Fenbufen pretreatment potentiates the anticonvulsant activity of CPPene and NBQX in DBA/2 mice

Group III mGlu receptor agonists potentiate the anticonvulsant effect of AMPA and NMDA receptor block

We report the anticonvulsant action in DBA/2 mice of two mGlu Group III receptor agonists: (R,S)-4-phosphonophenylglycine, (R,S)-PPG, a compound with moderate mGlu8 selectivity, and of (1S,3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid, ACPT-1, a selective agonist for mGlu4alpha receptors. Both compounds, given intracerebroventricularly at doses which did not show marked anticonvulsant activity, produced a consistent shift to the left of the dose-response curves (i.e. enhanced the anticonvulsant properties) of 1-(4'-aminophenyl)-3,5-dihydro-7,8-dimethoxy-4H-2,3-benzodiazepin-4-one hydrochloride, CFM-2, a noncompetitive AMPA receptor antagonist, and 3-((+/-)-2-carboxypiperazin-4-yl)-1-phosphonic acid, CPPene, a competitive NMDA receptor antagonist, in DBA/2 mice. In addition, (R,S)-PPG and ACPT-1 administered intracerebroventricularly prolonged the time course of the anticonvulsant properties of CFM-2 (33 micromol/kg, i.p.) and CPPene (3.3 micromol/kg, i.p.) administered intraperitoneally. We conclude that modest reduction of synaptic glutamate release by activation of Group III metabotropic receptors potentiates the anticonvulsant effect of AMPA and NMDA receptor blockade.

NMDA and AMPA/kainate receptors are involved in the anticonvulsant activity of riluzole in DBA/2 mice

The anticonvulsant activity of riluzole against sound-induced seizures was studied in the DBA/2 mouse model. Riluzole (0.1-4 mg kg(-1), intraperitoneal (i.p.)) produced dose-dependent effects with ED(50) values for the suppression of tonic, clonic and wild running phases of 0.72, 1.38 and 2.71 mg kg(-1), respectively. Riluzole also protected DBA/2 mice from seizures induced by an intracerebroventricular (i.c.v.) injection of N-methyl-D-aspartate (NMDA) with ED(50) values of 3.03 and 5.0 mg kg(-1) for tonus and clonus, respectively. Pretreatment with glycine, an agonist to the glycine/NMDA receptors, shifted the dose-response effect of riluzole to the right (ED(50)=6.53 against tonus and 9.34 mg kg(-1) vs. clonus). Similarly, D-serine, an agonist at the glycine site, shifted the ED(50) of riluzole against the tonic component of audiogenic seizures from 0.72 to 1.97, and that against clonus from 1.38 to 2.77 mg kg(-1). Riluzole was also potent to prevent seizures induced by administration of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), an AMPA/kainate receptor agonist (ED(50)=1.80 and 3.35 mg kg(-1), against tonus and clonus, respectively). Pretreatment with aniracetam, a positive allosteric modulator of AMPA/kainate receptors, shifted the dose-response curve of riluzole to the right (ED(50)=1.78 against tonus and 2.58 mg kg(-1) vs. clonus). The data indicate that riluzole is an effective anticonvulsant drug in the genetic model of seizure-prone DBA/2 mice. Our findings suggest that the anticonvulsant properties of riluzole depend upon its interaction with neurotransmission mediated by both the glycine/NMDA and the AMPA/kainate receptor complex.

Anticonvulsant activity of 5,7DCKA, NBQX, and felbamate against some chemoconvulsants in DBA/2 mice

The anticonvulsant effects of felbamate (10-300 mg/kg, intraperitoneally, IP), and those of two representative antagonists of the excitatory amino acid receptors, 5-7 dichlorokynurenic acid (5-7DCKA; 0.6-30 nmol/mouse, intracerebroventricularly, ICV), and 2, 3-dihydroxy-6 nitro-7-sulfamoylbenzo (F) quinoxoline (NBQX; 1.1-33.6 mg/kg, IP) were studied in the DBA/2 mice. All drugs protected the animals from sound-induced seizures. The drugs were also effective against seizures induced by stimulation of the excitatory amino acid receptor complex using the agonists N-methyl-D-aspartate (NMDA) or alpha-amino-3-hydroxy-5 methyl-4-isoxazolepropionic acid (AMPA). In separate studies, felbamate protected mice from seizures induced by ICV administration of the activator of dihydropyridine-sensitive calcium channels, methyl-1, 4-dihydro-2, 6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl) pyridine-5-carboxylate (Bay k 8644), with ED50 values of 26 and 46.9 mg/kg for tonus and clonus, respectively. Using Bay k 8644, NBQX (1-40 mg/kg IP) was uneffective, while 5,7DCKA (5-90 nmol/mouse, ICV) protected mice against tonus. Moreover, felbamate prevented seizures induced by blocking voltage-dependent K+ channels using alpha-dendrotoxin, with ED50 values of 22.6 mg/kg for tonus and of 34.8 mg/kg for clonus. Conversely, 5,7DCKA or NBQX did not significantly antagonize seizures induced by alpha-dendrotoxin. The present data indicate that felbamate is an effective anticonvulsant drug in DBA/2 mice with a broader anticonvulsant spectrum than 5,7DCKA and NBQX.

GYKI 52466 and related 2,3-benzodiazepines as anticonvulsant agents in DBA/2 mice

The behavioural and anticonvulsant effects of several 1-aryl-3,5-dihydro-4H-2,3-benzodiazepin-4-ones (2,3-BZs) and of 11b-aryl-7,11-dihydro-3-phenyl[1,2,4]oxadiazolo[5,4-a][2,3]benz odiazepin-6-ones (2,3-OBZs) were studied after intraperitoneal (i.p.) administration in DBA/2 mice, a strain genetically susceptible to sound-induced seizures. The seizures were evoked by means of auditory stimulation (109 dB, 12-16 kHz) in animals placed singly under a hemispheric Perspex dome. The 2,3-benzodiazepines studied after 30 min pretreatment were generally less potent than the related derivative 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride (GYKI 52466) except 3,5-dihydro-7,8-dimethoxy-1-phenyl-4H-2,3-benzodiazepin-4-one (2,3-BZ-2) and 2,3-BZ-2M (3-methyl derivative of 2,3-BZ-2) which showed comparable activity. Thirty minutes after i.p. administration of 2,3-benzodiazepines, the rank order of potency for anticonvulsant activity against clonus was 2,3-BZ-2 > GYKI 52466 > 2,3-BZ-2M > 2,3-BZ-1 > 2,3-BZ-3, > 2,3-OBZ-1, > 2,3-OBZ-2 2,3-OBZ-3. The intracerebroventricular (i.c.v.) injection of aniracetam on it own (12.5 - 100 nmol/mouse) had no convulsant activity, but it reversed the anticonvulsant effects of some 2,3-benzodiazepines. In particular, the pharmacological actions of GYKI 52466, 2,3-BZ-2 and 2,3-BZ-2M, which proved to be the most potent 2,3-benzodiazepine derivatives as anticonvulsants, were significantly reduced by an i.c.v. pretreatment with aniracetam (50 nmol/mouse). Concomitant treatment with aniracetam (50 nmol/mouse) shifted to the right the dose-response curves and significantly increased the ED50 values for GYKI 52466, 2,3-BZ-2 and 2,3-BZ-2M. After 30 min pretreatment 2,3-BZ-2 showed a similar potency to GYKI 52466 in antagonizing seizures induced by i.c.v. administration of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), thus suggesting a clear involvement of AMPA receptors in the anticonvulsant activity of these compounds. In addition, 2,3-BZ-2 and 2,3-BZ-2M showed anticonvulsant properties longer lasting than GYKI 52466.