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W Kamphuis

Publications and source records attributed to W Kamphuis.

At least 37 records · Page 2Linked to original sources
PubMed1995

Long-term and regional specific changes in [3H]flunitrazepam binding in kindled rat hippocampus.

The binding of the GABAA/benzodiazepine receptor agonist [3H]flunitrazepam was studied in the hippocampus of rats kindled by daily stimulation of the Schaffer collaterals, using semi-quantitative autoradiography. Two kindled stages were investigated: (i) 24 h after the last generalized tonic-clonic seizure (fully kindled) and (ii) 28 days after the last generalized seizure (long-term). The binding of [3H]flunitrazepam was determined at two concentrations, 3 and 16 nM. In the CA1 area, we found a small but significant decrease (ca. 10%), both in the 3 and 16 nM [3H]flunitrazepam binding at the fully kindled stage. In contrast, there was a significant increase in the 3 nM binding (c. 15%) at the long-term stage. The 16 nM binding was not significantly different from control binding at this stage. In the granular and molecular layers of the fascia dentata, we found at both kindled stages a significantly increased 3 nM (ca. 9 and 19%, respectively) and 16 nM (ca. 19 and 14%, respectively) binding. Furthermore, we found that muscimol was still able to enhance the [3H]flunitrazepam binding in kindled animals, indicating that the GABAA receptor agonist binding site and benzodiazepine agonist binding site are still functionally coupled. The changes in [3H]flunitrazepam binding at the fully kindled stage are in agreement with the recently observed kindling-induced changes in [3H]muscimol binding in the hippocampal formation of the same animals [Titulaer M. N. G. et al. (1994) Neuroscience 59, 817-826] and extend these observations to the benzodiazepine modulatory site of the GABAA receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Opposite changes in GABAA receptor function in the CA1-3 area and fascia dentata of kindled rat hippocampus.

Muscimol-stimulated radiotracer 36CI- uptake in synaptoneurosomes was used to investigate the function of the GABAA receptor complex in the CA1-3 area and fascia dentata (granular and molecular layers and hilus) of rats kindled by stimulation, twice a day, of the Schaffer collateral fibers. Two kindled groups were studied: (a) 24 h after the last generalized tonic-clonic seizure [fully kindled (FK) stage] and (b) 28 days after the last generalized seizure (long-term stage). Synaptoneurosomes were prepared in parallel from subslices of the CA1-3 area and fascia dentata. In FK animals, the muscimol-stimulated 36CI- uptake was significantly reduced by 21% in the CA1-3 area in comparison with nonstimulated controls, whereas a significant increase of 29% was found in the fascia dentata. Significant changes were no longer present at 4 weeks after the last generalized seizure. The observed changes in muscimol-stimulated 36CI- uptake at the FK stage closely parallel the recently observed changes in [3H]muscimol binding in the CA1 area and fascia dentata. These results indicate that kindling causes a transiently decreased GABAA receptor-mediated function in the CA1-3, in contrast to an increased GABAA receptor-mediated function in the fascia dentata.

Animals↗
PubMed1995

The expression of syntaxin1B/GR33 mRNA is enhanced in the hippocampal kindling model of epileptogenesis.

Syntaxin, a protein required for the docking of synaptic vesicles, may be involved in the manifestation of synaptic plasticity. The possible involvement of syntaxin in epileptogenesis was investigated by assessing the expression levels of syntaxin1B/GR33 mRNA by in situ hybridization at different stages of hippocampal kindling epileptogenesis and after the induction of generalized seizures. Densitometric analysis of the autoradiograms revealed that the expression was not changed in pyramidal and granular neurons of the hippocampal formation 24 h after the first kindling stimulation. However, the mRNA levels in CA1, CA3, and fascia dentata neurons were bilaterally enhanced after six afterdischarges and remained at this elevated level during the whole period along which afterdischarges were elicited. An immunoassay was unable to reveal a clear significant increase of syntaxin1B/GR33 protein levels in hippocampus homogenates of fully kindled animals. The use of syntaxin1B-specific antibodies is necessary to draw definite conclusions on the changes at the protein level. At long term, 4 weeks after the last kindling-elicited generalized seizure, no significant alterations in transcript levels could be detected. The results suggest that the induction of kindling epileptogenesis is associated with an enhanced expression of syntaxin1B/GR33, but this enhanced expression is not necessary for persistence of kindling-induced synaptic plasticity.

Animals↗
PubMed1994

Rat hippocampal kindling induces changes in the glutamate receptor mRNA expression patterns in dentate granule neurons.

The expression level of the mRNAs encoding the Flip and Flop versions of the AMPA-selective glutamate receptor subunits A, B, C and D was studied using in situ hybridization in the hippocampus of rats kindled by Schaffer collateral/commissural fibre stimulation. The expression levels of the Flip variant of GluR-A, B and C mRNAs were bilaterally enhanced in the dentate granule neurons of fully kindled animals 24 h after the last seizure. These changes were already observed after the sixth kindling stimulation (preconvulsive-stage), but not after a single afterdischarge. Four weeks after the last seizure, when the animals were still hypersensitive to kindling stimulations, only GluR-A Flip expression was enhanced. These results suggest that kindling epileptogenesis is accompanied by an increased number and enhanced sensitivity of the expressed AMPA type glutamate receptors in the fascia dentata, leading to an enhanced excitatory synaptic transmission which may contribute to the process of kindling epileptogenesis.

Animals↗
PubMed1994

GABAA receptor beta 1-3 subunit gene expression in the hippocampus of kindled rats.

The effect of Schaffer collateral/commissural fiber kindling on the expression levels of GABAA receptor beta 1, beta 2 and beta 3 subunit mRNA in the pyramidal and granular neurons of the rat dorsal hippocampus was studied, using semi-quantitative in situ hybridization. In pyramidal neurons of CA1 and CA3, only small changes (10-15%) were found. In dentate granule neurons, the expression level of GABAA R-beta 3 mRNA was significantly, enhanced, bilaterally, in animals that were partial or fully kindled. At long-term, 4 weeks after the last convulsion no significant changes were found in pyramidal or granular neurons.

Animals↗
PubMed1994

Further evidence for clustering of human GABAA receptor subunit genes: localization of the alpha 6-subunit gene (GABRA6) to distal chromosome 5q by linkage analysis.

GABAA receptors are hetero-oligomeric ion-channel complexes that are composed of combinations of alpha, beta, gamma, and delta subunits and play a major role in inhibitory neuro-transmission in the mammalian brain. We report here a microsatellite polymorphism within the human alpha 6-subunit gene (GABRA6). Mapping of this marker in a human-hamster hybrid cell-line panel and typing of the repeat in the Centre d'Etude du Polymorphisme Human (CEPH) reference families enabled the localization of this gene to chromosome 5q and established its linkage to the GABAA receptor alpha 1-subunit gene (GA-BRA1) with a maximum lod score (Zmax) of 39.87 at a theta of 0.069 (males) and 0.100 (females). These results reveal the clustering of GABRA6, GABRA1, and the GABAA receptor gamma 2-subunit gene (GABRG2) on distal chromosome 5q.

Animals↗
PubMed1994

Kindling induces time-dependent and regional specific changes in the [3H]muscimol binding in the rat hippocampus: a quantitative autoradiographic study.

To investigate possible changes in the GABAA receptor agonist site in the CA1 area and fascia dentata of rats kindled by stimulation of Schaffer collaterals, a quantitative autoradiographic study of the [3H]muscimol binding was carried out. Two kindled groups were studied, at 24 h (fully kindled stage) and at 28 days (long-term stage) after the last class V seizure. Several concentrations of [3H]muscimol were tested in the range of the high/intermediate (5-40 nM) and low-affinity (60-100 nM) binding sites. In the fully kindled group, the binding over the complete range of tested [3H]muscimol concentrations was significantly increased by 30-50% in the fascia dentata, while the binding was significantly decreased by 10-25% in the CA1 area. The high/intermediate-affinity binding was still significantly increased by 20-30% in the fascia dentata 28 days after the last seizure. In this long-term group there was still a significant decrease of 10-18% of the low-affinity binding in the CA1 area. These results show that kindling epileptogenesis induces long-lasting changes in the GABAA receptor agonist binding sites that are region specific. We hypothesize that the changes encountered at the fully kindled stage, i.e. increased binding in the fascia dentata and decreased binding in the CA1 area, may underly the electrophysiologically observed increased paired-pulse depression of field potentials in the former and the decreased paired-pulse depression in the latter area [Kamphuis et al. (1992) Neurosci. Lett. 141, 101-105; Kamphuis et al. (1988) Brain Res. 440, 205-215; Zhao and Leung (1991) Brain Res. 564, 220-229; Zhao and Leung (1992) Brain Res. 582, 163-167]. We conclude that the observed changes may not only contribute to the induction of kindling epileptogenesis but may also play a role in the maintenance of the kindled state.

Allosteric Site↗
PubMed1993

Social conflict situations in rats differentially affect the development of amygdala kindling.

Clinical studies revealed an association between the occurrence of convulsions and stress. However, the direction of such relations and their mechanisms are not quite clear. The present study investigated the influence of stress-inducing agonistic conflict situations on the progressive process of kindling epileptogenesis induced by daily tetanic stimulation of the amygdala. Whereas repeated exposure to defeat in an agonistic setting did not affect the development of amygdala kindling, repeated victory experiences resulted in a significant retardation of the kindling process. Moreover, the kindling process was retarded to a greater extent in rats that quickly displayed offensive behavior and won the confrontation. Possible underlying mechanisms and biological substrates are discussed in terms of the ability of the individual to control or cope with the nature of the stressor.

Amygdala↗
PubMed1992

Hippocampal kindling increases the expression of glutamate receptor-A Flip and -B Flip mRNA in dentate granule cells.

The level of the mRNAs encoding the AMPA-selective glutamate receptors-A and -B, alternatively splice variants, Flip and Flop, was studied by in situ hybridization in the brains of rats kindled by Schaffer collateral/commissural-fiber stimulation. In comparison to control animals, the expression level of the Flip variant of both GluR-A and GluR-B mRNAs was bilaterally enhanced in the dentate granule neurons of kindled animals 24 h after last-generalized seizure, whereas no obvious alterations were observed in the GluR-A Flop and GluR-B Flop mRNA variants. In kindled animals, studied 1 month after the last seizure, GluR-A Flip and GluR-B Flip mRNA had returned to control levels. We suggest that these changes may result in an enhanced glutamate receptor sensitivity in the fascia dentata during kindling.

Alternative Splicing↗
PubMed1992

Hippocampal kindling leads to different changes in paired-pulse depression of local evoked field potentials in CA1 area and in fascia dentata.

Monosynaptic evoked field potentials (EPs) in response to paired-pulse stimulation (20 ms interval) were recorded in area CA1 and fascia dentata of the same animal in the course of development of a kindled focus in the CA1 region. A significant reduction of paired pulse depression in response to medium and high stimulation intensity was found in CA1. A similar change was found in the fascia dentata in response to medium intensity stimulation of the angular bundle. In contrast, at high intensity, paired pulse depression was enhanced in the fascia dentata in the course of kindling. These results indicate that kindling epileptogenesis is accompanied by regionally different changes in recurrent inhibition: a reduction in CA1 and intensity dependent changes in fascia dentata.

Animals↗
PubMed1992

Current source density of sustained potential shifts associated with electrographic seizures and with spreading depression in rat hippocampus.

The membrane currents responsible for the sustained potential shifts associated with electrographic seizures and with spreading depression in hippocampus were studied in the anesthetized rat. Probes incorporating 16 sensors in a straight line, spaced at 150-microns distances, were recording the potential changes with DC-coupled amplifiers in CA1 and dentate gyrus (DG) of one hemisphere. Seizures and spreading depression were provoked by repetitive stimulation of different afferent pathways. Seizures always began in DG before CA1, regardless of the pathway stimulated. Tonic seizures were associated with a sustained negative potential shift that was largest in the cell body layers. Current source density was computed from these recordings and confirmed the presence of a current sink limited to the cell body layer throughout the duration of electrographic seizures. Spreading depression was associated with a very large sink located in the layer of apical dendrites, maximal among the proximal segment of dendrites, to which the cell body layer served as a source. We conclude that seizures are associated with an inward current in neuron cell bodies, probably flowing through membrane channels of as yet no know physiological function.

Animals↗
PubMed1992

Enhancement of endogenous release of glutamate and gamma-aminobutyric acid from hippocampus CA1 slices after in vivo long-term potentiation.

The effect of long-term potentiation (LTP) on endogenous amino acid release from rat hippocampus slices was studied. LTP was induced in vivo by application of a tetanus (200 Hz, 200 ms) to the Schaffer collateral fibers in unanesthetized rats. Endogenous release of glutamate and gamma-aminobutyric acid (GABA) was investigated 60 min after tetanization in CA1 subslices of potentiated and control rats. No significant effects of LTP were observed in basal and K(+)-induced Ca(2+)-independent release components of these amino acids. In contrast, K(+)-induced Ca(2+)-dependent release of both glutamate and GABA increased approximately 100% in slices from potentiated rats. No differences were observed in total content of glutamate and GABA between the subslices from control and LTP animals. These results suggest a persistent increase in the recruitment of the presynaptic vesicular pool of glutamate and GABA during LTP.

Animals↗
PubMed1991

Development of changes in endogenous GABA release during kindling epileptogenesis in rat hippocampus.

The calcium-dependent gamma-aminobutyric acid (GABA) and glutamate release from rat hippocampal CA1 slices, evoked by a 1-min depolarization with 50 mM K+, was investigated in different stages of kindling epileptogenesis. Kindling was induced by tetanic stimulation of the Schaffer collateral/commissural pathway. In agreement with our previous results, we found a significantly increased calcium-dependent GABA release compared to that of implanted controls, in a group of fully kindled animals 1 day after the last seizure and also 25-36 days after the last seizure. In addition, we found that the increase in GABA release was associated with late phases of kindling epileptogenesis since no significant alterations were found in partly kindled animals that had received only 6 kindling stimulations while a significant increase was apparent in animals that had received 14 tetanic stimuli. When the release protocol was carried out in the presence of SK&F 89776-A, a blocker of the GABA uptake carrier, an additional amount of GABA was found after depolarization. This additional amount of GABA, reflecting the amount of GABA taken up under conditions without blocker, was in kindled animals not different from controls which demonstrates that a reduced GABA uptake does not account for the observed enhanced release in kindled animals. The calcium-dependent release of glutamate evoked by 1 min of high potassium depolarization was not significantly changed in the kindled groups. Only after prolonged depolarization during 4 subsequent minutes a significant increase in animals of the fully kindled group and at long-term after kindling was observed. The threshold K+ concentration for eliciting a calcium-dependent release of GABA and glutamate, was not changed in the kindled animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

A long-lasting decrease in the inhibitory effect of GABA on glutamate responses of hippocampal pyramidal neurons induced by kindling epileptogenesis.

Experiments were carried out to test whether changes in the sensitivity of hippocampal pyramidal neurons to the neurotransmitters glutamate, GABA and noradrenaline may be associated with the establishment of an epileptogenic focus induced by kindling. The effects of iontophoretically applied neurotransmitters on the firing rate of single units were quantified in the rat hippocampal CA1 area in kindled and control animals. Kindling was induced by electrical tetanic stimulation of the Schaffer collateral/commissural fibers. Firing was evoked by local glutamate iontophoresis while simultaneous GABA or noradrenaline application suppressed this response. A significant reduction of the GABAergic inhibitory action on the firing rate in kindled animals studied around four or around 42 days after the last convulsion was found. In the same neurons, the suppressive effect of noradrenaline was not different from controls. The neurons of kindled animals, investigated around four days after the last seizure, had a reduced sensitivity for glutamate; more glutamate ejection current was needed to evoke firing or to evoke the maximum firing rate. In contrast, the responsiveness for glutamate was significantly increased long-term after the last convulsion. These findings demonstrate that hippocampal Schaffer collateral kindling is associated with a long-lasting reduced effectiveness of the GABA-mediated response on glutamate-evoked firing in CA1.

Analysis of Variance↗
PubMed1990

Neonatal clonidine treatment results in long-lasting changes in noradrenaline sensitivity and kindling epileptogenesis.

In the present experiment we tested the hypothesis that early interference with noradrenaline transmission can have permanent consequences for brain function in adulthood. Neonatal depletion of noradrenaline by daily subcutaneous injections of clonidine results in supersensitivity to noradrenaline in adult hippocampal CA1 cells as shown in our previous microiontophoretic study. These findings were confirmed and extended here with dose-response curves. Furthermore, we tested whether this form of neonatal interference with noradrenaline also permanently affects long-lasting plasticity as revealed in kindling epileptogenesis in adulthood. The initiation of the epileptic activity after the kindling stimulation was significantly delayed in the clonidine-treated group, and all measured parameters of seizure expression tended to be retarded in comparison with saline-treated control rats. This indicates that noradrenaline supersensitivity induced by neonatal clonidine treatment retards kindling development in adulthood.

Animals↗
PubMed1990

Kindling increases the K(+)-evoked Ca2(+)-dependent release of endogenous GABA in area CA1 of rat hippocampus.

The release of endogenous amino acids from hippocampal CA1 subslices under basal conditions and the release evoked by high potassium (50 mM K+) depolarization was studied during kindling epileptogenesis. Emphasis was put on the release of the amino acid neurotransmitters gamma-aminobutyric acid (GABA) and glutamate. Kindling was induced by tetanic stimulation of the Schaffer-collaterals/commissural fibers of the dorsal hippocampus of the rat. The calcium-dependent GABA release in the presence of high K+ was significantly increased (40-46%) in fully kindled animals, 24 h after the last seizure, in comparison to controls. At long-term, 28 days after the last seizure, the calcium-dependent GABA release was still significantly increased (45-49%). An increased release of GABA in kindled animals was still found when GABA uptake was blocked by nipecotic acid. In contrast, no significant alterations were encountered in the basal or high potassium induced release of the excitatory amino acids aspartate and glutamate. These results suggest that kindling epileptogenesis is accompanied by a specific and long-lasting enhancement of GABA exocytosis which may lead to a desensitization of the GABA receptor, and thus determine the increase of seizure sensitivity.

Animals↗