Neirofiziologiia = Neurophysiology最新文献

Focused ultrasound has been used to induce the following skin sensations: tactile and temperature ones; specific and unspecific pain, underskin or deep sensations: tactile sensations and some varieties of pain (muscle, periosteum and so on). It has been established that: somatic reception is attributed to mechanoreception; the same receptive structures are cold and warm ones; ultrasound has the sensibilized action. Sensation differences of corporal and auricular acupuncture points and some accidental skin underskin spots have been investigated.

The phenomenon of repetitive firing (RG) in motor nerve endings induced by 4-aminopyridine (4-AP) was studied in cut sartorius frog muscle under the voltage clamp conditions. In the presence of 4-AP (1.10(-4) mol/l) one stimulus applied to the nerve induced two end plate currents (EPC) in half of cells studied (n = 35). The elevation of calcium ion concentration up to 5.4 mmol/l or magnesium to 5-9 mmol/l or rhythmic activity (0.05 Hz and above) abolished RF. Substitution of calcium by strontium or barium enhanced RF (the number of EPC during the burst of RF). EPC with very slow time course were observed in some cells in the presence of barium, that disrupted to the burst of RF by repetitive nerve stimulation. Neostigmine, an anticholinesterase agent, increased the number of EPC in the burst of RF, but alpha-bungarotoxin exerted no effect on the RF. The role of calcium and calcium-activated potassium currents in generation and termination of RF in motor nerve endings is discussed.

Trans-ACPD, a cyclic analogue of glutamate, has been studied for its influence on field potentials and excitatory postsynaptic currents (EPSCs) in the CA1 layer. Being applied in concentration 50 microM and above, trans-ACPD completely and reversibly inhibited excitatory postsynaptic field potentials but has no effect on EPSCs. Trans-ACPD in the same concentration reversibly reduced the amplitude of antidromic population spike in the CA1 layer, but has an insignificant effect on antidromic population spike in the CA3 layer.

It is known that cooling of skin induces contraction of collagen fibres, which leads to deformation and excitation of mechanoreceptors. The action of moderate heat on the skin depresses or terminates its tonic activity. The collagen fibres in this case stretch out and the skin tension slackens. Yet, intense thermal stimulation up to 48 degrees C results in a greater afferent activity. This effect is associated with the so-called thermoreceptors. It is shown earlier that repeated stimulation by intense heat increases skin sensitivity to this stimulus. The paper reports the results of recording the time in which afferent activity increased under repeated stimulation of the skin at temperatures up to 48 degrees C and, simultaneously, of the skin tension variations. For each heating instance the skin stretched and contracted when its temperature approached the normal temperature, i. e. 30 degrees C. However, by the next heating (there was a 3--min. pause between them) the skin tension failed to restore completely. Multiple heating tests have shown a loss of the skin sensitivity, and the time in which increased afferent activity manifested itself has shortened. These two processes are simultaneous, which permits concluding that they are related.

The striate cortex electrocorticogram has been analyzed in 12 cats in following states: at rest with the eyes closed and with the eyes opened; after light electrical stimulation of ears; somnolence; eye opening after somnolence+; barbituric sleep. The behaviour of cats was controlled and the state of emotional excitability was determined. Spectral and periodometric analysis of ECoG has revealed state-dependent differences of cats in power spectra from 2 frequency ranges (2.8-5.0 Hz and 13.8-20.8 Hz). It is suggested that the ratio of ECoG power spectra in these frequency ranges can be used to evaluate the brain activation of cats.

Reciprocal inhibition (RI) has been studied for its effect on repetitive firing of single motoneurons in the extensor carpi ulnaris and soleus muscles of healthy subjects. The peristimulus time histograms (PSTHs) were plotted for different mean firing frequency of motoneurons. Changes in the interspike interval duration were analyzed. It was shown that the "effectiveness" of reciprocal volleys (as it was previously shown for other types of inhibition) depended on the firing rate of a motoneurons. It was found out that RI duration derived from the PSTH, duration of the "effective part" of the interspike interval, rate of the interspike interval lengthening depended on the motoneuron firing frequency. It was also found that the inhibitory effect of the motoneuron firing was pronounced mostly at its low-frequency range. The dependence of "effectiveness" of an inhibitory volley on the moment of its arrival within the interspike interval was analyzed as well.

Changes in impulse activity of afferent fibres of the spinal dorsal roots connected with thermal receptors of cat's skin have been studied during acute experiments. Thermal sensitivity of the man skin has been studied in psychophysical experiments. Three types of reactions of fibers from heat receptors of the animal skin and two types from cold ones are obtained. All of them are mechano-sensitive reactions. They differ from each other in the depth of changes in frequency of average impulse activity, dynamic sensitivity, latent period of the reaction as well as in thresholds of thermal and mechanic sensitivity. It is supposed that there exists certain analogy between thermoreceptors of animals and men.

The effects of iontophoretic application of glutamate and its blockers on neuronal activity of the sensorimotor cortex were studied in cat during fulfillment of conditioned instrumental placing reflex. 64 neurons were investigated. Application of glutamate caused reliable facilitation of neuronal impulse reactions to the conditioned stimulus. The facilitation appeared some seconds after beginning of the application of glutamate and continued for 5-10 min after cessation of the iontophoretic application. The similar inhibitory effect in neuronal activity was observed with application of APV, kinurenate, ketamine. It is suggested that the NMDA receptors under natural conditions take part in facilitation of the synaptic transmission in glutamatergic intracortical pathways.

Effect of bath application of L-DOPA, dopamine (DA), noradrenaline (NA) on the spontaneous activity--cyclical oscillations of electrotonic potentials in dorsal and ventral roots (DR and VR, respectively) generated by isolated spinal cord of 16-20-day-old chick embryo was studied. L-DOPA in low concentration (30-150 mumol/l) activated spinal generator: suprathreshold rhythms appeared (i.e., spike activity in DR and VR). High concentration (200-1000 mumol/l) of L-DOPA depressed generator activity, but in the course of washing of the spinal cord spontaneous activity was enhanced and suprathreshold rhythms appeared. DA and NA (50 mumol/l) did not influence the activity but in concentration 100 mumol/l they depressed spontaneous activity in DR and VR. Bath application of 2-amino-5-phosphonovaleric acid (20 mumol/l) blocked activity induced by small concentration of L-DOPA. Activity generated by the neuronal network of the isolated dorsal horn was intensified after bath-application of L-DOPA in small concentration. Rhythmic activity in the isolated ventral horn did not appear after bath-application of L-DOPA. It is concluded that excitatory action of L-DOPA on the neuronal network of dorsal horn chick embryo was direct (i.e., did not depend on catecholamines).