Hopfions emerge in ferroelectrics.

Paradigmatic knotted solitons, Hopfions, that are characterized by topological Hopf invariant, attract an intense attention in the diverse areas of physics ranging from high-energy physics, cosmology and astrophysics to biology, magneto- and hydrodynamics and condensed matter physics. Yet, while being of broad interest, they remain elusive and under-explored. Here we demonstrate that Hopfions emerge as a basic configuration of polarization field in confined ferroelectric nanoparticles. Our findings establish that Hopfions are of fundamental importance for the electromagnetic behavior of the nanocomposits and can result in advanced functionalities of these materials.

Changes in the spike activity of neurons in the ventrolateral nucleus of the thalamus in humans during performance of a voluntary movement.

The responses of neurons in the ventrolateral nucleus (VL) of the thalamus were studied in humans during performance of voluntary motor tests; recordings were made with microelectrodes during stereotaxic operations in patients with Parkinson's disease. Two previously classified types of polyvalent neurons (A, B) were found to show different patterns of responses during the functional stages of carrying out a voluntary movement (preparation, initiation, performance). A and B neurons showed concordant changes in the dynamics of ongoing network activity in the form of linked (activation-inhibition) and synergic (activation) response patterns, correlating with the preparation-trigger and performance phases of movements. It is suggested that the simultaneous activity of both types of neuron, with their common functional nature, reflects integrative processes occurring in the ventrolateral nucleus and associated with programming and processing of general signal parameters but not with the performance of any particular movement. The anterior (Voa nucleus) and posterior (Vop) parts of the ventrolateral nucleus were found to have different roles in organizing voluntary movements, associated with differences in their cellular organization and mechanisms of transmitting motor signals. It is suggested that the concordant changes in the activities of the two types of neurons in these areas seen during the performance of voluntary movements gives the ventrolateral nucleus a key role in the motor control system in humans.

Analysis of evoked activity patterns of human thalamic ventrolateral neurons during verbally ordered voluntary movements.

In the human thalamic ventralis lateralis nucleus the responses of 184 single units to verbally ordered voluntary movements and some somatosensory stimulations were studied by microelectrode recording technique during 38 stereotactic operations on parkinsonian patients. The tests were carried out on the same previously examined population of neurons classified into two groups, named A- and B-types according to the functional criteria of their intrinsic structure of spontaneous activity patterns. The evaluation of the responses of these units during functionally different phases of a voluntary movement (preparation, initiation, execution, after-effect) by means of the principal component analysis and correlation techniques confirmed the functional differences between A- and B-types of neurons and their polyvalent convergent nature. Four main conclusions emerge from the studies. (1) The differences of the patterns of A- and B-unit responses during the triggering and the execution phases of a voluntary movement indicate the functionally different role of these two cell types in the mechanisms of motor signal transmission. (2) The universal non-specific form of anticipatory A- and B-unit responses during the movement preparation and initiation of various kinds of voluntary movements reflect the integrative "triggering" processes connected with the processing and programming of some generalized parameters of a motor signal and not with the performance of a certain forthcoming motor act. (3) The expressed intensity of these "triggered" non-specific processes in the anterior parts of the ventralis lateralis nucleus indicates their relation not only to the motor but to the cognitive attentional functions forming a verbally ordered voluntary movement. (4) The appearance of the transient cross-correlations between the activities of adjacent A- and B-cells and also the synchronization of their 5 +/- 1 Hz frequency during and/or after motor test performances point to the contribution of these two populations to central mechanisms of the voluntary movement and the parkinsonian tremor. The functional role of two A- and B-cell types is discussed with references to the central mechanisms of verbally ordered voluntary movements and the parkinsonian tremor.

Purine nucleotide levels in host tissues of Ehrlich ascites tumor-bearing mice in different growth phases of the tumor.

The pool sizes of purine nucleotides, nucleosides, and nucleobases were measured in the host tissues liver, skeletal muscle, and blood of Ehrlich ascites tumor-bearing mice during the different periods of tumor growth. There were large differences of tissue concentrations of these metabolites between control animals, animals in the logarithmic growth period of the Ehrlich ascites tumor, and animals in the resting phase of tumor growth. The ATP concentrations in liver, muscle, and erythrocytes were higher during the proliferating phase of the tumor compared with the ATP levels of these organs in healthy animals. In liver and skeletal muscle the ATP concentration decreased during the transition from proliferating into resting phase of tumor growth. The concentrations of nucleosides and nucleobases within the RBC and blood plasma deceased during the logarithmic growth phase but restored during the plateau period. As well as in the organs/cells investigated and in the body fluids (plasma, ascites fluid) a tremendous increase of adenosine concentration during the resting phase of tumor growth was observed. From changes of total purine ribonucleotide pattern an activation period in the nucleotide metabolic pathways of liver and skeletal muscle during the proliferating phase of tumor growth is postulated.

Changes of nucleotide patterns in liver, muscle and blood during the growth of Ehrlich ascites cells: application of the reversed-phase and ion-pair reversed-phase high-performance liquid chromatography with radial compression column.

The pool of purine compounds was analysed in liver, skeletal muscle and blood of mice during the growth of Ehrlich ascites tumour cells. Three fast isocratic high-performance liquid chromatographic methods were used. (1) Determination of nucleotides by an isocratic ion-pair reversed-phase chromatography with a 10 mM ammonium phosphate buffer containing acetonitrile and tetrabutylammonium phosphate. (2) Separation of nucleosides and nucleobases in cell extracts by a reversed-phase system with methanol and 50 mM potassium phosphate buffer as eluent. (3) Nucleosides and nucleobases in body fluids were analysed by a reversed-phase system with 10 mM potassium phosphate containing methanol. These methods allow the rapid determination of purine compounds in small biological samples from various cell types and body fluids, with high accuracy and sensitivity. The pool of cellular nucleotides increased during the exponential phase of tumour growth. Adenosine accumulated significantly in all tissues in the stationary phase of tumour growth.

The catabolism of endogenous adenine nucleotides in rat liver mitochondria.

The degradation of intramitochondrial adenine nucleotides to nucleosides and bases was investigated by incubating isolated rat liver mitochondria at 37 degrees C under non-phosphorylating conditions in the presence of oligomycin and carboxyatractyloside. Within 30 min the adenine nucleotides were degraded by about 25 per cent. The main products formed were adenosine and inosine the contents of which increased five- to sevenfold. Compartmentation studies revealed that about 50 to 60 per cent of the adenosine formed remained inside the organelles whereas inosine was almost completely released into the surrounding medium. Outside the mitochondria only very small amounts of adenine nucleotides were detected. Similar incubations in the presence of [14C]-adenosine yielded no [14C]-inosine ruling out extramitochondrial adenosine deamination. It is concluded that endogenous adenine nucleotides can be degraded in mitochondria via AMP dephosphorylation and subsequent adenosine deamination. A purine nucleoside transport system mediating at least the efflux of inosine from the mitochondria is suggested.

Metabolism of purine and pyrimidine compounds in erythrocytes of tumor-bearing mice.

The pattern of purine and pyrimidine derivatives was studied in the erythrocytes of C3HA and ICR mice during Hepatoma 22 and Ehrlich ascites tumor cell growth. Concentrations of purine nucleotides, nucleosides and nucleobases of host erythrocytes were changed after the implantation of the tumors. The host erythrocytes markedly concentrated adenine and guanine nucleotides both during logarithmic and plateau phase of tumor growth (5th and 11-12th days after inoculation of the tumor). The contents of nucleosides and nucleobases in the red blood cells were decreased during the logarithmic growth phase but restored within the plateau phase.

Mitochondrial metabolism of guanine nucleotides. Possible role of guanosine.

The catabolism of intramitochondrial guanine nucleotides was examined. During 30 min incubation of rat liver mitochondria at 37 degrees C in the presence of oligomycin and carboxyatractyloside, guanine and xanthine were formed and appeared in the medium. Under these conditions, the direct conversion of GMP to guanine by hypoxanthine-guanine phosphoribosyltransferase is suggested to be the main catabolic route within the organelles. Only very small amounts of guanosine were produced and detected both inside and outside the organelles. [14C]Guanosine and [14C]inosine were taken up by the mitochondria. Therefore, guanosine is suggested to be a precursor of intramitochondrial guanine nucleotides.

Optimization of the ion-pair high-performance liquid chromatographic separation of purine derivatives in erythrocytes, thymocytes and liver mitochondria.

Various methods are described for the analysis of purine derivatives in biological samples by ion-pair high-performance liquid chromatography (HPLC) with both gradient and isocratic systems. A new approach is proposed that is suitable for the separation of nuclei acid constituents in different cells with a specific enzymatic activity pattern. The ion-pair HPLC methods were developed for the analysis of erythrocytes, lymphocytes and mitochondria acid-soluble fractions in clinical and experimental studies of normal and altered nucleotide metabolism. The results of studies of purine metabolite redistribution in mouse liver mitochondria during a 30-min incubation at 37 degrees C and data on purine metabolic alterations in mouse thymocytes during hepatoma growth are discussed.

Determination of nucleotides, nucleosides and nucleobases in cells of different complexity by reversed-phase and ion-pair high-performance liquid chromatography.

Procedures are presented for the analysis of profiles of purine and pyridine compounds in human and rabbit red blood cells by reversed-phase high-performance liquid chromatography and in Ehrlich ascites tumour cells of mouse by ion-pair high-performance liquid chromatography. These compounds are present in rabbit erythrocytes in higher concentrations than in human blood cells, and in rabbit reticulocytes the concentration of purine compounds is still higher. During glucose-free incubation, human red cells accumulate adenosine and adenine in the presence of coformycin owing to the inhibition of adenosine and AMP deamination. Ehrlich ascites tumour cells lose major portions of purine mono-, di- and triphosphates between the seventh and eleventh day after inoculation into mouse peritoneal cavities.