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R Beránek

Publications and source records attributed to R Beránek.

5 recordsLinked to original sources
PubMed1970

The organization of synaptic axcplasm in the lamprey (petromyzon marinus) central nervous system.

The fine structure of synapses in the central nervous system of lamprey (Petromyzon marinus) ammocoetes has been investigated. Both synapses within the neuropil and synaptic links between giant fibers (including Müller cells) and small postsynaptic units are described. The distribution of neurofilaments and microtubules in nerve profiles over a wide diameter range is described, and the possible role of these structures in intracellular transport is discussed. Electron micrographs indicate that small lucent "synaptic vesicles" occur sparsely throughout the axoplasm and in regular arrays in association with microtubules in the vicinity of synapses. Within a synaptic focus, immediately adjoining the presynaptic membrane, vesicles are randomly arranged and are not associated with microtubules. Neurofilaments are present, generally in large numbers, but these are not associated with vesicles or other particulates. The structural findings are considered in terms of current concepts of fast and slow transport in neurons and the mechanochemical control of intracellular movement of materials.

Animals↗
PubMed1968

The effect of atropine on the frog sartorius neuromuscular junction.

1. The effect of atropine sulphate and of (+)-tubocurarine chloride (TC) on the amplitude and time course of end-plate potentials (e.p.p.s) and miniature end-plate potentials (m.e.p.p.s) was studied in the sartorius muscle of the frog.2. Atropine sulphate reduces the amplitude of intracellularly recorded e.p.p.s and m.e.p.p.s, in concentrations 100 times higher than TC (6 x 10(-5)M for 50% reduction of amplitude compared with 6 x 10(-7)M for TC).3. Atropine sulphate causes a marked shortening of both e.p.p.s and m.e.p.p.s: when the amplitude of e.p.p.s or m.e.p.p.s is reduced by 50%, their rise-time and half-decay time are both shortened by 40%. The corresponding shortening produced by TC is 15%.4. E.p.p.s prolonged by prostigmine 10(-6) g/ml. undergo a larger shortening (30%) in TC, while atropine-induced shortening related to the corresponding drop of amplitude is the same whether prostigmine is used or not.5. On repeated applications after recovery of amplitude and time course, TC loses its shortening effect on e.p.p.s while the atropine shortening effect remains unchanged.6. Atropine sulphate shortens the rise-time but not the falling phase of brief depolarizations produced by electrophoretic applications of acetylcholine (ACh) to the muscle fibre surface in the end-plate region. It also reduces their amplitude, in the same way that it reduces the amplitude of e.p.p.s.7. Atropine sulphate in concentrations which markedly reduce the amplitude and time course of e.p.p.s has no effect on their quantum content.8. Atropine sulphate at a concentration of 10(-4)M does not change the amplitude and time course of an electrotonic potential produced by a rectangular current pulse passed through the end-plate region of a muscle fibre.9. It is suggested that either enhanced removal of ACh or a spatial gradient of effectiveness of the blocking drugs, or both these mechanisms, participate in shortening the e.p.p. by atropine sulphate and TC.

Acetylcholine↗
PubMed1967

The action of tubocurarine and atropine on the normal and denervated rat diaphragm.

1. The potency with which tubocurarine chloride (TC) and atropine sulphate (AS) influence the amplitude of the end-plate potentials was measured in the rat diaphragm. This effect was compared with the action of these drugs on brief depolarizations evoked by iontophoretic application of ACh to end-plate-free spots of the chronically denervated fibre.2. TC and AS act similarly on e.p.p.s, but the concentrations necessary to cause the same effect are 2000-times higher for AS.3. The dose-response curves for both inhibitors are unchanged by prostigmine.4. Ten to twenty-five days after denervation the ACh-potentials of the sensitized end-plate-free parts of the membrane are less responsive to curare than the normal e.p.p.s are. AS is as effective in blocking ACh potentials of denervated muscles as it is in blocking normal e.p.p.s. The curare/atropine coefficient (dose ratio for equal effect) is 0.0005 for e.p.p.s and 0.003 for ACh potentials of the denervated membrane.5. Both blocking drugs reduce the amplitude of ACh-potentials evoked in the end-plate region of normally innervated rat diaphragm fibres as effectively as they reduce the amplitude of e.p.p.s.6. Neither TC nor AS have a presynaptic action in concentrations markedly reducing the e.p.p. amplitude.

Acetylcholine↗