot slopes very close to 1.0. Against AMPA, observed pA2 values were 6.58 for DNQX, 6.43 for CNQX and 6.77 for NBQX. Against KA, pA2 values were 6.42 for DNQX, 6.56 for CNQX and 7.21 for NBQX.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Brain Chemistry; Chick Embryo; Electrophysiology; Glutamine; Kainic Acid; Kinetics; Oocytes; Quinoxalines; Receptors, Glutamate; RNA, Messenger; Xenopus