Biomedical subjects

G H Hansen

Publications and source records attributed to G H Hansen.

12 recordsLinked to original sources

PubMed1992

First direct electron microscopic visualization of a tight spatial coupling between GABAA-receptors and voltage-sensitive calcium channels.

Using cerebellar granule neurons in culture it was demonstrated that exposure of the cells to the GABAA receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) leads to an increase in the number of voltage-gated calcium channels as revealed by quantitative preembedding indirect immunogold labelling using a monoclonal antibody specific for phenylalkylamine and dihydropyridine sensitive Ca2+ channels. Using the same technique and a monoclonal antibody (bd-17) to the beta 2/beta 3-subunit of the GABAA-receptor, double labelling of Ca2+ channels and GABAA-receptors with gold particles of different and well defined sizes were performed. This showed that in THIP-treated cultures 20% of GABAA-receptors in cell processes were located in close proximity (i.e. within 40 nm) of Ca2+ channels in the plasma membrane. This was not observed in non-treated cultures nor was it observed in cell bodies of THIP-treated cultures. This suggests that primarily low affinity GABAA-receptors are closely associated with Ca2+ channels and this may be important for the ability of these receptors to mediate an inhibitory action on transmitter release even under extreme depolarizing conditions.

Animals↗

PubMed1992

3H-D-aspartate release from cerebellar granule neurons is differentially regulated by glutamate- and K(+)-stimulation.

Neurotransmitter release in response to either 55 mM K+ or 25 microM glutamate as well as its dependency on Ca2+ from different sources was compared in cultured glutamatergic cerebellar granule cells from rat brain. The intracellular Ca2+ concentration was monitored at the single cell level in neurites as well as cell bodies employing the fluorescent Ca2+ indicator fura-2. Transmitter release was assayed using 3H-D-aspartate to label the exogenously accessible glutamate pools, which in these neurons is believed to also include the transmitter pool. In an attempt to distinguish whether transmitter release was dependent on an intact cytoskeleton or not, the colchicine-like drug Nocodazole, which also blocks transport of vesicles, was used. K(+)-stimulated transmitter release consisted for the major part (around 70%) of a Ca(2+)-dependent, Nocodazole sensitive release component and this K(+)-induced release appeared to be almost exclusively dependent on N-type Ca2+ channels. In contrast, 50% of the glutamate-induced Ca(2+)-dependent release was triggered by Ca2+ from a Dantrolene sensitive intracellular Ca2+ pool. Since these neurons undergo a pronounced maturational change in which neurotransmitter vesicles become increasingly prominent, the Ca2+ responses and transmitter release evoked by the two different stimuli were investigated as a function of the culture period. K+ and glutamate were found to increase intracellular [Ca2+] differentially. In 1-day-old cultures K+ elicited a small albeit significant increase in [Ca2+]i while glutamate was completely without effect. In 7-day-old neurons both agents induced a large increase in [Ca2+].(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Immunogold labelling is a quantitative method as demonstrated by studies on aminopeptidase N in microvillar membrane vesicles.

Microvillar membrane vesicle preparations with varying content of aminopeptidase N were prepared from enterocytes of the pig small intestine. Postembedding immunogold labelling of aminopeptidase N was performed on these glutaraldehyde/paraformaldehyde-fixed, osmium tetroxide-treated and Epon-embedded microvillar membrane vesicles. The number of gold particles per micrometre microvillar membrane (labelling intensity) was calculated and compared to the corresponding enzymatic activity. A very close relationship was found between labelling intensity and aminopeptidase N activity, demonstrating that postembedding immunogold labelling can be used quantitatively.

Aminopeptidases↗

PubMed1992

Flexibacter ovolyticus sp. nov., a pathogen of eggs and larvae of Atlantic halibut, Hippoglossus hippoglossus L.

A psychrotrophic Flexibacter sp., Flexibacter ovolyticus sp. nov., was isolated from the adherent bacterial epiflora of Atlantic halibut (Hippoglossus hippoglossus L.) eggs and was shown to be an opportunistic pathogen for halibut eggs and larvae. The strains which we isolated had the enzymatic capacity to dissolve both the chorion and the zona radiata of the egg shells. A total of 35 isolates were characterized by using morphological and biochemical tests. These strains were rod shaped, gram negative, Kovacs oxidase positive, and pale yellow and exhibited gliding motility. They did not produce acid from any of the wide range of carbohydrates tested. Our isolates had the ability to degrade gelatin, tyrosine, DNA, and Tween 80. Starch, cellulose, and chitin were not degraded. The strains were catalase and nitrate reductase positive, did not produce H2S, and did not grow under anaerobic conditions. F. ovolyticus resembles Flexibacter maritimus, but differs from the latter species in several biochemical and physiological characteristics. DNAs from F. ovolyticus strains had guanine-plus-cytosine contents which ranged from 30.3 to 32.0 mol% (strains EKC001, EKD002T [T = type strain], and VKB004), and DNA-DNA hybridization studies revealed levels of relatedness between F. ovolyticus EKD002T and F. maritimus NCMB 2154T and NCMB 2153 of 42.7 and 30.0%, respectively. Compared with previously described Cytophaga and Flexibacter spp. with low guanine-plus-cytosine contents, F. ovolyticus constitutes a new species. Strain EKD002 (= NCIMB 13127) is the type strain of the new species.

Animals↗

PubMed1992

Effect of different holding regimens on the intestinal microflora of herring (Clupea harengus) larvae.

The aerobic intestinal microflora of 2-week-old herring (Clupea harengus) larvae was characterized by using conventional microbiological methods and electron microscopy. Larvae were hatched and kept in filtered seawater or in seawater with penicillin and streptomycin. The gastrointestinal tract of herring larvae is essentially a straight tube divided into two compartments. Light microscopy revealed bacteria present in a progressively increasing amount throughout the length of the gastrointestinal tract from esophagus to anus. The posterior region of the intestinal lumen appeared completely occluded with bacteria. The intestinal microflora consisted mainly of members of the genera Pseudomonas and Alteromonas in the larvae incubated in filtered seawater, whereas Flavobacterium spp. dominated in larvae exposed to antibiotics. The intestinal microflora of untreated fish larvae was sensitive to all tested antibiotics, whereas multiple resistance was found in the intestinal microflora of the group given antibiotics. Thus, a dramatic change in the microflora resulted from incubation with antibiotics. Nonpigmented yeasts were detected in both larval groups. Ciliated epithelial cells were observed in the midgut, probably propeling bacteria towards the hindgut, where endocytosis of bacteria has been demonstrated. These findings suggest that transport and sequestering mechanisms resembling those of invertebrates may be found in the gut of fish larvae. The possible significance for larval health and nutrition is discussed.

Animals↗

PubMed1991

Morphological and functional changes in the enterocyte induced by fructose.

In the presence of 10-50 mM-fructose, enterocytes of organ-cultured pig intestinal-mucosal explants fail to glycosylate correctly their newly synthesized microvillar enzymes, and instead degrade them [Danielsen (1989) J. Biol. Chem. 264, 13726-13729]. In the present work, this degradation was shown to occur extremely rapidly as the microvillar enzyme aminopeptidase N (EC 3.4.11.2) was hardly detectable after a 10 min pulse with [35S]methionine. The abnormal biosynthesis of membrane glycoproteins affected both the morphology and the function of the Golgi complex as well as the microvillar membrane. Thus the stack of Golgi cisternae was condensed and devoid of dilated rims, and the secretion of a non-glycosylated protein, apolipoprotein A-1, was almost completely blocked in the presence of fructose, showing that transport through the secretory pathway is disturbed even for proteins unaffected by the defective glycosylation. The microvilli of the brush-border membrane were markedly shortened (by about 40%) in the presence of fructose, and incorporation of newly made actin into the microvillar cytoskeleton was similarly decreased. By affecting membrane glycoprotein synthesis, the common dietary sugar fructose thus profoundly perturbs the exocytic membrane traffic in the enterocyte.

Aminopeptidases↗

PubMed1991

Effect of a GABA agonist on the expression and distribution of GABAA receptors in the plasma membrane of cultured cerebellar granule cells: an immunocytochemical study.

The effect of the gamma-aminobutyric acid (GABA) agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP, 150 microM) on the localization and density of GABAA receptors in the plasma membrane of rat cerebellar granule cells in primary cultures was studied at the electron microscope (EM) level by preembedding immunogold staining using the monoclonal antibody bd-17 directed against the beta-subunit of the GABAA receptor complex. In THIP-treated as well as untreated control cultures, GABAA receptors were found to be evenly distributed in the plasma membrane of cell bodies as well as processes. However, the density of the GABAA receptors was significantly increased in the THIP-treated cultures as compared to the control cultures and this effect of THIP was particularly pronounced in the processes. GABAA receptors were occasionally observed to form 'hot spots' in process-like structures and again the frequency of these areas with an extremely high density of GABAA receptors was greatly increased in the THIP-treated cultures compared to the controls. It has thus been demonstrated that the ability of GABA agonists to induce formation of low-affinity GABA receptors can be directly visualized and quantified at the EM level using the preembedding immunogold technique. It is likely that low-affinity GABAA receptors are preferentially located in the cell processes and to a considerable extent in the form of 'hot spots'. However, these 'hot spots' also contain high-affinity receptors.

Animals↗

PubMed1991

Light and electron microscopic localization of GABAA-receptors on cultured cerebellar granule cells and astrocytes using immunohistochemical techniques.

GABAA-receptors were localized in explant cultures of rat cerebellum and in dissociated primary cultures of rat cerebellar granule cells and rat cerebellar astrocytes using the monoclonal antibody bd-17 directed against the beta-subunit of the GABAA/benzodiazepine/chloride channel complex. At the light microscope level specific staining of GABAA-receptors was localized in various types of neurones in explant cultures of rat cerebellum using the indirect peroxidase-antiperoxidase (PAP) technique, whereas no specific staining was found in astrocytes. At the electron microscope level labeling of GABAA-receptors was observed in the plasma membrane of both the cell bodies and processes in dissociated primary cultures of cerebellar granule cells using an indirect preembedding immunogold staining technique which in contrast to the classical PAP technique allows quantitative estimations to be performed. Quantification of the labeling intensity revealed a higher concentration of GABAA-receptors per microns plasma membrane in the cell bodies than in the processes. In discrete areas an extremely high density of the GABAA-receptors was observed. No specific labeling of GABAA-receptors was observed in dissociated primary cultures of cerebellar astrocytes.

Animals↗

PubMed1991

Parallel expression of synaptophysin and evoked neurotransmitter release during development of cultured neurons.

Primary cultures of GABAergic cerebral cortex neurons and glutamatergic cerebellar granule cells were used to study the expression of synaptophysin, a synaptic vesicle marker protein, along with the ability of each cell type to release neurotransmitter upon stimulation. The synaptophysin expression and neurotransmitter release were measured in each of the culture types as a function of development for up to 8 days in vitro, using the same batch of cells for both sets of measurements to obtain optimal comparisons. The content and the distribution of synaptophysin in the developing cells were assessed by quantitative immunoblotting and light microscope immunocytochemistry, respectively. In both cell types, a close parallelism was found between the temporal pattern of development in synaptophysin expression and neurotransmitter release. This temporal pattern differed between the two types of neurons. The cerebral cortex neurons showed a biphasic time course of increase in synaptophysin content, paralleled by a biphasic pattern of development in their ability to release [3H]GABA in response to depolarization by glutamate or elevated K+ concentrations. In contrast, a monophasic, approximately linear increase in the synaptophysin content and stimulated [3H]D-aspartate release was found in the cerebellar granule cells. These results, particularly regarding the GABAergic neurons, offer correlative evidence in support of the notion that a vesicular pool of these amino acid neurotransmitters may be intimately involved in their release, subsequent to depolarization stimuli.

Animals↗

PubMed1990

Aminopeptidase N is directly sorted to the apical domain in MDCK cells.

In different epithelial cell types, integral membrane proteins appear to follow different sorting pathways to the apical surface. In hepatocytes, several apical proteins were shown to be transported there indirectly via the basolateral membrane, whereas in MDCK cells a direct sorting pathway from the trans-Golgi-network to the apical membrane has been demonstrated. However, different proteins had been studied in these cells. To compare the sorting of a single protein in both systems, we have expressed aminopeptidase N, which already had been shown to be sorted indirectly in hepatocytes, in transfected MDCK cells. As expected, it was predominantly localized to the apical domain of the plasma membrane. By monitoring the appearance of newly synthesized aminopeptidase N at the apical and basolateral surface, it was found to be directly sorted to the apical domain in MDCK cells, indicating that the sorting pathways are indeed cell type-specific.

Aminopeptidases↗

PubMed1979

Neonatal scabies.

Scabies contracted during the neonatal period demonstrates a distinct clinical pattern that differs greatly from manifestations seen in older individuals. Involvement of the face, neck, scalp, palms, and soles is a consistent finding, as is the tendency for these lesions to form pustules early in the course of the infestation. Poor feeding and failure to gain weight appropriately are also characteristic features. The skin lesions include erythematous papules, nodular crusts, and putules. The possibility of scabies should be entertained for any young infant who has these findings. Scrapings should be obtained from multiple sites to confirm the diagnosis. In the absence of positive findings for scrapings, examination of close contacts and a careful history should lead to the correct diagnosis.

Female↗

PubMed1977

Green hair.

Explore the source record for details and available documents.

Child↗