Stuart E. Smith

The anticonvulsant effect of the non-NMDA antagonists, NBQX and GYKI 52466, in mice

The excitatory amino acid antagonists, NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline) and GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine) that act on non-NMDA receptors, provide potent anticonvulsant protection against AMPA [RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)-induced seizures in Swiss mice and against sound-induced seizures in seizure-susceptible DBA/2 mice. Maximal anticonvulsant protection is observed 5-30 min after the i.p. administration of NBQX and 5-15 min after the i.p. administration of GYKI 52466 in DBA/2 mice. The ED50 values for the protection against AMPA-induced seizures by NBQX (30 min, i.p.) and GYKI 52466 (15 min, i.p.) are 23.6 (11.6-48.0) and 18.5 (11.5-29.5) mumol/kg, respectively. The ED50 values at 15 min for the protection against sound-induced seizures in DBA/2 mice are 31.3 (24.9-39.4) mumol/kg (NBQX, i.p.), 37.8 (21.2-67.4) mumol/kg (NBQX, i.v.) and 13.7 (11.5-16.5) mumol/kg (GYKI 52466, i.p.). In DBA/2 mice the therapeutic index (ratio of ED50 values for impaired rotarod performance and anticonvulsant action) is 6.6 for NBQX (15 and 30 min, i.p.) and 2.0 for GYKI 52466 (15 min, i.p.).

The non-N-methyl-D-aspartate receptor antagonists, GYKI 52466 and NBQX are anticonvulsant in two animal models of reflex epilepsy

The effect of i.p. or i.v. administration of the non-N-methyl-D-aspartate antagonists, GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylendioxy-5H-2,3-benzodiazepin e.HCl, molecular weight 330) and NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)-quinoxaline, molecular weight 342) on sound-induced seizures in rats and photically induced myoclonus in baboons was studied. In both species an anticonvulsant effect occurred 15-60 min after administration of GYKI 52466 or NBQX. The ED50 value for clonic seizure suppression for GYKI 52466 at 30 min was 39 (rats, i.p.) and at 15 min was 13 (Papio papio, i.v.) mumol kg-1 and for NBQX at 30 min was 40 (rats, i.p.) and at 15 min approximately 10 (Papio papio, i.v.) mumol kg-1. Side effects were not observed in rats; apparent side effects in baboons probably arose from drug formulation. The anticonvulsant actions of GYKI 52466 and NBQX suggest a possible role for non-NMDA antagonists in the therapy of epilepsy.

Cerebroprotective Effect of Lamotrigine After Focal Ischemia in Rats

BACKGROUND AND PURPOSE Glutamate receptor antagonists are protective in animal models of focal cerebral ischemia. Lamotrigine (3,5-diamino-6-[2,3-dichlorophenyl]-1,2,4-triazine) is an anticonvulsant drug that blocks voltage-gated sodium channels and inhibits the ischemia-induced release of glutamate. We describe the cerebroprotective effect of lamotrigine (as the isethionate salt) after middle cerebral artery occlusion in rats. METHODS Neurological deficit and infarct volume (visualized by the lack of reduction of 2,3,5-triphenyltetrazolium chloride) 24 hours after permanent left middle cerebral artery occlusion were studied in Fischer rats (n = 8 per group per dose). RESULTS Lamotrigine at 20 mg/kg i.v. over 10 minutes administered immediately after middle cerebral artery occlusion reduced total infarct volume by 31% and cortical infarct volume by 52%. Lamotrigine at 8 mg/kg i.v. over 10 minutes reduced cortical infarct volume by 38%. Lamotrigine at 50 mg/kg i.v. for 10 minutes was not cerebroprotective and induced a decrease of 29 +/- 15 mm Hg in mean arterial blood pressure (P < .05, n = 8). The optimum dose of lamotrigine (20 mg/kg i.v. over 10 minutes) when administered with a 1-hour delay after middle cerebral artery occlusion reduced cortical infarct volume by 41%. Lamotrigine (20 mg/kg i.v. over 10 minutes) with a 2-hour delay after middle cerebral artery occlusion was ineffective. Neurological deficits after 24 hours were improved after immediate treatment with lamotrigine at 20 mg/kg i.v. over 10 minutes. CONCLUSIONS The cerebroprotective effect of lamotrigine in rats is limited to a narrow dose range between 8 and 20 mg/kg. Lamotrigine or analogous compounds may be useful when given shortly after the onset of stroke.

Cerebroprotective effect of BW619C89 after focal or global cerebral ischaemia in the rat.

BW619C89 (4-amino-2-(4-methylpiperazin-l-yl)-5-(2,3,5-trichlorophenyl) pyrimidine) was evaluated for cerebroprotection after focal or global ischaemia. BW619C89, as the mesylate dihydrate salt, 20 mg kg-1, i.v. for 10 min immediately, or with a 1 h delay after permanent middle cerebral artery occlusion in Fischer rats reduces cortical infarct volume (visualized with (2,3,5-triphenyltetrazolium) by 49% (p < 0.05) or by 61% (p < 0.001) and improves neurological deficit. Administration of BW619C89 with a 2 h delay is ineffective. BW619C89, given i.p. 0 and 4 h after 20 min of transient bilateral common carotid artery occlusion in vertebral artery-occluded Wistar rats reduces glutamate release and neuronal cell loss in the hippocampal CA1 sector (p < 0.01) and striatum (p < 0.05). BW619C89 resembles BW1003C87 (5-(2,3,5-trichlorophenyl)-2,4-diaminopyrimidine) in inhibiting veratrine-induced glutamate release and protecting against ischaemic brain damage.

Receptor site specificity for the acute effects of β-N-methylamino-alanine in mice

DL-beta-N-methylamino-alanine (DL-BMAA; 1-10 mumol i.c.v.) in mice induced a syndrome of: ataxia, ptosis, scratching, jumping, myoclonic jerks, clonic muscle spasms and tonic seizure, which was unaffected by pretreatment with D(-)-4-(3-phosphonoprop-2-enyl)-piperazine-2-carboxylate (D(-)-CPPene; i.p.), or by co-administration of gamma-D-glutamylamino-methylsulphonate (gamma-D-GAMS with DL-BMAA; i.c.v.). Pretreatment with 1-(aminophenyl)-4-methyl-7,8-methylendioxy-5H-2,3-benzodiazepine (GYKI 52466; i.v.) decreased the incidence of clonic seizures for DL-BMAA, kainic acid and RS-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (RS-AMPA; i.c.v.). These results suggest an involvement of the AMPA/quisqualate subtype of excitatory amino acid receptors in acute BMAA toxicity.

The γ-aminobutyric acid uptake inhibitor, tiagabine, is anticonvulsant in two animal models of reflex epilepsy

The effects of i.p. administration of the gamma-aminobutyric acid (GABA) uptake inhibitors R(-)N-(4,4-di(3-methylthien-2-yl)-but-3-enyl) nipecotic acid hydrochloride (tiagabine; molecular weight 412.0), (1-(2-(((diphenylmethylene)-amino)oxy)ethyl)-1,2,5,6-tetrahydro-3- pyridinecarboxylic acid hydrochloride (NNC-711; molecular weight 386.9), and (+/-)-nipecotic acid (molecular weight 128.2) are compared with those of carbamazepine (molecular weight 236.3) on sound-induced seizures and locomotor performance in genetically epilepsy-prone (GEP) rats. The ED50 value against clonic seizures (in mumol kg-1 at the time of maximal anticonvulsant effect) for tiagabine was 23 (0.5 h), and for NNC-711 was 72 (1 h), and for carbamazepine was 98 (2 h). (+/-)-Nipecotic acid (0.4-15.6 mmol kg-1) was not anticonvulsant. High doses of NNC-711 (207-310 mumol kg-1) and of (+/-)-nipecotic acid (39-78 mmol kg-1) induced ataxia and myoclonic seizures 0.25-1 h. Tiagabine and carbamazepine did not induce myoclonic seizures and had similar therapeutic indices (locomotor deficit ED50/anticonvulsant ED50) ranging from 0.4 to 1.9. In Papio papio, we observed a reduction in photically induced myoclonic seizures with tiagabine (2.4 mumol kg-1 i.v.) accompanied with neurological impairment. Tiagabine has comparable anticonvulsant action to carbamazepine in rats and has anticonvulsant effects in non-human primates supporting the potential use of inhibitors of GABA uptake as therapy for epilepsy.

Excitatory amino acid antagonists, lamotrigine and BW 1003C87 as anticonvulsants in the genetically epilepsy-prone rat

Sound-induced seizures in genetically epilepsy-prone rats were used to compare the anticonvulsant effect of phenytoin and diazepam with compounds which decrease glutamatergic neurotransmission including excitatory amino acid antagonists acting at N-methyl-D-aspartate (NMDA) receptors: D(-)CPPene, CGP 37849 and MK 801 or at the glycine/NMDA site: ACPC (1-aminocyclopropane-dicarboxylic acid) (partial agonist) or non-NMDA receptors: NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzo[f]-quinoxaline.Li) and GYKI 52466 (1-(aminophenyl)-4-methyl-7,8-methylene-dioxy-5H-2,3-benzodiazepin e.HCl) or acting at sodium channels to decrease glutamate release: lamotrigine and BW 1003C87 (5(2,3,5-trichlorophenyl)-2,4-diaminopyrimidine ethane sulphonate). ED50 values against clonic seizures (in mumol/kg at the time of peak anticonvulsant effect) were: phenytoin 30.5 (2 h), diazepam 0.5 (0.5 h), MK 801 0.01 (4 h), D(-)CPPene 1.9 (4 h), CGP 37849 2 (1 h), GYKI 52466 24 (0.25 h), NBQX 40 (0.5 h), ACPC 1053 (0.5 h), BW 1003C87 2.2 (1 h), lamotrigine 4.8 (4 h). BW 1003C87, lamotrigine, MK 801, phenytoin, diazepam and CGP 37849 had the most favourable therapeutic indices (rotarod locomotor deficit ED50/anticonvulsant ED50).

The glycine-site NMDA receptor antagonist, R-(+)− cis-β-methyl-3-amino-1-hydroxypyrrolid-2-one, L-687, 414 is anticonvulsant in baboons

The glycine-site NMDA receptor antagonist, R-(+)cis-beta-methyl-3-amino-1-hydroxypyrrolid-2-one (L-687,414) was administered i.t. to photosensitive baboons. The anticonvulsant action of L-687,414 (5-45 mg kg-1) was dose-dependent and peaked between 15 min and 2 h after administration. Gross behavioural effects were not observed at the doses tested. L-687,414 is a potent systemically acting anticonvulsant apparently devoid of serious side effects.

The protein kinase C activators, phorbol 12-myristate,13-acetate and phorbol 12,13-dibutyrate, are convulsant in the pico-nanomolar range in mice

Administration of phorbol 12-myristate,13-acetate (PMA, 10 fmol-10 nmol) or phorbol 12,13-dibutyrate (PDB, 0.2-495 nmol) (i.c.v.) to mice induced: hindlimb scratching, tremor, myoclonic jerks, hyperlocomotion, clonic seizure, followed by death or recovery. CD50 values for clonic seizures for PMA and PDB were 1.0 pmol and 1.2 nmol. 4-alpha-Phorbol (68-686 nmol) was inactive. The effects of PDB (24-247 nmol) were reduced by pretreatment with staurosporine (30 nmol, i.c.v.). Protein kinase C activators are potent convulsants in vivo.

Acute and chronic anticonvulsant effects of d(−)CPPene in genetically epilepsy-prone rats

Acute administration (0.4-12 mumol/kg, i.p.) of the NMDA antagonist D(-)CPPene (3-(2-carboxypiperazin-4-yl)propenyl-1-phosphonic acid; molecular weight = 250.2) dose-dependently reduced the incidence of sound-induced clonic seizures in genetically epilepsy-prone (GEP) rats. The ED50 value against clonic seizure at +1 h was 2.6 (2.2-3.2) and at +4 h was 1.7 (1.3-2.3) mumol/kg (i.p.). Twelve hours after chronic administration of an anticonvulsant dose of D(-)CPPene (4 mumol/kg, i.p., twice daily at 09.00 and 21.00 h, for 14 days), repeat administration of D(-)CPPene (1.2-12 mumol/kg, i.p.) gave ED50 values against clonic seizure at +1 h of 3.4 (2.5-4.8) mumol/kg and at +4 h of 2.8 (2.0-3.9) mumol/kg (i.p.). There was no significant difference observed between ED50 values for these acute and chronic groups. The duration of the anticonvulsant effect observed between +1 h and +8 h after D(-)CPPene (0.4-12 mumol/kg, i.p.) was similar in the acute and chronic groups. The ED50 values for D(-)CPPene-induced impairment of locomotor performance (using a rotarod) at +3 h were 6.8 (4.4-10.4) and 6.4 (4.1-10.1) mumol/kg (i.p.) for the acute and chronic groups respectively. At +7 h after D(-)CPPene administration the ED50 value for locomotor impairment was 19.5 (10.6-36.0) mumol/kg (i.p.) in the acute group. In this study there is no evidence of tolerance to the anticonvulsant effects and little evidence of tolerance to the adverse effects (ataxia) of D(-)CPPene in GEPRs.