Biomedical subjects

T Gavrilenko

Publications and source records attributed to T Gavrilenko.

16 recordsLinked to original sources

PubMed2002

Identification of mitotic chromosomes of tuberous and non-tuberous solanum species (Solanum tuberosum and Solanum brevidens) by GISH in their interspecific hybrids.

GISH (genomic in situ hybridization) was applied for the analysis of mitotic chromosome constitutions of somatic hybrids and their derivatives between dihaploid clones of cultivated potato (Solanum tuberosum L.) (2n = 2x = 24, AA genome) and the diploid, non-tuberous, wild species Solanum brevidens Phil. (2n = 2x = 24, EE genome). Of the primary somatic hybrids, both tetraploid (2n = 4x) and hexaploid (2n = 6x) plants were found with the genomic constitutions of AAEE and AAEEEE, respectively. Androgenic haploids (somatohaploids) derived from the tetraploid somatic hybrids had the genomic constitutions of AE (2n = 2x = 24) and haploids originating from the hexaploid hybrids were triploid AEE (2n = 3x = 33 and 2n = 3x = 36). As a result of subsequent somatic hybridization from a fusion between dihaploid S. tuberosum (2n = 2x = 24, genome AA) and a triploid somatohaploid (2n = 3x = 33, genome AEE), second-generation somatic hybrids were obtained. These somatic hybrids were pentaploids (2n = 5x, genome AAAEE), but had variable chromosome numbers. GISH analysis revealed that both primary and second-generation somatic hybrids had lost more chromosomes of S. brevidens than of S. tuberosum.

Chromosomes↗

PubMed2001

Effects of maturity and training on bimanual ballistic isometric handgrip.

We studied maturity and training effects on maximal force and accuracy of force targeting during ballistic handgrips. Male right-handed nontrained adolescents (16-20 yrs.), trained adolescents (oarsmen--16-18 yrs.) and nontrained adults (21-44 yrs.) did right (R) unilateral (UL), left (L) UL handgrip and bilateral (BL) maximal ballistic handgrips. Next, they targeted 30% of maximal respective UL handgrip. We found peak force L:R ratios in adolescents significantly closer to 1 compared to nontrained adults suggesting less hemisphere dominance in adolescents, especially in trained ones. Nontrained adolescents showed smaller bilateral deficit for L hand than the other groups. Adolescents showed a significant underestimation of L hand during BL task (-4.6%), especially oarsmen (-8.7%), while adults showed neither overestimation, nor underestimation during all tasks. The disappearance of the asymmetry of bilateral deficit and L hand errors of force targeting suggest a diminution of neural cross-talk from dominant to non-dominant hand and its better estimate with maturity.

Adolescent↗

PubMed1996

Mechanically evoked cerebral potentials to sudden ankle dorsiflexion in human subjects during standing.

Mechanically evoked cerebral potentials (MECP) were studied in humans standing on a movable platform with three different stance widths. A sudden platform tilt of 4 degrees produced ankle dorsiflexion and resulted in scalp potentials of five distinct components, the earliest being a positive deflection at 35/60 ms. Their latencies have shown fairly consistent values among the three stance widths, while the amplitudes underwent some significant changes under the wide stance condition as compared with tightly close feet. These findings were interpreted as purporting evidence of altered somaesthetic afferent input from lower limbs during standing with widely apart support surface.

Adult↗

PubMed1994

Somatosensory evoked potentials modification related to isometric voluntary contraction.

Somatosensory evoked potentials were elicited by applying an electrical stimulus to the median nerve while the subjects performed a handgrip isometric contraction. Somatosensory evoked potentials (SEPs) were recorded from scalp positions C3 + 2 and C3-2. SEPs during the increase phase and decrease phase of force, and during the hold phase (period of maintenance of steady force) of isometric contraction were compared with potentials during rest. SEPs during the three phases of isometric contraction were also compared. Changes in SEP latencies were not observed. The increase or decrease phase of force and the hold phase caused suppression of the relatively late N55-P100 component when compared to rest. There was no difference in the amplitude of SEPs during the increase or decrease phase. During the hold phase the early N20-P30 component was increased when compared to the other two phases. The selective changes of SEPs during the three phases of isometric-anisotonic contraction suggested task dependence of the gating process.

Adult↗

PubMed1992

Modulation of somatosensory evoked potentials during isometric contraction in relation to hand use.

The aim of the study was to assess the effect of the hand used on the modulation of somatosensory evoked potentials (SEPs) during isometric contraction. SEPs to median nerve stimulation were assessed during dynamic (increase and decrease of force) and hold phases of isometric contractions. The experiments were carried out with the right or left hand. The changes in the SEP amplitude were found to vary with the hand used. When isometric contractions were performed by the right hand the amplitudes of the later components diminished during the dynamic phases, except for the component N140-P190 which increased. The amplitude of N55-P100 diminished during both the dynamic and hold phases. When isometric contractions were performed by the left hand the amplitudes of the early components diminished during the dynamic phases. These results show that the changes in SEP during isometric contraction depend on the hand used.

Adult↗

PubMed1991

Movement related brain potentials accompanying a non-productive voluntary action in humans.

This study assessed the effects of training and ability to execute a voluntary movement upon movement-related brain potentials (MRBPs). A self-paced thumb flexion initiated a sequence of autotriggered electrical stimuli over the median nerve that caused a twitch opposing the intended thumb extension. The MRBPs had earlier onsets during the first runs of skill acquisition than during later training sessions; they occurred earlier when they preceded a stimulus train than when they preceded a single stimulus; the onset was earlier over the vertex than over the premotor area. MRBP duration was longer during train stimulation when a voluntary effort had to be maintained against tetanic contraction. MRBP amplitude did not reflect task requirements under these experimental conditions.

Adult↗

PubMed1991

Somatosensory evoked potentials during standing posture on different support surface.

Somatosensory evoked potentials in response to stimulation of the posterior tibial nerve at the ankle were recorded during standing on stable ground or on unstable support surface (seesaw) or on support surface short in relation to foot length. During standing on the seesaw and on the short support surface a decrease in the amplitude of the early component (N32-P39) was observed. The amplitude of N49-P58 decreased during standing on the short support surface. The amplitude of the later components (N49-P58; P58-N76; N76-P117) decreased during standing on the seesaw in comparison to that during standing on the stable ground and on the short support surface. Thus, the attenuation of the cerebral potential during standing depend on the conditions for maintenance of posture.

Adult↗

PubMed1991

Spatio-temporal characteristics of SEP to tibial nerve stimulation.

Source derivation techniques have recently been applied to analyse the spatial distribution of brain potentials. Somatosensory evoked potentials (SEPs) to tibial nerve stimulation recorded at 8 sites were analysed by using 2 source derivation techniques: Laplacian and criterion, presented by Kossev et al. (1988). First SEP recorded as a function of time were averaged and thus their basic components P39, N49, P58 were enhanced. In most of the subjects these components had maximal amplitudes at Ez rather than Cz. These sites were taken as nodes and the source derivation techniques were applied for all SEP components. Spatial derivatives (potential gradients) between adjacent leads were also computed. The current density at the nodes for different time points of SEP was obtained using Laplacian technique. For the chosen electrodes places and subjects it was found that the maximal source density did not correspond always to the SEP peak amplitudes. According to the criterion used it might be supposed that the generators of P39, N49 and P58 were located close to the scalp surface. Because of the significant individual variety of the results obtained more research is needed for choosing the appropriate scalp sites and for the contribution of the base line when measuring the SEP amplitudes.

Adult↗

PubMed1990

Effect of body and foot positions on the somatosensory evoked potentials.

Somatosensory evoked potentials in response to stimulation of the posterior tibial nerve at the ankle were recorded during sitting and standing with variable foot positions. During standing a decrease in the amplitude of the early positive component was observed. The deviation of the foot from a horizontal position was associated with an increase in the amplitude of the early negative component. The combined influence of body and foot positions showed a decrease in the amplitude of both early and late components. The standing position induced changes in more components than the varied foot positions. This suggests that maintenance of the standing posture is a more complex task than the maintenance of the foot position itself.

Adult↗

PubMed1986

Somatosensory evoked potentials upon electrical stimulation triggered by voluntary movement.

The autotriggered signal was presented with a varying delay. SEP obtained without movement of the thumb (control series), SEP of autotriggered stimuli and movement-related brain potentials (MRBP) without stimuli were registered. The EEG was recorded from C3 + 2 and C3 = 2. The following results were obtained: the amplitude of all components diminished when the stimulation was autotriggered compared to the control series; the suppression was most pronounced with a stimulus delay about 150-200 ms; the effect of the suppression did not disappear up to 500 ms after the beginning of the movement.

Brain↗

PubMed1984

Changes in the Bereitschaftspotential due to subsequent voluntary autotriggered stimulus.

The Bereitschaftspotential (BP) has been studied in two different tasks: simple voluntary isometric flexion/opposition of the thumb and same movement, followed by a mild electrical shock over the median nerve, autotriggered by the movement itself. When the two tasks were organized in separate series, the subject being told about the outcome of the movement beforehand, it was found that: The BP started later; Its amplitude was smaller; The maximum negatively (N2) was smaller, when expecting electrical shock compared to simple voluntary contraction. The decrease was more pronounced over the postcentral areas. When the sequence of the autotriggered electrical shocks was equiprobably intermixed with the simple voluntary presses in single series it was found that virtually no difference existed between different potential measures. This differential influence of equal physical requirements with different subjective sequels upon the potentials related to voluntary movements implied the preferential role of the subject's attitude and state of preparedness upon the brain potentials. Both the elevated stress level and the selective suppression in specific cortical areas might take place in tasks with predictable unpleasant electrical shock.

Action Potentials↗

PubMed1980

Asymmetry of the visual evoked potentials of stimuli presented in different halves of the field and in the centre of the field.

Visual evoked potentials of nonverbal stimuli presented in the left or right visual fields, or verbal stimuli presented in the centre of the field, were studied in ten healthy right-handed subjects. The study comprised the following three series: isolated presentation of nonverbal stimuli - control study; combination of nonverbal and verbal stimuli; again isolated presentation of nonverbal stimuli. Brain evoked potentials (EP) are recorded in the occipital, associative areas of the two hemispheres and the vertex. Hemispheric differences were established in the EP of the nonverbal stimuli in the three series for the occipital regions. These differences were pronounced with respect to the latency and insignificant with respect to the amplitude. The late positive component had a shorter latency in the right hemisphere. No interhemispheric difference in the EP parameters were established for verbal stimuli, presented in the centre of the visual field. The functional interhemispheric asymmetry, assessed through the brain EP, is manifested in cases of isolated presentation of stimuli in the two halves of the visual field.

Acoustic Stimulation↗

PubMedDate not supplied

Modulation of somatosensory evoked potentials during coordination between posture and movement.

Somatosensory evoked potentials (SEPs) elicited during execution of voluntary movements undergo modification in their amplitude ('gating'). We have studies SEP changes during a motor task that includes anticipatory postural adjustment and focal movement. Upright standing subjects were performing fast forward elevation of one arm. The electrical stimulus was presented over the ipsilateral posterior tibial nerve within two different time frames: (1) preceding the EMG activity of femoral biceps muscle, known to be first in occurrence in such task; (2) during this EMG activity, yet before the EMG occurrence in anterior deltoid muscle-prime mover for the forward arm elevation. The following significant changes in SEPs preceding focal movements as compared with control SEPs during quiet stance were found: The early component P42-N50 showed a marked decrease, regardless of its time relation to the anticipatory activity in the leg. Component N50-P60 increased in amplitude, more so when elicited within an earlier time frame. Thus, diminution of amplitude as an expression of gating, was found to exist already before the occurrence of anticipatory postural adjustment activity and to persist during the ensuing focal movement.

Acoustic Stimulation↗

PubMedDate not supplied

Somatosensory evoked potentials during natural and learning rearrangements of posture accompanied by limb elevation in dogs.

Changes in the functional state of the sensorimotor cortex associated with reorganization of the natural pattern of postural rearrangement before limb elevation (the "diagonal" patten and of an artificial rearrangement (the "unilateral" pattern) were studied in dogs. The state of cortical structures on postural rearrangement was assessed in terms of the pattern of somatosensory evoked potentials produced in response to stimulation of the forelimb during postural preparation of the animal for elevating the hindlimb (acquired avoidance response to a sound signal). Evoked potentials during the natural postural preparation (the "diagonal" pattern) were compared with those during the altered pattern of postural preparation (the "unilateral" pattern), this preparation taking place prior to elevation of the limb. Controls consisted of evoked potentials in the resting state. Decreases were seen in the latencies and amplitudes of most components of evoked potentials during postural rearrangement. In general, changes in evoked potentials were less marked in the "unilateral" pattern than in the "diagonal" pattern, though the differences were significant only for the amplitude of the first negative component. Changes in evoked potentials were similar regardless of whether the supporting forces of the limb to which the test stimulus was applied increased or decreased during postural rearrangement. It is suggested that differences in evoked potentials may reflect changes in the interaction between neuronal populations within the sensorimotor cortex during reorganization of the pattern of postural rearrangement associated with learning.

Animals↗

PubMedDate not supplied

[Somatosensory evoked potentials during natural and learned patterns of postural adjustment, accompanying limb movements in dogs].

A goal of the study was to investigate cortical reorganization corresponding to inhibition of innate motor patterns during motor learning. Functional changes in the sensorimotor cortex during learned rearrangement of the natural diagonal pattern of postural adjustment (PA) accompanying a hindlimb movement into a new one, the so-called unilateral pattern, were studied in dogs by testing somatosensory evoked potentials (SEP) in response to stimulation of a forelimb during PA immediately before the limb movement onset. During PA the latency and the amplitude of several SEP components decreased. In general, changes in SEP were less pronounced in the learned unilateral pattern of postural adjustment in comparison with the innate diagonal pattern, but the difference was significant only for some SEP components. The SEP late positivity in the learned postural pattern was replaced by a negativity. The SEP changes were similar independently of whether the test stimulus was applied on the forelimb loaded or unloaded during postural adjustment. The data suggest that changes in interrelations between different neuronal populations in the sensorimotor cortex during formation and realization of a learned motor program can be reflected in SEP changes.

Animals↗

PubMedDate not supplied

Somatosensory evoked potentials during compound thumb movement.

The aim of the study was to assess the influence of a biphasic flexion-extension movement upon somatosensory evoked potentials (SEPs). Voluntary thumb flexion initiated a sequence of either single or single PLUS sustained electrical stimulation upon the median nerve. In cases of sustained stimulation the subjects had to overcome the induced tetanic thumb flexion. During movements the latencies of early components were longer compared to rest; during simple movements the amplitudes of most components were diminished compared to rest; the amplitudes of early components were further diminished in movements against tetanic contraction compared to simple ones; the suppression of SEP amplitudes was similar regardless of possibility to overcome the opposing tetanic contraction; the changes in SEP amplitudes were not dependent on training.

Adult↗