A kinetic model for magnetostriction of a ferrogel with physical networking.

Kinetics of magnetostriction of ferrogel with physical networking based on natural polysaccharide guar gum with embedded strontium hexaferrite magnetic particles were studied in the uniform magnetic field 420 mT. An ellipsoidal sample was elongated by 37% along the applied field and contracted by 15% in the transverse direction, while its volume was kept constant. The characteristic time of magnetostriction was 440 s. Dynamic mechanical analysis in an oscillatory mode showed that the deformation of ferrogel is mostly elastic rather than viscous. Its storage modulus was almost constant in a frequency range of 0.1-100 Hz and by at least an order of magnitude larger than the loss modulus. Meanwhile, a developed theoretical model based on the elasto-viscous behaviour of the ferrogel failed to estimate correctly the experimental value of its magnetostriction. Calculated values of the elongation of ferrogel in the field were several orders of magnitude lower than those observed in the experiment for the ferrogel with physical networking. Consistency between the experiment and the theory was achieved using the alternative consideration based on the deformation of a liquid droplet of ferrofluid. The applicability of such an approach was discussed concerning structural relaxation properties of the ferrogel with physical networking. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.

[Functional asymmetry of electric processes in the rabbit brain cortex at formation of the hunger dominant].

The motivational condition of hunger and formation of the hunger dominant after daily food deprivation was studied in the conditions of chronic experiments on rabbits. It was shown, that the hunger condition was accompanied by left sided interhemispher asymmetry on indicators of spectral capacity of EEG frontal and right-hand asymmetry sensorimotor areas of the cortex. A hunger dominant was accompanied by falling of spectral capacity of EEG of areas of both hemispheres. The condition of hunger and a hunger dominant were characterized by right-hand asymmetry on average level of EEG coherence of frontal and sensorimotor areas. At transition of a condition of hunger in a hunger dominant there was an average level of EEG coherence decrease in areas of the right hemisphere. Electric processes of the cortex of the brain at a motivational condition of hunger and a hunger dominant were different.

[Experimental evidence for simultaneous existence of two dominantas in the central nervous system].

For the first time a possibility of simultaneous existence of two dominants was demonstrated: the polarization in the cortical representation of the forelimb and the dominanta of hunger. The two foci of stable excitation were created at the subthreshold level. A sound stimulus simultaneously produced a movement of the forelimb and a gulp. Manifestation of the two dominantas could be observed over the course of the experiment (about 1 h).

[Interaction of stationary excitation foci in the rabbit brain].

Influence of "animal hypnosis" on the motor polarization dominanta created by direct anodic current applied on the left sensorimotor cortex of the rabbit ("left" dominanta) was studied in chronic experiments. Animal behavior and electrophysiological characteristics were recorded. It was impossible to elicit the "animal hypnosis" during the optimum of the "left" dominanta. The state of "animal hypnosis" could be easily elicited against the background of the latent focus of the "left" dominanta on the next day after its formation. The "animal hypnosis" restored the "left" dominanta after its extinction. It was accompanied by formation of a new pattern of the cortical EEG coherence in the delta range, which was different from the patterns characteristic of each kind of dominanta. After the "animal hypnosis" session, the formation of the "left" dominanta produced two kinds of nonstable foci. During testing, the "left" dominanta reached its optimum and then inhibited the tonic activity of the right forelimb characteristic of the "animal hypnosis". The interaction of the "animal hypnosis" and the dominant foci in the left and right sensorimotor cortex were different.

[The dynamics of modification of electrical activity of the rabbit brain during consistent "animal hypnosis" series].

The dynamics of modification of individual rhythms of electrical activity in both hemispheres was studied under condition of chronic experiments in rabbits during "animal hypnosis" sessions. It was shown that, after the first "animal hypnosis" session, significant changes in the spectral power of electrical activity appeared only in the right premotor cortical area. They consisted in an increase in the spectral power of the delta1 and delta2 rhythms and a decrease in the spectral power of the other rhythms. During the next "animal hypnosis" sessions, changes in the electrical activity became stronger, especially in the right hemisphere. Significant changes in the spectral power of the delta and theta rhythms appeared not at the beginning of the "animal hypnosis" session but 4-6 min later. During the third "animal hypnosis" session, the power of the alpha and beta rhythms in the premotor and sensorimotor cortical areas of both hemispheres varied in an undulatory way.

Intrasteric inhibition of ATP binding is not required to prevent unregulated autophosphorylation or signaling by the insulin receptor.

Receptor tyrosine kinases may use intrasteric inhibition to suppress autophosphorylation prior to growth factor stimulation. To test this hypothesis we made an Asp1161Ala mutant in the activation loop that relieved intrasteric inhibition of the unphosphorylated insulin receptor (IR) and its recombinant cytoplasmic kinase domain (IRKD) without affecting the activated state. Solution studies with the unphosphorylated mutant IRKD demonstrated conformational changes and greater catalytic efficiency from a 10-fold increase in k(cat) and a 15-fold-lower K(m ATP) although K(m peptide) was unchanged. Kinetic parameters of the autophosphorylated mutant and wild-type kinase domains were virtually identical. The Asp1161Ala mutation increased the rate of in vitro autophosphorylation of the IRKD or IR at low ATP concentrations and in the absence of insulin. However, saturation with ATP (for the IRKD) or the presence of insulin (for the IR) yielded equivalent rates of autophosphorylation for mutant versus wild-type kinases. Despite a biochemically more active kinase domain, the mutant IR expressed in C2C12 myoblasts was not constitutively autophosphorylated. However, it displayed a 2.5-fold-lower 50% effective concentration for insulin stimulation of autophosphorylation and was dephosphorylated more slowly following withdrawal of insulin than wild-type IR. In tests of the regulation of the unphosphorylated basal state, these results demonstrate that neither intrasteric inhibition against ATP binding nor suppression of kinase activity is required to prevent premature autophosphorylation of the IR. Finally, the lower rate of dephosphorylation suggests invariant residues of the activation loop such as Asp1161 may function at multiple junctures in cellular regulation of receptor tyrosine kinases.

An aromatic stacking interaction between subunits helps mediate DNA sequence specificity: operator site discrimination by phage lambda cI repressor.

Sequence specific DNA binding by regulatory proteins provides the basis for regulation of initiation of transcription. A great deal of progress has been made toward understanding sequence specific recognition by individual protein subunits. An additional level of control that needs to be understood is that due to coupling between the subunits of oligomeric regulatory proteins. An example is the bacteriophage lambda cI repressor, a dimeric protein that regulates the lysogenic to lytic genetic switch of the phage. Two levels of specificity are critical to this regulation. First, like all transcriptional regulators, dimers distinguish operator from nonspecific DNA. Direct readout of the DNA sequence by the recognition helix is considered the well understood mechanism for this. However, differential affinity for O(R)1, O(R)2 and O(R)3 is equally critical to the switch because it mediates opposing regulation of divergent promoters. Site specificity at this second level is less well understood. Conformational adaptation by both the repressor and the different operators appears to be important. To evaluate how subunit-subunit interactions are involved in this process, we investigated the effects on both dimer stability and operator binding of amino acid substitutions at the contacts between the symmetrically related helices-5 in the dimer interface. Substitutions for Tyr88 alter dimer stability and greatly perturb differential operator affinity, but generally do not affect operator versus non-operator specificity. The pattern of these effects suggests that the geometry of the face-to-face aromatic stacking interaction between symmetrically related Tyr88 in each subunit, a group in the dimer interface but far removed from the DNA binding interface, plays a critical role in operator discrimination. Conformational changes in the tertiary structure of the subunits appears to be involved. By contrast, the significant effect of I84S substitution is to greatly decrease affinity for all three operators. Presumably, the altered packing of the dimer interface causes a quarternary structural change that moves the two helix-turn-helix motifs out of register with successive DNA major grooves.

The influence of the stimulation of the CA3 field of the dorsal hippocampus on the motor polarization dominant in rabbits.

The influence of the stimulation of the CA3 field of the dorsal hippocampus on the course of a motor polarization dominant produced by the action of a constant current on the sensorimotor area of the rabbit cortex was investigated. It was demonstrated that stimulation of the hippocampus by a 1 mA current (0.5 msec; 100 Hz; 0.2 sec) against the background of the optimum of the dominant elicits its [the dominant's] inhibition, which is manifested in the suppression of the motor "dominant" reaction of the forelimb in response to test stimuli, and in the abolition of the coherent associations of the theta-range electrical activity of the sensorimotor cortex and the CA3 field of the dorsal hippocampus. On the other hand, stimulation of the hippocampus with a weak current (30-50 microA; 0.5 msec; 30 Hz; 0.2 sec) at the optimum of the dominant reinforces it [the dominant], eliciting a movement of the "dominant" extremity, and against the background of an unstable dominant promotes it activation and stabilization and restores the dominant in the following days during its extinction.

Effect of stimulation of the medial geniculate body on the motor polarization dominant in rabbits.

Studies were carried out on the effects of stimulation of the medial geniculate body on the course and recovery of a cortical motor polarization dominant created in the sensorimotor cortex of the right hemisphere in rabbits. Stimulation of the medial geniculate body, on a background of an optimum dominant, elicited a movement response of the "dominant" limb. Spectral-coherent analysis of the electrical activity of the sensorimotor cortex and medial geniculate body showed that stimulation produced changes characteristic of the dominant state in the power spectra of the total activity of these structures of the right "dominant" half of the brain, as well as in the coherence spectra.

A spectral correlation analysis of the electrical activity of the sensorimotor cortex and the medial geniculate body in the presence of a motor polarizational dominant.

The dynamics of the changes in the structure of the coherence relationships of the electrical activity of the sensorimotor cortex and the medial geniculate body (MGB) of the rabbit in the presence of a motor polarizational dominant created by the action of a direct current anode on the region of the sensorimotor cortex were investigated by the method of spectral correlation analysis. It was demonstrated that, in addition to an increase in the components of the delta range in the interstimulus intervals in the presence of a dominant, a clear maximum in the alpha rhythm range in the electrical activity of the MGB of the "dominant" hemisphere appears in the power spectra of the electrical activity of the MGB during the action of an acoustic signal. An increase in the coherence of the delta range of the electrical activity of the MGB and of the sensorimotor cortex in the "dominant" half of the brain is manifested exclusively in the period of action of the acoustic stimulus.

Influence of "animal hypnosis" on the motor polarizational dominant in rabbits.

The influence of the state of "animal hypnosis" in rabbits on the course and preservation of the motor polarizational dominant created by the action of a direct current anode on the region of the sensorimotor cortex was investigated. The mechanogram of both forelimbs was recorded. It was demonstrated that the state of "animal hypnosis" induced against the background of the optimum of the dominant inhibits the motor reaction of the "dominant" limb to sensory test stimuli. This inhibition is maintained for a long time, up to two to four days. The motor polarizational dominant does not extinguish under the influence of "animal hypnosis," but is inhibited; after the extinction of the traces of the "hypnosis," the motor dominant reaction recovers under the influence of sensory test stimuli alone, without the repeated use of the direct current.

The structure of cortical-subcortical relationships between electrical processes of the brain during a motor polarization dominant.

Coherence analysis of electrical activity was applied to chronic experiments on rabbits and showed that the formation of a motor polarization dominant, created by the action of an anodic direct current applied to the sensorimotor cortex, evoked a general rearrangement of the structure of cortical-subcortical relationships between electrical processes not only in the "dominant," but also in the opposite half of the brain. Zones of primary excitation foci became isolated in the cortex of the "dominant" hemisphere, with a reduction in their coherent electrically active connections, in the delta range, with other areas of the cortex. In conditions of an optimal dominant, interstimulus intervals showed asymmetry in delta-range coherence in the electrical activity of the sensorimotor cortex and the ventrolateral nucleus of the thalamus and field CA3 of the hippocampus of the "dominant" and "non-dominant" halves of the brain, which was increased in response to sound stimuli. Asymmetry in the alpha and beta ranges of coherence spectra for the electrical activity of the areas studied, coinciding with the performance of a motor "dominant" response, was associated with the processes involved in organizing the movement.

[Effect of stimulation of field CA3 in the dorsal hippocampus on the motor polarization dominant in rabbits]. / Vliianie stimuliatsii polia CA3 dorzal'nogo gippokampa na dvigatel'nuiu poliarizatsionnuiu dominantu u krolikov.

The influence was studied of the stimulation of the CA3 field of the dorsal hippocampus on the course of motor polarization dominant created by the action of the direct current on the rabbit's cortical sensorimotor area. It is shown that hippocampus stimulation by 1 mA current (0.5 ms, 100 Hz, 0.2 s) against the background of the dominant optimum elicits its inhibition. It is manifested in depression of the motor "dominant" reaction of the forelimb to testing stimuli and in abolition of coherent connections of theta-range electrical activity of the sensorimotor cortex and CA3 field of the dorsal hippocampus. On the contrary, the hippocampus stimulation by a weak current (30-50 mcA, 0.5 ms, 30 Hz, 0.2 s) during optimum dominant reinforces it, eliciting a movement of the "dominant" limb. Against the background of an unstable dominant it provides for its activation and stabilization and recovers the dominant in the following days during its extinction.

[Coherent analysis of the EEG during development of trace processes of the polarization dominant in the rabbit]. / Kogerentnyi analiz EEG pri razvitii sledovykh protsessov poliarizatsionnoi dominanty u krolikov.

By the method of spectral-correlation analysis, the dynamics was studied of changes in intercentral relations of electrical activity in the sensorimotor and premotor cortices of both cerebral hemispheres during formation, course, recovery and extinction of motor dominant created by a single action of DC anode in rabbits sensorimotor cortex. The motor dominant is capable to be preserved during the test for a long time after DC switching off and to recover in subsequent days under the action of testing stimuli. It should be noted that the recovery of the structure of intercentral relations of electrical brain activity, characteristic of dominant state, takes place much earlier than the motor "dominant" reaction.

[Intercentral relations of the electrical processes of the rabbit brain with a polarization dominant]. / Mezhtsentral'nye otnosheniia élektricheskikh protsessov mozga krolika pri poliarizatsionnoi dominante.

The dynamics of changes in intercentral relations of electrical activity of the sensorimotor and premotor zones of both hemispheres and the ventroposterolateral (VPL) nucleus of the left and right thalamus at formation of motor dominant under the action of the DC anode in the rabbit sensorimotor cortex was studied by the method of spectral-correlation analysis. It is shown that in the much less than dominant much greater than motor analyzer (the sensorimotor cortex and VPL) highly coherent connections of electrical processes are formed in the delta-range with conjugated lowering of biopotential connections between the structures of the motor analyzer of the much less than nondominant much greater than part of the brain. At the same time differently directed connections of electrical processes are formed between the structures of the motor analyzer, and between the premotor cortex and focus area. Thus, during formation of the much less than polarization much greater than dominant, a new structure of the intercentral relations of electrical processes is established not only in the much less than dominant much greater than but also in the other half of the brain.

[A spectral-correlational analysis of the electrical activity of the sensorimotor cortex and the internal geniculate body during a motor-polarization dominant]. / Spektral'no-korreliatsionnyi analiz élektricheskoi aktivnosti sensomotornoi kory i vnutrennego kolenchatogo tela pri dvigatel'noi poliarizatsionnoi dominante.

By spectral-correlative analysis the dynamics was studied of structural changes of coherent relations of the electrical activity of the sensorimotor cortex and medial geniculate body (MGB) of the rabbit under motor polarization dominant created by the action of DC anode on the sensorimotor cortex area. It was shown, that in the power spectra of the MGB, besides the increase of the delta-region components in interstimulus intervals at the dominant, during the action of the sound stimulus a distinct maximum appeared in the alpha-rhythm range of the electrical activity of MGB of the "dominant" hemisphere. The coherence increase of the delta-range of the MGB and the sensorimotor cortex electrical activity in the "dominant" part of the brain was manifested exclusively in the period of sound stimulus action.

[The effect of "animal hypnosis" on the motor polarization dominant in rabbits]. / Vliianie "zhivotnogo gipnoza" na dvigatel'nuiu poliarizatsionnuiu dominantu u krolikov.

Influence of "animal hypnosis" on the process of development of motor polarization dominant created by the action of DC anode on the cortical sensorimotor area was studied in rabbits. It was shown that "animal hypnosis" induced at the dominant optimum elicited long-term (up to 2-4 days) inhibition of motor reaction of the "dominant" limb to sensory test stimuli. Motor polarization dominant was inhibited rather than eliminated by the "animal hypnosis", since after extinction of trace processes of "animal hypnosis" the motor "dominant" reaction could be recovered solely by the test stimuli without repeated DC application.

[The effect of "animal hypnosis" on the motor dominant created by the action of direct current on the cortex of the left hemisphere]. / Vliianie "zhivotnogo gipnoza" na dvigatel'nuiu dominantu, sozdannuiu deistviem postoiannogo toka na koru levogo polushariia.

The state of "animal hypnosis" in rabbits was created by the DC current anode applied to the sensorimotor cortical area of the left hemisphere. It was impossible to elicit the "animal hypnosis" during the optimum of the dominant. The state of "animal hypnosis" could be easily elicited against the background of weak motor dominant on the next day after its creation. The "animal hypnosis" restored the "left" motor dominant after its extinction.

[Role of intervals between "conditioned" and "unconditioned" stimuli during elaboration of a cellular analog of a temporary connection]. / Rol' intervalov mezhdu "uslovnym" i "bezuslovnym" stimulami pri vyrabotke kletochnogo analoga vremennoi sviazi.

A cellular model of temporary connection was used to study the effect of intervals between stimulation of ventrobasal thalamic complex (conditioned stimulus) and local activating polarization (unconditioned stimulus) on plastic changes in the neuronal responses of sensorimotor cortex inalert rabbit. It was found that a prolongation of the interval between paired stimuli from 0 to 150 msec. produced a decrease from 60 to 28 per cent in the number of neurones in which after pairings the responses to the conditioned stimulus underwent significant plastic rearrangments. Inspite of the general trend each cell has its own optimal interval between combined stimuli where changes are most pronounced. The fact that rearrangments in cellular responses occur in a time interval corresponding to reinforcement in pairings supports the idea about a selective increase in the efficiency of those excitatory synapses that were activated simultaneously with the cell discharge.

[The structure of the cortical-subcortical relationships of the cerebral electrical processes during a motor polarization dominant]. / Struktura korkovo-podkorkovykh otnoshenii élektricheskikh protsessov mozga pri dvigatel'noi poliarizatsionnoi dominante.

Under conditions of rabbit chronic experiments, it was shown by means of the spectral-coherence analysis that the motor polarization dominant formed by the application of DC anode to the sensorimotor cortex produced a novel structure of the intercentral relations between electrical processes not only in the ipsi-, but in the contralateral brain hemisphere. A certain "isolation" of the primary focus was observed in the cortex of the "dominant" hemisphere, which was manifested in a decrease in its delta-range coherent relations with the other cortical areas. At the dominant optimum (in interstimulus intervals), an interhemispheric asymmetry in the EEG coherence spectra was observed in the delta band between the sensorimotor cortical areas, ventroposterolateral thalamic nuclei, and CA3 fields of the dorsal hippocampi. The asymmetry increased during the testing auditory stimulation. Development of the alpha- and beta-band interhemispheric asymmetry in the structures in question coincided with realization of the motor "dominant" reaction and was suggested to be associated with movement organization.