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Erfahrungsbericht zum Projekt Untersuchung der Regulierung axonaler Exzitabilität in peripheren sensorischen und motorischen Axonen mittels der „Threshold tracking“ – Methode
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Noradrenergic modulation of calcium currents and synaptic transmission in the olfactory bulb of Xenopus laevis tadpoles.
No full textNorepinephrine (NE) has various modulatory roles in both the peripheral and the central nervous systems. Here we investigate the function of the locus coeruleus efferent fibres in the olfactory bulb of Xenopus laevis tadpoles. In order to distinguish unambiguously between mitral cells and granule cells of the main olfactory bulb and the accessory olfactory bulb, we used a slice preparation. The two neuron types were distinguished on the basis of their location in the slice, their typical branching pattern and by electrophysiological criteria. At NE concentrations lower than 5 microM there was only one effect of NE upon voltage-gated conductances; NE blocked a high-voltage-activated Ca(2+)-current in mitral cells of both the main and the accessory olfactory bulbs. No such effect was observed in granule cells. The effect of NE upon mitral cell Ca(2+)-currents was mimicked by the alpha(2)-receptor agonists clonidine and alpha-methyl-NE. As a second effect, NE or clonidine blocked spontaneous synaptic activity in granule cells of both the main and the accessory olfactory bulbs. NE or clonidine also blocked the spontaneous synaptic activity in mitral cells of either olfactory bulb. The amplitude of glutamate-induced currents in granule cells was modulated neither by clonidine nor by alpha-methyl-NE. Taken together, the main effect of the noradrenergic, presynaptic, alpha(2)-receptor-mediated block of Ca(2)+-currents in mitral cells appeared to be a wide-spread disinhibition of mitral cells in the accessory olfactory bulb as well as in the main olfactory bulb
Noradrenergic modulation of calcium currents and synaptic transmission in the olfactory bulb of Xenopus laevis tadpoles.
No full textNorepinephrine (NE) has various modulatory roles in both the peripheral and the central nervous systems. Here we investigate the function of the locus coeruleus efferent fibres in the olfactory bulb of Xenopus laevis tadpoles. In order to distinguish unambiguously between mitral cells and granule cells of the main olfactory bulb and the accessory olfactory bulb, we used a slice preparation. The two neuron types were distinguished on the basis of their location in the slice, their typical branching pattern and by electrophysiological criteria. At NE concentrations lower than 5 microM there was only one effect of NE upon voltage-gated conductances; NE blocked a high-voltage-activated Ca(2+)-current in mitral cells of both the main and the accessory olfactory bulbs. No such effect was observed in granule cells. The effect of NE upon mitral cell Ca(2+)-currents was mimicked by the alpha(2)-receptor agonists clonidine and alpha-methyl-NE. As a second effect, NE or clonidine blocked spontaneous synaptic activity in granule cells of both the main and the accessory olfactory bulbs. NE or clonidine also blocked the spontaneous synaptic activity in mitral cells of either olfactory bulb. The amplitude of glutamate-induced currents in granule cells was modulated neither by clonidine nor by alpha-methyl-NE. Taken together, the main effect of the noradrenergic, presynaptic, alpha(2)-receptor-mediated block of Ca(2)+-currents in mitral cells appeared to be a wide-spread disinhibition of mitral cells in the accessory olfactory bulb as well as in the main olfactory bulb
Dual effect of ATP in the olfactory epithelium of Xenopus laevis tadpoles: Activation of both receptor and sustentacular supporting cells
No full textATP activates both receptor and sustentacular supporting cells in the olfactory epithelium of Xenopus laevis tadpoles
No full textNucleotides and amino acids are acknowledged categories of water-borne olfactory stimuli. In previous studies it has been shown that larvae of Xenopus laevis are able to sense amino acids. Here we report on the effect of ATP in the olfactory epithelium (OE) of Xenopus laevis tadpoles. First, ATP activates a subpopulation of cells in the OE. The ATP-sensitive subset of cells is almost perfectly disjoint from the subset of amino acid-activated cells. Both responses are not mediated by the well-described cAMP transduction pathway as the two subpopulations of cells do not overlap with a third, forskolin-activated subpopulation. We further show that, in contrast to amino acids, which act exclusively as olfactory stimuli, ATP appears to feature a second role. Surprisingly it activated a large number of sustentacular supporting cells (SCs) and, to a much lower extent, olfactory receptor neurons. The cells of the amino acid- and ATP-responding subsets featured differences in shape, size and position in the OE. The latencies to activation upon stimulus application differed markedly in these subsets. To obtain these results two technical points were important. We used a novel dextran-tetramethylrhodamine-backfilled slice preparation of the OE and we found out that an antibody to calnexin, a known molecular chaperone, also labels SCs. Our findings thus show a strong effect of ATP in the OE and we discuss some of the possible physiological functions of nucleotides in the OE
Alpha-2-receptors modulate calcium currents and synaptic transmission in the olfactory bulb of Xenopus laevis
No full textLow frequency voltage clamp: recording of voltage transients at constant average command voltage
No full textWe implemented a simple feedback system that modifies the conventional current clamp mode of a patch clamp amplifier so that transient potentials, such as action potentials and synaptic potentials, can be measured as in the usual current clamp, while the average membrane potential is kept constant at a value chosen by the user. The circuit thus works like the current clamp for high frequency signals and like a voltage clamp for low frequency signals. We delineate its transfer properties and give application examples. (C) 2000 Elsevier Science B.V. All rights reserved
Neuronal representation of odourants in the olfactory bulb of Xenopus laevis tadpoles
No full textWhen an odourant enters the nose, olfactory receptor neurons (ORNs) convey information about it to the olfactory bulb (OB), where this information is processed and where the first central representations of the odourant are generated. In this paper we show how odourants are represented by ensembles of OB neurons, in particular mitral cells (MCs) which are the output neurons of the OB. We were able to demonstrate for the first time that the intracellular calcium concentrations ([Ca2+](i)) in the somata of these neurons undergo specific changes and that different stimuli are represented by different neuronal [Ca2+](i) patterns. The similarity of patterns was assessed by cross-correlation analysis. We further show that noradrenaline (NA), which is reported to be involved in olfactory memory formation and to modulate synaptic transmission at dendrodendritic synapses in the OB, profoundly changes the representation of odourants at the level of MCs
Alpha-2-receptors modulate calcium currents and synaptic transmission in the olfactory bulb of Xenopus laevis
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