Search PubMed⌕ Search

Biomedical subjects

H Rahmann

Publications and source records attributed to H Rahmann.

At least 91 records · Page 5Linked to original sources
PubMed1991

Ultrastructural aluminium detection in amphibian tissues by electron spectroscopic imaging and electron energy-loss spectroscopy.

Aluminium causes a variety of toxic effects in living organisms but very little is known about its uptake, pathways and locations of deposition. We have applied electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS) to locate aluminium at the ultrastructural level in amphibian larvae from acidic ponds. It is found diffusely bound or precipitated in cell organelles. The spatial resolution of aluminium detection is high. The elemental composition of small areas can be demonstrated by EELS. Three different fixation procedures give similar results. The two- and three-window methods at the K- and L-edges are compared.

Aluminum↗
PubMed1991

Lead and zinc block a voltage-activated calcium channel of Aplysia neurons.

1. The effects of Pb2+ and Zn2+ on the peak of the voltage-activated calcium current of Aplysia neurons were examined. Calcium currents were reversibly blocked by Pb2+ at concentrations that did not significantly affect potassium and sodium currents and by Zn2+ at concentrations associated with a delay and reduction of peak sodium and potassium currents. 2. The block by both was concentration dependent, and percentage blockade was reduced in elevated Ca2+. The threshold Pb2+ concentration for blockade in 20 mM Ca artificial sea water (ASW) was approximately 1 microM, whereas for Zn2+ it was 2 mM. The Hill coefficient for Pb2+ action was near 1.0 under all conditions, whereas for Zn2+ it was 1.4-1.6. 3. With addition of Pb2+, the voltage at which peak calcium current was generated shifted to hyperpolarized voltages, an effect similar to that caused by reduction of Ca2+ concentration in the absence of Pb2+. Zn2+ shifted the voltage at which peak current was generated in a depolarizing direction. 4. Pb2+ did not significantly change inactivation but shifted the voltage dependence of activation to hyperpolarized voltages in a dose-dependent manner. Zn2+ shifted both activation and inactivation in a depolarizing direction in a dose-dependent fashion. 5. The blockade of calcium currents by Pb2+ but not Zn2+ was highly voltage dependent and increased with depolarization. 6. Our results suggest that Pb2+ is a specific, potent, competitive, and reversible blocker of calcium currents. These observations are consistent with a competition by Pb2+ with Ca2+ at a binding site within the calcium channel. In contrast, the blockade of calcium currents by Zn2+ is probably through actions at fixed charge sites external to the channel.

Animals↗
PubMed1991

Effects of inorganic and triethyl lead and inorganic mercury on the voltage activated calcium channel of Aplysia neurons.

Using conventional two electrode voltage clamp techniques we have studied the effects of Pb2+, triethyl lead (TEL) and Hg2+ on voltage-activated calcium channels of Aplysia neurons and found that all three metals are potent inhibitors at micromolar concentrations. However, the time course of current reduction or block and its reversibility vary when comparing Pb2+ to TEL and Hg2+. With application of Pb2+ the calcium current decreases immediately and a steady state is reached within three to seven minutes, depending upon the concentration of Pb2+ (IC50 = 61 microM). The block was easily reversed upon wash out of Pb2+ with a time course similar to that of onset. Perfusion with either TEL (5 to 50 microM) or Hg2+ (5 to 200 microM) resulted only in a small reduction of current when the substances reached the cell membrane but with clear reduction within 2 min. The decrease continued at about the same speed for the total duration of the application. Upon washing there was no recovery of the response. At the onset of washing the rate of current decline stopped for several minutes, but then the current continued to decline at a slower rate in the absence of toxicant. Our data suggest that Pb2+ acts by a direct and reversible blockade of the calcium channel. In contrast TEL and Hg2+ act slowly and irreversibly to block calcium channels at concentrations which do not greatly affect membrane potential or resistance. In spite of the slow time course these substances are probably acting directly on the calcium channel.

Animals↗
PubMed1991

Morphogenetic development of the area octavolateralis in the cichlid fish Oreochromis mossambicus.

In the cichlid fish Oreochromis mossambicus the area octavolateralis in the brain stem was studied using histological techniques and labelling of afferents from the inner ear and the lateral line system with horseradish peroxidase (HRP). Adult fish and fish larvae aged 2, 4, 7, 10, and 15 days post hatching were investigated in order to analyze the ontogenetic development of these sensory systems during the critical phase of maturation from relatively immobile stages to actively swimming larvae. In adult Oreochromis seven nuclei can be detected in the octavolateral area while in the larvae a steady differentiation from a mostly periventricular concentration of perikarya in the first two days post hatching via increasing accumulations of neuronal cell bodies in the more peripheral regions up to four discernible nuclei in the age of 15 days post hatching was observed. The HRP-labelling of afferents from the lateral line organ and the inner ear in early stages indicates that the sensory organs precedes the histologically detectable differentiation in the octavolateral area. Both sensory components are clearly separated already in very early developmental stages.

Aging↗
PubMed1990

Zn2+ blocks the voltage activated calcium current of Aplysia neurons.

We have investigated the effect of Zn2+ on voltage-activated calcium currents of Aplysia neurons, using conventional two-electrode voltage-clamp techniques. The peak of these currents was reversibly reduced by Zn2+ (50% reduction at 3.75 mM; total block at 20 mM), while the current-voltage relation and the activation and inactivation curves were shifted to depolarized voltages. The effects of Zn2+ were concentration-dependent. The Hill coefficient was 1.62. The high concentrations required, the shift of the current-voltage relation and the effects on activation and inactivation are best explained by a charge-screening effect combined with a specific binding site for Zn2+ near the entrance of the channel.

Animals↗
PubMed1990

Neuronal substrates involved in processing of communicative acoustic signals in tree shrews: a 2-deoxyglucose study.

Autoradiography with [14C]2-deoxyglucose (2-DG) was used to map functional differences in activation of the central auditory pathway in adult tree shrews during presentation of particular acoustic stimuli (low frequency, LFS, and high frequency, HFS, pure sinus tones; social calls, SC). Individuals stimulated with broadband-noise (BBN) were used as controls. Stimulus-specific labelling was found in autoradiographs of cochlear nucleus, superior olivary complex, inferior colliculus and auditory cortex. These findings imply a tonotopic organization at least in these auditory brain areas and indicate differences in the processing of sounds with different functional significance.

Acoustic Stimulation↗
PubMed1990

Ultrastructural localization of endogenous calcium in the teleost retina.

The ultrastructural localization of endogenous calcium in the retina of adult cichlid fish Oreochromis mossambicus (Teleostei) was studied using the cytochemical osmiate-bichromate method of Probst (1986). The specificity of this method for calcium localization was proven by means of EGTA treatment of ultrathin sections and electron-spectroscopic-imaging technique (ESI) with an energy-filtering transmission electron microscope (CEM 902, Zeiss). Large amounts of electron-dense calcium containing deposits were found in the outer segments of rods, in the synaptic vesicles of receptor terminals and bipolar cells, in the perinuclear space of photoreceptors and in the endoplasmic reticulum of different cell types, especially in the inner segment and fibres of photoreceptor cells. In the inner plexiform layer calcium was detected in the extracellular space with greater accumulations in the synaptic cleft. Principal differences in the localization of calcium between rods and cones and between several types of synapses and vesicles are shown. The possible role of calcium in the subcellular structures of retinal cells is discussed.

Animals↗
PubMed1990

Lead inhibits the voltage-activated calcium current of Aplysia neurons.

Lead is a potent and reversible inhibitor of the voltage-dependent calcium current of Aplysia neurons in a concentration range (1-1000 microM) similar to that which elicits toxic effects in man. The threshold for inhibition is 1 microM and the dissociation constant about 90 microM. The inhibition is due to reduction of the peak current amplitude, and not due to alteration of the voltage dependence of the activation or inactivation. The effect of lead is specific to the calcium current as the delayed rectifier potassium and the sodium currents are not affected by concentrations of lead (200 microM) which give near-maximal inhibition. The calcium current of Aplysia neurons appears similar to the current flowing through the mammalian L-type calcium channel. This suggests that inhibition of the investigated calcium channel may contribute to the toxic effects of lead in mammals.

Animals↗
PubMed1990

Cytochemical localization of high-affinity Ca2(+)-ATPase activity in synaptic terminals.

High-affinity Ca2(+)-ATPase activity in the optic tectum of the brain of cichlid fish was cytochemically localized using cerium ions to precipitate phosphate. Activation of the enzyme with micromolar instead of millimolar calcium concentrations (i.e., physiological cytoplasmic instead of extracellular concentrations) resulted in intracellular localization of reaction product attached to the cytoplasmic side of plasma membranes and to synaptic vesicles. The plasmalemmal enzyme activity was concentrated in synaptic regions. Synaptic vesicles in some terminals exhibited high amounts of ATPase activity, whereas others were free of reaction product. By use of electron energy-loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) techniques, even small amounts of cerium-containing precipitates could be analyzed and precisely localized. The cytochemical observations are in good agreement with biochemical findings and therefore indicate that the calcium pump of neuronal plasma membranes can be successfully localized.

Animals↗
PubMed1990

Ultrastructural localization of gangliosides, calcium and a high-affinity Ca(2+)-ATPase in nerve terminals: a contribution to the possible functional role of gangliosides.

By means of newly developed electron microscopical techniques (electron spectroscopic imaging, ESI; electron energy loss spectroscopy, EELS; immunogold labelling) a specific accumulation of endogenous calcium within the synaptic cleft and a distinct localization of a high-affinity Ca(2+)-ATPase at the inner sides of the pre- and postsynaptic membrane of nerve cells from fish brain have been demonstrated. Additionally, a differentiation-dependent expression of polysialoganglioside epitopes on the outer surface of nerve terminals in clustered arrangements was demonstrated using their ultracytochemical detection by means of the monoclonal antibody Q211. These results which are in agreement with parallel biochemical investigations on modulatory effects of exogenous gangliosides on a high-affinity Ca(2+)-ATPase in the CNS of vertebrates support our hypothesis that Ca(2+)-ganglioside complexes act as modulators for the processes of synaptic transmission and long-term neuronal adaptations.

Animals↗
PubMed1989

Comparative monolayer investigations of surface properties of negatively charged glycosphingolipids from vertebrates (gangliosides) and invertebrates (SGL-II, lipid IV).

The surface properties of four negatively charged glycosphingolipids from vertebrates, the sialo-glycosphingolipids (= gangliosides) GM1, GD1a, GT1b and a sulfo-glycosphingolipid (= sulfatide), and of the two negatively charged glycosphingolipids from lower invertebrates, the glucurono-glycosphingolipid Lipid IV and the aminophosphono-glycosphingolipid SGL-II were investigated in monolayers at the air/water interface. The molecular peculiarities under investigation were surface pressure (pi) and surface potential (delta V) which are described for Lipid IV and SGL-II for the first time. The surface pressure/area isotherms of all glycosphingolipids were typical of a liquid-expanded monolayer and, with the exception of SGL-II, exhibited a phase transition to a liquid-condensed state at surface pressures above 20 mN/m. The surface potential/molecular area data found for gangliosides in the closely packed state at pi = 30 mN/m (GM1: delta V = -17 mV; GD1a: delta V = -35 mV; GT1b: delta V = -39 mV) showed only a slight influence of the additional number of negatively charged residues. For Lipid IV, the surface behavior was very similar to GM1 both possessing one negative group per molecule, whereas in SGL-II also the surface potential data (delta V = +173 mV) were different compared with GD1a both possessing two negative groups per molecule. The addition of Ca2+ condensed the monolayers of all glycolipids and increased the potential in the direction to more positive values, but these findings were less effective in SGL-II films. On the basis of monolayer results presented here, in biological membranes of invertebrates especially Lipid IV might play a similar role as the ganglioside GM1 in vertebrate cells.

Acidic Glycosphingolipids↗
PubMed1989

Possible involvement of polysialogangliosides in nerve sprouting and cell contact formation: an ultracytochemical in vitro study.

In Cichlid fish (Oreochromis mossambicus) primary cell cultures from whole brain and optic tectum, the differentiation-dependent distribution of polysialogangliosides on the outer cell surface has been followed on an ultrastructural level. For this, a two-step labeling technique with the monoclonal mouse antibody Q211, recognizing a polysialoganglioside-associated epitope, followed by a secondary IgM antibody, coupled to colloidal gold sols as an electron-dense marker, has been used. The gold grains are not uniformly distributed over the whole cell surface, but rather are clearly arranged clusters. In cells from freshly hatched larvae, both cell bodies and nerve fibers strongly exhibit the polysialoganglioside epitope on their surface. With progressing development, neuronal cell labeling is more and more restricted to nerve fibers and especially to cellular adhesion zones, including synaptic terminals, thus suggesting a functional involvement of polysialogangliosides in nerve sprouting and initiation of both cell-to-extracellular matrix and cell-to-cell contacts.

Animals↗
PubMed1989

Effects of exogenous ganglioside and cholesterol application on excitability of Aplysia neurons.

The effects of pressure-ejected gangliosides GM1 and GMix ("Cronassial") and cholesterol dissolved in sea water on the electrophysiological characteristics of Aplysia neurons were studied using voltage-clamp recording techniques. Two types of electrophysiological effects were found. In about 5% of neurons brief pulses (0.1-0.2 sec) of GM1 or GMix elicited fast and large currents associated with an increase in membrane conductance and clear reversal potentials. These currents were similar to those elicited by common neuro-transmitters. Thus it appears that gangliosides may activate a membrane-bound receptor on at least some neurons. Most (about 85%) of the 121 neurons studied showed responses to longer pulses (1.0-2.5 sec) of gangliosides. These responses were much smaller, usually had a relatively slow component, and could be mimicked by application of cholesterol. The currents elicited were either inward or outward and were often biphasic, with an small initial outward component followed by a larger slow inward current. The responses often became larger upon repeated application at short intervals, and long periods of wash were required for recovery. This type of response appears to reflect changes in the electrical properties of the cell induced by incorporation of small amounts of gangliosides or cholesterol into the membrane.

Animals↗
PubMed1988

Effect of calcium and temperature on mixed lipid-valinomycin monolayers. A comparison of glycosphingolipids (ganglioside GT1b, sulphatides) and phosphatidylcholine.

The influence of calcium and temperature on pure lipid (bovine brain PC, sulphatides, ganglioside GT1b), valinomycin and mixed lipid-valinomycin monolayers at the air/water interface was studied. In mixed films, evidence was found that the two components were miscible. On the other hand, at higher surface pressures, phase separation occurs in the cases of PC and sulphatides. Measuring the area requirement and the collapse pressure the stability of both lipid and the peptide was increased in particular due to ganglioside-valinomycin interaction. The addition of 10(-5) M calcium into the subphase at 20 and 37 degrees C and surface pressures of 10 and 20 mN/m led to a condensing effect in ganglioside mixtures, with formation of aggregates as indicated also by the nearly ideal behaviour of two component monolayers.

Calcium↗
PubMed1988

Axonal transport of intraocularly injected [3H-Sph]-GD1a in the chicken optic system and the fate of the exogenous ganglioside distributed by blood.

Twelve-day-old chicks (White Leghorn) received an injection of 481 kBq (8.1 nmol) of [3H-Sph]-GD1a, which was labeled in its sphingoid, into the right eye. Structures of the injected and the non-injected (control) optic system (retinae, optic nerves, chiasm, optic lobes), the cerebrum, blood liver, kidney, and fly-muscle were analyzed 1, 4, 8 and 14 days later, with respect to total non-volatile radioactivity and to that bound to lower-phase lipids and gangliosides. It was demonstrated that exogenous [3H-Sph]-GD1a was taken up by the retina and mainly catabolized. 3H-label, reincorporated into the lower-phase lipids and gangliosides as well as authentic exogenous [3H-Sph]-GD1a were transported rapidly anterogradely in the entire optic system. [3H-Sph]-GD1a, distributed via the blood stream, was taken up by liver, kidney and muscle and was metabolized faster in these organs than in the retina. The cerebrum and the brain structures of the control optic system incorporated 3H-radioactivity to a much lower extent than the non-neural organs.

Animals↗
PubMed1987

Seasonal variability of sialo-glycoconjugates in the brain of the Djungarian hamster (Phodopus sungorus).

The influence of season, photoperiod and ambient temperature on the content of proteins, sialo-glycoproteins and gangliosides and on the composition of gangliosides of three different brain regions (cortex, cerebellum and basalbrain) of the Djungarian dwarf hamster (Phodopus sungorus) had been investigated. Concomittantly changes in body wt and fur colouration were recorded. Dwarf hamsters living under natural photoperiod and ambient temperature conditions ("outside") showed a distinct annual cycle in body wt (summer: about 45 g; winter: about 25 g) and fur colouration (summer: dark grey; winter: whitish). Among the three brain regions the mean concentration of proteins ranged between 120 and 155 mg protein/g wet wt. The sialo-glycoprotein content varied between 260 and 410 micrograms NeuAc/g wet wt, and that of gangliosides between 800 and 1650 micrograms NeuAc/g wet wt. Seasonal fluctuations were not found. The composition of brain gangliosides remained uninfluenced throughout the year in the cerebellum, whereas seasonal variations were observed in cortex and basalbrain. Consequently the concentration ratio of the two major mammalian ganglioside fractions GD1a vs GT1b remained almost stable in cerebellum (0.3). In contrast to this the seasonal values of cortex and basalbrain changed from 0.6 and 0.8 in winter to 0.7 and 1.1 in summer. This indicated a higher polarity of the gangliosides in these brain regions during cold adaptation. The results are discussed with regard to modulatory functions of neuronal gangliosides for the process of synaptic transmission during seasonal adaptation.

Animals↗