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P Fromherz

Publications and source records attributed to P Fromherz.

At least 37 records · Page 2Linked to original sources
PubMed1994

Cable properties of a straight neurite of a leech neuron probed by a voltage-sensitive dye.

We measured a time-resolved map of electrical activity in a thin straight neurite (1.5 microns thick, 500 microns long) at a resolution of 8 microns and 0.4 ms. The neurite was obtained by guided outgrowth of an identified neuron of the leech on lanes of extracellular matrix protein. The electrical signals were detected by a fluorescent voltage-sensitive dye. We observed the voltage that was caused by an action potential elicited at the soma and by a Gaussian hyperpolarization induced at the soma, respectively. We compared the data with numerical solutions of the cable equation using the Hodgkin-Huxley parametrization. We could attribute the experimental results of depolarization and of hyperpolarization to the propagation of an action potential along an "active" cable and to the spread along a "passive" cable, respectively, if we assigned rather high specific resistances to the cytoplasm (RI = 250 omega.cm) and to the membrane (RM = 22 k omega.cm2). This assignment explained the slow velocity of 150 microns/ms of a pulse by active propagation and the limited range of 200 microns of a pulse by passive spread.

Action Potentials↗
PubMed1993

Voltage-sensitive fluorescence of amphiphilic hemicyanine dyes in neuron membrane.

Fluorescent amphiphilic hemicyanine dyes were adsorbed to the plasma membrane of isolated Retzius neurons of the leech. Voltage steps were applied to the neuron by the patch-clamp technique in whole-cell configuration. The change of fluorescence was observed as induced by the voltage jump. The relative changes of the excitation spectrum and of the emission spectrum of fluorescence were recorded. The complete set of spectral data for each dye was fitted by five parameters: shifts of the emission and the excitation spectrum, a change of fluorescence quantum yield and changes of the widths of the excitation and of the emission spectrum. The only common feature for all dyes was a blue-shift of the excitation spectrum and a drop of the yield when the neuron was stained from the outside and a positive voltage was applied to the inside. With respect to the shift of the emission spectrum and the changes of width qualitatively different results were obtained for different dyes. It is not attempted to assign a physical mechanism--probably a superposition of several mechanisms--of voltage-sensitivity.

Animals↗
PubMed1993

Exclusive-OR function of single arborized neuron.

We designed four arborized neurons which are able to evaluate the exclusive-or (XOR) function from two inputs. The input neurons form exclusively excitatory synapses on a dendritic tree which is a patchwork of "passive" (ohmic) and "active" cable segments. The active segments are described by the Hodgkin-Huxley model. The dynamics of the neurons and their output are obtained by numerical integration of the cable equation. In neurons 1 and 2 the XOR function is based on the annihilation of colliding action potentials. In neuron No. 3 the design takes advantage of the refractory period of action potentials. In neuron No. 4 voltage inversion is used as it occurs for inactivated sodium conductance in the Hodgkin-Huxley model. In all cases the XOR function depends critically on an appropriate timing of the input signals and on delays of the voltage transients in different branches of the dendrite.

Action Potentials↗
PubMed1992

Cable properties of arborized Retzius cells of the leech in culture as probed by a voltage-sensitive dye.

Retzius cells of Hirudo medicinalis were cultivated on extracellular matrix protein so that extended arborizations were formed. The propagation of voltage transients along 1-microns-thick neurites was observed at a resolution of 8 microns at 10 kHz by use of a voltage-sensitive dye. Delay and width of the fluorescence transients caused by hyperpolarization of the soma are described by passive spread of voltage in a homogeneous cable (time constant, 10 ms; space constant, 320 microns). The local sensitivity of the dye was determined from a comparison of the amplitudes of fluorescence and of fitted voltage. The fluorescence transients caused by depolarization were scaled using the sensitivity profile. Action potentials were found to pervade the neurites without significant change of amplitude but with enhanced pulse width.

Action Potentials↗
PubMed1991

Spectra of voltage-sensitive fluorescence of styryl-dye in neuron membrane.

The voltage sensitivity of fluorescence of an aminobenzstyryl-pyridinium dye (di4-ANEPPS) is characterized in Retzius cells dissociated from the leech. The modulation of the complete spectra of excitation and emission is determined. The spectral changes induced by depolarization are described by a blue shift of the absorption spectrum, by a weaker blue shift and an enhanced width of the fluorescence spectrum and by a decrease of the yield of fluorescence. These changes are attributed tentatively to a superposition of electrochromism and of field-induced resolvation.

Animals↗
PubMed1991

Guided outgrowth of leech neurons in culture.

Sensory neurons of Hirudo medicinalis were cultivated on patterns of extracellular matrix (ECM) protein which were prepared by UV irradiation using copper grid masks. The relation of the patterns and of the outgrowth of neurites was observed by scanning electronmicroscopy after gold decoration. The neurites were guided by narrow (10 microM) lanes of ECM protein. Branching of neurites was induced by branched lanes. Bent neurites were pulled off bent lanes at some distance behind the growth cone such that their length was reduced. Regularly spaced sites of adhesion became visible which remained connected to the neurites by extended filaments.

Animals↗
PubMed1991

A neuron-silicon junction: a Retzius cell of the leech on an insulated-gate field-effect transistor.

An identified neuron of the leech, a Retzius cell, has been attached to the open gate of a p-channel field-effect transistor. Action potentials, spontaneous or stimulated, modulate directly the source-drain current in silicon. The electronic signals match the shape of the action potential. The average voltage on the gate was up to 25 percent of the intracellular voltage change. Occasionally weak signals that resemble the first derivative of the action potential were observed. The junctions can be described by a model that includes capacitive coupling of the plasma membrane and the gate oxide and that accounts for variable resistance of the seal.

Action Potentials↗
PubMed1991

Core-coat conductor of lipid bilayer and micromachined silicon.

We have etched a groove into a (110) plane of silicon and have covered it with a bilayer of glycerol monooleate. We have varied the depth of the groove, the concentration of salt in the electrolyte and the density of gramicidin in the membrane. We have clamped one end of the groove at a constant voltage with respect to the bath keeping the other end sealed or electrically open with respect to the bath. We have measured (i) the voltage at the center of the groove and at the sealed distal end and (ii) the current through the system in sealed and open configuration. We have found that the spread of voltage is in quantitative agreement with the stationary solutions of Kelvin's equation for a homogeneous cable.

Electric Conductivity↗
PubMed1989

Selforganization of a membrane in synaptic geometry.

The self-organization of mobile membrane proteins in a synaptic structure is computed. The model of dissipative condensation is used which takes into account the intermolecular interactions due to electrical channel currents and electrophoretic charges as they occur in a leaky membrane. An instability of the homogeneous fluid mosaic of charged channels is observed in the region of the synapse. Periodic accumulations of channels appear which are modulated by the attraction of protein from the perisynaptic membrane. The sensitivity of the process with respect to the geometrical constraints and to electrochemical parameters is discussed.

Electric Conductivity↗
PubMed1988

Spatio-temporal patterns in the fluid-mosaic model of membranes.

The lateral distribution of integral proteins in a fluid membrane is studied in a phenomenological model. The electrical interaction of the proteins (forming ion channels and bearing electrophoretic charges) with the membrane potential is considered. Stationary and oscillatory patterns appear far from electrochemical equilibrium under conditions which may well exist in natural membranes.

Algorithms↗
PubMed1988

Self-organization of the fluid mosaic of charged channel proteins in membranes.

Electrically charged ion channels in a fluid membrane may form dissipative structures driven by a concentration gradient of salt. On a molecular level the effect is due to dissipative attractive forces; the channel currents induce local gradients of the membrane potential that interact with the protein charge. Self-organization by "charged channel condensation" is treated on a phenomenological level: Smoluchowski's equation describing diffusion and drift of the membrane proteins and Kelvin's equation describing the dynamics of the membrane potential are considered as a coupled system of equations. The patterns of the two morphogens, the membrane protein and the membrane potential, are controlled by global parameters--the average density of charged channels, the level of their reversal potential, and the size of the membrane.

Ion Channels↗
PubMed1975

Interaction of electrically charged lipid monolayers with malate dehydrogenase.

Malate dehydrogenase was adsorbed onto monomolecular lipid films, using a multicompartment trough. The quantity of adsorbed protein and its enzymatic activity were studied with monolayers of various electrical charge densities and subphases of various electrolyte compositions. A closely packed layer of enzyme molecules was adsorbed onto negatively charged films, whereas considerably less protein was adsorbed onto neutral and positively charged monolayers. Electrolytes reduce the quantity of adsorbed protein. The adsorption was found to be irreversible even at high ionic strength. When adsorbed to uncharged lipid films the enzyme is nearly inactive, whereas negatively charged lipid headgroups enhance the specific activity of the enzyme.

Animals↗