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.

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.

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.

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.

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.

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.

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.

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.

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%.

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.

[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.

Investigations on GABAB receptor-mediated autoinhibition of GABA release.

In this study, we have investigated the effects of phaclofen on the [3H] overflow from [3H]GABA prelabelled rat cortical slices and its interaction with the effects of (-)-baclofen in dependence of the stimulation frequency. (-)-Baclofen strongly depressed the [3H] overflow in the frequency range of 0.125 to 4 Hz to a constant residual level (IC50 = 0.

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.

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 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.

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.