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Biomedical subjects

B Ebert

Publications and source records attributed to B Ebert.

At least 55 records · Page 3Linked to original sources
PubMed1997

Excitatory amino acid receptor antagonists: resolution, absolute stereochemistry, and pharmacology of (S)- and (R)-2-amino-2-(5-tert-butyl-3-hydroxyisoxazol-4-yl)acetic acid (ATAA).

We have previously shown that (RS)-2-amino-2-(5-tert-butyl-3-hydroxyisoxazol-4-yl)acetic acid (ATAA) is an antagonist at N-methyl-D-aspartic acid (NMDA) and (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptors. We have now resolved ATAA via diastereomeric salt formation using N-BOC protected ATAA and (R)- and (S)-phenylethylamine. Enantiomeric purities (ee > 98%) of (R)- and (S)-ATAA were determined using the Crownpak CR(-) and CR(+) columns, respectively. The absolute configuration of (R)-ATAA was established by an X-ray crystallographic analysis of the (R)-phenylethylamine salt of N-BOC-(R)-ATAA. Like ATAA, neither (R)- nor (S)-ATAA significantly affected (IC50 > 100 microM) the receptor binding of tritiated AMPA, kainic acid, or (RS)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid, the latter being a competitive NMDA antagonist. Electrophysiological experiments, using the rat cortical wedge preparation, showed the NMDA antagonist effect as well as the AMPA antagonist effect of ATAA to reside exclusively in the (R)-enantiomer (Ki = 75 +/- 5 microM and 57 +/- 1 microM, respectively). Neither (R)- nor (S)-ATAA significantly reduced kainic acid-induced excitation (Ki > 1,000 microM).

Animals↗
PubMed1997

Serotonin1A receptor autoradiography during alcohol-withdrawal kindling.

A series of autoradiography experiments were conducted in order to test the theory that the serotonin (5-HT) receptor subtype 5-HT(1a) is involved in alcohol-withdrawal kindled convulsive behaviour. Alcohol-withdrawal kindling was performed by subjecting male Wistar rats to multiple episodes consisting of 2 days of alcohol intoxication and 5 days of alcohol withdrawal. In the first episode alcohol intoxication led to focal downregulation of [3H]-8-hydroxy-2-(di-n-propylamino)tetralin ([3H]-8-OH-DPAT) binding sites in septum and subregions of frontal cortex, hippocampus, and entorhinal cortex. This alcohol-induced response was blunted in both alcohol-withdrawal kindled animals and in animals exposed to repeated alcohol dependence in which the previous withdrawal reactions were blocked by diazepam administration. A paradoxical upregulation of [3H]-8-OH-DPAT binding sites was found in septum and subregions of frontal cortex, hippocampus, and entorhinal cortex in control animals which were fed isocalorically with the alcohol-withdrawal kindled animals and subsequently exposed to 2 days of alcohol intoxication. It was concluded that the alterations in the alcohol induced 5-HT(1a) receptor regulation after multiple episodes of alcohol dependence were not caused by alcohol-withdrawal kindling processes per se, but were due to both alcohol specific and alcohol non-specific effects.

Animals↗
PubMed1997

Bioisosterically modified dipeptide excitatory amino acid receptor antagonists containing 3-oxygenated isothiazole ring systems.

The AMPA receptor agonist Thio-AMPA, the 3-isothiazolol analogue of AMPA was converted into the selective NMDA antagonist, 2, in which a 3-isothiazolone unit is a bioisosteric analogue of the peptide bond of the NMDA antagonist, gamma-(R)-Glu-Gly. The isomeric 3-oxygenated isothiazole amino acid, 3, and the corresponding isothiazole phosphono amino acid 4 were also synthesized, and were shown to be selective AMPA receptor antagonists. Compound 1, in which the peptide bond of gamma-(R)-Glu-Gly is replaced by an ester group, was synthesized and shown to be unstable in the test buffer system.

Animals↗
PubMed1997

Fetal villosity and microvasculature of the bovine placentome in the second half of gestation.

The architecture of the fetal villous tree and its vasculature in the bovine placentome were studied in the second half of gestation using both conventional histology and histology of ink-filled blood vessels. These were compared with corrosion casts of plastic fillings of the vasculature, prepared for scanning electron microscopy. This combination of morphological methods allows perception of the villous tree throughout gestation from broad-conical to tall-conical form where branch ramification occurs mainly at right angles to the stem. The stem villus typically contains a single central artery and several peripheral veins arranged in parallel. The proximal branches to the stem, the intermediate villi, contain a central arteriole and accompanying venules. The distal branches, the terminal villi, enclose capillary convolutions which consist of an afferent arterial capillary limb, capillary loops and efferent venous capillary limbs. Vascular interconnections exist within the terminal villi, as capillaries or venules between the capillary convolutions, serially bridging them in up to 5 places, and as capillary anastomoses between the capillary loops. Coiling and sinusoidal dilatations of these loops develop near the end of gestation. The intraplacentomal rearrangement of villous trees with progressive gestation and their morphological vascular adaptations are discussed in relation to placental function, including the ever increasing need for transplacental substance exchange. This adaptation allows the blood to traverse the shortest possible arterioarteriolar route to the periphery of the trees where exchange takes place. The need for an increasing blood flow stimulates capillary growth and at the same time optimises the blood flow reaching the placental barrier represented by the vessel cast surface. The capillaries also carry the blood back into the very voluminous system of venules and veins where back diffusion may occur. The total volume of terminal villi of bovine placentome, the 'working part' of villous trees, hence distinctly increases with respect to the stem and intermediate villi, the 'supplying part' of the villous tree. In morphological terms the efficiency of the bovine transplacental diffusional exchange is higher than in the closely related 'co-ruminants' sheep and goats and distinctly higher when compared with the human placenta.

Animals↗
PubMed1997

[Anesthesia and analgesia in intravenous drug dependent patients with injection abscesses of the upper extremity. Case report].

The morbidity and mortality rate of drug addicts is characteristically higher than in a normal population. Especially abscesses of the hand and the forearm region are frequent consequences of unsterile injection techniques. Pre-, intra-, and postoperative anaesthetic management has to take into consideration that the choice of the anaesthetic procedure should not interfere with the very special conditions of the drug addicts. In our experience, continuous axillary brachial plexus block offers a number of advantages in pain management in drug addicts as well as in former drug addicts.

Abscess↗
PubMed1997

Differences in agonist/antagonist binding affinity and receptor transduction using recombinant human gamma-aminobutyric acid type A receptors.

Using human gamma-aminobutyric acid type A (GABAA) receptor subunit combinations, expressed in cell lines and Xenopus laevis oocytes, the pharmacology of a number of ligands interacting directly with the GABA recognition site has been studied in [3H]muscimol binding and electrophysiologically. The binding affinity of GABAA agonist and antagonist ligands showed small but statistically significant dependence on the subunit composition of receptors that include gamma 2 and different alpha and beta subunits. The potency of antagonist ligands was largely independent of receptor subunit composition, whereas the composition of receptors expressed in oocytes strongly influenced the EC50 value of agonists. An apparent reciprocal correlation between subunits favoring agonist binding and antagonist binding, respectively, was observed. Whereas antagonists showed comparable potencies in binding and functional studies, the potency of agonists in binding studies was generally two to three orders of magnitude higher than the agonist potencies measured electrophysiologically. 5-(4-Piperidyl)isothiazol-3-ol, which behaves as a low efficacy partial agonist at GABAA receptors in cultured cortical neurons, showed no efficacy in oocytes, but produced pure antagonist effects with a binding/functional affinity ratio between those observed for the agonists and antagonists. It is concluded that the GABAA receptor mechanisms transducing binding into physiological response, but not the binding per se, is dependent on the receptor subunit composition.

Animals↗
PubMed1997

[Axillary plexus catheter block in childhood and adolescence].

During the past two years (1994 and 1995), eight patients with the average age of eleven and a half years (four to fifteen years) received continuous axillary plexus anaesthesia subsequent to severe injuries of their upper extremities. The advantage of intra-, peri-, and postoperative anaesthesia and postoperative pain management are presented as a case report.

Adolescent↗
PubMed1996

Functional partial agonism at cloned human muscarinic acetylcholine receptors.

We have previously defined the concept of functional partial agonism as the partial agonist responses recorded in brain slices after administration of full ionotropic glutamate receptor agonists and competitive antagonists at fixed ratios. Functional partial agonism can be established at any level of maximal response, depending on the molar ratio of agonist and antagonist used. Using recombinant human muscarinic acetylcholine receptors (m1 and m5) and the functional assay, receptor selection and amplification technology (R-SAT), we have now shown that co-administration of the full agonist, carbachol, and a competitive antagonist, atropine or pirenzepine, at fixed ratios display functional partial agonism. The levels of apparent intrinsic activity of the functional partial agonist responses were shown to be dependent of the receptor density and G-protein concentration in the same manner as that determined for the true partial muscarinic agonist, 4-[N-(3-chlorophenyl)carbamoyloxy]-2-butynyltrimethylammonium chloride (McN A-343). Thus, functional as well as true partial agonist responses became more efficacious and potent with increasing receptor and G-protein levels. The level of maximal functional partial agonist response, which is dependent on the agonist/antagonist ratio, is predictable from the Waud equation, describing competitive receptor/ligand interactions. In agreement with the relative antagonist potencies of pirenzepine at m1 and m5, a 10:1 ratio of carbachol and pirenzepine produced very low-efficacy functional partial agonism, approaching full antagonism, at m1 but virtually full agonism at the m5 subtype.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗
PubMed1996

A new highly selective metabotropic excitatory amino acid agonist: 2-amino-4-(3-hydroxy-5-methylisoxazol-4-yl)butyric acid.

The homologous series of acidic amino acids, ranging from aspartic acid (1) to 2-aminosuberic acid (5), and the corresponding series of 3-isoxazolol bioisosteres of these amino acids, ranging from (RS)-2-amino-2-(3-hydroxy-5-methylisoxazol-4-yl)acetic acid (AMAA, 6) to (RS)-2-amino-6-(3-hydroxy-5-methylisoxazol-4-yl)hexanoic acid (10), were tested as ligands for metabotropic excitatory amino acid receptors (mGlu1 alpha, mGlu2, mGlu4a, and mGlu6). Whereas AMAA (6) and (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propinoic acid (AMPA, 7) are potent and highly selective agonists at N-methyl-D-aspartic acid (NMDA) and AMPA receptors, respectively, the higher homologue of AMPA (7), (RS)-2-amino-4-(3-hydroxy-5-methylisoxazol-4-yl)butyric acid (homo-AMPA, 8), is inactive at ionotropic excitatory amino acid receptors. Homo-AMPA (8), which is a 3-isoxazolol bioisostere of 2-aminoadipic acid (3), was, however, shown to be a specific and rather potent agonist at mGlu6, approximately 4 times weaker than the nonselective excitatory amino acid receptor agonist (S)-glutamic acid. 2-Aminoadipic acid (3), which shows a complex excitatory amino acid synaptic pharmacology, was an agonist at mGlu6 as well as mGlu2. AMPA (7) and the higher homologue of homo-AMPA (8), (RS)-2-amino-5-(3-hydroxy-5-methylisoxazol-4-yl)pentanoic acid (9), showed relatively weak agonist effects at mGlu6. It is concluded that homo-AMPA (8) is likely to be a useful tool for studies of the pharmacology and physiological role of mGlu6. We describe a new versatile synthesis of this homologue of AMPA and the synthesis of compound 10.

Alanine↗
PubMed1996

Synthesis and pharmacology of highly selective carboxy and phosphono isoxazole amino acid AMPA receptor antagonists.

(RS)-2-Amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA, 5) and the selective AMPA receptor antagonist (RS)-2-amino-3-[3-(carboxymethoxy)-5-methyl-4-isoxazolyl]propionic acid (AMOA, 7) have been used as leads for the design and synthesis of a number of potential AMPA receptor antagonists. Two parallel series of AMOA analogs were synthesized, containing either a distal carboxylic acid (compounds 8b-g and 11b) or a phosphonic acid (compounds 9a-g, 10c, and 11c). Pharmacological characterization of the synthesized compounds was carried out using a series of receptor binding assays and by in vitro electrophysiological experiments using the rat cortical slice model. The two analogs with a tert-butyl substituent, (RS)-2-amino-3-[5-tert-butyl-3-(carboxymethoxy)-4-isoxazolyl]pr opi onic acid (ATOA, 8b) and the corresponding phosphonic acid analog ATPO (9b), were the most potent and selective AMPA antagonists within each series. ATOA and ATPO showed IC50 values of 150 and 28 microM, respectively, toward AMPA-induced depolarizations in the cortical slice model compared to IC50 = 320 microM for the parent compound, AMOA. These two new competitive AMPA antagonists were significantly more selective than AMOA, showing no antagonism (up to 1 mM) toward NMDA-induced responses, whereas AMOA (at 1mM) showed weak (19%) inhibition toward NMDA-induced responses. The structure-activity relationships for the two series of compounds revealed considerable differences with respect to the substituents effects, and the phosphonic acid analogs generally exhibited significantly higher potencies compared to the carboxylic acid analogs.

Animals↗
PubMed1996

N-methyl-D-aspartic acid receptor agonists: resolution, absolute stereochemistry, and pharmacology of the enantiomers of 2-amino-2-(3-hydroxy-5-methyl-4-isoxazolyl)acetic acid.

(R,S)-2-Amino-2-(3-hydroxy-5-methyl-4-isoxazolyl)acetic acid [(R,S)-AMAA, 4] is a potent and selective agonist at the N-methyl-D-aspartic acid (NMDA) subtype of excitatory amino acid receptors. Using the Ugi "four-component condensation" method, the two diastereomers (2R)- and (2S)-2-[3-(benzyloxy)-5-methyl-4-isoxazolyl]N-tert-butyl-2- [N-[(S)-1-phenylethyl]benzamido]-acetamide (16 and 17, respectively) were synthesized and separated chromatographically. The absolute stereochemistry of 16 was confirmed by an X-ray analysis. Deprotection of these intermediates did, however, provide (R)- (8) and (S)- (9) AMAA, respectively, in extensively racemized forms. N-BOC-protected (R,S)-AMAA (21) was successfully resolved via diastereomeric salt formation using cinchonidine. The stereochemical purity and stability of 8 and 9 obtained via this resolution were determined using chiral HPLC. (R)-AMAA (8) showed peak affinity for [3H]AMPA receptor sites (IC50 = 72 +/- 13 microM) and was shown to be a more potent inhibitor of [3H]CPP binding (IC50 = 3.7 +/- 1.5 microM) than (S)-AMAA (9) (IC50 = 61 +/- 6.4 microM). Neither enantiomer of AMAA affected [3H]kainic acid receptor binding significantly. In electrophysiological studies using rat brain tissue, 8 (EC50 = 7.3 +/- 0.3 microM) was 1 order of magnitude more potent than 9 (EC50 = 75 +/- 9 microM) as an NMDA receptor agonist.

Acetates↗
PubMed1996

Glutamate and benzodiazepine receptor autoradiography in rat brain after repetition of alcohol dependence.

During repeated alcohol withdrawal, convulsive withdrawal behavior has been shown to be increased in a kindling-like manner in both clinical and experimental studies. In the present experiment, quantitative autoradiography was used to investigate binding of tritiated ligands to glutamate receptor subtypes and the benzodiazepine/GABA (BZ/GABA) receptor complex in rats exposed to 14 episodes of alcohol withdrawal. Seizures were detected in 25% of the animals during withdrawal episode 10-13. Repeated alcohol withdrawal resulted in a decrease in the number of [3H]-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ([3H]-AMPA) binding sites in striatum and sub-regions of the entorhinal cortex, the cerebellum and the hippocampus, while the [3H]-flunitrazepam binding was down-regulated in the frontal cortex. There was no differences between the controls and the multiple withdrawal animals regarding the [3H]-dizocilpine ([3H]-MK801) binding and the [3H]-kainic acid binding. However, within the latter group, those animals in which withdrawal seizures were observed had increased [3H]-MK801 binding sites in focal regions of entorhinal cortex and hippocampus, compared to those in which seizures were not observed. The decreased AMPA binding suggested impaired glutamate neurotransmission. As such, this receptor probably did not contribute to alcohol withdrawal kindling, but rather was involved in seizure protective mechanisms during this process.

Alcoholism↗
PubMed1996

Zinc changes AMPA receptor properties: results of binding studies and patch clamp recordings.

The influence of zinc ions on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors was investigated using binding studies with [3H]AMPA to rat cortical membranes and patch clamp recordings from cultured superior colliculus neurones. In Tris-HCl buffer, zinc (1-10 mM) significantly increased the specific binding of [3H]AMPA whereas this increase was negligible in the presence of CaCl2 (2.5 mM) and KSCN (100 mM). This effect was associated with a dramatic increase in Bmax but a decrease in both agonist and antagonist affinity. Association and dissociation experiments showed that equilibrium [3H]AMPA binding is reached with faster kinetics in the presence of zinc. At low concentrations (0.3 mM) zinc also concentration-dependently potentiated both peak and plateau components of whole cell current responses to AMPA (100 microM). This effect was accompanied by a reduction of the degree, and slowing of the rate, of AMPA receptor desensitisation. In contrast, higher concentrations of zinc (1-3.0 mM) inhibited AMPA responses to some degree, but slowed desensitisation further. This ability of zinc to change AMPA receptor properties may be relevant to neurotoxicity associated with AMPA receptor activation.

Animals↗
PubMed1996

Functional partial agonism at ionotropic excitatory amino acid receptors.

(RS)-2-Amino-3-(3-hydroxy-5-phenyl-4-isoxazolyl)propionic acid (APPA), which is an analogue of (RS)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA), shows the characteristics of a partial AMPA receptor agonist. Since (S)-APPA is a full AMPA agonist and (R)-APPA a competitive antagonist, the partial agonism observed for APPA, which is a 1:1 mixture of (S)- and (R)-APPA, is only apparent. These observations have prompted comparative pharmacological studies of different molar ratios of a series of AMPA and N-methyl-D-aspartic acid (NMDA) agonists and respective competitive antagonists, and of these agonists in the presence of fixed concentrations of antagonist. Using the rat cortical wedge preparation, the latter series of experiments showed the expected rightward parallel shifts of the dose-response curves. The former type of experiments, on the other hand, produced dose-response curves at different levels of maximal response, depending on the molar ratios of agonist and antagonist used. This phenomenon, which is in agreement with the theory for competitive receptor interaction, has been termed functional partial agonism, a new pharmacological concept of potential therapeutic utility. These results were obtained using AMPA, the AMPA agonist (RS)-2-amino-3-(5-tert-butyl-3-hydroxy-4-isoxazolyl)propionic acid (ATPA), the competitive AMPA antagonists (RS)-2-amino-3-(3-carboxymethoxy-5-methyl-4-isoxazolyl)propionic acid (AMOA) and 6-nitro-7-sulfamoylbenzo[f] quinoxalin-2,3-dione (NBQX), NMDA, and the competitive NMDA antagonist (RS)-3-(2-carboxy-4-piperazinyl)propyl-1-phosphonic acid (CPP).

Alanine↗
PubMed1996

The opioid ketobemidone has a NMDA blocking effect.

There are clinical observations that neurogenic pain can respond well to the opioid ketobemidone, in contrast to pethidine and morphine. This has led us to the hypothesis that the analgesic effect of ketobemidone in neurogenic pain may be due to both opioid as well as additional non-opioid effects. The present study was therefore made to evaluate the effects of ketobemidone. The study consists of two parts. (1) Single unit recordings were made from dorsal horn neurones in the halothane-anaesthetised rat. Neurones were activated by transcutaneous electrical stimulation of their receptive fields at C-fibre strength and their responses quantified. The wind-up of the neurones, due to N-methyl-D-aspartate (NMDA) receptor activation, leading to marked increases in C-fibre responses and an associated post-discharge was also measured. Ketobemidone, applied to the spinal cord, equivalent to an intrathecal injection, dose-dependently and selectively reduced C-fibre evoked responses. Ketobemidone was also found to block wind-up more effectively than morphine at equieffective doses, but unlike morphine in a non-naloxone-reversible manner. (2) In a binding study ketobemidone was shown to inhibit [3H]MK-801 binding with a Ki value of 26 microM. Therefore, ketobemidone appears to possess both mu opioid agonist as well as NMDA blocking effects.

Analgesics, Opioid↗
PubMed1995

Annulated heterocyclic bioisosteres of norarecoline. Synthesis and molecular pharmacology at five recombinant human muscarinic acetylcholine receptors.

A series of O-alkylated analogs of 5,6,7,8-tetrahydro-4H-isoxazolo[4,5-c]azepin-3-ol (THAO) were synthesized and characterized as ligands for muscarinic acetylcholine receptors (mAChRs). O-Methyl-THAO (4a), O-ethyl-THAO (4b), O-isopropyl-THAO (4c), and O-propargyl-THAO (4d) were shown to be potent inhibitors of the binding of tritiated quinuclidinyl benzilate (QNB), pirenzepine (PZ), and oxotremorine-M (Oxo-M) to tissue membrane preparations. In the [3H]-Oxo-M binding assay, receptor affinities in the low nanomolar range were measured for 4a (IC50 = 0.010 microM), 4b (IC50 = 0.003 microM), 4c (IC50 = 0.011 microM), and 4d (IC50 = 0.0008 microM). Pharmacological effects (EC50 or Ki values) and intrinsic activities (per cent of maximal carbachol responses) were determined using five recombinant human mAChRs (m1-m5) and the functional assay, receptor selection and amplification technology (R-SAT). Compound 4c antagonized carbachol-induced responses at m1, m3, and m5. With the exception of 4b, which was an antagonist at m5, 4a,b,d showed partial agonism at m1-m5 with very similar subtype selectivity (m2 > m4 > m1 > or = m3 > m5). Agonist index values for 4a-d, which were calculated from [3H]QNB (brain) and [3H]Oxo-M (brain) binding data, were shown to be predictive of pharmacologically determined intrinsic activities at m1-m5, the same rank order of intrinsic activity being observed at all five mAChRs (4a > 4d > 4b > 4c). It is concluded that within this class of high-affinity mAChR (m1-m5) ligands, containing secondary amino groups, minor changes of the bioisosteric ester alkyl groups have marked effects on potency and, in particular, intrinsic activity.

3T3 Cells↗
PubMed1995

Thiomuscimol, a new photoaffinity label for the GABAA receptor.

Thiomuscimol inhibits [3H]muscimol binding to brain GABAA receptors. Exposure of Ag(+)-treated membrane preparations to UV radiation at 254 nm for 40 min in the presence of thiomuscimol (10(-5) M) produced a 20-30% irreversible decrease in high-affinity [3H]muscimol binding sites. The photoaffinity labeling of thiomuscimol was inhibited by GABA (10(-4) M) added prior to exposure to UV light. The data show that thiomuscimol can label the GABAA receptor site and that the ligand can be used as a photoaffinity label for purification and identification of GABA binding sites within the GABAA receptor complex.

Affinity Labels↗