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A Schierwagen

Publications and source records attributed to A Schierwagen.

7 recordsLinked to original sources
PubMed1998

An equivalent cable model for neuronal trees with active membrane.

A non-uniform equivalent cable model of membrane voltage changes in branching neuronal trees with active ion channels has been developed. A general branching condition is formulated, extending Rall's 3/2 power rule for passive dendritic trees so that non-uniform cable segments can be treated. The theoretical results support the use of the dendritic profile model of Clements and Redman. The theory is then applied to dendrites of different morphological type yielding qualitative different response behaviour.

Computer Simulation↗
PubMed1994

Interlayer neurones in the rat superior colliculus: a tracer study using Dil/Di-ASP.

Five different populations of interlayer neurones (ILNs) can be described after DiI/Di-ASP tracing in rat superior colliculus (SC). All of these labelled neurones preferentially lay in the rostro-medial part of the SC. Most of them are located in the stratum opticum and in the stratum griseum superficiale. Our results indicate that ILNs represent a minority of neurones in the superficial layers but may constitute a substantial population of neurones in the stratum opticum connecting the visual and the multimodal collicular layers.

Animals↗
PubMed1988

Dendritic anatomy and electrotonic transfer properties of cat superior colliculus neurons.

Detailed morphometrical and corresponding electrotonic characteristics on three classes of cat superior colliculus (SC) neurons have been derived. The sample of cells selected for analysis comprised ascending projection neurons (APNs), inter-layer neurons (ILNs) and tecto-reticulo-spinal neurons (TRSNs) recorded intracellularly and stained with HRP. Superficial SC neurons (APNs, ILNs) could be attached to the allo- and idiodendritic type while deep layer neurons (TRSNs) belong to the isodendritic type. For each neuron, the branching pattern, lengths and diameters of the dendritic trees were determined. These data served as input to the computer program "DENDRIT" from which electrotonic membrane and transfer properties were calculated. Both the morphometrical data and the electronic properties underline the contrasting features of superficial vs deep layer neurons in the SC. Our results support the hypothesis that on the neuron level a close relationship between dendritic pattern and neuron function might exist.

Animals↗
PubMed1986

Segmental cable modelling of electrotonic transfer properties of deep superior colliculus neurons in the cat.

A segmental cable model of tecto-reticulo-spinal neurons of cat superior colliculus was constructed, based on detailed anatomical measurements from three neurons. The calculated membrane resistance for which the model best fitted the measured input resistance was 2,300-3,000 omega cm2. Electrotonic length of dendrites fell under 0.59-1.20 and 0.52-1.05 length constants, while the mean electrotonic length for the three cells averaged 0.91, 0.79, 0.81 and 0.80, 0.70, 0.71 (for sealed-end and open-end cable termination, respectively). Dendrite-to-soma conductance ratios averaged 16.0, 10.7, 7.5 and 21.3, 14.1, 11.4 for the two different end conditions, respectively. Synaptic efficacy was estimated by the transfer of steady-state voltage or current reaching the soma from distal dendritic locations. While voltage transfer was less than 1%, almost 60% of injected current (or charge) reached the soma. Analysis of voltage transients recorded experimentally in TRSNs demonstrated considerable difference between parameters derived from either equivalent-cylinder model or segmental cable model. The obvious deviations of TRSNs both in anatomical and electrotonic respect from the assumptions of the equivalent-cylinder model indicate that the detailed cable model will give a more appropriate description of these neurons. The significance of the estimated electrotonic parameters for the particular burst generation mechanism of TRSNs is discussed.

Animals↗
PubMed1986

Quantitative morphological analysis of deep superior colliculus neurons stained intracellularly with HRP in the cat.

Neurons of the deep collicular layers were identified electrophysiologically, stained intracellularly with horseradish peroxidase and reconstructed from serial sections. Three neurons located in the stratum griseum intermedium were selected for detailed, light microscopic analyses. 7-10 dendritic stems arose from the polygonally shaped perikarya; they branch out in up to 8 successive bifurcations, giving rise to a mean of 9.1 tips per dendrite, or equivalently 78.7 tips per neuron. Dendrites extended up to 700 microns from soma, with tip diameters below 1 micron. Dendritic lengths were shown to be independent on branch order; mean branch length amounted to 72.3 microns, 96.3 microns and 99.4 microns. In each of the neurons, intermediate branches were significantly shorter than terminating branches. By excluding all of the end-branches, an inverse length-diameter relation could be demonstrated in each neuron to exist. Dendritic membrane surface area constituted more than 90% of the total soma-dendritic surface; dendritic-to-somatic surface area ratios were 9.8, 13.2 and 21.4, respectively. Measurements at 92 bifurcations of first to fourth order led to branch power n = 1.47 showing that the 3/2 power relationship is fulfilled on the average. All collicular neurons exhibited drastic arborizational taper due to disappearance of terminal branches, not to dendritic thinning within the tree. In spite of some differences among these deep collicular neurons in their general morphology, on many of the feature characterizing their dendritic trees they proved to be clearly similar confirming a previous description as single class of isodendritic, collicular neurons.

Animals↗
PubMed1983

Passive membrane properties, afterpotentials and repetitive firing of superior colliculus neurons studied in the anesthetized cat.

Intracellular recording and staining with HRP were used to characterize cat superior colliculus neurons with identified projection into the tecto-bulbo-spinal tract (TBSNs). TBSNs are large multipolar neurons with heavy stem dendrites. First and second order dendrites bifurcate with an average branch power n of about 3/2. More peripheral branch points have n less than 1.5. Input resistances of TBSNs range from 0.9 to 4.6 M omega. Most TBSNs display 'anomalous rectification'. Based on Rall's steady-state cable equations, input resistances were calculated for 3 TBSNs labelled with HRP. Assuming a specific membrane resistance of 2,300-2,600 omega cm2 the/calculated values agree well with the experimentally determined estimates from another set of non-stained TBSNs. Membrane time constants of TBSNs range from 3.0 to 5.6 ms. The electrotonic length was calculated using the ratio tau 0/tau 1. The respective average value was 1.13. TBSNs respond to orthodromic, antidromic and direct stimulation with action potentials of 60-80 mV, composed of IS- and SD-components. The critical interval for IS-SD-invasion was on average 1.6 ms. Spike decomposition occurs usually at M-level. The postspike conductance increase underlying hyperpolarizing afterpotentials (HAP) decays exponentially, with the time constants tau F = 1.5 ms and tau S = 13 ms. The HAP was equilibrated at membrane potentials of -73 to -90 mV. When tested by antidromic stimuli at varying intervals most TBSNs show very poor "summation" of HAPS. A pronounced depolarizing hump (DD) follows antidromic action potentials. Discharging at short intervals leads to a substantial increase and prolongation of DD. This apparent DD-potentiation is interpreted as a phenomenon secondary to the reduction of hyperpolarizing currents. In response to directly injected currents, TBSNs discharge with frequencies up to 1,100 imp/s. The frequency-current curves of TBSNs are characterized by 3 ranges. The average f-i-slopes of the adapted discharge were 19.2 imp/s/nA and 56.4 imp/s/nA for the 1st and 2nd range, respectively. At intermediate current intensities (2nd range) TBSNs discharge in groups of 2 to 7 action potentials, following each other at intervals of 1.0-2.8 ms. The spike groups are separated by pauses of 3.5-6.3 ms duration. The transition from 1st (low frequency continuous) discharge range to 2nd (grouped) discharge range is related to the appearance of extra-spikes. Extra-spikes are generated from a decreased firing level, from the peak of an enhanced DD.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗