Effects of monomethylarsonic and monomethylarsonous acid on evoked synaptic potentials in hippocampal slices of adult and young rats.

Arsenite and its metabolites, dimethylarsinic or dimethylarsinous acid, have previously been shown to disturb synaptic transmission in hippocampal slices of rats (Krüger, K., Gruner, J., Madeja, M.

Effects of dimethylarsinic and dimethylarsinous acid on evoked synaptic potentials in hippocampal slices of young and adult rats.

In this study, the effects of pentavalent dimethylarsinic acid ((CH(3))(2)AsO(OH); DMA(V)) and trivalent dimethylarsinous acid ((CH(3))(2)As(OH); DMA(III)) on synaptic transmission generated by the excitatory Schaffer collateral-CA1 synapse were tested in hippocampal slices of young (14-21 day-old) and adult (2-4 month-old) rats. Both compounds were applied in concentrations of 1 to 100 micromol/l. DMA(V) had no effect on the amplitudes of evoked fEPSPs or the induction of LTP recorded from the CA1 dendritic region either in adult or in young rats.

Effects of monomethyltin and dimethyltin compounds on heterologously expressed neuronal ion channels (Xenopus oocytes) and synaptic transmission (hippocampal slices).

The aim of this study was to investigate the effects of monomethyltin trichloride (MMT) and dimethyltin dichloride (DMT) on various neuronal ion channels heterologously expressed in Xenopus oocytes and on synaptic transmission in hippocampal slices of young (14-21 days old) and adult (2-4 months old) rats. The Xenopus oocyte expression system was chosen to allow direct assessment of the effects of MMT and DMT both on glutamate receptors sensitive to AMPA and NMDA and on various voltage-operated potassium and sodium channels. Hippocampal slices were used to analyze the effects of MMT and DMT on synaptic potentials generated by the important excitatory Schaffer collateral-CA1 synapse.

Effects of arsenite on long-term potentiation in hippocampal slices from young and adult rats.

The effects of trivalent arsenite were tested at the Schaffer collateral-CA1 synapse of adult (2-4 month) and young (14-21 days) rats. Exposure of 100micromol/l arsenite led to a slight and reversible reduction of the amplitudes of evoked excitatory postsynaptic field potentials in adult and young rats, while exposure of 0.1 and 1micromol/l arsenite had no effects.

Blockade and enhancement of glutamate receptor responses in Xenopus oocytes by methylated arsenicals.

Pentavalent and trivalent organoarsenic compounds belong to the major metabolites of inorganic arsenicals detected in humans. Recently, the question was raised whether the organic arsenicals represent metabolites of a detoxification process or methylated species with deleterious biological effects. In this study, the effects of trivalent arsenite (AsO(3) (3-); iA(III)), the pentavalent organoarsenic compounds monomethylarsonic acid (CH(3)AsO(OH)(2); MMA(V)) and dimethylarsinic acid ((CH(3))(2)AsO(OH); DMA(V)) and the trivalent compounds monomethylarsonous acid (CH(3)As(OH)(2), MMA(III)) and dimethylarsinous acid ((CH(3))(2)As(OH); DMA(III)) were tested on glutamate receptors and on voltage-operated potassium and sodium channels heterologously expressed in Xenopus oocytes.

Intrinsic excitability, synaptic potentials, and short-term plasticity in human epileptic neocortex.

Although studies of epileptic human hippocampus suggest changes of synaptic and intrinsic excitability, few changes, save the appearance of spontaneous field/synaptic potentials, are known in epileptic neocortical tissue. However, invasive EEG and histological studies suggest that neocortical tissue, even in mesial temporal lobe epilepsy, can play an important role as an irritative zone or extrahippocampal focus. We hypothesized that intrinsic neuronal and synaptic excitability, as well as short-term plasticity, are altered in neocortical areas, particularly with elevated K+ levels as occur during seizures.

Blockade of glutamatergic and GABAergic receptor channels by trimethyltin chloride.

1. Organotin compounds such as trimethyltin chloride (TMT) are among the most toxic of the organometallics. As their main target for toxicity is the central nervous system, the aim of the present study was to investigate the effects of TMT on receptor channels involved in various processes of synaptic transmission.

Contribution of the cytoskeleton and the phospholipase C signaling pathway to fluid stream-induced membrane currents.

A fluid stream induced by a concentration clamp system evokes in Xenopus oocytes a deformation of the membrane which results in transient chloride currents of high amplitude (stream-evoked inward current, I(i,st)) during calcium-activated chloride current oscillations. The involvement of cytoskeleton elements and of components of the phospholipase C-dependent signaling pathway on the generation of the I(i,st) were investigated. Incubation of the oocytes with cytoskeleton-disrupting agents exerted no effects on generation of the I(i,st), suggesting that the mechanotransduction is not mediated by these structures.

RNA editing (R/G site) and flip-flop splicing of the AMPA receptor subunit GluR2 in nervous tissue of epilepsy patients.

Editing and alternative splicing of mRNA are posttranscriptional steps probably involved in pathophysiological aspects of epilepsy. The present study analyses the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunit GluR2 with respect to the expression of (i) editing at the R/G site and (ii) flip-flop cassettes. Nervous tissue from patients with temporal lobe epilepsy was analysed by RT-PCR followed by restriction enzyme assays.

Diurnal actions of melatonin on epileptic activity in hippocampal slices of rats.

Since melatonin receptors have been found in the hippocampus of mammals it has been suggested that melatonin can modulate neuronal functions of hippocampal cells. The effect of melatonin (10 nM/l and 1 microM/l) on frequency and amplitude of epileptiform field potentials (EFP) elicited by low Mg(2+) or by bicuculline was tested in the CA1 region of hippocampal slices of rats. In the low Mg(2+) model, melatonin, applied in a near physiological concentration of 10 nM/l, exerts no effect on EFP in slices prepared at night or during the day.

Gene expression and functional characterization of melatonin receptors in the spinal cord of the rat: implications for pain modulation.

Recently, a species-dependent distribution of melatonin binding sites have been found in lamina I-V and lamina X of the spinal cord. In order to learn more about the function of spinal melatonin receptors, we investigated (i) the gene expression for melatonin receptor subtypes in lumbar and thoracal spinal cord tissue by means of the reverse-transcriptase polymerase chain reaction (RT-PCR) technique, and (ii) the electrophysiological and pharmacological properties of melatonin receptors heterologously expressed in Xenopus oocytes after injection of spinal cord mRNA by means of the voltage clamp technique. Because ample evidence indicates an antinociceptive effect of melatonin, (iii) the role of spinal melatonin receptors for maintaining mechanical and thermal hyperalgesia was studied in a rat model for postoperative pain.

Molecular site of action of the antiarrhythmic drug propafenone at the voltage-operated potassium channel Kv2.1.

The effects of the antiarrhythmic drug propafenone at Kv2.1 channels were studied with wild-type and mutated channels expressed in Xenopus laevis oocytes. Propafenone decreased the Kv2.

Receptor (MT(1)) mediated influence of melatonin on cAMP concentration and insulin secretion of rat insulinoma cells INS-1.

Recent functional, autoradiographic, and molecular investigations have shown that the pineal secretory product melatonin reduces the forskolin-stimulated insulin secretion from isolated pancreatic islets of neonate rats. Autoradiographic and binding studies as well as reverse transcriptase-polymerase chain reaction (RT-PCR) experiments proved that these effects are mediated through specific, high-affinity pertussis-toxin-sensitive Gi-protein-coupled MT(1) receptors and subsequent inhibition of the adenylyl cyclase/cyclic adenosine monophosphate (cAMP) system. This hypothesis was proved by blocking the intracellular signal transduction pathway using the non-hydrolyzable guanosine triphosphate analog guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) or the competitive melatonin receptor antagonist luzindole.

Melatonin receptors in rat hippocampus: molecular and functional investigations.

Since binding sites for melatonin have been found in the hippocampus of several mammals, it has been suggested that the pineal hormone melatonin is able to modulate neuronal functions of hippocampal cells. In order to get more insight into the role of melatonin for the functions of hippocampal cells, the following experiments were performed: male rats, maintained under a 12/12-h light-dark cycle, were sacrificed by decapitation at zeitgeber times (h) ZT2, ZT8, and ZT15 (ZT0 = lights on); for experiment 1, gene expression for melatonin receptors was detected in the hippocampus and in hippocampal subfields by means of the RT-PCR technique; for experiment 2, electrophysiological and pharmacological properties of melatonin receptors heterologously expressed in Xenopus oocytes after injection of mRNA from the hippocampus were analyzed by means of voltage clamp technique; and for experiment 3, effects of melatonin on the spontaneous firing rate of action potentials in the CA1 regions of hippocampal slices were analyzed by means of extracellular recordings. The RT-PCR data revealed that transcripts for both the MT1 and MT2 melatonin receptors are present in the dentate gyrus, CA3, and CA1 regions, and the subiculum of the hippocampus.

RNA editing at the Q/R site for the glutamate receptor subunits GLUR2, GLUR5, and GLUR6 in hippocampus and temporal cortex from epileptic patients.

Posttranscriptional editing of mRNA is a phenomenon that generates molecular heterogeneity and functional variety. With the intention to test if RNA editing plays a role in pathological processes, which contribute to seizure maintenance, we examined the ratio of the unedited (Q) to edited (R) form of the AMPA receptor subunit GluR2 and kainate receptor subunits GluR5 and GluR6 in the hippocampus and temporal cerebral cortex, both excised from patients with pharmacoresistant temporal lobe epilepsies. We compared the data with samples from nonepileptic human control tissue (autopsy tissue).

Blocking effects of the antiarrhythmic drug propafenone on the HERG potassium channel.

Propafenone has been shown to affect the delayed-rectifier potassium currents in cardiomyocytes of different animal models. In this study we investigated effects and mechanisms of action of propafenone on HERG potassium channels in oocytes of Xenopus laevis with the two-electrode voltage-clamp technique. Propafenone decreased the currents during voltage steps and the tail currents.

Expression and functional characterization of the mt1 melatonin receptor from rat brain in Xenopus oocytes: evidence for coupling to the phosphoinositol pathway.

Melatonin-sensitive receptors were expressed in Xenopus laevis oocytes following an injection of mRNA from rat brain. The administration of 0.1-100 micromol/L melatonin to voltage-clamped oocytes activates calcium-dependent chloride currents via a pertussis toxin-sensitive G protein and the phosphoinositol pathway.

Effects of antiarrhythmic drugs on cloned cardiac voltage-gated potassium channels expressed in Xenopus oocytes.

The effects of 17 commonly used antiarrhythmic drugs on the rapidly activating cardiac voltage-gated potassium channels (Kv1.1, Kv1.2, Kv1.

Vigabatrin reduces epileptiform activity in brain slices from pharmacoresistant epilepsy patients.

Human neocortical temporal lobe tissue resected for treatment of pharmacoresistant epilepsy was investigated. In slices prepared from this tissue, epileptiform field potentials (EFP) were induced by omission of magnesium from the artificial cerebrospinal fluid (ACSF). The effects of the gamma-aminobutyric acid transaminase inhibitor vigabatrin on EFP were tested.

Alternative splicing of the NMDAR1 glutamate receptor subunit in human temporal lobe epilepsy.

It has been demonstrated in animal models that chronic epilepsy is associated with increased excitability which may result from abnormal glutamatergic transmission involving altered properties of N-methyl-D-aspartate (NMDA) receptors. We have investigated whether human temporal lobe epilepsy is associated with changes in the NMDA receptor at the molecular level by assessing the relative expression of mRNAs of the different splice variants at the N-terminal (exon 5) and C-terminal (exon 21) position for the NMDAR1 subunit. Specimens of hippocampus and temporal lobe cortex from patients with refractory epilepsy were obtained during neurosurgical operations and analyzed by means of the reverse transcription reaction followed by polymerase chain reaction.

Evidence for a melatonin receptor within pancreatic islets of neonate rats: functional, autoradiographic, and molecular investigations.

In a recent perifusion investigation, we showed that the pineal secretory product melatonin reduces insulin secretion from isolated pancreatic islets of neonate rats stimulated with potassium chloride (KCl), glucose, and forskolin. This effect of melatonin was reproduced with doses ranging from 200 pmol/L to 5 micromol/L. Because it is generally accepted that melatonin exerts some of its biological effects through specific, high-affinity pertussis-toxin-sensitive G-protein-coupled receptors, we blocked the putative melatonin receptor of pancreatic islets using both the non-hydrolyzable guanosine triphosphate analog guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS, 30 micromol/L) and the melatonin antagonist luzindole (10 micromol/L).

Sensitivity of native and cloned hippocampal delayed-rectifier potassium channels to verapamil.

The effects of the phenylalkylamine verapamil on native and cloned hippocampal voltage-operated potassium channels were investigated. Native channels were studied in acutely isolated CA1 neurons from the guinea pig with the whole-cell patch-clamp technique. Cloned channels were expressed in oocytes of Xenopus laevis and studied with the two-electrode voltage-clamp technique.

Glutaric aciduria type I: pathomechanisms of neurodegeneration.

In organotypic corticostriatal and hippocampal slice cultures from rat brain, 3-hydroxyglutaric acid but not glutaric and glutaconic acids induced neurodegeneration by activation of NMDA receptors. Electrophysiological investigations (Xenopus laevis oocytes expressing glutamate receptors; rat mixed cortex culture) revealed no direct interaction of 3-hydroxyglutaric acid with glutamate receptors. We speculate that 3-hydroxyglutaric acid induces a mild energy deprivation that interferes with the voltage-dependent Mg(2+)-block of NMDA receptors.

Effects of 2-phenoxyethanol on N-methyl-D-aspartate (NMDA) receptor-mediated ion currents.

The actions were examined of 17 frequently used glycol ether compounds on the glutamate receptor-mediated ion currents. The receptors were expressed in Xenopus oocytes by injection of rat brain mRNA. Most of the 17 glycol ethers exerted no effects on the glutamate subreceptors activated by kainate and N-methyl-D-aspartate (NMDA), whereas 2-phenoxyethanol (ethylene glycol monophenyl ether) caused a considerable reduction of NMDA-induced membrane currents in a reversible and concentration-dependent manner.

Gabapentin potentiation of the antiepileptic efficacy of vigabatrin in an in vitro model of epilepsy.

1. An enhancement of promoted release of gamma-aminobutyric acid (GABA) and a change in GABA-metabolism have been suggested as mechanisms of action of gabapentin. Vigabatrin is supposed to act mainly via inhibition of GABA-transaminase but it also interferes with GABA-release and GABA-uptake.