PubMed Health⌕ Search

Biomedical subjects

P Wicki

Publications and source records attributed to P Wicki.

At least 19 recordsLinked to original sources
PubMed2000

Studies on the in vitro assembly of a beta 1-40: implications for the search for a beta fibril formation inhibitors.

The progressive deposition of the amyloid beta peptide (Abeta) in fibrillar form is a key feature in the development of the pathology in Alzheimer's disease (AD). We have characterized the time course of Abeta fibril formation using a variety of assays and under different experimental conditions. We describe in detail the morphological development of the Abeta polymerization process from pseudo-spherical structures and protofibrils to mature thioflavin-T-positive/Congo red-positive amyloid fibrils. Moreover, we structurally characterize the various polymorphic fibrillar assemblies using transmission electron microscopy and determine their mass using scanning transmission electron microscopy. These results provide the framework for future investigations into how target compounds may interfere with the polymerization process. Such substances might have a therapeutic potential in AD.

Amyloid beta-Peptides↗
PubMed1995

Effects of the putative P-type calcium channel blocker, R,R-(-)-daurisoline on neurotransmitter release.

The alkaloid and medicinal herb constituent, R,R-(-)-daurisoline, was originally reported to be a N-type Ca2+ channel blocker, but newer evidence indicates that it is a blocker of P-type Ca2+ channels. To clarify its specificity with respect to N- and P-channels, we compared its effects on the electrically induced release of endogenous glutamate, 3H-GABA and 3H-noradrenaline, from brain slices with those of omega-agatoxin IVA and omega-conotoxin GVIA. Like omega-agatoxin IVA (but with about 1000-fold lower potency), and unlike omega-conotoxin GVIA, R.R-(-)-daurisoline inhibited the release of 3H-GABA and glutamate, with IC50 values of 8 and 18 microM. However, inhibition particularly of 3H-GABA release was more complete than by omega-agatoxin IVA, indicating interaction with one or more additional voltage-sensitive Ca2+ channels, possibly the Q-type. Its potency to inhibit glutamate release elicited either electrically, by veratrine or by high concentrations of K+ was similar, in contrast to sodium channel blockers. The effects of R,R-(-)-daurisoline on the release of 3H-noradrenaline, 3H-dopamine and 3H-acetylcholine were in agreement with previous knowledge from experiments with omega-agatoxin IVA suggesting an involvement of P-channels. A weak inhibition of 3H-noradrenaline release at 10 microM, similar to that by omega-agatoxin IVA at 0.03 microM, was occluded by alpha 2-antagonistic properties and could be unmasked in presence of rauwolscine. At 10 microM, it also inhibited electrically evoked 3H-dopamine and 3H-5-hydroxytryptamine release and caused a marked spontaneous release of all three monoamines in a reserpine-like manner. Spontaneous and evoked release of 3H-acetylcholine was inhibited by about 25% at 10 microM. In radioligand binding studies, R,R-(-)-daurisoline interacted with alpha 1- and alpha 2-adrenoceptors, 5-HT2 and muscarinic cholinergic receptors with IC50 values close to 1 microM, and with mu opiate receptors even with 0.18 microM. Atropine reduced the weak inhibitory effect of R,R-(-)-daurisoline on 3H-acetylcholine release somewhat, suggesting that it was brought about by both P channel blockade and cholinergic agonist activity. The effect on 3H-GABA release was unaffected by naloxone, indicating that the interaction of R,R-(-)-daurisoline with mu opiate receptors is antagonistic. The pattern of effects on neurotransmitter release observed with R,R-(-)-daurisoline resembles that of omega-agatoxin IVA and supports previous electrophysiological data suggesting that the compound blocks P-type voltage-sensitive Ca2+ channels. However, the more complete blockade of amino acid release by R,R-(-)-daurisoline suggests interaction with additional Ca2+ channel subtypes. Although it does also possess other pharmacological properties, we think that the compound is suitable to test whether blockade of glutamate release via voltage-sensitive Ca2+ channels is a viable concept to obtain novel neuroprotective and/or anticonvulsant compounds.

Acetylcholine↗
PubMed1995

Similar potency of carbamazepine, oxcarbazepine, and lamotrigine in inhibiting the release of glutamate and other neurotransmitters.

We compared the effects of the antiepileptic drugs carbamazepine, oxcarbazepine, and lamotrigine on the release from rat brain slices of endogenous glutamate, [3H]-GABA, and [3H]-dopamine, elicited by the Na+ channel opener, veratrine, and of the same transmitters as well as [3H]-noradrenaline, [3H]-5-hydroxytryptamine, and [3H]-acetylcholine, elicited by electrical stimulation. The three antiepileptic drugs inhibited veratrine-induced release of endogenous glutamate, [3H]-GABA, and [3H]-dopamine, with IC50 values between 23 and 150 microM, in or near the concentration range in which they interact with Na+ channels, and there was little difference between the compounds. They were five to seven times less potent in inhibiting electrically as compared with veratrine-stimulated release of [3H]-GABA and [3H]-dopamine; similarly, carbamazepine and tetrodotoxin were more potent in inhibiting veratrine-induced as compared with electrically induced release of endogenous glutamate. Carbamazepine, oxcarbazepine, and lamotrigine also inhibited electrically stimulated release of [3H]-5-hydroxytryptamine (IC50 values, 150 to 250 microM) and [3H]-acetylcholine (IC50 values, 50 to 150 microM); [3H]-noradrenaline release was affected to a lesser degree. The active concentration ranges of these drugs with respect to inhibition of veratrine-stimulated neurotransmitter release matched the therapeutic plasma and brain concentrations. It is uncertain whether these effects are relevant in vivo at anticonvulsant doses, because the drugs are markedly less potent in inhibiting the more physiologic release elicited by electrical stimulation. Therefore, the hypothesis that inhibition of glutamate release is the mechanism of anticonvulsant action of lamotrigine (or carbamazepine and oxcarbazepine) is doubtful. Other consequences of Na+ channel blockade may have an important role.

Animals↗
PubMed1994

GABA release in rat cortical slices is unable to cope with demand if the autoreceptor is blocked.

Electrically stimulated release of neurotransmitters in brain slices normally displays frequency dependence because of progressive activation of autoreceptors by endogenously released transmitter, which is abolished by blockade of autoreceptors. In consequence, the maximal increase caused by an autoreceptor antagonist in percent of the corresponding controls should be greater at higher than at lower frequencies. In the case of gamma-aminobutyric acid (GABA), we have previously found a marked deviation from this expectation. Among several explanations envisaged, computer simulation suggested only one to be compatible with the experimental data: the release mechanism may not be able to cope with high demand. This hypothesis was tested by investigating the frequency dependence of the release of 3H-GABA in the presence and absence of a high concentration of the potent GABAB antagonist, CGP 55845, using extremely short stimulation periods. To this end, slices were stimulated with groups of 4 POPs (a POP--pseudo-one-pulse--consists of 4 pulses delivered at 100 Hz). The intervals between the POPs within a group were varied from 60-0.5 s, corresponding to frequencies within the POP group of 0.0167-2 Hz. Under such circumstances, the theoretically expected pattern was indeed observed: the GABAB antagonist abolished the frequency dependence. In a second series of experiments, fractional release per POP was determined when 4-32 POPs were delivered at 2 Hz, with and without CGP 55845. The increase of GABA release elicited by the GABAB antagonist gradually subsided with increasing number of POPs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

GABA and glutamate release affected by GABAB receptor antagonists with similar potency: no evidence for pharmacologically different presynaptic receptors.

1. The effects of a series of nine GABAB receptor antagonists of widely varying potencies on electrically stimulated release from cortical slices of [3H]-GABA in the absence or presence of 10 microM of the GABAB agonist, (-)-baclofen and of endogenous glutamate in the presence of (-)-baclofen were compared. 2. The concentrations of the compounds half maximally increasing [3H]-GABA release (EC50's) at a stimulation frequency of 2 Hz correlated well with the IC50 values obtained from the inhibition of the binding of the agonist, [3H]-CGP 27492, to GABAB receptors in rat brain membranes (rank order of potency: CGP 56999 A > or = CGP 55845 A > CGP 52432 > or = CGP 56433 A > CGP 57034 A > CGP 57070 A > or = CGP 57976 > CGP 51176 > CGP 35348). 3. Likewise, the concentrations causing half-maximal increases of [3H]-GABA in the absence or presence of (-)-baclofen, and of endogenous glutamate in the presence of (-)-baclofen, correlated well with each other. Reports in the literature suggesting the CGP 35348 exhibits a 70 fold preference for inhibition of (-)-baclofen's effects on glutamate over [3H]-GABA release, and that CGP 52432 shows a 100 fold preference in the opposite sense, could not be confirmed in our model. 4. Therefore, our results suggest that, if there are pharmacological differences between GABAB autoreceptors and GABAB heteroreceptors on glutamatergic nerve endings in the rat cortex, they are not revealed by this series of compounds of widely different potencies. 5. In particular, our results with CGP 35348 and CGP 52432 do not support the hypothesis that GABAB autoreceptors and GABAB heteroreceptors on glutamatergic nerve endings represent subtypes with different pharmacology.

Animals↗
PubMed1993

Autoreceptor-mediated regulation of GABA release: role of uptake inhibition and effects of novel GABAB antagonists.

While the role of GABAB autoreceptors in the regulation of GABA release in synaptosomes and brain slices is well established, little is known about their role in vivo. Doubts have arisen because there is an apparent discrepancy between the frequencies at which GABA neurons fire and the frequency range within which autoreceptor regulation is observed in vitro. To see whether this apparent mismatch could be due to the use of a GABA uptake inhibitor in the release experiments in slices, we have compared the frequency dependencies of GABA release in the presence and absence of uptake inhibition. Before-hand, the previously incomplete frequency curve in the presence of uptake inhibition was extended at the lower end. To achieve this, stimulation was performed by means of groups of 4 pseudo-one-pulses (POP's) at inter-POP intervals corresponding to frequencies of 0.015625-0.5 Hz. It could be shown that activation of the GABAB autoreceptor by endogenously released GABA begins at a stimulation frequency as low as 0.0625 Hz. Experiments with the antagonist, CGP 35348, at inter-POP intervals of 1 min, at which the preceding POP has no longer an effect on GABA release during the next one, showed that basal release alone already substantially activated the autoreceptor. The frequency dependence in the absence as compared to the presence of uptake inhibition was shifted towards higher frequencies by a factor of 4. We do not consider this enough to remove our doubts about the in vivo operativity of GABAB autoreceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Release of endogenous glutamate from rat cortical slices in presence of the glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid.

The effect of the new glutamate uptake inhibitor, L-trans-pyrrolidine-2,4-dicarboxylic acid (L-trans-PDC), on the electrically evoked release or, rather, overflow of endogenous glutamate in superfusates from rat cortical slices was compared with that of dihydrokainate. In the absence of these presumed uptake inhibitors, electrical stimulation for 4 min at 1 Hz did not elicit a measurable glutamate overflow over baseline at all. Basal overflow increased concentration-dependently in the presence of 10-100 microM L-trans-PDC, about 5-fold at 100 microM. Also, electrical stimulation caused increases of glutamate overflow over basal levels progressive with increasing concentrations of trans-PDC; a stimulated overflow corresponding to about 50% of basal overflow was obtained at 100 microM. Basal as well as evoked release in the presence of dihydrokainate did not exceed ca. 60% of that obtained with 100 microM L-trans-PDC. In synaptosomes, L-trans-PDC much more than dihydrokainate caused a transient increase of spontaneous glutamate release which was diminished in the absence of Na+, indicating that it is transported into the cytoplasm by the glutamate carrier and induces some efflux of the amino acid from this compartment. Moreover, trans-PDC caused a weak to moderate inhibition of K(+)-evoked glutamate release from synaptosomes at 10-300 microM, without obvious concentration-dependence. Glutamate overflow elicited from rat cortical slices by electrical field stimulation at 1 Hz was Ca(2+)-dependent to about 80%. Tetrodotoxin (0.3 microM) reduced it by about 90%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effects of CGP 28014 on the in vivo release and metabolism of dopamine in the rat striatum assessed by brain microdialysis.

The effects on rat striatal dopamine (DA) metabolism of systemic and local administration of CGP 28014, an inhibitor of catechol-O-methyl-transferase (COMT), were studied by in vivo microdialysis. CGP 28014 (30 mg/kg i.p.) significantly reduced the levels of homovanillic acid (HVA), but did not modify DA and 3,4-dihydroxyphenylacetic acid (DOPAC). The intrastriatal administration (via the microdialysis probe) of 5, 7.5, 10, and 20 mM of CGP 28014 elicited a concentration-dependent, several-fold increase in extracellular DA but did not alter the levels of HVA and DOPAC. Thus, the effects of CGP 28014 observed after i.p. injection (decrease in HVA levels) are different from those measured after intrastriatal administration (increase in DA release). Therefore, the inhibition of COMT is likely to be due to the action of a metabolite of CGP 28014 formed in the periphery and not in the brain.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1992

Comparison of staple and Gambee techniques for enterotomy closure in the normal bovine jejunum.

Two suturing techniques for closure of jejunal enterotomies--the stapling and the Gambee technique--were compared in 7 bulls. Stapling was less time consuming (P less than 0.0001) and reduced the overall duration of surgery by 15%. Furthermore, the lumen diameter was significantly less decreased in the stapled intestine at 8 weeks after surgery (P less than 0.05). The diameter of the intestine increased significantly between 8 and 13 weeks after the Gambee suture had been applied (P less than 0.05) and the difference in diameter between intestines sutured according to Gambee and the stapled intestines disappeared. The intestinal diameter did not change significantly between 13 and 18 weeks in both techniques. The application of Gambee sutures resulted in fewer adhesions (P less than 0.01) and less thickening of the intestinal wall (P less than 0.0001). The surgery did not seem to affect the performance of the bulls significantly.

Animals↗
PubMed1991

Cellular reactions in the small intestine of rats after infection with Fasciola hepatica.

Groups of five rats each were infected with metacercariae of Fasciola hepatica according to two experimental procedures. In the first experiment, they received 20 metacercariae 0, 1, 2 or 3 times at intervals of 4 weeks. In the second, both the inoculation dose and the interval between doses were varied. After the animals had been killed, the small intestine was prepared for histology and tissue sections were stained for the detection and quantification of mucosal mast cells (MMCs), eosinophils and goblet cells. The density of eosinophils and MMCs increased significantly with each reinfection in the first experiment; in the second, the MMC reaction reached a peak at 4 weeks post-infection (p.i.), whereas the eosinophils peaked at 4 and 17 weeks p.i. In addition, the reaction of these cells depended on the infectious dose. In both experiments, goblet cells reacted only weakly. These findings thus clearly reflect a considerable intestinal response against migrating juvenile F. hepatica. The pattern of these defence reactions in the small intestine suggests some similarities with the mechanisms of antibody-dependent cell-mediated cytotoxicity that have been shown to take place during Schistosoma mansoni reinfection.

Animals↗
PubMed1991

[Intestinal cellular reaction of cattle after infection by Fasciola hepatica].

Defence reactions of cattle against Fasciola hepatica take place not only in the liver but also on a prehepatic level. The aim of the present experiments is to identify and quantify the cellular response in the small intestine. Five groups of two bulls (Simmental x Red Holstein, 6 months old) were infected by oesophageal probe with metacercariae of F. hepatica (MC) according to two experimental procedures. Two groups of bulls served as controls. In the first experiment both infected groups received 1000 MC once or twice at an interval of five weeks. The intestinal tissue was taken before infection and 5, 10 and 19 weeks p.i., respectively 5 and 14 weeks p. reinf. (p.ri.). In the second experiment, three infected groups received 400, 2 x 400 MC (at an interval of five weeks) and 800 MC respectively. Biopsies were taken one week ante infectionem, 6, 11 and 19 weeks p.i., respectively 1, 6 and 14 weeks post reinfectionem (p. ri.). The biopsies of the small intestine were prepared for histology and the tissue sections stained as follows: Astra blue for mucosal mast cells (MMC), Lendrum for eosinophils (EOS) and Periodic Acid Schiff (PAS) for goblet cells (GC). The density of the three cell populations in the mucosa was determined microscopically and quantified. In both experiments the density of the MMC and EOS increased with each reinfection and depended on the infectious dose. There was no significant variation of the GC-numbers. The described intestinal cellular reactions suggest a participation of the small intestinal wall in the immunity against the common liver fluke.

Animals↗
PubMed1989

Release of endogenous GABA from the substantia nigra is not controlled by GABA autoreceptors.

The characteristics of the release of GABA from slices of the rat substantia nigra, elicited by electrical stimulation at frequencies of 0.5-48 Hz and by elevated K+ concentrations ranging from 15-35 mmol/l, was studied. Comparisons were made with cortical slices where the data were not available from previous studies. No GABA release could be evoked from rat nigral slices by electrical stimulation between 0.5 and 4 Hz, in contrast to cortical slices, in which this pool is sensitive towards inhibition by (-)-baclofen. Also, comparatively less GABA release could be evoked from nigral than from cortical slices by K+ concentrations between 15 and 25 mmol/l. While (-)-baclofen at 10 mumol/l inhibited release caused by 15 mumol/l K+ in cortical, it did not in nigral slices. GABA release caused by higher frequencies (8-48 Hz) or 30 mmol/l K+ concentrations was Ca2+-dependent and in the former case also tetrodotoxin-sensitive. It had similar characteristics as in cortical slices and was insensitive towards (-)-baclofen, muscimol and bicuculline. Even more markedly than in the cortex, 30 mmol/l K+ released greater amounts of GABA than electrical stimulation at 24 Hz of a similar duration, suggesting the existence of one or several additional pool(s) of lesser excitability.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

The measurement of the release of endogenous GABA from rat brain slices by liquid chromatography with electrochemical detection.

A method for the determination of GABA by derivatization with 2,4,6-trinitrobenzenesulphonic acid and subsequent separation and quantitation by HPLC with electrochemical detection was characterized with respect to specificity, reproducibility and sensitivity. No other amino acid occurring in significant amounts in the brain was found to interfere; however, adequate separation of the derivatives of GABA and tryptophan must be carefully checked in each experiment. The sensitivity of the method is essentially determined by baseline noise, which mainly depends on the quality of the HPLC pump; under our conditions, it was about 2 ng/ml analyte. The coefficients of variation determined at two different concentrations relevant for the subsequent experiments were well below 10%. The method proved useful for the assessment of endogenous release of GABA from superfused rat cortical slices by electrical stimulation, which, in contrast to the basal release, was found to be completely calcium-dependent at stimulation frequencies of 5 and 12 Hz, under our conditions. Both stimulated and basal release of GABA was enhanced 4-5-fold by the inhibitor of GABA uptake, SK&F 89976 (10 microM).

Amino Acids↗
PubMed1988

Potential involvement of a baclofen-sensitive autoreceptor in the modulation of the release of endogenous GABA from rat brain slices in vitro.

The effects of the GABAA agonist, muscimol, and of the enantiomers of the GABAB agonist, baclofen, on the release of endogenous GABA from slices of the rat cerebral cortex, striatum and hippocampus were measured by means of a HPLC method with electrochemical detection. Moreover, the effect of the GABAA antagonist, bicuculline, and of the frequency of stimulation were studied in cortical slices. The amount of endogenous GABA released per impulse from cortical slices decreased by about 50% when the frequency was increased from 0.25 Hz to 1 Hz. This might indicate that GABA inhibited its own release (-)-Baclofen at 1 and 10 microM, but not its (+)-enantiomer, markedly inhibited the release of endogenous GABA, to a similar extent in all 3 areas investigated. The effect of (-)-baclofen was dependent on the frequency of stimulation: at lower frequencies (0.25 and 0.5 Hz) it was more marked than at a higher one (4 Hz). This would be expected from the results showing that the release of endogenous GABA decreases with increasing frequency, which suggests that this amino acid inhibits its own release. Muscimol at 10 microM, on the other hand, was ineffective in all 3 areas at a stimulation frequency of 0.5 Hz. Bicuculline (10 microM) at 4 Hz, at which autosuppression of GABA release is maximal did not enhance the release of endogenous GABA from cortical slices. With cerebellar or nigral slices, no adequate stimulation-induced release of endogenous GABA could be obtained under comparable conditions. These data are compatible with, but do not prove the existence of GABAB-type presynaptic autoreceptors modulating the release of this amino acid. More definite conclusions may possibly be drawn when a GABAB antagonist becomes available, which is expected to enhance GABA release under appropriate conditions.

Animals↗
PubMedDate not supplied

Ca2+-dependent release of endogenous GABA from rat cortical slices from different pools by different stimulation conditions.

The previously reported inhibitory effect of (-)-baclofen on the electrically evoked release of endogenous GABA from rat brain slices indicated the possibility of existence of GABAB autoreceptors. In this study, we have tested an alternative explanation, i.e. the possibility that (-)-baclofen reduced an excitatory glutamatergic input to GABAergic neurons by inhibiting glutamate release, by investigating the interaction of 1 mmol/l L-glutamate with the inhibitory effect of 10 mumol/l (-)-baclofen. L-Glutamate did not affect the electrically evoked release of GABA on its own and did not abolish the effect of (-)-baclofen, suggesting that the latter was not secondary to a reduction of glutamate release. On the other hand, it greatly increased the basal release of GABA and more than doubled the GABA content of the slices at the end of the perfusion, indicating a marked enhancement of GABA synthesis. This additional GABA, apparently formed from exogenous L-glutamate, was not releasable by electrical stimulation at 0.5 or 24 Hz, but at least in part by stimulation with 30 mmol/l K+. The previously reported increase of GABA release at 12 Hz as compared to 4 Hz was studied in more detail. GABA released by electrical stimulation at 8-48 Hz was Ca2+-dependent and tetrodotoxin-sensitive. No evidence was obtained for a decrease of the amount of GABA released per impulse with increasing frequency in this range.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗