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Biomedical subjects

W Hanke

Publications and source records attributed to W Hanke.

At least 55 records · Page 3Linked to original sources
PubMed1998

Distribution of gap junctions in the chicken retina.

Coupling between cells of neuronal tissue can be due to electrical or chemical synapses. The molecular basis of an electrical synapse is the gap junction channel. Gap junctions have been found between neurones and glial cells, however, in some tissue their presence in the membranes of different cell types is still under discussion. In the retina of vertebrates, which is a true part of the CNS, the presence of gap junctions in the specialised glial cells of the retina, the Müller cells is not clear for chicken. Since these cells span the whole retina vertically, for some tasks, like spatial buffering of potassium, such gap junctions would not be required, in contrast to other parts of the CNS. The spatial buffering of potassium among others plays an important role in the propagation of excitation-depression waves in neuronal tissue, especially in the chicken retina. However, gap junctions could be involved in creating an electrical syncitium of glial cells, which might also contribute to excitation-depression wave propagation. In this paper we present an about complete screening of the presence of gap junctions in the chicken retina, including the proof that the Müller cells of this retina do not have gap junctions. This finding is discussed considering the highly specialised morphological structure of the Müller cells of the chicken retina, which have an extremely extended endfeet tree.

Animals↗
PubMed1997

The chicken retina as an experimental model for investigation of central nervous lesions.

The aim of this study was to establish an experimental model to investigate neuronal lesions. The retina is an easy accessible model system to study central nervous system (CNS) disorders or neuronal effective drugs. It consists of only a few characteristic layers and is easy to prepare as an intact piece of tissue. In the retina the typical cell swelling of a developing lesion is accompanied by a very strong intrinsic optical signal (IOS) which is simultaneous with the electrical signal and is based on changes in light scattering. The IOS can be easily observed during the whole experiment and can be recorded with non-invasive optical methods for further quantification of damage. In the developed model, the lesions are elicited electrically with a tungsten microelectrode (0.1 M[omega]). The degree of damage depends on the magnitude of the stimulus. The parameters for the quantification of damage are the area and the brightness of the affected tissue. The growth of the lesions can be influenced with drugs added to the perfusion system. In the present study we tested, glycerol, mannitol and ketamine which are known to be neuroprotective in other animal models.

Animals↗
PubMed1997

Neuroendocrine effects on adrenal hormone secretion in carp (Cyprinus carpio).

The responses of interrenal and chromaffin tissues of carp to acetylcholine (Ach) and its agonists/antagonists were studied in an in vitro perifusion system of head kidney. There was a dose-dependent release of epinephrine and norepinephrine to Ach between 0.01 and 100 mM added for 15 min to the incubation medium. Cortisol secretion was also stimulated, but the response peaked at 1.0 mM Ach and was attenuated with 10 or 100 mM Ach. The maximal release occurred about 30 min after addition of the transmitter. Nicotine stimulated the catecholamines, but had no effect on cortisol, while carbamylcholine, a nicotinic agonist, increased both the catecholamines and cortisol. Muscarine increased cortisol secretion, but affected catecholamines only at higher doses. In contrast, pilocarpine, a muscarinic agonist, stimulated catecholamines more than cortisol. Atropine was not antagonistic, rather it increased the secretion of catecholamines in a dose-dependent manner, and inhibited the release of cortisol. It is concluded that both tissues are influenced by the autonomic nervous system, with the sympathetic system acting on chromaffin cells and the parasympathetic system acting on interrenal cells. However, the nerve supply cannot clearly be defined by agonists or antagonists as in mammals. There is evidence for paracrine effects, e.g., catecholamines inhibit cortisol release and cortisol influences catecholamine secretion.

Acetylcholine↗
PubMed1997

Stage-dependent changes in adrenal steroids and catecholamines during development in Xenopus laevis.

Changes in adrenal hormones during the complete developmental cycle from egg to juvenile were investigated in the amphibian Xenopus laevis. Whole-body concentrations of the adrenal steroids corticosterone (B), and aldosterone (Aldo) were determined by radioimmunoassay and those of the adrenal catecholamines epinephrine (E), norepinephrine (NE), and dopamine (D) were determined by HPLC. In addition, the catecholamine-synthesizing enzymes tyrosine hydroxylase, dopamine beta-hydroxylase, and phenylethanolamine N-methyltransferase were immunocytochemically localized for the characterization of chromaffin adrenal cells. B and Aldo were not detectable in the whole body before hatching. B levels rose earlier than Aldo levels from stage 36 onward. B had already peaked at stage 46, whereas the largest amounts of Aldo were found at stage 54. After peaking, both steroids decreased gradually to 2.7 +/- 0.62 (B) and 0.4 +/- 0.1 (Aldo) ng/g body wt (mean +/- SEM, n = 10) in juvenile animals. E, NE, and D were detected just after hatching, when E and D showed an early peak at stage 40. E and NE increased moderately during development and demonstrated a sharp increase at the end of metamorphosis from stages 62 onward to 14.4 +/- 1.7 (E) and 34.1 +/- 4.67 (NE) ng/g body wt (mean +/- SEM, n = 6). Interestingly, D levels had a distinct pattern, because concentrations of D remained lower than those of NE and E over nearly the complete development, but showed a dramatic rise during the latest stages, reaching 707 +/- 54 ng/g body wt in juveniles. This dramatic shift in catecholamine levels was confirmed by immunocytochemistry in parallel. A large increase in chromaffin cells labeled with tyrosine hydroxylase immunoreactivity occurred in the latest developmental stages. The catabolic rates for all catecholamines in vivo were similar, which indicates that the different levels are due to various rates of synthesis. Thus, adrenal corticosteroids as well as catecholamines may have regulatory effects during premetamorphosis and metamorphic climax.

Adrenal Cortex Hormones↗
PubMed1997

Exogenous application of gangliosides changes the state of excitability of retinal tissue as demonstrated by retinal spreading depression experiments.

Gangliosides are amphiphilic, sialic acid-containing glycosphingolipids which are found preferentially in complex composition in the cellular membranes of the nervous system of vertebrates, including the vertebrate retina as well as in other membranes. They are always exposed to the extracellular side of the membranes. By virtue of the negative charges they carry at their headgroup, they contribute to the surface charge of the membrane and may affect ion distribution, mainly that of protons and calcium ions, at the outer side of the membranes. Using retinal spreading depression (RSD) as a tool, we show in this study that the addition of exogenous gangliosides to the extracellular space can change the state of excitability of the retinal tissue. In RSD experiments it reduces the propagation velocity as well as the intrinsic optical signal of RSD waves. These effects are concentration dependent (IC50 about 20 microM) and increase with the increasing negative charge of the ganglioside headgroup. As a possible mechanistic basis of the changes found, the change of the calcium homeostasis of the extracellular space by the exogenously added gangliosides is discussed. Gangliosides have been reported to be useful in the treatment of some neuropathological syndromes, including migraine, although experimental verification has not been possible up to now. Taking into account that the retina is a true part of the CNS, our data may be interpreted as the requested verification.

Animals↗
PubMed1997

Second messenger-controlled membrane conductance in locust (Locusta migratoria) olfactory neurons.

The membrane conductance of olfactory neurons of Locusta migratoria was examined using the whole-cell configuration of the patch-clamp technique. Intracellular application of the second messenger inositol 1,4,5 trisphosphate (IP(3)) via a dual pipette technique elicited a clear increase in the membrane conductance. The IP(3)-induced conductance increased due to a rise in the extracellular concentration of calcium from 100&mgr;M to 4mM. Micromolar concentrations of ruthenium red partially blocked the IP(3)-induced increase in membrane conductance. Stimulating olfactory neurons with odour (hexenoic acid) resulted in an increase in the membrane conductance partially similar to that mediated IP(3). These findings suggest that stimulation with appropriate odours as well as intracellular application of IP(3) activate the same calcium-permeable ion channels in the plasma membrane of insect olfactory neurons.

Journal Article↗
PubMed1997

Hormonal control of the in vitro uptake of [35S]sulfate by cartilage of Xenopus laevis tadpoles.

The influence of various mammalian hormones and growth factors on the skeletal growth in the clawed toad was examined in vitro by monitoring the uptake of [35S]sulfate by tadpole's hindlimbs. Autoradiographic studies demonstrated that the isotope was mainly incorporated into the cartilage. Sulfate uptake was significantly stimulated by 13 nM insulin-like growth factor I (IGF-I) in all experiments. The effect of 13 nM IGF-II was statistically significant only in approximately 50% of the experiments. Insulin was inconsistently effective. A significant stimulation was found using 1300 nM insulin. Neither prolactin and growth hormone nor the thyroid hormones thyroxine and triiodothyronine affected the [35S]sulfate uptake in vitro. The results indicate that cartilage growth in amphibians is mainly stimulated by IGF-I and to a less extended by IGF-II like in mammals.

Animals↗
PubMed1997

Alpha7 and alpha8 nicotinic receptor subtypes immunopurified from chick retina have different immunological, pharmacological and functional properties.

Nicotinic receptors are present in the chick retina, but their structure and functional characteristics are still unclear. Using anti-alpha7 and anti-alpha8 subunit-specific antibodies, we immunopurified the alpha7 and alpha8 subtypes of chick retina neuronal nicotinic receptors. When analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, the two purified subtypes consistently showed a similar peptide composition characterized by the presence of two major peptides of M(r) 58 +/- 1 and 54 +/- 1 kDa, and two minor peptides of 67 and 61 +/- 1 kDa. In the alpha7 subtype, the 58 kDa peptide was recognized by anti-alpha7 but not by anti-alpha8 antibodies; in the alpha8 subtype, the 58 kDa peptide was recognized only by anti-alpha8 antibodies. The alpha7 subtype had a single class of [125I]alpha-bungarotoxin binding sites with a K(D) value of 1.2 nM, whereas the purified alpha8 subtype had two classes of binding sites, one with a K(D) of 5.5 nM and the other with very high affinity (KD 52 pM), but present in only 8% of the receptors. Competition binding experiments also showed the presence on the alpha8 subtype of high- and low-affinity classes of binding sites; the affinity for cholinergic drugs of the former was greater than that of the single class present on the alpha7 subtype. When reconstituted in planar lipid bilayers, both subtypes formed ligand-gated cation channels with major conductance levels of 42 and 52 pS but with different lifetimes; the two channels were activated by agonists and blocked by d-tubocurarine and the glycinergic antagonist strychnine. In line with the binding data, the reconstituted alpha8 subtype had greater agonist sensitivity than the alpha7 subtype.

Animals↗
PubMed1997

[The effect of stress in the workplace on the risk of ischemic heart diseases--the role of epidemiologic studies].

Among numerous areas of occupational medicine, the studies of the impact of psychosocial factors on the development of cardiovascular diseases have been progressing most rapidly. The role of epidemiological studies in analysing the effect of this group of stressors on the incidence of ischaemic heart disease is discussed. The most significant outcome of the studies regarding selected psychological reactions referred to Karasek and Theorell's model of psychic burden/control, the role of life events, A type behavior and other selected personality changes. The authors stress that issues such as so called 'selection phenomenon', adequate size of the populations investigated, accurate selection of measurement methods, control of confounding factors and the cause-effect inference based on cross-sectional studies, are the major limitations in epidemiological studies of the effect of occupational stress on the state of health. Further progress in this area depends on how far these limitations could be overcome.

Chronic Disease↗
PubMed1996

Influence of insulin-like growth factors and insulin on the [35S]sulfate uptake by cartilage of the axolotl (Ambystoma mexicanum).

The actions of mammalian insulin-like growth factors (IGF-I and IGF-II) and insulin on skeletal growth of the axolotl, Ambystoma mexicanum, were examined by monitoring the in vitro uptake of [35S]sulfate by cartilage. Both growth factors stimulated sulfate uptake significantly at a concentration of 13 nM. The increase after incubation with 130 nM insulin was similar (uptake ca. 160% of control), but the effect was not significant. Further, the binding of 125I-IGF-I and 125I-IGF-II was studied in the skeletal tissue by quantitative in vitro autoradiography. Specific binding sites for both growth factors were localized in the perichondrial tissue. 125I-IGF-II binding sites were saturated at the used doses. Scatchard and Hill plots demonstrate heterogeneous binding sites exhibiting positive cooperativity. IGF-II was more effective than IGF-I in competitively displacing both labeled ligands. Insulin only slightly affected the binding at the highest concentrations. These results indicate that the insulinlike growth factors regulate skeletal growth in urodeles as in mammals.

Ambystoma mexicanum↗
PubMed1996

Effects of antimigraine drugs on retinal spreading depression.

It has been suggested that spreading depression may play a role in triggering classical migraine. In this study the retinal spreading depression was used as a pharmacological tool to test the neuronal effects of several common antimigraine drugs. As the chicken retina is void of any blood vessels the observed effects must be of pure neuronal origin. It is shown that propranolol, sumatriptan, methysergide, paracetamol and acetylsalicyclic acid decrease the propagation velocity of retinal spreading depression waves, accelerate the recovery of the optical and electrical signal and reduce the amplitude of the negative potential shift, concomitant with the spreading depression. Barbiturate increases the spreading velocity, and the amplitude of the potential shift. Ergotamine, clonidine, lisuride and iprazochrome have no significant influence on retinal spreading depression.

Acetaminophen↗
PubMed1996

Studies of the interaction of gravity with biological membranes using alamethicin doped planar lipid bilayers as a model system.

Gravity interacts with biological systems on different levels of complexity. For the understanding of the action of gravity on such systems at higher degrees of organisation, the investigation of interactions on the membrane and even on the molecular level is crucial. To do such studies, planar lipid bilayers with incorporated transport mediating molecules, i.e. membranes of defined biochemical composition, are close to perfect model systems. In our experiments we have used painted planar lipid bilayers doped with alamethicin. Alamethicin is especially suitable for such studies because of its high sensitivity to applied external forces, which is a result of its special pore forming mechanism. Additional, different to most other transport mediating molecules, a big amount of data from the literature is available about the dependency of alamethicin pores on physical and chemical membrane parameters. We found that the conductance of alamethicin doped bilayers is dependent on the angle of the bilayer with the gravitational vector and that it furthermore can be reduced significantly under hyper gravity conditions in a centrifuge. The effect of gravity here is not an effect on the pore conductance or the membrane-aqueous solution interface, but it is due to an interaction of gravity with the pore forming mechanism, as can be shown by investigating the dependency of the alamethicin pore kinetics on the applied forces.

Alamethicin↗
PubMed1996

[Tobacco smoking--a risk factor for intrauterine growth retardation, preterm delivery and low birth weight].

The risk of intrauterine growth retardation (IUGR) and preterm delivery, in the group of 551 females from the area of Lódź, was related to the amount of cigarettes smoked per day. In subjects smoking more than 20 cigarettes, the risk of IUGR and preterm delivery was five times as high as in the nonsmoking females. The average weight of the newborns was found to be 510 g lower in the group of the most heavy smokers as compared with the nonsmoking subjects. The study has not provided any clear evidence for the pre-pregnancy smoking and the passive smoking as the risk factors for the pathologies under study.

Female↗