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Y Dunant

Publications and source records attributed to Y Dunant.

108 records · Page 6Linked to original sources
PubMed1972

Some properties of the presynaptic nerve terminals in a mammalian sympathetic ganglion.

1. Superior cervical ganglia of adult rats were excised and maintained in vitro in stable conditions. Potentials were recorded with external electrodes. After transmission was blocked by mecamylamine, a small potential change was recorded from the rostral area of the ganglion in response to preganglionic stimulation.2. This electrical response was identified as the presynaptic action potential recorded from the nerve terminals by a number of criteria based on histological and physiological considerations including the disappearance of the spike in a glucose free solution. As shown by Nicolescu, Dolivo, Rouiller & Foroglou-Kerameus (1966) on the same preparation this condition causes an irreversible and selective lesion of the presynaptic nerve endings.3. A suitable concentration of mecamylamine permitted the presynaptic response and the excitatory post-synaptic potential (EPSP) to be recorded simultaneously. As the stimulus was increased, the EPSP increased linearly with the amplitude of the presynaptic response.4. After replacement of potassium ions in the bathing solution by caesium and during the early phase of post-tetanic facilitation there was an increase in the presynaptic response accompanied by a disproportionate increase in the EPSP.5. No changes in the presynaptic response were found in the presence of the following drugs, all of which depressed the EPSP: acetylcholine, hemicholinium, curare, further doses of ganglion-blocking agents, and high Mg(2+) and low Ca(2+) concentrations.6. Ouabain (4.5 x 10(-4)M) reversibly decreased the amplitude of the presynaptic response and increased the spontaneous release of transmitter. The EPSP was at first enhanced and then depressed.

Acetylcholine↗
PubMed1970

Diffusion of drugs through stationary water layers as the rate limiting process in their action at membrane receptors.

1. Preparations bathed in a well stirred solution have been considered as heterogeneous systems in which the solid phase is enveloped by a thin layer of stationary liquid. Any substance applied into the bulk solution must pass through this layer by diffusion before reaching the receptors.2. The rate of diffusion through the stationary layer can govern the time course of the cellular responses to applied drugs provided that (i) all receptors involved in the response are situated at an equal distance from the solution and (ii) interaction with the receptor and consequent cellular events are very rapid.3. These conditions have been verified for two responses: the contraction of guinea-pig ileum by acetylcholine (ACh), carbamylcholine (CCh), histamine and KCl, and the depolarization of the rat isolated sympathetic ganglion by ACh in the presence of eserine. A method of analysis has been applied which allows a complete dose-response curve to be obtained from only two responses.4. Diffusion half-times measured for pieces of ileum were 4.13 +/- 0.13 s (S.E. of mean) for Ach, 3.60 +/- 0.05 s for CCh and 1.01 + 0.05 s for KCl. The equivalent thickness of the stationary layer calculated from these values was respectively 93 mum, 87 mum and 70 mum. The average diffusion half-time for ACh in sympathetic ganglia was 14.19 +/- 1.05 s. This gives an equivalent thickness of 173 mum.5. Diffusion half-times were increased by increasing the viscosity of the bathing solution without changing the concentration response relationship.6. The time course of contractions of guinea-pig ileum are no longer diffusion limited in the presence of a competitive antagonist or when the temperature is lowered from 35 degrees to 25 degrees C.

Acetylcholine↗