Extracellular amino acid levels in hippocampus during pilocarpine-induced seizures

Extracellular levels of aspartate, glutamate and glutamine were monitored by microdialysis in the dorsal hippocampus of freely moving rats following the administration of a convulsant dose of pilocarpine (400 mg/kg, i.p.). Rats were either pretreated with the glutamate uptake inhibitor, 1-trans-pyrrolidine-2,4-dicarboxylic acid (PDC, 1 mM in the perfusion medium, -25 min), or received pilocarpine directly. All rats injected with pilocarpine (with or without PDC pretreatment) developed limbic seizures (latency 15.4 +/- 2.4 min). Without PDC pretreatment there were no significant changes in extracellular levels of aspartate, glutamate and glutamine following pilocarpine administration until the onset of limbic seizures when glutamine levels fell by 35%. Following PDC pretreatment there were large and sustained increases in extracellular hippocampal aspartate (250%) and glutamate (55%) levels, but no significant change in the glutamine level. When pilocarpine was administered to this group of rats, there were further selective, significant, transient increases in the extracellular levels of aspartate (31%) and glutamate (18%) which preceded the onset of seizures. Aspartate and glutamate levels were not significantly increased (relative to PDC controls) during seizures. The conditions for pilocarpine-induced increases in aspartate and glutamate release were established in parallel groups of anaesthetised rats where pilocarpine was administered via a microdialysis probe in the dorsal hippocampus. Following the infusion of 10 mM pilocarpine there were large and rapid increases in the levels of aspartate (143%) and glutamate (179%), which were completely abolished by the absence of calcium in the perfusion medium, or by the presence of atropine (20 mM) or tetrodotoxin (1 microM).

Cerebroprotective effect of a non-N-methyl-D-aspartate antagonist, NBQX, after focal ischaemia in the rat

The cerebroprotective effect of the non-N-methyl-D-aspartate antagonist, NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)-quinoxaline.NA) on neurological deficit and infarct volume (visualised with 2,3,5-triphenyltetrazolium) 24 h after permanent middle cerebral artery (MCA) occlusion in Fischer rats (n = 6 per dose) was studied. NBQX (10, 20 or 30 mg Kg-1, i.p., 0,30,60 min) immediately after MCA occlusion reduced cortical infarct volume by 45% (not significant), 70% (p < 0.05) or 75% (p < 0.05) respectively. NBQX (30 mg Kg-1, i.p., 60, 90, 120 min) reduced cortical infarct volume by 58% (p < 0.05). With a 2 h delay NBQX was ineffective. Neurological deficits (with blinded assessment) were improved with immediate or delayed NBQX (3 x 30 mg Kg-1, i.p.). The main adverse behavioral effect of NBQX (3 x 20 or 3 x 30 mg Kg-1, p.i.) was ataxia. The cerebroprotective effect of NBQX in rats suggests a possible therapeutic role for non-N-methyl-D-aspartate antagonists given shortly after stroke onset.

Reduction of glutamate release and protection against ischemic brain damage by BW 1003C87

BW 1003C87, 5-(2,3,5-trichlorophenyl)-2,4-diaminopyrimidine ethane sulphonic acid, has been tested for its in vitro and in vivo effects on glutamate release in rat brain tissue, and for its cerebro-protective action in two rodent models of cerebral ischemia. In rat brain slices the release of glutamate evoked by veratrine is inhibited by BW 1003C87 (IC50 = 1.6 microM). In anaesthetised rats with microdialysis probes implanted in the dorsal hippocampus the increase in extracellular glutamate evoked by veratrine is markedly reduced by co-infusion of BW 1003C87, 100 microM. In anaesthetised rats with microdialysis probes implanted in the cortex and the caudate nucleus ipsilateral to a middle cerebral artery (MCA) occlusion the increase in dialysate glutamate concentration seen in the first 2 h following MCA occlusion is markedly attenuated by the prior administration of BW 1003C87, 20 mg/kg i.v. In rats subjected to 10 min of bilateral common carotid artery occlusion the loss of CA1 pyramidal neurons (assessed 7 days later) is reduced by administration of BW 1003C87 (20 mg/kg i.v., at the time of ischemia and 4 h later). The volume of cortex showing infarction 72 h after unilateral MCA occlusion is reduced by treatment with BW 1003C87 (20 mg/kg, i.v., beginning 5 min after occlusion). Inhibition of glutamate release may provide a therapeutic approach in cerebral ischemia as well as in epilepsy.

Anticonvulsant profile of MDL 27,266: an orally active, broad-spectrum anticonvulsant agent

The novel anticonvulsant substance MDL 27,266 was tested in a variety of anticonvulsant models to assess its anticonvulsant profile, behavioral toxicity and oral bioavailability. Intraperitoneally (i.p.) administered MDL 27,266 afforded complete protection against sound-induced seizures in DBA/2J and Frings audiogenic-seizure (AGS)-susceptible mice (ED50s: 5.0 and 5.1 mg/kg, respectively). It was also effective following i.p. administration to CF#1 mice against maximal electroshock (MES)-, pentetrazole-, picrotoxin-, quisqualic acid-, and strychnine-induced seizures (ED50s: 24.9, 13.8, 43.3, 8.05, and 60.5 mg/kg, respectively). MDL 27,266, in well tolerated oral doses, prevented the expression of stage 5 behavioral seizures in the corneal-kindled rat and myoclonic seizures in the photosensitive baboon, Papio papio. Chronic administration of MDL 27,266 to AGS-susceptible mice did not markedly affect its anticonvulsant potency or efficacy against sound-induced seizures. These results suggest that MDL 27,266 possesses a broad anticonvulsant profile which most closely approximates that of the broad-spectrum prototype antiepileptic drug valproate.

Excitatory neurotransmitters in the lateral habenula and pedunculopontine nucleus of rat modulate limbic seizures induced by pilocarpine

The involvement of the excitatory neurotransmitter system in the lateral habenula and pedunculopontine nucleus in the initiation and propagation of limbic seizures induced by pilocarpine has been investigated in the rat. Limbic seizures occur in animals following bilateral microinjection into the lateral habenula of N-methyl-D-aspartate (NMDA) (5 and 12.5 nmol) or kainate (100 and 200 pmol), 15 min prior to a subconvulsant dose of pilocarpine (150 mg/kg, i.p.). In the absence of pilocarpine NMDA (5 and 12.5 nmol) or kainate (100 and 200 pmol), injected focally into the lateral habenula or pedunculopontine nucleus, produced sniffing, grooming and tremor but no electrographic or behavioural seizures. Limbic seizures also occur after a subconvulsant dose of pilocarpine when it is preceded by injection of NMDA (5 and 12.5 nmol) or kainate (50, 100 and 200 pmol) into the pedunculopontine nucleus. Behavioural and electrographic signs of limbic seizures following pilocarpine (380 mg/kg, i.p.) were attenuated or completely antagonized by focal injection into the lateral habenula of the NMDA antagonist, 2-amino-7-phosphonoheptanoate (AP7) (10 and 50 pmol) or kainate antagonist, gamma-D-glutamylaminomethylsulphonate (GAMS) (20 nmol). In addition, AP7 (0.05, 0.1 and 1.0 nmol) or GAMS (40 nmol) injected into the pedunculopontine nucleus suppressed limbic seizures induced by i.p. administration of pilocarpine (380 mg/kg). The relative efficacy of NMDA and non-NMDA receptor antagonists revealed that the selective NMDA antagonist, AP7, was more potent in its anticonvulsant activity in comparison to GAMS, a non-NMDA receptor antagonist.

Potent indole- and quinoline-containing N-methyl-D-aspartate antagonists acting at the strychnine-insensitive glycine binding site

The N-methyl-D-aspartate (NMDA)-preferring glutamate receptor subtype possesses, in addition to the recognition site for glutamate, a binding site for glycine. We report here on the pharmacological properties of 3-(4,6-dichloro-2-carboxyindol-3-yl)-propionic acid (MDL 29,951) and 4-carboxymethylamino-5,7-dichloroquinoline-2-carboxylic acid (MDL 100,748), two novel glycine antagonists of NMDA receptor activation in vitro and in vivo. We have measured in parallel the effects of two previously described glycine antagonists, 7-chlorokynurenic acid and 5,7-dichlorokynurenic acid. All were potent inhibitors of [3H]glycine binding. Ki values (microM) were 0.36 (7-chlorokynurenic acid), 0.08 (5,7-dichlorokynurenic acid), 0.07 (MDL 100,748) and 0.14 (MDL 29,951). MDL 100,748 and MDL 29,951 were approximately 2000-fold selective for the glycine binding site relative to the glutamate recognition sites. All four compounds completely inhibited the use-dependent binding of [3H]N-[1-(2-thienyl) cyclohexyl]-piperidine and were noncompetitive, glycine-reversible inhibitors of both NMDA-induced biochemical and electrophysiological responses in brain slice preparations. A competitive interaction with the glycine binding site was also evident in that MDL 29,951 and MDL 100,748 produced parallel rightward shifts in the glycine requirement for demonstration of NMDA-stimulated elevations in cytosolic calcium in cultured neuronal preparations. The glycine antagonists were potent anticonvulsants after their i.c.v. administration to audiogenic seizure-susceptible DBA/2J mice. Because the compounds chosen encompass a variety of chemical structures, the results indicate that glycine is required for NMDA receptor activation and that bioavailable glycine antagonists may form the basis of a novel therapy for epilepsy.

Excitatory amino acid receptors and disease

Recent advances in the molecular biology of excitatory amino acid receptors are reviewed. Evidence that drugs blocking the excitatory action of glutamate at the N-methyl-D-aspartate (NMDA) and non-NMDA receptors may be of clinical use in epilepsy, Parkinson's disease, cerebral ischaemia and trauma, acquired immune deficiency syndrome (AIDS) encephalopathy and neuropathic pain is summarized.

Excitatory amino acids in epilepsy and potential novel therapies

Evidence that an abnormality of excitatory neurotransmission may contribute to the epileptic phenomena in various animal and human syndromes is reviewed. Altered glutamate transport or metabolism may be a contributory factor in some genetic syndromes and enhanced responsiveness to activation of NMDA receptors may be significant in various acquired forms of epilepsy. Decreasing glutamatergic neurotransmission provides a rational therapeutic approach to epilepsy. Potent anticonvulsant effects are seen with the acute administration of NMDA antagonists in a wide range of animal models. Some competitive antagonists acting at the NMDA/glutamate site show prolonged anticonvulsant activity following oral administration at doses free of motor side effects and appear suitable for clinical trial.

Cerebroprotective effect of a non-N-methyl-D-aspartate antagonist, GYKI 52466, after focal ischemia in the rat

BACKGROUND AND PURPOSE

Cerebroprotection after the administration of N-methyl-D-aspartate antagonists has been well documented. The present study sought to determine whether a cerebroprotective effect could be achieved with the administration of a non-N-methyl-D-aspartate antagonist, GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylene-dioxy-5H-2,3-benzodiazep ine hydrochloride; molecular weight, 330) after middle cerebral artery occlusion in the rat.

METHODS

Neurological deficit and infarct volume 24 hours after permanent left middle cerebral artery occlusion in Fischer rats (n = 7-13 per group per dose) were studied. Cerebral infarcts was visualized by the lack of reduction of 2,3,5-triphenyltetrazolium chloride.

RESULTS

GYKI 52466 (10 mg.kg-1 i.p. at 0, 2, 4 hours) after middle cerebral artery occlusion had no effect on infarct volume. GYKI 52466 (10 mg.kg-1 i.v. for 5 minutes followed by 15 mg.kg-1.hr-1 i.v. for 2 hours immediately after middle cerebral artery occlusion reduced cortical infarct volume by 68% (from 69 mm3 in vehicle-treated to 22 mm3 in GYKI 52466-treated animals; p less than 0.05). A 1-hour delay before initiation of drug infusion resulted in a 48% reduction in cortical infarct volume (from 60 mm3 vehicle-treated rats to 31 mm3 in GYKI 52466-treated rats; p less than 0.05). A 2-hour delay before initiation of drug infusion had no effect on cortical infarct volume. Neurological deficits (with blinded assessment after 24 hours) were improved after immediate treatment and after delayed treatment (1 or 2 hours).

CONCLUSIONS

The cerebroprotective effect of GYKI 52466 in the rat suggests a possible therapeutic role for non-N-methyl-D-aspartate antagonists given shortly after the onset of stroke.

Electrolytic lesions of the locus coeruleus or 6-hydroxydopamine lesions of the medial forebrain bundle protect against excitotoxic damage in rat hippocampus

Unilateral lesioning of the rat locus coeruleus by an electric current (0.3 mA/10 s) reduces the ipsilateral hippocampal tissue content of dopamine (DA) and noradrenaline (NA) by 80% and 60% respectively, and protects against the excitotoxic action of bilateral kainate injections (1.1 nmol/microliters) in the hippocampus. On the ipsilateral side hippocampal CA1, CA2 and DG cells were protected; lesser protection of CA1 cells was seen on the contralateral side. The unilateral injection of 6-hydroxydopamine (8.8 micrograms/2 microliters/5 min) into the medial forebrain bundle abolishes the increase in extracellular NA concentration induced by kainate in the ipsilateral hippocampus without altering the low extracellular DA levels. This medial forebrain bundle lesion protects (on the ipsilateral side) against kainate toxicity (500 microM through the probe for 20 min) in the hippocampus (CA1, CA2 and DG cells). The noradrenergic innervation of the hippocampus apparently potentiates the excitotoxic effect of focal injection of kainate.

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.

GYKI 52466 blocks the increase in extracellular glutamate induced by ischaemia

In vivo microdialysis has been used to study the effect of pre- or post-ischaemic administration of the non-NMDA antagonist 1-(4-amino-phenyl)-4-methyl-7, 8-methyl-endioxyl-5H-2,3- benzodiazepine hydrochloride (GYKI 52466), on the increases in extracellular glutamate levels induced by 20 minutes of four vessel occlusion in rats. In control rats, ischaemia resulted in transient increases in glutamate (4 fold), aspartate (6 fold) and gamma-aminobutyric acid (GABA) (15 fold) and decreases in glutamine (0.5 fold). Intravenous administration of GYKI 52466 (10 mg kg-1 bolus followed by 10 mg kg-1 h-1 infusion) beginning 20 minutes prior to the induction of ischaemia abolished ischaemia-induced glutamate release without affecting the increases in aspartate and GABA and the decrease in glutamine. Administration of GYKI 52466 immediately post-ischaemia resulted in a more rapid return of glutamate levels to basal values.

The glycine-site NMDA receptor antagonist, R-(+)-cis-beta-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 non-NMDA antagonists, NBQX and GYKI 52466, protect against cortical and striatal cell loss following transient global ischaemia in the rat

The cerebroprotective action of non-NMDA receptor blockade has been assessed in a model of transient global ischaemia using NBQX, 2,3-dihydro-6-nitro-7-sulphamoyl-benzo(F)quinoxaline, and GYKI 52466, 1-(amino-phenyl)-4-methyl-7,8-methylendioxy-5H-2,3-benzodiazepine. HCl. In Wistar rats, prior cauterisation of the vertebral arteries was followed by occlusion of the common carotid arteries for 20 min, with a 7 day survival period before histological evaluation. NBQX, 40 mg/kg, or GYKI 52466, 40 mg/kg, was administered intravenously starting directly after the end of carotid occlusion and ending 3 h later. Both compounds produced significant protection against selective cell loss in the striatum and cortex. Less consistent changes were seen in the hippocampus; protection by NBQX was significant in CA3 but neither compound produced significant protection in CA1. This pattern of protection is interpreted in terms of a blockade of glutamate's action at non-NMDA receptors limited to the initial 3 h of reperfusion.

Interactions of the beta carboline abecarnil with the high pressure neurological syndrome in a primate model

The neurophysiological interactions between the high pressure neurological syndrome (HPNS) and a new beta carboline, abecarnil, were studied in the non-human primate Papio anubis. Abecarnil is a partial agonist at the benzodiazepine site on the GABA/benzodiazepine receptor. Six animals were exposed on two occasions to pressures of 91 ATA in an environment of helium and oxygen. One exposure was pretreated with a total dose of abecarnil 1.0 mg/kg, the other with an equivalent volume of vehicle. Treatment with abecarnil prevented the severe signs of HPNS occurring between 51 and 91 ATA. Onset pressures of the various signs were unaffected. Some signs, e.g. myoclonus, became more frequent when abecarnil was used. A residual protective effect of abecarnil was present 4 weeks after the dose was given, active at pressures less than 71 ATA. Changes with pressure in the EEG were recorded primarily from the frontal cortex, but were also present in the parietal and occipital areas of the left cortex. Amplitude and frequency spectra were calculated and changes with pressure in the four conventional wavebands, plus two others, analysed. The most striking change was the prevention by abecarnil of the pressure-induced 100% increase in alpha wave amplitude in the frontal region. It is concluded that modulation of GABA transmission is important in controlling the expression of HPNS.

Non-NMDA antagonists protect against kainate more than AMPA toxicity in the rat hippocampus

Single focal injection of the excitatory amino acids (EAAs) kainic acid (KA, 1.1 nmol/microliters) and (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (S)-AMPA, 6 nmol/microliters) into rat dorsal hippocampus resulted in widespread neurodegeneration with 90-100% loss of hippocampal pyramidal cells in CA1, CA2, CA3 and CA4 subfields, and 50-70% loss of dentate granule (DG) cells. Focal injection of NMDA (30 nmol/microliters) under the same conditions resulted in 70-90% loss of CA1 cells with less damage in CA2, CA3, CA4 and DG cells (30-50%, 10-30%, and 30-50%, respectively). The non-NMDA antagonists NBQX (2,3-dihydro-6-nitro-7-sulphamoyl-benzo(f) quinoxaline) and GYKI 52466 (1-(amino)phenyl-4-methyl-7,8-methylendioxy-5H-2,3,benzodiazepine. HCl) co-injected (24 nmol/microliters) with EAAs or given as i.v. infusion (30 mg/kg/3h), protected against KA toxicity in CA1, CA2 and DG cells, with no protection in CA3 and CA4. NBQX i.v. protected against (S)-AMPA toxicity in the DG cells but no protection was observed against (S)-AMPA toxicity in hippocampal subfields (CA1, CA2 and CA4). Intravenous administration of NBQX and GYKI 52466 (30 mg/kg/3 h) also failed to protect against NMDA toxicity in the hippocampus. Systemic injections of D(-)-CPPene, (E)-4-(3-phos-phonoprop-2-enyl)-piperazine-2-carboxylic acid, (10 and 5 mg/kg, i.p., 20 min prior and 3 h post EAA injection) protected against NMDA and KA toxicity in the CA1, CA2 and DG subfield with no protective effect against (S)-AMPA toxicity.

Brain nuclei and neurotransmitters involved in the regulation of the high pressure neurological syndrome in the rat

The role of glutamatergic (NMDA), cholinergic and purinergic neurotransmission in the pedunculopontine nucleus, red nucleus, ventrolateral thalamic nucleus, entopeduncular nucleus, and the substantia nigra in the development of the high pressure neurological syndrome (HPNS) was investigated in the rat. Focal injection of D-2-amino-7-phosphonoheptanoate (D-APH, 5 nmol per side) into the red nucleus or the pedunculopontine nucleus was protective against HPNS-induced convulsions. Carbachol (10 nmol), injected into the red nucleus, did not influence the severity of the symptoms of HPNS. Injection of carbachol into the pedunculopontine nucleus, significantly lowered the threshold pressure for convulsions and increased the threshold pressure for tremor. 2-Chloroadenosine (5 nmol), injected into the red nucleus, produced a potent antitremorgenic effect and a similar but less pronounced effect when injected into the pedunculopontine nucleus. 2-Chloroadenosine, injected into the substantia nigra (12.5 nmol) or the ventrolateral thalamic nucleus (25 nmol), facilitated the development of tremor and, in the entopeduncular nucleus (25 nmol), facilitated the occurrence of convulsions. These results show the complexity of neurotransmitter interactions in different regions of the brain, under high pressure. They also indicate that the biochemical and anatomical substrates, involved in the convulsions produced by HPNS, differ substantially from those in other experimental models of epilepsy.

L-glutamate diethyl ester and deaminated analogues as excitatory amino acid antagonists in rat cerebral cortex

1. The effects of L-glutamate diethyl ester (GDEE) HCl, glutarate diethyl ester (GlrDEE) and glutarate dimethyl ester (GlrDME) on depolarizing responses to alpha-amino-3-hydroxy-5- methyl-4-isoxazolepropionate (AMPA), kainate (Kain), N-methyl-D-aspartate (NMDA) and quisqualate (Quis), and spontaneous paroxysmal discharges (SPDs) were examined. Experiments were performed on slices of rat cingulate cortex using the in vitro grease gap recording technique in nominally Mg(2+)-free Krebs medium. 2. GDEE HCl (3-14 mM) caused a concentration-dependent depolarization of the d.c. baseline potential. L-Glutamate (0.1-0.5 mM), HCl (15 mM) and sucrose (30 mM) also depolarized the baseline. GlrDEE (3-12 mM) and GlrDME (4-26 mM) had no consistent effect on baseline potential. 3. GDEE HCl (10 mM) had no effect on depolarizing responses to AMPA, Kain and NMDA, but caused potentiation of those to Quis with a dose-ratio of 0.53 (0.44-0.63) (n = 4). In two other experiments, where the depolarization of the baseline induced by GDEE HCl was large, a depression of Quis response amplitude was observed. 4. GlrDEE (10 mM) antagonized depolarizing responses to Kain, and to a lesser extent NMDA, with dose-ratios of 2.14 (1.92-2.38) and 1.61 (1.39-1.87), respectively. This concentration of GlrDEE had no effect on AMPA responses, but potentiated Quis responses, with a dose-ratio of 0.64 (0.58-0.71). 5. GlrDME (10 mM) antagonized depolarizing responses to Kain and to Quis, with dose-ratios of 1.66 (1.48-1.85) and 1.22 (1.15-1.29), respectively, and had no effect on responses to NMDA. 6. The SPDs were inhibited by GDEE HCI (IC50 6.7 +/- 0.37mM), GlrDEE (IC50 5.6 +/- 0.38 mM) and GlrDME (IC50 10.4 +/- 0.73 mM). 7. In conclusion, there is little evidence that GDEE HCI is an antagonist of the postsynaptic excitatory amino acid receptors in the rat neocortex, and its effects may result from its contamination with Lglutamate and increased osmolarity of the bathing medium at high concentrations. The deaminated analogues of GDEE are very weak Kain antagonists.

Changes in motor activity and forebrain [propionyl-3H]propionylated-CCK-8 binding in mice after repeated administration of drugs affecting cholecystokinin receptors

The effects of acute or repeated treatment of male albino BKW mice with caerulein, a cholecystokinin octapeptide (CCK-8) agonist, and with devazepide (MK-329) and L-365,260, antagonists at CCKA ('peripheral') and CCKB ('central') receptors respectively, on motor activity and [propionyl-3H]propionylated-CCK-8 ([3H]pCCK-8) binding were studied. Acute treatment with a large dose of caerulein (100 micrograms/kg s.c.) suppressed motor activity (line crossings and rearings) whereas devazepide (2 mg/kg i.p.) had the opposite action. L-365,260 (2 mg/kg i.p.) increased only the number of rearings. Tolerance developed to the locomotor effects of caerulein and devazepide when these same doses were administered once daily (caerulein) or twice daily (devazepide) for 10 days. Twice daily administration of L-365,260 (2 mg/kg) for 10 days did not significantly alter the locomotor activity of mice. The sedative effect of caerulein (20 micrograms/kg s.c.) was markedly reduced in mice receiving repeated injections of either a larger amount of caerulein (100 micrograms/kg) or devazepide but not after L-365,260. The stimulant effect of (+)-amphetamine (2 mg/kg s.c.) on motor activity was increased by subchronic administration of either devazepide or caerulein, but not by L-365,260. All three compounds (caerulein, devazepide and L-365,260) increased the number of [( 3H]pCCK-8 binding sites in mouse forebrain but the increase was only significant after L-365,260. The effects of long-term treatment with caerulein are probably related to the stimulation of CCKA receptors, whereas the paradoxically similar action of devazepide may be linked to the blockade of both subtypes of the CCK-8 receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Changes in rat brain extracellular glutamate concentration during seizures induced by systemic picrotoxin or focal bicuculline injection: an in vivo dialysis study with on-line enzymatic detection

An on-line enzymatic assay of dialysis fluid has been used to monitor the extracellular glutamate concentration in the rat hippocampus. Perfusion with artificial cerebrospinal fluid containing a glutamate uptake inhibitor (either dihydrokainate or 4,4'-diisothiocyanatostilbene-2,2' disulfonic acid) produced a marked stable increase in glutamate concentration; 10 min perfusion with 100 mM K+ produced a transient increase. Sustained epileptiform EEG discharges were induced in the hippocampus by focal injection of bicuculline into the piriform cortex or by systemic injection of picrotoxin. Extracellular glutamate did not change significantly during seizure activity, either in the absence or in the presence of glutamate uptake inhibitors. It is concluded that seizure activity is not necessarily accompanied by an overall increase in extracellular glutamate concentration.

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.).

Anticonvulsant activity of two orally active competitive N-methyl-D-aspartate antagonists, CGP 37849 and CGP 39551, against sound-induced seizures in DBA/2 mice and photically induced myoclonus in Papio papio

Two novel N-methyl-D-aspartate (NMDA) antagonists, DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid CPG 37849 and the corresponding 1-ethyl ester CGP 39551, were tested as anticonvulsants in DBA/2 mice and photosensitive Senegalese baboons, Papio papio. In DBA/2 mice, CGP 37849 is more potent than CGP 39551 when administered intracerebroventricularly (i.c.v.) or intraperitoneally (i.p.) (ED50 for suppression of clonic seizures at 60 min: i.c.v. 0.038 and 0.21 nmol; i.p. 3.40 and 19.1 mumol/kg, respectively). When administered orally in mice, the two compounds are approximately equipotent (ED50 CGP 37849, 35.2 mumol/kg; ED50 CGP 39551, 28.1 mumol/kg). The time course of action of CGP 39551 is exceptionally prolonged: 42 mumol/kg i.p. protects against clonic seizures for 48 h. Protection provided by other NMDA antagonists in mice is of much shorter duration: 2-amino-5-phosphono-pentanoic acid (AP5) 1 h, 2-amino-7-phosphono-heptanoic acid (AP7) 4 h, 2-amino-7-phosphono-heptanoic acid 1-ethyl ester 3 h, 4-(3-phosphonopropyl)-2-piperazine carboxylic acid (CPP) 2 h, cis-4-(phosphonomethyl)-2-piperidine-carboxylic acid (CGS 19755) 4 h, and CGP 37849 4 h. After oral administration of the drugs, the therapeutic index (TI = ratio of the ED50 values for rotorod performance and anticonvulsant protection) remains relatively constant at 5.9-7.2 for 3 h (CGP 37849) and 4.0-6.1 for 24 h (CGP 39551). After i.p. administration, the TI values are CGP 37849 at 1 h 2.4, and at 3 h 20.0, CGP 39551 at 1 h 2.3, at 3 h 7.1, and at 24 h 3.6. In baboons, acute administration of CGP 37849 at doses of 48-191 mumol/kg intravenously (i.v.) suppresses photically induced myoclonus for at least 285 min, with severe side effects at the highest dose tested. CGP 39551 at doses of 169-675 mumol/kg i.v. shows weak anticonvulsant activity only at the highest dose tested (accompanied by severe side effects). CGP 37849 at 48-96 mumol/kg orally (p.o.) fails to protect against photically induced myoclonus up to 4 h after administration, but 191 mumol/kg (40 mg/kg) p.o. produces complete suppression of seizures after 24 h. On the other hand, CGP 39551 at 169 mumol/kg (40 mg/kg) p.o. produces total suppression of seizure activity at 4 h with a longer duration of anticonvulsant action (2-3 days).(ABSTRACT TRUNCATED AT 400 WORDS)