Effects of AWD 140-190 on stimulus-induced field potentials and on different patterns of epileptiform activity induced by low calcium or low magnesium in rat entorhinal cortex hippocampal slices

Glutamate and dopamine receptors contribute to the lateral spread of epileptiform discharges in rat neocortical slices

PURPOSE

The effects of AMPA-type glutamate receptor as well as dopamine D1 and D2 receptors on the lateral propagation of epileptiform field potentials (EFP) were studied across adjacent areas of rat neocortical tissues.

METHODS

Epileptiform burst discharges were induced by superfusion of Mg(2+)-free artificial cerebrospinal fluid. Simultaneous field potential recordings of EFP were obtained from four microelectrodes placed 2-3 mm apart across coronal slices in the third layer of the neocortex. The effects of AMPA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), dopamine D1 receptor agonist SKF 81297, and dopamine D2 receptor agonist quinpirole on lateral propagation of burst discharges were investigated.

RESULTS

CNQX, applied focally between recording sites, blocked rapid propagation across treated areas and resulted in the emergence of spatially separate, independent pacemakers. Focal application of SKF 81297 between recording sites increased the repetition rate of EFP, but reduced the amplitude as well as the duration of epileptic discharges. However, addition of SKF 81297 to the bath medium abolished EFP. Both local and systemic applications of quinpirole irreversibly enhanced repetition rate of epileptiform burst discharges.

CONCLUSIONS

The results indicate the prerequisite of AMPA synaptic transmission for synchronized lateral propagation of Mg(2+)-free ACSF-induced epileptic activity and the modulatory effects of dopamine D1 and D2 receptors on both EFP initiation and propagation in epileptic tissues.

The effect of estrogen and progesterone on spreading depression in rat neocortical tissues

Although gender differences in the incidence of migraine with aura appear to be related to high circulating levels of ovarian hormones, the underlying mechanisms are not yet fully understood. Several studies have suggested a major role for spreading depression (SD) in the pathogenesis and symptomatology of migraine with aura. To investigate a possible role of SD in the association of high female hormones and attacks of migraine with aura, the effects of beta-estradiol and progesterone on SD were studied in rat neocortical tissues. Application of both hormones enhanced the repetition rate as well as the amplitude of SD in neocortical slices treated with hypotonic artificial cerebrospinal fluid. beta-Estradiol and progesterone also dose dependently increased the amplitude of SD induced by KCl microinjection. Both hormones exhibited a pronounced, persisting, and significant enhancement of long-term potentiation of the field excitatory postsynaptic potential in the neocortical tissues. The changes in SD characteristics in the presence of estrogen and progesterone may responsible for increased migraine with aura attacks associated by high female hormones. These hormones may exert their effects on SD via facilitation of synaptic transmission.

AWD 140-190: a potent anticonvulsant in the amygdala-kindling model of partial epilepsy

PURPOSE

Evaluation of the effect of the new anticonvulsant drug, AWD 140-190 [4-(p-bromophenyl)-3-morpholino-1H-pyrrole-2-carboxylic acid methyl ester] on focally induced seizures and on epileptogenesis in the kindling model.

METHODS

Effects of AWD 140-190 were studied in amygdala kindled rats after oral and intraperitoneal administration. In addition, the effect on kindling development was evaluated. In all experiments, behavioral changes in the rats in response to AWD 140-190 were monitored closely.

RESULTS

AWD 140-190 exerted potent anticonvulsant activity against focal seizures. After intraperitoneal and oral administration in fully kindled rats, the substance dose-dependently increased the threshold for induction of afterdischarges starting at 15 mg/kg. AWD 140-190 only weakly influenced the seizure severity of the animals after stimulation at the elevated afterdischarge threshold current. No adverse effects were observed up to 30 mg/kg after intraperitoneal and oral administration in the open field and in the rotarod test. No differences were found between kindled and nonkindled rats when comparing neurotoxicity of AWD 140-190. Prolonged treatment with AWD 140-190 during kindling acquisition did not prevent kindling, but significantly retarded the development of fully kindled seizures during the treatment.

CONCLUSIONS

This study demonstrates that AWD 140-190 has anticonvulsant effects in the amygdala kindling model in rats, suggesting that the substance is particularly effective against partial seizures. AWD 140-190 is orally active and devoid of neurotoxic effects in anticonvulsant doses, thus indicating that this compound has potential for antiepileptic therapy. AWD 140-190 retards the kindling development during the treatment. This effect could be explained by the acute anticonvulsant effect of the substance.

Modulation of burst frequency, duration, and amplitude in the zero-Ca(2+) model of epileptiform activity

Incubation of hippocampal slices in zero-Ca(2+) medium blocks synaptic transmission and results in spontaneous burst discharges. This seizure-like activity is characterized by negative shifts (bursts) in the extracellular field potential and a K(+) wave that propagates across the hippocampus. To isolate factors related to seizure initiation, propagation, and termination, a number of pharmacological agents were tested. K(+) influx and efflux mechanisms where blocked with cesium, barium, tetraethylammonium (TEA), and 4-aminopyridine (4-AP). The effect of the gap junction blockers, heptanol and octanol, on zero-Ca(2+) bursting was evaluated. Neuronal excitability was modulated with tetrodotoxin (TTX), charge screening, and applied electric fields. Glial cell function was examined with a metabolism antagonist (fluroacetate). Neuronal hyperpolarization by cation screening or applied fields decreased burst frequency but did not affect burst amplitude or duration. Heptanol attenuated burst amplitude and duration at low concentration (0.2 mM), and blocked bursting at higher concentration (0.5 mM). CsCl(2) (1 mM) had no effect, whereas high concentrations (1 mM) of BaCl(2) blocked bursting. TEA (25 mM) and low concentration of BaCl(2) (300 microM) resulted in a two- to sixfold increase in burst duration. Fluroacetate also blocked burst activity but only during prolonged application (>3 h). Our results demonstrate that burst frequency, amplitude, and duration can be independently modulated and suggest that neuronal excitability plays a central role in burst initiation, whereas potassium dynamics establish burst amplitude and duration.

The novel anticonvulsant AWD 140-190 acts as a highly use-dependent sodium channel blocker in neuronal cell preparations

The effect of the new anticonvulsant drug AWD 140-190 (4-(p-bromophenyl)-3-morpholino-1H-pyrrole-2-carboxylic acid methyl ester) on neuronal sodium channels was evaluated in differentiated NG 108-15 cells using the patch clamp technique. AWD 140-190 blocked neuronal sodium channels more potently than phenytoin in a dose-dependent manner (1-30 microM). As with phenytoin, the blocking effect was voltage and frequency dependent. However, comparing equi-effective doses of AWD 140-190 and phenytoin, the frequency dependence was two to three times stronger. This pronounced use dependent effect of AWD 140-190 may be the reason for the superior tolerability and anticonvulsant activity in experimental models of epilepsy.