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Biomedical subjects

L H Jensen

Publications and source records attributed to L H Jensen.

At least 19 recordsLinked to original sources
PubMed1992

Time- and temperature-dependent forebrain ischemic damage in Mongolian gerbils.

The influence of transient bilateral carotid artery occlusion time, core body temperature regulation and post-operative survival time was examined on delayed neuronal death in the hippocampal subregions of Mongolian gerbils. A simple and rapid histologically based scoring system was used. A carotid artery occlusion time of 5 min with stabile core body temperature at 37.5-38.0 degrees C and a post-operative survival time of 4 days was sufficient to induce a reproducible and almost total neuronal damage in the hippocampal subfields. Furthermore, the use of gerbils with ages varying from 50 to 100 days did not markedly influence the development of the neuronal damage although the variation in the severity of the damage seemed to decrease with age. The addition of a drop of room tempered (21-22 degrees C) isotonic water, to avoid adherence between the clips and the carotid artery, reduced neuronal damage in some animals.

Animals↗
PubMed1992

The structure of water in protein crystals.

Protein crystals grown from aqueous media invariably contain substantial amounts of the crystallizing solution, and the structure of the protein molecules and surrounding solvent can be determined from X-ray diffraction data. Electron density maps of crystalline proteins based on such data show networks of water peaks in the solvent space within approximately 6A of the protein surface. In general, the peaks are highest for water molecules within hydrogen bonding distance of acceptor or donor atoms on the protein. With increasing distance from the protein, the water peaks decrease in height, and beyond approximately 6A they merge into the structureless solvent continuum, typical of most crystalline proteins. A few water sites are often found within the protein molecule. These water molecules appear to be trapped within the protein and presumably are more tightly bound than water external to the protein.

Crystallization↗
PubMed1991

Refined crystal structure of ferredoxin II from Desulfovibrio gigas at 1.7 A.

The crystal structure of ferredoxin II from Desulfovibrio gigas has been determined using phasing from anomalous scattering data at a resolution of 1.7 A and refined to an R-factor of 0.157. The molecule has an overall chain fold similar to that of the other bacterial ferredoxins of known structure. The molecule contains a single 3Fe-4S cluster with geometry indistinguishable from the 4Fe-4S clusters, and a disulfide bond near the site corresponding to the position of the second cluster of two-cluster ferredoxins. The cluster is bound by cysteine residues 8, 14 and 50. The side-chain of cysteine 11 extends away from the cluster, but could rotate to become the fourth cysteine ligand in the four-iron form of the molecule given a local adjustment of the polypeptide chain. This residue is modified, however, by what appears to be a methanethiol group. There are a total of eight NH . . . S bonds to the inorganic and cysteine sulfur atoms of the Fe-S cluster. There is an additional residue found that is not reported for the chemical sequence: according to the electron density a valine residue should be inserted after residue 55.

Amino Acid Sequence↗
PubMed1991

Structure of rubredoxin from Desulfovibrio vulgaris at 1.5 A resolution.

The X-ray model of rubredoxin from Desulfovibrio vulgaris has been refined against 1.5 A X-ray diffraction data collected on a diffractometer. The final model comprises 395 non-hydrogen protein atoms, and 180 solvent O atoms. The final R-value for the model with calculated H atom positions included as fixed contributions is 0.098 over all reflections greater than 2 sigma I from infinity to 1.5 A. The error in co-ordinates is estimated to be 0.08 A. The solvent model was twice redetermined during the later stages of refinement and was instrumental in its success. One sequence error has been detected and corrected (Thr21----Asp). The iron-sulfur site bond angles are distorted from true tetrahedral symmetry, as found in other rubredoxin structures. A significant deviation from tetrahedral angles is seen at C alpha atoms 9, 10, 42 and 43, interior angles of the loops binding the iron atom. The planes of two aromatic groups, Tyr4 and Trp37, are nearly parallel to, and lie under, an extended system of atoms that includes the peptide bonds preceding the first cysteine residue of each cysteine loop as well as the cysteine side-chain, the iron, and the cysteine side-chain of the opposite loop, forming a previously unrecognized extended system that may function in electron transfer.

Amino Acid Sequence↗
PubMed1990

Dopamine release in the nucleus caudatus and in the nucleus accumbens is under glutamatergic control through non-NMDA receptors: a study in freely-moving rats.

Perfusion with quisqualate (5 x 10(-6) M) and kainate (5 x 10(-7) M), selective agonists of glutamate receptors, enhanced the release of dopamine in both caudate and accumbens nuclei of freely-moving rats, measured by the transcerebral microdialysis technique. In contrast, N-methyl-D-aspartate (NMDA) did not affect dopamine release, except at very high concentrations (10(-2) M). The quisqualate-kainate antagonist, FG 9041 (DNQX), antagonized the elevation of dopamine release induced by quisqualate and, furthermore, reduced that of kainate. CPP, a selective NMDA antagonist, did not counteract the quisqualate- or kainate-induced stimulation of dopamine release. The enhancement of dopamine release after quisqualate and kainate was accompanied by behavioural stimulation characterized by grooming, rearing, hypermotility with sniffing and confined sniffing. This behavioural syndrome could be blocked by haloperidol. Conversely, perfusion with NMDA did not activate behaviour even at high concentrations. These results indicate that the dopaminergic system, within the caudate and the accumbens nuclei, is under glutamatergic control through kainate and quisqualate receptors, while the NMDA receptors do not appear to be involved.

Animals↗
PubMed1990

Solvent model for protein crystals: on occupancy parameters for discrete solvent sites and the solvent continuum.

On the basis of test calculations, Kundrot & Richards [Acta Cryst. (1987), B43, 544-547] suggest that for models of protein crystal structures based on limited-resolution X-ray data, it is not appropriate to vary both the occupany (Q) and thermal (B) parameters for the solvent molecules during refinement. There are compelling reasons, however, to adjust both parameters. If the data are sufficiently extensive to include a B parameter for each solvent site, then an adjustable Q parameter should also be included if the model is to represent physical reality. To fix Q at some arbitrary value as suggested, means that differences in occupancy will be absorbed in the 'thermal' parameters, leading to the errors corresponding to the electron density plots of Kundrot & Richards. Although the errors appear to be relatively small, they will be accentuated in Fourier maps of complex structures based on real data, causing error peaks, both positive and negative, that may greatly exceed the random errors. The current practice of using the scattering factor of the O atom, fO, for the water molecule neglects the scattering from the H atoms. A modified scattering factor based on fO- would approximate the scattering from water molecules better. Finally, the solvent continuum should be included in the model, and the low-order data included in calculating the Fourier maps from which the Q parameters are estimated.

Chemical Phenomena↗
PubMed1990

Refinement of triclinic lysozyme: I. Fourier and least-squares methods.

X-ray diffraction data to 1.5 A resolution have been collected for triclinic crystals of hen egg white lysozyme. The triclinic model was derived from the tetragonal one by the rotation function and refined initially by Fo-Fc and differential difference syntheses against 2 A resolution data. Refinement was continued by differential difference cycles against the 1.5 A data until R was reduced to 0.220. Although the initial refinement was rapid, it was subsequently a matter of attrition, leading to a complete recheck of the data and the discovery of systematic error which affected primarily the high-resolution data. Refinement was continued against the corrected 2 A data by block-diagonal least squares. After five cycles the refinement was terminated at R = 0.254 because of the imminent availability of a preferred refinement program. Problems with the protein model, the solvent, and the interaction of the scale and thermal parameters are discussed. The experiences gained in this study are summarized.

Fourier Analysis↗
PubMed1990

Refinement of triclinic lysozyme: II. The method of stereochemically restrained least squares.

Refinement of triclinic lysozyme by restrained least squares against the 2 A resolution X-ray data is described, beginning with the model from cycle 17 of the preceding paper [Hodsdon, Brown, Sieker & Jensen (1990). Acta Cryst. B46, 54-62]. After 20 refinement cycles, R stood at 0.172. Nevertheless, serious errors involving both main-chain and side-chain atoms still remained, requiring numerous model rebuilding sessions interleaved with refinement cycles. After 63 cycles R = 0.124 for the model which includes all protein atoms, 249 water oxygen sites and five nitrate ions. Although the overall B is relatively low, 10.5 A2, B's for atoms in the region of residues 101-103, toward the termini of some of the longer side chains, and in the region of the C terminus of the main chain exceed 20 A2, indicating relatively high atomic mobilities, disorder, or remaining errors in the model.

Computer Simulation↗
PubMed1990

The structure of rubredoxin from Desulfovibrio desulfuricans strain 27774 at 1.5 A resolution.

The structure of a small rubredoxin from the bacterium Desulfovibrio desulfuricans has been determined and refined at 1.5 A resolution. The hairpin loop containing seven residues in other rubredoxins is missing in this 45 residue molecule, and once that fact was determined by amino acid sequencing studies, refinement progressed smoothly to an R value of 0.093 for all reflections from 5 to 1.5 A resolution. Nearly all of the water molecules in the well-ordered triclinic unit cell have been added to the crystallographic model. As in the other refined rubredoxin models, the Fe-S4 complex is slightly distorted from ideal tetrahedral coordination.

Amino Acid Sequence↗
PubMed1990

Inhibition of photosensitive seizures in man by the beta-carboline, ZK 95962, a selective benzodiazepine receptor agonist.

A single-dose study of the beta-carboline, ZK 95962, on photosensitive generalized paroxysmal activity in the EEG was conducted in 6 patients with primary generalized epilepsy. Four of the patients were newly diagnosed and did not receive any antiepileptic drug or other medication during the study. Two were receiving current therapy with carbamazepine. A double-blind cross-over study with 2 injections of ZK 95962 (20 micrograms/kg body weight repeated 10 min after 1st injection) and 2 placebo injections were carried out in a randomized order, with 4 h intervals between the injections with active drug and placebo. On the day before the trial, the sensitivity range (standardized photosensitivity range, SPR) was determined hourly using flash frequencies of 2, 6, 8, 10, 15, 20, 30 and 40 Hz for 4 sec in ascending and descending order until generalized spikes or spike waves occurred. A significant reduction in photosensitivity was observed 2-12 min after injection of ZK 95962 in all patients, lasting 2-3 h. No change in the SPR was observed after placebo injections. The feelings of uneasiness and myoclonic jerks, provoked by photostimulation, were also abolished by ZK 95962, but not by placebo injections. Side effects, including sedation were not observed. The results suggest that benzodiazepine receptor ligands such as ZK 95962 may be potent antiepileptic drugs.

Adolescent↗
PubMed1990

Abecarnil, a metabolically stable, anxioselective beta-carboline acting at benzodiazepine receptors.

Abecarnil (isopropyl 6-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate) is a novel ligand for central benzodiazepine (BZ) receptors, possessing anxiolytic and anticonvulsant properties, but with considerably reduced muscle relaxant effects in comparison to diazepam (DZP). In vitro, abecarnil inhibited the binding of the BZ [3H]lormetazepam to rat cerebral cortex membranes with an IC50 value of 0.82 nM in comparison to 56 nM for DZP. The ability of abecarnil to displace [3H]lormetazepam was enhanced 1.24-fold in the presence of 30 microM gamma-aminobutyric acid; the corresponding value for DZP was 2.8-fold. DZP and abecarnil were equally effective in enhancing the binding of t-[35S]butylbicyclophosphorothionate to rat cortical membranes. In vivo, abecarnil exhibited a 3- to 6-fold higher affinity to forebrain BZ receptors than DZP. Abecarnil was from 2 to 10 times more potent than DZP in most rodent tests of anxiolytic activity, and in reducing locomotor activity in mice and rats thoroughly habituated to the test chamber. However, in rats newly exposed to a novel cage, abecarnil was less potent than DZP in reducing locomotor activity. In tests of motor coordination, abecarnil, in contrast to DZP, showed no or only weak activity, and in potentiating the effects of ethanol and hexobarbital on motor performance abecarnil was 4 to 25 times less potent than DZP. Abecarnil antagonized the effects of BZs in the chimney and loss of righting reflex tests, but not in the rotarod test.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Anticonvulsant action of the beta-carboline abecarnil: studies in rodents and baboon, Papio papio.

Abecarnil (ZK 112119; isopropyl-6-benzyloxy-4-methoxymethyl-beta-carboxylate) is a metabolically stable beta-carboline derivative with potent anxiolytic and few sedative and ataxic effects in rodents. The anticonvulsant and muscle relaxant actions of abecarnil have been evaluated in mice, rats, gerbils and baboons. Abecarnil raised the threshold for tonic electroconvulsions in mice after corneal but not after auricular application, had no effect on maximal electroshock-induced tonic convulsions triggered by either method, protected mice against the tonic hindlimb extension in PTZ-, picrotoxin- and 3-mercaptopropionate-induced seizures and blocked clonus after PTZ, DMCM (methyl-4-ethyl-6,7-dimethoxy-9H-pyrido-(3,4-b)-indol-3-carboxylate) and 3-mercaptopropionate. Abecarnil had no effect on convulsions induced by bicuculline and strychnine. Furthermore, abecarnil blocked kindled seizures after chronic administration of PTZ and FG 7142 (beta-carboline-3-carboxylic acid methylamide) and protected mice and rats against limbic convulsions induced by pilocarpine. Severity and afterdischarge duration of amygdala-kindled seizures were reduced in rats treated with abecarnil. Abecarnil also antagonized selectively convulsions induced by i.c.v. administration of kainate, but not those triggered by N-methyl-D-aspartate or quisqualate. In genetic models of reflex epilepsy, abecarnil was effective against sound-induced convulsions in DBA/2 mice, against air blast-induced generalized seizures in gerbils and against myoclonus in baboons Papio papio. The anticonvulsant effect of abecornil in a PTZ seizure model in mice was potentiated by ethosuximide, whereas no significant potentiation was found with diazepam, clonazepam, diphenylhydantoin, carbamazepine and phenobarbital. Electromyographic monitoring in a etorphine model of muscle rigidity in rats showed no or little muscle relaxant effect of abecarnil.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

A potent antagonist of the strychnine insensitive glycine receptor has anticonvulsant properties.

5.7-Dinitro-quinoxaline-2.3-dione (MNQX) displaced [3H]glycine binding to cortical membranes but had no effect n [3H]3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid ([3H]CPP) binding. MNQX potently antagonized N-methyl-D-aspartate (NMDA)-evoked release of [3H]GABA from cultured cortical neurones, NMDA evoked spreading depression and NMDA depolarizations in the rat neo-cortex. All of these responses were reversed by addition of glycine to the perfusion media. These results suggested that MNQX is an antagonist at the strychnine-insensitive glycine receptor associated with the NMDA receptor/ionophore complex. Furthermore the compound was found to antagonise audiogenic seizures in DBA-2 mice indicating the potential of glycine antagonists of this type in anticonvulsant therapy.

Animals↗
PubMed1989

The crystal structure of the three-iron ferredoxin II from Desulfovibrio gigas.

The crystal structure of oxidized ferredoxin II from the sulfate-reducing bacterium Desulfovibrio gigas has been determined and refined at 1.7 A resolution. The folding of the polypeptide chain is similar to that of the 2[4Fe-4S] ferredoxin in Peptococcus aerogenes, except for an extended helical segment near the C-terminus. The single [3Fe-4S] cluster in D. gigas is similar to a [4Fe-4S] cluster, but lacks one Fe atom and is coordinated to Cys-8, -14 and -50. The side chain of Cys-11 is not bound to the cluster, but is rotated toward the solvent and modified by some, as yet undetermined, chemical group. Cys-18 and Cys-42 form a disulfide bridge. A previously undetected extra amino acid is found after residue 55.

Desulfovibrio↗
PubMed1988

Structure of ferredoxin I from Azotobacter vinelandii.

The structure of Azotobacter vinelandii ferredoxin I (Av FdI, 106 amino acids) has been redetermined, based on x-ray diffraction data from tetragonal crystals of the native protein and two heavy atom derivatives. The current model differs greatly from the one previously reported and is in agreement with arguments based on various spectroscopic and other methods. The unit cell parameters are a = b = 55.62 A and c = 95.51 A, whereas the space group was found to be P4(1)2(1)2 instead of P4(3)2(1)2. The sequence of the first half of Av FdI is closely homologous with ferredoxin from Peptococcus aerogenes (Pa Fd, 54 amino acids) and the fold of the corresponding chain is almost identical. The ligands of the 3Fe complex are Cys-8, -16, and -49, corresponding to three of the four ligands in complex I of Pa Fd; the ligands of the 4Fe complex are Cys-20, -39, -42, and -45, corresponding to the four ligands in complex II of Pa Fd.

Azotobacter↗
PubMed1987

Chronic treatment with lorazepam and FG 7142 may change the effects of benzodiazepine receptor agonists, antagonists and inverse agonists by different mechanisms.

Treatment of mice with lorazepam 10 mg/kg p.o. or FG 7142 40 mg/kg i.p. once a day for 14 days changed the effects of benzodiazepine (BZ) receptor ligands injected acutely on the threshold of pentylenetetrazol (PTZ)-induced seizures. The effects of the two pretreatments differed qualitatively as well as quantitatively. Lorazepam elicited a shift in the effects of all BZ receptor ligands tested, whereby the agonists lorazepam and ZK 93423 now acted like partial agonists given acutely, the partial agonist ZK 91296 acted like an antagonist and the antagonists Ro 15-1788 and ZK 93426 like partial inverse agonists. The proconvulsant effects of the partial inverse agonist FG 7142 and the full inverse agonist DMCM on the PTZ-induced seizures did not change. However, FG 7142 became a full inverse agonist i.e. became convulsant, and DMCM may have increased in potency as a convulsant. After FG 7142 pretreatment lorazepam and ZK 93423 behaved like partial agonists given acutely whereas there was no change in effect for ZK 91296, Ro 15-1788 and ZK 93426. FG 7142 became convulsant (i.e. kindling occurred) and the potency of DMCM as a convulsant was non-significantly increased, while their proconvulsant effects with respect to PTZ-induced seizures were not altered. The fact that the effects of the two very different pretreatments on the BZ receptor ligand continuum were in the same direction may be explainable by assuming two different mechanisms, both of which may involve the GABA receptors.

Animals↗
PubMed1987

Modulation of anxiety by beta-carbolines and other benzodiazepine receptor ligands: relationship of pharmacological to biochemical measures of efficacy.

Several beta-carbolines and other benzodiazepines (BZ) receptor ligands have been investigated for anxiolytic or anxiogenic action in 4 unrelated animal models of anxiety using rats. The substances could be grouped into essentially 2 groups. The first, anxiolytics, exhibited antipunishment activity in a lick-suppression test, antagonised the discriminative stimulus provided by pentylenetetrazol, resembled chlordiazepoxide (CDP) in a drug discrimination test, and reduced the rise in plasma corticosterone levels following swim stress. Such substances included several benzodiazepines, the beta-carboline ZK 93 423, and the triazolapyridazine CL 218 872. A subgroup of anxiolytics were active in only some of these tests. They included two beta-carbolines, ZK 91 296 and ZK 95 962, and the pyrazoloquinoline CGS 9896, and these 3 substances were also distinguishable in not producing rate-decreasing effects in any of the 3 operant tests. The second group were anxiogenic in that they produced a discriminative stimulus resembling that of PTZ, they antagonised the CDP cue, exhibited propunishment effects in the lick-suppression test, and themselves caused increases in plasma corticosterone in otherwise unstressed animals. Such substances included the beta-carbolines DMCM, FG 7142 and ZK 90 886, and the pyrazoloquinoline CGS 8216. Two substances, Ro 15-1788 and ZK 93 426 had little or only weak activity in any test. The classification of these substances into anxiolytics or anxiogenics could be predicted qualitatively both by their ability to enhance (anxiolytics) or decrease the binding of 35S-TBPS to rat brain membranes and by whether their own binding was increased (anxiolytics) by adding the GABA agonist muscimol to the in vitro incubation medium. For the limited number of substances for which full data was available, there was also a quantitative relationship between the degree of enhancement of 35S-TBPS binding by a substance and its potency in the CDP cue test when such potency was expressed as numbers of BZ receptors occupied at the ED50 value in the pharmacological test. Furthermore, for the anxiolytics, activity in the CDP cue correlated significantly with potency in 2 other tests. Otherwise, surprisingly weak correlations existed between potencies in the different tests. In particular, the beta-carboline ZK 95 962 was highly potent in antagonising the PTZ cue but inactive in both a conflict test and in protecting against stress. These results are discussed in terms of differences in the neuropharmacologies of the 4 tests and in selectivity of the BZ receptor ligands for subtypes of BZ receptor.

Animals↗