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Biomedical subjects

M E Varga

Publications and source records attributed to M E Varga.

At least 19 recordsLinked to original sources
PubMed1990

[The dynamic changes in somatosensory input into the cortical motor area after damage to the somatosensory cortical zones in dogs].

Dynamics of changes in the somatosensory evoked potentials (EPs) in the foreleg motor cortex (MI) was studied in awake dogs in chronic experiments following lesions of the forelimb area in the somatosensory cortex (SI) or in area 5. Cortical ablations reduced the amplitude of the primary positive-negative wave of the EPs in ipsilateral MI down to 28-63% of the original one. Within three weeks recovery of the EPs was insignificant or was absent at all. So there was no correlation between the EPs changes and spontaneous recovery of precise avoidance movements of the foreleg which takes place two weeks after local ablation of the SI. After area 5 lesion the EPs in the MI did not recover in spite of complete recovery of the EPs in the adjoining area of SI after its initial reduction down to 53%. The long-lasting EPs reduction was apparently a result of destruction of somatotopic sensory inputs from SI (or area 5) to MI, since EPs in MI of the intact hemisphere and in the hindlimb area of MI on the side of the lesion either did not change or recovered during one or two weeks.

Animals↗
PubMed1982

The number of consecutive clicks in the train as positive or differential conditioned stimulus in dogs.

Conditioned reflexes were elaborated to trains of identical signals (clicks) of a constant number with variable interstimulus interval. The negative conditioned stimulus differed from the positive one only by the number of elements in the train. In classical defensive conditioned reflexes the latent period of motor conditioned responses to the positive stimulus was shorter than to the negative one. There were differences in the latent periods and in the speed of running to the feeding box to the positive and negative stimuli when alimentary instrumental reflexes were elaborated. The dogs ran faster to the feeding box after the positive stimuli. In 30 percent of the total number of negative stimulus presentations they did not run to the feeding box at all. There was no correlation between the reaction parameters and duration of the trains. These parameters correlate only with the number of elements in the train. Experimental data suggest that the quantitative assessment of signal trains effected in the dogs’ central nervous system, i.e. the simple count of elements may be used in its adaptive behavior.

Animals↗
PubMed1974

"Counting" of clicks, as reflected in amplitude of potentials evoked in auditory cortex of the dog.

In eight dogs with chronically implanted electrodes click-evoked potentials were recorded in the ectosylvian and suprasylvian gyri. During daily sessions clicks were presented in several short trains with a steady interclick interval of 1 s and not followed by any unconditional stimulus. The largest amplitudes resulted from the first and last clicks in the series so that curves plotted for each series assumed a U-shape. Changing the intensity or interclick interval disrupted this pattern.

Acoustic Stimulation↗
PubMedDate not supplied

Physiological role of GlpB of anaerobic glycerol-3-phosphate dehydrogenase of Escherichia coli.

Anaerobic sn-glycerol-3-phosphate dehydrogenase of Escherichia coli is encoded by an operon of three genes, glpACB. The promoter distal gene, glpB, encodes a 44-kilodalton polypeptide that is not part of the purified soluble dehydrogenase. By recombinant plasmid complementation, in a strain harboring a chromosomal deletion of glpACB, we found that all three genes were essential for anaerobic growth on glycerol-3-phosphate (G3P). By isolation of inner membrane preparations we confirmed the cytoplasmic membrane localization of GlpB. GlpB displayed an electron paramagnetic resonance spectrum that suggested the presence of iron-sulfur center(s) within GlpB. We used this spectrum to show that the center(s) were reduced by the artificial reductant dithionite and by the physiological substrate G3P but not by lactate or formate. The center(s) were oxidized by fumarate. These data indicated that GlpB mediates electron transfer from the soluble GlpAC dimer to the terminal electron acceptor fumarate via the membrane-bound menaquinone pool.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

[Forward and backward conditioning].

A discussion. The evolution of the concept of the forward and backward conditioning is traced. An attempt to define more precisely the widely distributed term such as a "feedback", is made.

Animals↗
PubMedDate not supplied

[Changes in evoked potentials during systematic exposure to a series of similar signals with variable intersignal intervals].

Series of clicks, standard by the number of stimuli and greatly varying by the length of interstimuli intervals in each series, were systematically presented to dogs without reinforcement. Evoked potentiale (EP) in the cortical auditory zone were recorded. It has been found that a typical U-shaped distribution of amplitude values of averaged EP is elaborated in the series in the course of repeated presentations; a maximal amplitude is observed in response to the first and last clicks, and a minimal, in the middle of the series. Such a regularity was previously found for the action of standard series with a constant interstimuli interval. It is assumed that an estimation may take place in the dog CNS of the number of signals used in a series, whose mechanism is not necessarily based on the time factor. The ability to estimate the number of signals in the series may be regarded as an elementary model of counting in the dogs' CNS.

Acoustic Stimulation↗
PubMedDate not supplied

[Evoked potentials in the auditory cortex with systematic use of standard series of stimuli on the internal geniculate body].

Standard series of short electrical stimuli of the medial geniculate body were systematically applied to dogs with chronically implanted electrodes. Gradual formation was observed of a dependence of amplitudes of averaged EPs in the auditory cortex on the consecutive place of the stimulus in the series. This points to the existence in the dog's central nervous system of an elementary form of counting not only adequate signals, as has been previously shown, but also electrical stimuli of the thalamic nucleus. In contrast to what was observed in response to clicks, the EPs amplitude of MGB electrical stimulations increases by the middle of the series and diminishes by its end. It has been assumed that the cortical level of the analyser to which the stimulation was applied, suffices for the formation of the above phenomenon.

Animals↗