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T Vetter

Publications and source records attributed to T Vetter.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1989

[Not Available].

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France↗
PubMed1971

[Not Available].

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Denmark↗
PubMedDate not supplied

Transport of small organic cations in the rat liver. The role of the organic cation transporter OCT1.

The kidneys and the liver are the principal organs for the inactivation of circulating organic cations. Recently, an organic cation transporter (OCT1) has been cloned from rat kidney. In order to answer the question whether OCT1 is involved also in hepatic uptake of organic cations, the pharmacological characteristics of organic cation transport in hepatocytes were compared to the characteristics of transiently expressed OCT1. Primary cultures of rat hepatocytes avidly accumulated the small organic cation 3H-1-methyl-4-phenylpyridinium (3H-MPP+). At equilibrium, the hepatocytes accumulated 3H-MPP+ 56-fold. Initial rates of specific 3H-MPP+ transport in hepatocytes were saturable. The half-saturating concentration was 13 mumol/l. 3H-MPP+ transport was sensitive to quinine (Ki = 0.79 mumol/l) and cyanine863 (Ki = 0.097 mumol/l). Quinine and cyanine863 are known inhibitors of type I hepatic transport of cationic drugs and of renal excretion of organic cations, respectively. To compare the functional characteristics of 3H-MPP+ transport in hepatocytes with those of OCT1, OCT1 has been heterologously expressed and characterized in a mammalian cell line (293 cells). Initial rates of 3H-MPP+ transport were saturable, the Km being 13 mumol/l. The rank order of inhibitory potencies of various inhibitors was almost identical in hepatocytes and 293 cells transiently transfected with OCT1. There was a positive correlation between the Ki's for the inhibition of 3H-MPP+ transport in isolated hepatocytes and transfected 293 cells (r = 0.85; P < 0.01; n = 8). The results indicate that OCT1 is functionally expressed not only in the kidney but also in hepatocytes where it is responsible for the transport of small organic cations which, in the past, have been classified as type I substrates.

Animals↗
PubMedDate not supplied

View-based models of 3D object recognition: invariance to imaging transformations.

This report describes the main features of a view-based model of object recognition. The model does not attempt to account for specific cortical structures; it tries to capture general properties to be expected in a biological architecture for object recognition. The basic module is a regularization network (RBF-like; see Poggio and Girosi, 1989; Poggio, 1990) in which each of the hidden units is broadly tuned to a specific view of the object to be recognized. The network output, which may be largely view independent, is first described in terms of some simple simulations. The following refinements and details of the basic module are then discussed: (1) some of the units may represent only components of views of the object--the optimal stimulus for the unit, its "center," is effectively a complex feature; (2) the units' properties are consistent with the usual description of cortical neurons as tuned to multidimensional optimal stimuli and may be realized in terms of plausible biophysical mechanisms; (3) in learning to recognize new objects, preexisting centers may be used and modified, but also new centers may be created incrementally so as to provide maximal view invariance; (4) modules are part of a hierarchical structure--the output of a network may be used as one of the inputs to another, in this way synthesizing increasingly complex features and templates; (5) in several recognition tasks, in particular at the basic level, a single center using view-invariant features may be sufficient.

Depth Perception↗
PubMedDate not supplied

Propagation of voltage transients in arborized neurites of Retzius cells of the leech in culture.

Propagation of electrical signals is studied in Retzius cells of the leech in culture using voltage-sensitive fluorescent dyes at a spatial resolution of 8 x 8 microns 2 and 14 x 14 microns 2 and at a sampling interval of 0.12 ms. The neurons are stimulated by a microelectrode impaled in the soma. Action potentials of a half width of 2-3 ms are triggered close to the end of the primary neurite dissociated from the leech. They propagate back to the soma at invariant half width at a velocity of 50-230 microns/ms. They pervade extended aborized secondary neurites which are grown on extracellular matrix protein. Their width is enhanced up to a factor two. The velocity is around 100-150 microns/ms such that delays up to 3.5 ms are observed. Accordingly the neuritic trees are not isopotential. The features of propagation are found to be incompatible with passive spread.

Action Potentials↗