Biomedical subjects
Publications and source records attributed to A V Zeveke.
A nerve activity in heating of the cat hairy skin was studied in acute experiments in order to find out if the C-receptors take part in peripheral coding of heat information. An integrative cross-correlation technique was used to analyse neurograms in the real time. No C-afferent activity was found in the thermal stimulation up to 41 degrees C of the hairy skin.
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A paradoxical feeling of heat appeared after secondary cooling of the human forearm surface skin layer at low constant temperature of the subskin layer. Formation of the pattern of afferent flow from the skin receptors during the heat illusion, is discussed.
Cooling of the cat paw skin augmented the afferent activity in the n.n. plantaris whereas warning of the paws exerted an opposite affect. The code of thermomechanical sensory signals depended on the physical-mechanical condition of the skin.
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.
Vibrational stimulation of cat's skin by the frequencies of 10, 30 and 50 per second evoked response of mechanoreceptors innervated with A beta and A delta-fibers, responding to each vibration stimulus. The higher vibrostimulation frequency, the more distinct changes appear in the "on"--and "off"--responses which are caused by a decreasing number of pulses for each vibration impact. The mechanoreceptors innervated with the C-fibers are not excited by these frequencies. After a preliminary vibrostimulation the part of mechanoreceptors innervated with C-fibers do not respond to the mechanical stimulus tested. The higher the frequency of preliminary vibrostimulation, the fewer receptors respond to the tested stimulus.
Experimental studies on the relations between the afferent flows in A-beta and A-delta and C-fibres of a cutaneous nerve for different stimulations of cutaneous receptors provided the basis for modelling of various digital and graphical codes of the known and unknown sensations.
The results of model tests accomplished for precision and evaluation of present restrictions in the collision method are demonstrated in this work. The reduction of induced antidromic potential due to its "collision" takes place in the interelectrode area. This fact is of a great importance for the use of the collision method as it increases probable encounters of anti- and orthodromic impulses and possible intervals between stimulation and exploring electrodes.
Nociceptive reactions for damage and week actions on hairless and hairy skin was studied in acute experiments on cats. The damage stimulation of the hairless skin did not result in nociceptive reflexes, and in the case of hairy skin it always did. Using a cross-correlation method, some quantitative characteristics of afferent impulse discharges in the nerve plantaris of the cat were obtained under exposure damage and weak stimuli on the hairy and hairless skin. The afferent flow from the hairy skin has the C-afferent activity whereas in the case of hairless skin this activity was not observed. Peripheral coding of nociceptive signals under the damage action on pads of the cat is, obviously, impossible due to the absence of the C-afferent system in this kind of the hairless skin.
The afferent flow in A delta-fibres was studied in acute experiments on cats. A decrease in the number of fibres was registered 5s and 35s after excitation of sympathetic efferents. Analogous changes in the afferent flow were observed when adequate excitations were provided by stretching and cooling of skin. The obtained results show that for the first 30s of sympathetic influence its effect on the afferent flow is due to a change in the mechanic state of tissues surrounding the receptors.
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Using a crosscorrelation method some quantitative characteristics of afferent impulse discharges in the n. saphenus of cat were obtained during skin cooling. A 10 degrees C drop in the skin temperature at different cooling gradients caused activity in the A beta-, A sigma- and C-fibres. The C-fibres were activated first, than A delta-, A beta- and the quick-conductive A beta-groups successively. The latent period of the escitation of the C-fibres remained constant at different cooling rates of the skin, while for the A-fibres it increased with slowing down of the temperature drop rate. Both in A- and C-fibres the level of the maximum activity did not depend on the gradient of the skin cooling. But in all the mentioned groups of the fibres the starting time of the maximum activity decreased with the rise in the cooling rate.
Combining the colliding impulses method with the methods of singling out the nerve's weak signals from the equipment noise shows that most nonmyelinated fibers of C1 and C2 groups develop impulses under cooling the cat hairy skin. In some nonmyelinated fibers of the C2 group there takes place an inhibition of spontaneous impulses in response to cooling.
The collision method combined with some techniques improving the signal-to-noise ratio showed that the activation in the nerve fiber group A gamma 1, A delta, A delta 2 and in "mixed" fibers group was changed by hairy skin heating. A relatively great number of nerve fibers of these groups were activated and only an insignificant part of them inhibited their activity in response to the cutaneous receptor heating. A spontaneous activity increase and skin relaxation under heating. were shown.
The relative quantity of the cutaneous nerve unmyelinated fibers that conduct the excitation impulses from mechanoreceptors under contraction of pilomotors without and during cooling of the skin by 10 degrees C at a rate of 1 degree C per second was measured by the integrating method of colliding impulses. The same mechanoreceptors are shown to be excited by pilomotors both under skin deformation and cooling. A conclusion is made about absence of specific cold receptors in the cat skin.
The afferent activation in cat cutaneous nerve fibres in response to cooling was analyzed using the collision method and the method improving the signal-to-noise ratio in the antidromic action potential neurogram. It was found that the nerve fibres of groups Adelta1 and Adelta2 were activated under cutaneous receptors cooling. The activity of a small group of nerve fibres with conduction velocity 13.0--7.5 m/s was inhibited in response to cooling. A group of "mixed" fibres inhibited mainly its activity, but only an insignificant part of these fibres activated in response to cutaneous receptors cooling.
Using the cross-correlation method, the pattern of impulses flow coding a nociceptive signal is studied in the n. saphenus of the cat. It is found that nociceptive solutions of KCl (125-1000 mM) stimulate both myelinated and nonmyelinated fibres. The flow density increases with time of the stimulation action, reaching a level sufficient for the appearance of nociceptive pressure reflexes. The maximum of these reflexes coincides with the appearance of synchronous pulsations in the group of non-myelinated fibres. Thus a nociceptive signal caused directly by the exposure of the nerve to strong solutions of KCl is coded by a high density of the impulse flow, in which synchronous pulsations are likely to be found.
Analysis of the afferent activity in the myelinated Adetla-fibers was carried out using the modified colliding impulses method. Frequency characteristics of the orthodromic impulses pattern without any preliminary electrical stimulation of Adelta-fibers and after its application to the nerve were compared. It was found that the antidromic impulses appearing under the electrical stimulation of the nerve caused an increase in the frequency of impulses in the afferent pattern in adequate stimulation of the cutaneous receptors.