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Biomedical subjects

Y Dunant

Publications and source records attributed to Y Dunant.

At least 91 records · Page 5Linked to original sources
PubMed1979

Rapid acetylcholine and adenosine triphosphate oscillations triggered by stimulation of the Torpedo electric organ.

1. When the electric organ of Torpedo is stimulated a large number of synchronized cholinergic synapses are activated. This permits the measurement of changes in the tissue level of ACh associated with the release process, usually recorded as an electric discharge. 2. At 5 Hz stimulation the output per impulse and the amount of cytoplasmic (free ACh) declines for about 30 s. The output then remains constant while ACh is synthesized for about 90 s. Finally, the output and cytoplasmic ACh are exhausted after 120 s. These 'slow wave' changes in ACh represent about 50% of the total. 3. Superimposed on the 'slow wave' are rapid oscillations of 5 s period, which represent about 30% of the total ACh. 4. The amount of ATP oscillates in phase with ACh. These oscillations might result from regulation of enzymes involved in the synthesis of transmitter. 5. The amplitude of electrical discharge does not normally oscillate. Transmitter output is therefore not directly related to ACh concentration changes. The mechanism releasing ACh is a saturable process.

Acetylcholine↗
PubMed1978

Localization of thiamine in cholinergic nerve terminals: a histofluorescence study in the electric organ of Torpedo.

Thiamine (vitamin B1) and its phosphoric acid esters were found at a surprisingly high level in the electric organ of the fish Torpedo marmorata. The localization of the vitamin was investigated by a sensitive reaction in which the thiamine molecule was converted into a blue fluorescent thiochrome by treatment with an alkaline potassium ferricyanide solution. Whereas only slight fluorescence occurred in the electroplaque cells, a strong fluorescent reaction took place in their nerve supply. Intense fluorescence was observed not only in the myelinated nerve fibres but also at the nodes of Ranvier; moreover, preterminal branches and nerve endings, which are non-myelinated, were also strongly stained. The emission spectrum of this fluorescent material was found to be nearly identical to that of standard thiochrome. These findings substantiate the hypothesis that vitamin B1 plays an important role in acetylcholine metabolism and release.

Animals↗
PubMed1977

Oscillation of acetylcholine during nerve activity in the Torpedo electric organ.

The amount of transmitter in the electric organ of Torpedo was measured with a time resolution of 1 sec in the course of stimulation. In parallel, the modifications of the electrophysiological response were analysed by determining the conductance increase (deltaG) and the electromotive force of electroplaques. Large changes in the level of total acetylcholine (ACh) were seen during stimulation. These changes were two-fold: a slow wave and, superimposed on it, a rapid oscillation. The slow wave raised total ACh to the initial level, or even higher. It was probably related to modifications in the amount of ACh released since it corresponded to characteristic inflections in the evolution of the deltaG curve. The slow wave and this physiological parameter were similarly affected when the experiments were performed at a reduced temperature. The rapid oscillation had an amplitude of about 20-40% of the total ACh. It was undamped and its period was 4-5 sec. In contrast to the slow wave, no clear physiological change associated with the rapid oscillation has been observed. The slow wave and rapid oscillation occurred in the 'free pool' of ACh, whereas bound ACh, the fraction associated with synaptic vesicles, was not affected by these changes. A dynamic description of synaptic activity is proposed. The content of 'free' ACh is used and renewed completely after a few tens of impulses, so that transmission seems to imply the continual recycling of the same pool of transmitter rather than utilization of a large preloaded store. The release process must then be integrated in rapid metabolic loops.

Acetylcholine↗
PubMed1975

[Periodical variations of the level of acetylcholine during stimulation of torpedo electric organ].

When tissue samples of the electric organ of the Torpedo fish, are taken every second during a period of stimulation at 5/s, it is noticed that their acetylcholine level oscillates in a quasi-sinusoidal shape. The amplitude of the oscillation is of about 350 nmoles/g and its period of 4 to 6 seconds. The speed of acetylcholine formation during such a process is extremely high.

Acetylcholine↗
PubMed1974

A peculiar substructure in the postsynaptic membrane of Torpedo electroplax.

Freeze-etching of Torpedo marmorata electroplax reveals an unusual substructure in one of the fracture faces of the postsynaptic membrane. This substructure consists of a lattice of closely spaced particles that are smaller than the usual 80- to 90-A particles present in other membrane types. The lattice occurs exclusively on the B-face of the postsynaptic membrane.

Animals↗