https://pure.mpg.de/pubman/item/item_601392_3/component/file_2255622/601392.pdf

Definition of the Readily Releasable Pool of Vesicles at Hippocampal Synapses

By subjecting isolated adrenal medullary cells to intense electric fields of brief duration it is possible to gain access to the cell interior without impairing the ability of the cell to undergo exocytosis. After a single exposure to a field of 2 kV/cm, τ=200 μsec, adrenal medullary cells behave as if their plasma membrane contains two pores of effective radius 2 nm. At 37°C these ‘equivalent pores’ remain patent for up to 1 hr. The formation and stability of these ‘pores’ is not affected by the Ca content of the bathing solution. The ‘pores’ permit externally applied catecholamine and Ca-EGTA to equilibrate rapidly with the cell water.

Calcium-dependence of catecholamine release from bovine adrenal medullary cells after exposure to intense electric fields.

1. The action of adenosine on neuromuscular transmission has been studied on the rat phrenic nerve—diaphragm preparation.



2. Adenosine (0·025–10 m M) reversibly reduced the quantum content of end-plate potentials and the frequency of miniature end-plate potentials to about half the control values in preparations in which transmission was blocked with high Mg2+ and/or low Ca2+ concentrations. Where transmission was blocked with tubocurarine, the amplitude of end-plate potentials was reduced to about half the control values by adenosine.



3. In solutions with very low Ca2+ concentrations (no added Ca2+ and 1 m M-EGTA) adenosine had a smaller effect on the frequency of miniature end-plate potentials.



4. The effect of adenosine (0·025 and 0·05 m M) was abolished by theophylline (1·8 m M).



5. The results are discussed in relation to the increase in cyclic AMP in brain slices caused by adenosine and the abolition of this effect by theophylline (Sattin & Rall, 1970).

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1972.sp009916

The effect of adenosine on the release of the transmitter from the phrenic nerve of the rat

It has been found that cells in the region of the supraoptic nucleus (SON) of the hypothalamus are sensitive to osmotic stimuli in a physiological range, and have studied the mechanism by which the osmotic sensitivity arises. An in vitro hypothalamic brain slice preparation has been used to make intracellular recordings from the SON. Cells lying in the SON respond to small increases (9--40 mosmol l-1) in the osmolarity of their external environment with a marked increase in firing rate. They respond to NaCl and mannitol although not to glucose. The osmotic sensitivity of SON neurones has a complex origin at both a pre- and a postsynaptic level, being composed first of depolarization of the primary SON neurone by an increase of extracellular osmolarity and second by an increased rate of occurrence of excitatory synaptic events which markedly augment firing rate. These results are consistent with Jewell and Verney's suggestion that osmoreception in the mammalian brain occurs in the region of the anterior hypothalamus, and extends this localization by indicating that the SON neurones are themselves both directly osmosensitive and part of an osmoreceptive complex.

Supraoptic neurones of rat hypothalamus are osmosensitive

Black widow spider venom causes exhaustion of miniature end-plate activity and depletes the nerve terminal of vesicles.

Effects of Black Widow Spider Venom on the Frog Neuromuscular Junction: Effects on End-plate Potential, Miniature End-plate Potential and Nerve Terminal Spike

1. The nerve-muscle preparation of the cutaneous pectoris of the frog has been used to study quantal transmitter release.2. When the osmotic pressure of the external solution is raised 1.5-2 fold, the frequency of miniature end-plate potentials (m.e.p.p.s) rises by 1.5-2 orders of magnitude. This effect is independent of the presence of Ca(2+) ions and of the nature of the substances by which the osmotic pressure has been increased.3. In Ca(2+) free hypertonic solution the nerve impulse still invades the nerve terminals but does not alter the frequency of the m.e.p.p.s.4. The arrival of the impulse in the terminals causes an immediate increase in the rate of quantal release, provided divalent cations are present whose passage through the axon membrane is facilitated by excitation (Ca(2+), Sr(2+), Ba(2+)).5. Divalent cations which penetrate only slightly (Mg(2+), Be(2+)) lower the frequency of m.e.p.p.s and suppress the end-plate potential (e.p.p.) evoked by an impulse, in the presence of Ca(2+) ions. Be(2+) is a more effective inhibitor than Mg(2+).6. In Ca(2+) free solutions, adding Mg(2+) causes an increase in the frequency of m.e.p.p.s evoked by depolarization of the nerve endings or by treatment with ethanol.7. The trivalent cation La(3+) is more effective than divalent cations are in increasing the frequency of m.e.p.p.s. The tetravalent cation Th(4+) also raises the m.e.p.p. frequency.8. The observations summarized in paragraphs 2-7 indicate that the frequency of m.e.p.p.s at a constant temperature depends only on the concentration of uni-, di- and trivalent cations inside the nerve ending. It is suggested that the internal cation concentration influences the adhesion between synaptic vesicles and the membrane of the nerve ending.9. For a model experiment, artificial phospholipid membranes have been used to study the effect of uni-, di-, tri- and tetravalent cations on the adhesion process. At pH 7-7.4, the time required for adhesion to take place decreases with increasing cation concentration in the bath. Ca(2+) ions are 100-1000 times more effective than K(+) ions; La(3+) and Th(4+) ions are still more effective. The ;adhesion time' decreases when the pH is lowered; it increases greatly with lowering of temperature.10. The hypothesis is put forward that the mutual adhesion of artificial vesicles made of phospholipid membranes, and the adhesion between synaptic vesicles and the membrane of the nerve ending arise by a common mechanism. In both cases, the important factor is the influence of cations on the electric double layer at the membrane surface.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1968.sp008637

A study of the mechanism of quantal transmitter release at a chemical synapse

The paper presents a model of structured objects in a grayscale or color image, described by means of optimal piecewise constant image approximations, which are characterized by the minimum possible approximation errors for a given number of pixel clusters, where the approximation error means the total squared error. An ambiguous image is described as a non-hierarchical structure but is represented as an ordered superposition of object hierarchies, each containing at least one optimal approximation in g0 = 1, 2,..., etc., colors. For the selected hierarchy of pixel clusters, the objects-of-interest are detected as the pixel clusters of optimal approximations, or as their parts, or unions. The paper develops the known idea in cluster analysis of the joint application of Ward’s and K-means methods. At the same time, it is proposed to modernize each of these methods and supplement them with a third method of splitting/merging pixel clusters. This is useful for cluster analysis of big data described by a convex dependence of the optimal approximation error on the cluster number and also for adjustable object detection in digital image processing, using the optimal hierarchical pixel clustering, which is treated as an alternative to the modern informally defined “semantic” segmentation.

/pdf/a-model-of-pixel-and-superpixel-clustering-for-object-3753ze87.pdf

A Model of Pixel and Superpixel Clustering for Object Detection

Abstract. When developing modern unmanned aerial vehicle-based onboard small-sized radar systems, which are used for monitoring of coastal zones for their operational and environmental purposes, adequate mathematical models are needed of reflections from the corresponding resolution elements of the underlying surfaces, located on the water–land interface. We consider the development of some mathematical models for such applications. We analyze two modern approaches used in developing mathematical models for input signals reflected both separately from the terrestrial and marine surfaces and simultaneously from two aforementioned surfaces at once. A statistical approach and two families of distributions are chosen for modeling the signals, which enable synthesis of efficient algorithms for modeling the fluxes of random variables. The input signals of sea surface reflections are approximated by the log-normal law, while the reflections from the land surface are approximated by the Weibull distribution. For edge-coastal modeling, it is proposed to use the law of distribution of the vector sum of the flux of random variables comprising the input signals reflected from elementary land and sea areas that simultaneously fall within the corresponding resolution element. A highlight of the models developed is the consideration of both the probability distribution laws of the reflected signals and their correlation-spectral characteristics between resolution elements, as well as the anisotropy of reflections when monitoring surfaces from several angles. The presented mathematical models are consistent with experimental data sets of reflections, obtained from coastal zones. The development of coastal reflection models and corresponding modeling algorithms reduces the required number of actual field tests and saves time for implementation of monitoring systems, and hence, limits the overhead of this implementation.

Modeling of input signals reflected from coastal zones and observed by small-sized radar systems from UAVs

Algorithm for estimating the coordinates of the state of the helicopter in the onboard radar station

A method has been developed for combining radar data collected in bistatic and monostatic modes of aviation monitoring based on small-sized airborne radars (AR) of a twoposition spatially distributed system implemented on the basis of integrated radar image processing (RI). A spatially distributed system is proposed that implements monostatic and bistatic modes of formation of two radar stations of the observed territory from two different viewing angles. These two modes of radar formation are combined on the basis of the method of combining different-angle radar information, which makes it possible to increase the resolution of the resulting RI being formed, which is impossible to obtain one AR from one angle.

V. A. Nenashev

Papers

A study of the mechanism of quantal transmitter release at a chemical synapse

A Model of Pixel and Superpixel Clustering for Object Detection

Modeling of input signals reflected from coastal zones and observed by small-sized radar systems from UAVs

Algorithm for estimating the coordinates of the state of the helicopter in the onboard radar station

Combining Data from Airborne Spatially Distributed Modes of Radar Imaging in Small-Sized Airborne Radars