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U R Wyss

Publications and source records attributed to U R Wyss.

6 recordsLinked to original sources
PubMed1977

Membrane associated particles of the presynaptic active zone in rat spinal cord. A morphometric analysis.

The distribution of membrane-associated particles in the presynaptic membrane was investigated in the spinal cord of unanesthetized and anesthetized rats by freeze etching electron microscopy. Both 'external' face (EF) and 'protoplasmic' face (PF) were examined. Particles were classified according to size in two categories: small particles (diameter 5.0-8.7 nm) and large particles (diameter 8.7-13.7 nm). The presynaptic region was subdivided into an active and a surrounding zone, depending on specific ultrastructural criteria. The density of large particles in the PF was found to be significantly higher in the active as compared with the surrounding zone in both unanesthetized and anesthetized rats. Thus, the presence of large particles represents an important feature of the active zone. Considerably more large particles were found in the waking than in the barbiturized state. This difference is paralleled by a vast increase of vesicle attachment sites in the presynaptic membrane of unanesthetized animals reported by Streit et al. and confirmed in the present study. It is suggested that the two phenomena could be interrelated and that the large particles may represent calcium channels and thus provide the morphological substrate for the mechanism of excitation-secretion coupling.

Animals↗
PubMed1977

The Ranvier nodes in the neurogenic electric organ of the knifefish Sternarchus: a freeze-etching study on the distribution of membrane-associated particles.

The two types of Ranvier nodes (type I with narrow gap, type II with giant gap) and internodes in nerve fibers composing the Sternarchus electric organ have been studied by means of freeze-etching electron microscopy. Numerical analysis of the distribution of membrane-associated particles revealed the following features: (1) the P-faces of both types of nodes and of the internodal axon bear a similarly high density of particles (1000-1200 particles/sq. micron on the average). (2) particle density is differential in E-faces: the histogram for type I nodes has a wider range of particle concentrations (114-1522 particles/sq. micron) than that for type II nodes (45-576 particles/sq. micron) whose density values are in the same range as those of the internodal axon. At least some type I nodes (narrow gaps) generate spikes and probably have a low resistivity; these nodes may be those with high particle density on E-faces. The low particle density on E-faces of type II nodes may be associated with high resistivity and absence of excitability. Similarly, the low particle density in internodes may reflect inexcitability. There is evidence that the transition from one nodal type to the next is gradual: as the gap width of type I nodes increases, there is an occurrence of surface elaborations and the density of E-face particles tends to drop towards the range of type II nodes.

Animals↗
PubMed1975

Relation of activity in precentral cortical neurons to force and rate of force change during isometric contractions of finger muscles.

The activity of single neurons within the hand area of the precentral motor cortex of primates was recorded during the performance of a maintained precision grip between the thumb and forefinger. The finger opposition forces were exerted against a strain gauge which allowed force changes to be studied under near isometric conditions. Task performance required the generation of a force ramp (the dynamic phase) and thereafter the maintenance of a stable force for one second (the static phase). Intracortical stimulation through the recording electrode was used to verify that the recordings were made from the appropriate somatotopographic area of the motor cortex. From a total of 221 recorded neurons, 76 were found to be either activated or deactivated during performance of the task. Among the 51 activated neurons, most discharged at higher frequencies during the dynamic phase, than during the static phase. The discharge of some of these neurons could be related to both force (F) and rate of force change (dF-dt) whereas certain others could only be correlated with dF-dt. The change in discharge frequency for these neurons generally occurred prior to the onset of EMG activity. Eight neurons were more active during maintained force than during the force ramp. The discharge frequency could not be correlated with dF-dt and only one showed a significant positive relation to force. The change in discharge frequency for these neurons either coincided or occurred after the onset of EMG activity.

Animals↗