Biomedical subjects

I D Dietzel

Publications and source records attributed to I D Dietzel.

At least 19 recordsLinked to original sources

PubMed2006

Integration of a scanning ion conductance microscope into phase contrast optics and its application to the quantification of morphological parameters of selected cells.

We have previously described a pulse-mode scanning ion conductance microscope to investigate membrane surfaces and volume changes of individual cells in culture. We have now developed a miniaturized scanning headstage that enables us to select individual cells for recording under phase contrast optics, considerably improving the selection of individual cells for scanning as well as the positioning of the scanning frames with respect to the position of the cell somata. We show an application in which surfaces and volumes of somata and processes of cultured cells from the central nervous system were quantified separately.

Animals↗

PubMed2004

Thyroid hormone regulates excitability in central neurons from postnatal rats.

A lack of thyroid hormone in the postnatal period causes an irreversible mental retardation, characterized by a slowing of thoughts and movements accompanied by prolonged latencies of several evoked potentials and slowed electroencephalographic rhythms. Here we show that in cultured hippocampal and cortical neurons from postnatal rats treatment with thyroid hormone not only up-regulates Na(+)-current densities but also increases rates of rise, amplitudes and firing frequencies of action potentials. Furthermore, we show that the regulation of the Na(+)-current density by thyroid hormones also occurs in vivo: recordings from acutely isolated cortical neurons obtained from hypothyroid, euthyroid and hyperthyroid postnatal rats showed that hypothyroidism decreases the ratio of Na(+) inward- to K(+) outward-currents while hyperthyroidism upregulates Na(+)-currents with respect to K(+)-currents. Our observation of a regulation of neuronal excitability by thyroid hormone offers a direct explanation for the origin of various neurological symptoms related to thyroid dysfunction.

Action Potentials↗

PubMed2004

[Corticoids protect oligodentrocyte precursor cells against cytokine-induced damage].

In preterm fetuses an ascending intrauterine inflammation before or during birth can be associated with periventricular leukomalacia (PVL). PVL is characterised by a disrupted. myelination [corrected] due to a loss of oligodendrocyte progenitors. Inflammatory cytokines not only induce apoptotic cell death but in addition prevent the differentiation of the immature A2B5 oligodendrocytc progenitors into the myelinating phenotype. The aim of the present study was to clarify whether corticosteroids can protect oligodendrocyte progenitors from such injury. Cultures [corrected] of more than 90 % A2B5 positive progenitors were prepared from neonatal sprague dawley rats. After 1 day in proliferation medium, cells were treated with interferon-gamma [corrected] (IFN-gamma; 10 U/ml) and tumour necrosis factor-alpha [corrected] (TNF-alpha; 10 ng/ml) for 48 h. In addition, corticosterone (C), deoxycorticosterone (DC), or dexamethasone (DEX) (1 micro M) were applied to the incubation medium of the study groups. After treatment cultures were transferred to media containing factors to promote differentiation of progenitors into thc myelinating phenotype. At culture day 9 total cell [corrected] number was determined. In addition, cells were analysed by immunocytochemistry for A2B5 as well. as by RT-PCR [corrected] and western-blot-analysis of the [corrected] myelin-specific proteins [corrected] MBP, MAG and CNP. Application of INF-gamma and TNF-alpha caused a dramatic decrease in cell number culture day 9 [corrected] More than 30 % of the surviving cells were A2B5-positive compared to 1 % in control dishes. Protein expression of MBP, MAG and CNP as well as mRNA expression, of MAG and MBP were considerably reduced after administration of INF- and TNF-. Co-treatment with, corticosteroids significantly increased total cell count, dexamethasone showing the strongest protective effect.Moreover, corticosteroids alleviated the cytokine induced inhibition in protein- and mRNA-expression [corrected] of MBP, MAG and CNP. Corticosteroids therefore protect oligodendrocyte progenitors from cytokine-induced cell damage.

Adrenal Cortex Hormones↗

PubMed2003

Monitoring cell movements and volume changes with pulse-mode scanning ion conductance microscopy.

Here we describe the use of pulse-mode scanning ion conductance microscopy (SICM) to observe volume changes and cell membrane movements during the locomotion of cultured cells in the range of minutes to several hours. The microscope is based on the pulse-mode SICM previously developed for stable imaging of single cells in culture. Our instrument uses current pulses to control the distance between cell surface and electrode tip as well as a back-step mode to prevent contact of tip and membrane during lateral movements of the probe. We performed repeated scans of cell surfaces using feedback-controlled piezoactors to position the electrode. Using patch-clamp-type electrode tips the height of cells could reproducibly be measured with a standard deviation of 50 nm. To quantify and separate changes in cell position and volume occurring between consecutive scans, a program was written to subtract images and calculate volume changes. Examples of repeated scans show that membrane movements in the range of 30 min to a few hours can be quantitatively monitored with a lateral resolution of 500 nm using difference images and that faster movements in the range of minutes can be recorded at defined cell sections using the line scan mode. Difference images indicate that volume changes can affect cell surfaces inhomogeneously, emphasizing the role of the cytoskeleton in the stabilization of cell shape.

Animals↗

PubMed2002

Pulse-mode scanning ion conductance microscopy--a method to investigate cultured hippocampal cells.

Scanning ion conductance microscopy (SICM) takes advantage of the increase in the resistance which occurs if a glass microelectrode is closely approached to a poorly conducting membrane (Science 243 (1989) 641) and has been shown to be a promising technique to study membranes of living cells (Biophys J 73 (1997a) 653; J Microsc 188 (1997b) 17). Based on a newly designed set-up on top of an inverted light microscope in combination with a speed optimized low noise intracellular amplifier, a novel mode for control of the distance between the probe and surface has been developed. By application of current pulses, the change in the resistance is monitored independently from electrode drift and parasitic DC currents. We demonstrate the applicability by showing first high-resolution images of neural cells produced with the pulse-mode operated SICM.

Animals↗

PubMed2000

Protein expression patterns of identified neurons and of sprouting cells from the leech central nervous system.

It has previously been shown that cephalic, segmental, and caudal ganglia from the medicinal leech show differences in their protein composition. Here we studied whether the neuronal reorganization that occurs in cultured segmental ganglia from the medicinal leech is accompanied by detectable changes in the protein expression pattern. Using silver-stained two-dimensional gels we showed that after 5 and 12 days in culture changes in the protein patterns can be detected in isolated ganglia. The changes observed in the two-dimensional gels occurred concomitantly with a sprouting of serotoninergic neurites and a decreased transmitter content of dopaminergic neurites as shown by using the glyoxylic acid condensation reaction. In addition, we present evidence that Retzius cells, which can be identified by their characteristic morphology and action potential waveform, exhibit biochemically unique properties with respect to their protein expression pattern.

Animals↗

PubMed1999

Sensory impairments and delayed regeneration of sensory axons in interleukin-6-deficient mice.

Interleukin-6 (IL-6) is a multifunctional cytokine mediating inflammatory or immune reactions. Here we investigated the possible role of IL-6 in the intact or lesioned peripheral nervous system using adult IL-6 gene knockout (IL-6(-/-)) mice. Various sensory functions were tested by applying electrophysiological, morphological, biochemical, and behavioral methods. There was a 60% reduction of the compound action potential of the sensory branch of IL-6(-/-) mice as compared with the motor branch in the intact sciatic nerve. Cross sections of L5 DRG of IL-6(-/-) mice showed a shift in the relative size distribution of the neurons. The temperature sensitivity of IL-6(-/-) mice was also significantly reduced. After crush lesion of the sciatic nerve, its functional recovery was delayed in IL-6(-/-) mice as analyzed from a behavioral footprint assay. Measurements of compound action potentials 20 d after crush lesion showed that there was a very low level of recovery of the sensory but not of the motor branch of IL-6(-/-) mice. Similar results of sensory impairments were obtained with mice showing slow Wallerian degeneration (Wlds) and a delayed lesion-induced recruitment of macrophages. However, in contrast to WldS mice, in IL-6(-/-) mice we observed the characteristic lesion-induced invasion of macrophages and the upregulation of low-affinity neurotrophin receptor p75 (p75LNTR) mRNA levels identical to those of IL-6(+/+) mice. Thus, the mechanisms leading to the common sensory deficiencies were different between IL-6(-/-) and WldS mice. Altogether, the results suggest that interleukin-6 is essential to modulate sensory functions in vivo.

Action Potentials↗

PubMed1998

The Drosophila ebony gene is closely related to microbial peptide synthetases and shows specific cuticle and nervous system expression.

The previously detected ebony (e) locus (Caizzi et al., 1987) consists of a complex gene structure that is divided into seven exons. An open reading frame encoding the putative Ebony protein of 98.5 kDa exhibits homology to a family of peptide synthetases (Stachelhaus and Marahiel, 1995), in good correlation with the proposed function as beta-alanyl-dopamine synthetase. Multiple ebony transcripts are detected throughout development. P-factor mediated transformation of genomic DNA rescues the cuticle, electrophysiological and behavioural phenotypes. Fusion of the ebony reading frame with that of beta-galactosidase of E. coli reveals expression in cuticle and nervous system. Strong staining in the first and, to a lesser extent, in the second optic neuropile may reflect the pronounced visual defect observed in ebony mutants. In addition, weak central brain and thoracic ganglion expression is detected in flies. Conservation of a multidomain protein structure known from peptide synthetases should have functional implications on the putative reaction mechanism of peptide bond formation.

Amino Acid Sequence↗

PubMed1997

Thyroid hormone regulates Na+ currents in cultured hippocampal neurons from postnatal rats.

The causes for mental retardation due to perinatal hypothyroidism are not fully understood. Here we show that the most potent component of thyroid hormone, 3,5,3'-triiodo-L-thyronine (T3), selectively increases the density of voltage-activated Na+ currents in hippocampal neurons from newborn rats. Thus, the well known effects of thyroid hormone on energy expenditure and Na+/K+ ATPase activity could to some extent result from the enhanced Na+ influx through voltage-activated Na+ channels. In addition, a down-regulation of the Na+ current density in neurons could contribute to some of the neurological symptoms accompanying hypothyroidism, including slowing of mentation, of neuronal conduction velocities, the alpha rhythm of the electroencephalogram, and increased latencies of evoked potentials and reflexes.

Animals↗

PubMed1997

Differential modulation of AMPA receptor mediated currents by evans blue in postnatal rat hippocampal neurones.

1. The modulation of non-N-methyl-D-aspartate (NMDA) receptor-mediated whole cell currents and of glutamatergic synaptic transmission by purified Evans Blue (EB) was investigated in rat cultured postnatal hippocampal neurones by use of patch clamp recordings and a fast drug application system. 2. Three different groups of neurones could be distinguished with respect to the type of modulation obtained with 10 microM EB: EB was either a predominant inhibitor of desensitization (13% of the neurones), a predominant inhibitor of current amplitudes (42%) or a mixed inhibitor of both properties (45%). Both effects were not use-dependent and reached maximal levels after 30 s of pre-equilibration with the diazo dye. 3. Dose-response curves obtained from glutamate activated whole cell currents yielded an IC50 value for EB of 13.3 microM (Hill coefficient: 1.3) for the inhibition of desensitization, and an IC50 value of 10.7 microM (Hill coefficient: 1.2) for the inhibition of current amplitudes. 4. Chicago acid SS (100 microM) which is one of the synthesis precursors of EB had no effect on current amplitudes of glutamate activated whole cell currents but was a weak inhibitor of desensitization in all hippocampal neurones investigated, irrespective of the type of modulation obtained with EB in the same neurone. 5. Oxidatively modified EB (the so-called VIMP (10 microM)) had no effect on the kinetics but was a partial inhibitor of glutamate-activated whole cell currents in all hippocampal neurones investigated. 6. EB (10 microM) inhibited the amplitudes of non-NMDA receptor mediated autaptic currents to the same extent (to 39 +/- 19% of control) as observed for glutamate activated whole cell currents (to 41 +/- 17% and 56 +/- 20%). However, the decay of the autaptic responses remained uninfluenced upon EB application, indicating that either receptor desensitization does not dominate the time course of the synaptic response or that the non-NMDA receptors sensitive to modulation of desensitization by EB are not present in the postsynaptic membrane. 7. In conclusion, EB differentially modulates alpha-amino-3-hydroxy-5-methyl -4-isoxazole propionic acid (AMPA) receptor gating in different subsets of neurones. Upon identification of the cellular determinants for the differential modulation (e.g. AMPA receptor subunit composition) EB could become a useful tool to investigate receptor subtypes during electrophysiological recordings.

Animals↗

PubMed1995

Enhancement of postsynaptic serotonin-activated Cl- currents by depolarization-induced Ca2+ entry into leech neurons.

Postsynaptic Ca2+ signals are a precondition for many types of synapse modification, including long-term potentiation. Here we describe a postsynaptic mechanism that augments synaptic currents at the serotonergic Retzius-P cell synapse of the leech. Depolarizations large enough to elicit Ca2+ currents evoked an increase in the amplitude of serotonin-activated Cl- currents in isolated embryonic neurons as well as at the Retzius-P cell synapse. The effect on embryonic whole cell currents lasted for up to one hour and was abolished in solutions containing Cd2+ as a Ca2+ channel blocker. Hence, Ca2+ influx into the postsynaptic neuron may be a common step regulating the plasticity of various vertebrate as well as invertebrate synapses.

Animals↗

PubMed1995

Voltage-gated ion currents in embryogenesis.

Excitability is not an exclusive property of differentiated cells, as egg cells already express a surprising variety of species-specific combinations of voltage-gated ion channels. After fertilization, ion currents are generally down-regulated and reappear at about the time of the last mitosis of neuronal precursor cells. When ganglia have formed, Na+ and Ca2+ currents are generally present. The first voltage-gated ion currents in differentiating neurons are unambiguously identified by kinetic and pharmacological criteria according to the channel classifications defined for ion currents in more mature cells. Specialization of different neuronal subtypes with respect to the expression of characteristic patterns of ion channels occurs before neurites grow out and contact their targets. During maturation of committed neurons, the densities of ion currents change. Whereas low voltage-activated Ca2+ current are only transiently expressed in several types of cells Na+, high voltage activated Ca2+, and K+ currents are usually up-regulated until stable final values are reached in adult cells. The most challenging questions to be answered by future research concern the molecular mechanisms regulating the expression of the specific patterns of ion channels characteristic of different subtypes of neurons.

Animals↗

PubMed1995

Two kinetically distinct 5-hydroxytryptamine-activated Cl- conductances at Retzius P-cell synapses of the medicinal leech.

The properties of serotonin (5-HT)-activated Cl- receptor/ion channel complexes in neurons of the CNS of the medicinal leech were analyzed. These channels mediate the postsynaptic response at the serotoninergic Retzius P-cell as well as Retzius-Retzius cell synapses. 5-HT-induced Cl- currents were activated by fast superfusion of transmitter on cells dissociated from embryonic leeches including histochemically identified Retzius cells. Whole-cell currents elicited by partial superfusion of the membrane and summated single-channel currents of outside-out patches showed times to peak of 18 +/- 4 msec and 10 +/- 5 msec, respectively, and desensitized with time constants of 28 +/- 3 msec and 20 +/- 11 msec. Persistence of single-channel openings in the outside-out configuration as well as lack of effect of dialysis of the whole cell with AMP-PNP or GDP-beta-S indicated that 5-HT directly gates the Cl- channels without involving second messenger cascades. In outside-out patches, two single-channel conductances of 13 pS and 32 pS were identified. While the 13 pS conductance desensitized, the 32 pS conductance activated within several tens of msec and showed no desensitization. We postulate that two subtypes of channels are coactivated by 5-HT and that the activation of the fast desensitizing channel could be responsible for the fast decaying component of the post-synaptic response. The slow conductance explains the second slower decay time constant of the postsynaptic response and could account for the tonic component sometimes observed at Retzius P-cell synapses.

Animals↗

PubMed1991

Development of serotonin-induced ion currents in identified embryonic Retzius cells from the medicinal leech (Hirudo medicinalis).

Retzius cells and the cutaneous baroreceptive P-cells of adult medicinal leeches (Hirudo medicinalis) respond to 5-HT by Cl- as well as by monovalent cation conductances (Drapeau et al., 1989). However, chemical synaptic connections between Retzius cells (Liu and Nicholls, 1989) as well as Retzius cells and P-cells in culture (Drapeau and Sanchez-Armass, 1988) are mediated by postsynaptic Cl- currents in response to 5-HT release from the presynaptic cell. It was the aim of the present study to find out whether the response, which has been shown to be involved in synaptic transmission or whether the cation current, which has so far only been observed upon extrasynaptic 5-HT application, dominates during embryogenesis. Currents induced by transmitter application with a fast perfusion system were measured with a single-electrode voltage clamp and patch pipettes in whole-cell configuration. Control experiments, performed on Retzius cells from adult leeches after 1 d in culture, showed Cl- currents in response to 5-HT application in all cells investigated. Ninety percent of the cells tested showed additional 5-HT-elicited Na+, K+, or both currents. However, the conductance of cation currents amounted only to 10% of the Cl- currents. Embryonic Retzius cells were identified in dissociated cultures by their violet-blue fluorescence acquired by preincubation of intact ganglia or embryos in culture medium containing the autofluorescent 5-HT analog 5,7-dihydroxytryptamine. The first responses to 5-HT were measured at embryonic day 10 (E10), after voltage-activated Ca2+ and Na+ currents had already developed. 5-HT application induced exclusively Cl- currents until E16. This suggests that the receptor-channel complex, which also mediates synaptic responses, is expressed first in measurable quantities. Hence, there is currently no indication that extrasynaptic receptors dominate in immature cells in this preparation.

Animals↗

PubMed1989

Proton-induced Na+ current develops prior to voltage-dependent Na+ and Ca2+ currents in neuronal precursor cells from chick dorsal root ganglion.

Proton-induced Na+ currents (INa(H] were measured in precursor cells from chick dorsal root ganglia with whole-cell patch-clamp recording. Precursor cells were isolated using the method of Rohrer et al. (EMBO. J., 4 (1985) 1709-1714) and fast pH changes were applied with a technique developed by Davies et al. (J. Physiol. (Lond.), 400 (1988) 159-187). Proton-induced transient Na+ currents showing the same properties as in more mature neurons could be elicited already early in differentiation, before high-voltage activated Ca2+ currents and voltage-dependent Na+ currents develop.

Animals↗

PubMed1989

Proton-induced chloride current and voltage-activated Na+ and Ca2+ currents in embryonic neurons from the medicinal leech (Hirudo medicinalis).

Voltage-activated ionic currents and currents induced by step changes in proton concentration (pH 7.9-6.7) were studied in early embryonic neurons from Hirudo medicinalis. Ganglia were dissociated at embryonic day (E) 8-15, and the largest neurons were investigated using whole-cell patch clamp recording. All cells studied displayed voltage-activated Na+ and Ca2+ currents. Step changes in pH induced sustained currents which reversed at the equilibrium potential for Cl- and were blocked by substituting Cl- with acetate or sulfate. These currents thus differ in their ion selectivity from proton-induced currents in vertebrate neurons which are carried by Na+.

Animals↗

PubMed1988

Development of dopamine-containing neurons and dopamine uptake in embryos of Hirudo medicinalis.

The embryonic development of neurons which contain or take up dopamine was studied with glyoxylic acid histofluorescence in Hirudo medicinalis. Beginning at the time of the formation of the tail ganglion, one pair of dopamine-containing neurons was stained per segmental ganglion. The normal outgrowth of the cell bodies into the anterior roots was prevented in isolated and cultured chains of embryonic ganglia. Preincubation of intact embryos in dopamine led to the staining of additional neurons at certain developmental stages. These neurons presumably are the precursors of serotonin-containing cells, which have a temporary capability of taking up and storing dopamine.

Animals↗

PubMed1988

Development of inward currents in chick sensory and autonomic neuronal precursor cells in culture.

The development of ionic inward currents was studied in cultured neuronal precursors from chick sensory dorsal root ganglia (DRG) and compared with neuronal precursors from the cholinergic ciliary ganglia (CG) using whole cell patch-clamp recording. Neuronal precursors devoid of neuron-specific surface markers were isolated during the period of neuronal birth, i.e., at embryonic day (E) 6 from DRG and at E4.5 from CG. All neuronal precursor cells from DRG, as well as CG, showed outward K+ currents directly after they had attached to the substrate. During the first 5 hr in culture, half of the DRG cells had no inward currents at all, whereas the other half displayed a rapidly and fully inactivating Ca2+ current, which was activated with small depolarizing pulses from a holding potential of -80 mV to a -50 mV membrane potential (low-voltage-activated current, LVA). At these early stages, no other inward currents were resolved. TTX-blockable Na+ currents and slowly inactivating classical Ca2+ currents, which were activated with larger depolarizing pulses to a -20 mV membrane potential (high-voltage-activated currents, HVA) appeared concurrently after 15-20 hr in culture. In contrast, more than half of the CG cells showed LVA currents, as well as Na+ currents, as early as during the first 5 hr in culture. The HVA Ca2+ currents from the majority of the cells could be recorded only after 10-15 hr in culture. In both types of precursor-derived neurons, the LVA Ca2+ current preceded the classical HVA Ca2+ current. However, the temporal relation of the first Na+ currents to the first HVA Ca2+ currents seemed to be different in the 2 preparations. In DRG cells, Na+ and HVA Ca2+ currents appeared at the same time, whereas in CG cells, the HVA Ca2+ current showed a time lag with respect to the Na+ current. In addition, the relative amplitudes of the currents differed in the CG and DRG cells. This shows that as early as E4-6, shortly after their terminal mitosis, neurons from distinct peripheral ganglia in chick vary in the development of their basic ionic currents.

Animals↗