Characteristics of thermo-mechanosensitive receptors in human and animal skin

With local thermal and mechanical stimulation in precise experiments on cats, a study was made of changes in impulse activity of afferent fibers of spinal dorsal roots connected with skin thermoreceptors in the extremities. Psychophysiological studies were done on the characteristics of thermosensitive points of the skin of the upper extremities of man. According to changes in average frequency of impulse activity, dynamic sensitivity, latent period of reaction, and thresholds of temperature and mechanical sensitivity, three groups of heat receptors and two of cold receptors were identified in the skin of the cat. All heat and cold receptors are mechanosensitive. According to quality and intensity of perceptions elicited by thermal stimulation and thresholds of sensitivity to mechanical and temperature effects, thermosensitive points in human skin can also be divided into three groups of heat receptors and two groups of cold receptors. All heat and cold points are mechanosensitive. An analogy between the skin thermoreceptors of animals and man is suggested.Institute of Physiology, Kazakhstan, Academy of Sciences. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 314–322, May–June, 1992.     

Relation between pain and temperature reception of human skin

On healthy volunteers we studied the effect of local cooling (14–16°C) and heating (40–42°C) of the skin of various zones of the leg to pain sensitivity, for evaluating which we used the method of recording the flexor reflex (FR) and electromyography of the anterior tibial muscle. It was established that changes in the FR depend not on the modality of thermo stimulation but on localization of the place of its application: on stimulating the skin above the tested flexor, the FR is facilitated, and on thermostimulation above the antagonist or contralateral agonist, the FR of the anterial tibial muscle is mainly inhibited. It was assumed that loss of the temperature modality is due to convergence of temperature and pain information on spinal interneurons of the "bimodal type" unidirectionally changing impulse activity under the effect of both temperature modalities. The different character of reaction of the FR to thermostimulation of different leg zones is examined from the position of control of afferent information by the spinal generator of locomotion.Institute of Physiology, Kazakhstan Academy of Sciences, Alma-Ata. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 604–611, September–October, 1992.     

Mechanism of effect of sympathetic nervous system on skin receptors

While researching the mechanism underlying the effect of the sympathetic nervous system on the operation of skin receptors, we demonstrated that a tremendous role in this process is played by smooth muscles, whose condition also mediates the sympathetic effect on receptors. The increase in the activity of the sympathetic nerve fibers results in an increase in the tonus of the smooth muscles which in turn alters the mechanical condition of the tissues surrounding the receptors. It was established that the change in the tonus of the smooth muscles in the skin itself affects the reaction of the receptors that is evoked by mechanical stimulation. The change in the tonus of the smooth muscles of the vessels affects the response of receptors caused by cooling of the skin.Nizhegorod Medical Institute, Russian Federation Ministry of Health. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 552–558, September–October, 1992.     

Characteristics of the formation of temperature information in afferent units

The impulse activity of single afferent fibers of the dorsal roots of the cat spinal cord is studied for local mechanical, heat, and cold influences on the skin receptor fields. A probability analysis of the impulse flux suggests that a change occurs in the distributions of the intervals between impulses in accordance with the stimuli presented, regardless of the variations in the mean frequency of impulsation. It is hypothesized that the afferent fibers acquire polyfunctional properties on account of their multichannel information.Institute of Physiology, Kazakhstan, Academy of Sciences, Alma-Ata. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 582–591, September–October, 1992.     

Mechanism of sympathetic efferent control of c-receptor responses to skin cooling in cats

The effect of sympathetic efferents on the afferent flow in C fibers was studied in acute experiments on cats. The number of C fibers active during skin cooling was found to be increased 5–7 sec but reduced 30–40 sec after stimulation of the sympathetic chain. The increase in activity in C-afferents can be explained by a change in the mechanical state of the skin during contraction of its contractile elements. The decrease in activity in C afferents, on the other hand, is evidently due to the effect of sympathetic nervous system mediators on C receptors or directly on afferent C fibers.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii Gor'kii State University. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 373–378, July–August, 1982.     

Changes in heated and autoclaved forest soils of S.E. Australia. I. Carbon and nitrogen

The effect of heating and autoclaving on extractable nitrogen, N mineralisation and C metabolism was studied by heating five forest soils in the laboratory, simulating the range of effects of heat due to bushfire. Top soil (0–5 cm) was heated to 60 °C, 120 °C and 250 °C for 30 minutes; unheated soil was taken as a control. Samples of the soil heated to 250 °C were also inoculated with fresh soil to accelerate the recovery of the microbial population. Soil autoclaving was carried out as another heat treatment (moist heat). Soils were analysed immediately after heating and 3 times during seven months of incubation to assess immediate and longer-term effects of heating.Extractable N (organic and mineral forms) increased after heating to 120 °C, but decreased with further heating to 250 °C suggesting the volatilisation of N. N associated with microbial biomass diminished with heating and was barely detectable after the 250 °C treatment. Microbial biomass was an important source of soluble N in heated soils, and only partly recovered during subsequent long incubation. The amount of N mineralised during incubation depended on both soil and temperature. Nitrification did not occur when soils were heated to 250 °C (with or without inoculum), or after autoclaving, demonstrating the high sensitivity of nitrifiers to heat. At the beginning of soil incubation, respiration was enhanced in heated soils (250 °C, 250 °C inoculated) and autoclaved soils, but after 30 days of incubation respiration decreased to values either similar to or lower than those in control. This respiration pattern indicated that a fraction of labile C was released by heating, which was quickly mineralised within 30 days of incubation. These results demonstrate some effects of soil heating on C and N dynamics in forest soils.     

Cutaneous mechanism of electroreceptor temperature sensitivity of the ampullae of Lorenzini

The potential difference on the receptor epithelium of the ampullae of Lorenzini and on the skin and also spike discharges of single electroreceptor nerve fibers in response to temperature stimulation of the region of the pores of the ampullae were studied in the Black Sea skateRaja clavata. Heating the skin in the region of the pore led to the appearance of a positive potential on the skin and on the epithelium of the ampulla, and to inhibition of spike activity. The time course of the change in potential reflected the course of change of temperature; the temperature coefficient was 100–150 µV/°C. Cooling the skin was accompanied by a negative deviation of potential on the skin and in the ampullary canal and by excitation of spike activity. During cooling the temperature coefficient was 30–50 µV/°C. It is concluded that spike activity of electroreceptors reflects changes in potential on the skin due to changes in temperature. The mechanism and biological significance of the phenomena discovered are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 307–314, May–June, 1981.     

Effect of Elevated Temperature on Nitrite and Nitrate Reduction in Leaves and Intact Chloroplasts

Barley (Hordeum vulgare L.) leaves and intact spinach (Spinacia oleracea L.) chloroplasts were exposed to short-term heating, and the aftereffects of heat treatment on in vitro andin vivo activities of nitrate reductase and noncyclic electron transport associated with nitrite reduction were studied. Heating of leaves at temperatures above 40°C led to a monotonic decrease in nitrate reductase in vitro activity. On the contrary, the in vivo enzyme activity, assayed in intact leaf tissues after 5-min heat treatment, increased 1.5 times upon elevating the pretreatment temperature from 37 to 40°C and gradually decreased at higher temperatures. Noncyclic electron transport related to CO₂ fixation in intact chloroplasts decreased gradually after heat exposures above 39°C, unlike the electron transport to nitrite as a terminal acceptor, which was stimulated by heating of intact chloroplast suspensions in the temperature range from 33 to 40°C. The heating at higher temperatures inhibited nitrite photoreduction. It is concluded that the heating of phototrophic cells at sublethal temperatures stimulates the mobilization of inorganic nitrogen and thereby facilitates the repair of thermally induced injuries of proteinaceous cell structures. The stimulation of nitrate reductase activity in vivo at the temperature range 37–40°C provides an evidence for the increase in the availability of reductants in the cytosolic compartment of the leaf cell.     

Unit activity of the posterior hypothalamus during brain and skin temperature changes in unanesthetized rabbits

Changes in the firing rate of posterior hypothalmic neurons in response to local elevation of the brain temperature by 0.6–1.5°C and to a rise and fall (separately and simultaneously) of the skin temperature by 3–5°C were investigated in unanesthetized rabbits. Neurons responding selectively to changes in brain temperature and skin temperature and neurons responding to both temperature stimuli were found in the posterior hypothalamus. During combined stimulation the unit activity was changed much more than in response stimulus. It is concluded that the region of the posterior hypothalamus participates in the integration of impulses from central and peripheral temperature receptors.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 490–496, September–October, 1973.     

Activity of myelinated fibers under heat and burn influences on the skin

The dynamics of the activity of myelinated fibers of a cutaneous nerve under heat and burn influences on hair-covered skin was investigated in acute experiments on cats using the method of cross-correlation functions. Under heat influence on the skin the total activity of the nerve was reduced chiefly at the expense of the rapidly conducting myelinated fibers, whereas in the case of painful heating of the skin the A fibers were activated. The results obtained make it possible to solve the problem of the heat-information code from the standpoint of the flow "pattern" theory.S. M. Kirov Medical Institute, Ministry of Health of the Russian Federation, Nizhnii Novgorod. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 567–577, September–October, 1992.     

Effect of preliminary mechanical and antidromic influences on orthodromic activity in C fibers from mechanoreceptors of the cat skin

Analysis of afferent activity in unmyelinated fibers of a cutaneous nerve was carried out by the colliding impulses method in cats. The effect of antidromic excitation of the nerve and mechanical stimulation of the receptors on subsequent orthodromic activity during stretching of the skin was investigated. Both these factors were shown to reduce subsequent orthodromic activity evoked by testing stimulation. The reduction in activity was greatest 10–15 sec after stimulation. The duration of the inhibitory effect was greater after mechanical than after antidromic stimulation. Combined mechanical stimulation and antidromic excitation resulted in a greater decrease of afferent activity and an increase in the time of its recovery. An increase in the frequency of antidromic excitation potentiated the inhibitory effect of preliminary stimulation on orthodromic activity in C fibers.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii Gor'kii State University. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 307–312, May–June, 1977.     

Convergence of impulses on anterior hypothalamic neurons during local temperature stimulation of the skin

Unit responses in the medial preoptic region of the anterior hypothalamus and septum to local temperature stimulation of various parts of the skin were studied in chronic experiments on rabbits. The temperature of an area of skin on the back (zone I) and head (zone II) was altered by means of thermodes: heated to 38–40°C and cooled to 22–26°C. Of 111 neurons tested 21 responded to a change of skin temperature (mainly to cooling). Temperature-sensitive hypothalamic neurons were shown to react to temperature stimulation of both skin zones stimulated. The types of the responses recorded are described.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 4, pp. 365–370, July–August, 1981.     

The Effect of Heat Shock on the Capacity of Wheat Plants to Restore Their Photosynthetic Electron Transport after Photoinhibition or Repeated Heating

The shoots of 16-day-old spring wheat plants (Triticum aestivumL., cv. Albidum 29) were subjected to heat shock (HS) at 40, 41, or 43°C for 10 min. The activity of the Hill reaction in chloroplasts isolated immediately after HS was 83, 61, and 30% of the initial value, respectively. The activity of the Hill reaction was also estimated after plant return to the initial growth conditions for one day. It was completely restored after heating at 40°C and achieved 82 and 30–33% of the initial level after heating at 41 and 43°C, respectively. Thereafter, the shoots were heated repeatedly at 42, 43, or 43.5°C for 10 min, and the activity of the Hill reaction was measured immediately or one day after this heating. Immediately after the second heating, the activity decreased again as compared to its value before heating. The percent of inhibition of the Hill reaction was similar in the control plants not subjected to preliminary HS and HS-treated plants independently of the temperature used. However, after one-day growth under normal conditions, the activity of the Hill reaction was restored almost completely in HS-treated plants but not more than by 10% in the control plants. The conclusion is that different mechanisms underlie the development of the tolerance to HS and recovery. Some plants were tested for the effect of HS (40°C) on their tolerance to photoinhibition. The degree of the Hill reaction inhibition after plant exposure to the light of 65–75 klx for 3 h was essentially similar in detached leaves from the HS-treated and unheated plants and comprised about 40% of the activity before light stress. After the leaves were returned to the low-light conditions for 3 h, the Hill reaction was restored and attained about 75% of that before photoinhibition in both HS-treated and untreated plants. The lack of the HS-induced stimulation of the Hill reaction recovery after photoinhibition is evidently related to the fact that heating and excess light damage different sites of photosystem II, which implies the different pathways for the recovery of its functional activity.     

Neuronal firing activity in the lateral vestibular nucleus during locomotion in the guinea pig

The effects of spontaneous locomotor activity on neuronal background firing in the lateral vestibular nucleus was investigated during experiments on decerebrate guinea pigs. The onset of rhythmic muscular activity in the extramities was found to produce a rise in the rate of such discharges, which increased from 10–15 to 100 spikes/sec in most neurons. A higher rate occurred as activity began in the ipsilateral forelimb extensor muscles (the stage corresponding to the end of the swing phase and start of the stance phase in the locomotor cycle). The alterations noted in vestibular neuronal activity during locomotion are thought to ensure the background of high anti-graveity muscle tonus against which rhythmic limb movements take place.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 536–541, September–October, 1991.     

Effects of adequate vestibular stimulation on locomotor activity in the guinea pig fore- and hindlimb muscles. Tilting around a transverse axis

The effects of adequate vestibular stimulation occurring as the animal tilted around its transverse axis on locomotor activity of the fore- and hindlimb muscles produced by electrical brainstem stimulation were investigated during experiments on guinea pigs decerebrated at the precollicular level. An increase and decrease in forelimb and hindlimb extensor activity, respectively, at the standing phase of the locomotor cycle were observed when the animal was tilted head-downward. The reverse changes took place in the limb extensor muscles when the animal was tilted head-up. Forelimb extensor activity during the swing phase increased and decreased when the animal was tilted head-up and head-downward, respectively. Phase shifts of changes in locomotor activity of the forelimb extensors altered from 60 to –30°, from –150 to 220° in hindlimb extensors, and from –140 to –220° in forelimb flexors during sinusoidal tilting in the 0.02–0.4 Hz frequency range and an amplitude of ±20°. Mechanisms underlying the changes observed in locomotor muscle activity are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 833–838, November–December, 1987.     

Effect of nociceptive stimulation of signal transmission from low-threshold cutaneous afferents in the somatosensory system

In cats anesthetized with chloralose nociceptive heating of the skin of the foot to 44–60°C led to a two- to fourfold increase in amplitude of primary cortical responses to direct stimulation of neurons of the spinocervical tract receiving information from the heated area of skin, but did not affect primary responses evoked by stimulation of axons of these neurons in the dorsolateral funiculus, and actually inhibited the response to stimulation of the nerve innervating the heated area of skin. Inhibition was accompanied by depolarization of central terminal of low-threshold fibers of this nerve: During heating the amplitude of the antidromic discharges evoked in the nerve by stimulation of its presynaptic endings in the spinal cord was increased two- to threefold. After abolition of presynaptic depolarization with picrotoxin (0.2–0.7 mg/kg, intravenously) or as a result of asphyxia, nociceptive heating acquired the ability to facilitate primary responses arising as a result of stimulation of the nerve also. The amplitude of the responses was increased under these circumstances by 3–20 times. It is concluded that acute nociceptive stimulation causes such powerful presynaptic inhibition of impulse transmission from low-threshold fibers of the cutaneous nerve that it virtually abolishes the facilitating effect of nociceptive impulses on sensory neurons of the spinal cord. It is suggested that it is this inhibitory mechanism which prevents the development of hyperalgesia during acute nociceptive stimulation.Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 6, pp. 621–627, November–December, 1981.     

Dynamic Mapping of the Temperature Fields of the Brain

The thermal fields and biopotentials of the brain were studied in 11 healthy subjects in the states of quiet wakefulness and sleep (stages I–IV). To this end, a new method of dynamic radiomapping was applied in parallel with the traditional method of EEG recording. The method of dynamic radiomapping is based on measuring the brain thermal radiation in the decimeter (40 cm) wave range. It allows the integral brain temperature to be recorded from deep inside and up to 2.5 cm from the surface with the help of 12 antennas applied to the skin. The temperature of the cerebral cortex of the human subject in the state of quiet wakefulness varied stochastically in the range of deviations of ±0.3°C in all areas. Changes in the brain functional state, i.e., the transition from wakefulness to sleep, were accompanied by either an increase in the variation range to ±0.5°C or the appearance of stationary foci of heating (by 0.9–1.3°C) or cooling (by –0.7°C) of individual locations and amplitudes.     

Electrical activity of neurons in the cat cortex during cooling

Changes of the activity of cortical neurons were studied in the posterior crucial gyrus and in the middle parts of the suprasylvian and ectosylvian gyri on cooling the brain to 18°C and below. In exact experiments it was noted that cooling the cortex to 18.8–21.8° causes a complete cessation of neuron activity. The kinetics of the change of activity under these conditions follows a definite order: first an increase of the frequency of spike discharges is observed (31–27°), then a decrease of their amplitude (at 25–22°), and finally a complete disappearance of neuron activity (at 21.8–18.8°). Discontinuation of the cooling leads to restoration of the activity of the nerve cells in inverse order: low-amplitude high-frequency discharges manifest (at 23–26°), the amplitude of the spikes increases (at 29–31°) and then the initial activity is restored (at 31–32°). The decrease of neuron activity depends on the rate of temperature drop in the cortex. The faster the cortex is cooled, the lower is the temperature at which the neurons cease to function. And conversely, slow cooling of the cortex causes an inactivation of the spike potentials at a higher temperature.S. M. Kirov Gorki State Medical Institute. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 59–63, January–February, 1970.     

Predicting survival time for cold exposure

The prediction of survival time (ST) for cold exposure is speculative as reliable controlled data of deep hypothermia are unavailable. At best, guidance can be obtained from case histories of accidental exposure. This study describes the development of a mathematical model for the prediction of ST under sedentary conditions in the cold. The model is based on steady-state heat conduction in a single cylinder comprised of a core and two concentric annular shells representing the fat plus skin and the clothing plus still boundary layer, respectively. The ambient condition can be either air or water; the distinction is made by assigning different values of insulation to the still boundary layer. Metabolic heat production (M) is comprised of resting and shivering components with the latter predicted by temperature signals from the core and skin. Where the cold exposure is too severe forM to balance heat loss, ST is largely determined by the rate of heat loss from the body. Where a balance occurs, ST is governed by the endurance time for shivering. End of survival is marked by the deep core temperature reaching a value of 30° C. The model was calibrated against survival data of cold water (0 to 20° C) immersion and then applied to cold air exposure. A sampling of ST predictions for the nude exposure of an average healthy male in relatively calm air (1 km/h wind speed) are the following: 1.8, 2.5, 4.1, 9.0, and >24 h for –30, –20, –10, 0, and 10° C, respectively. With two layers of loose clothing (average thickness of 1 mm each) in a 5 km/h wind, STs are 4.0, 5.6, 8.6, 15.4, and >24 h for –50, –40, –30, –20, and –10° C. The predicted STs must be weighted against the extrapolative nature of the model. At present, it would be prudent to use the predictions in a relative sense, that is, to compare or rank-order predicted STs for various combinations of ambient conditions and clothing protection.     

Effect of cooling on spike trains from skin receptors

Quantitative characteristics of the afferent flow in a cutaneous nerve during cooling of the skin in cats were determined by the cross-correlation method. Lowering the skin temperature by 10°C with different gradients of cooling led to the appearance of activity in A-, A-, and C-fibers. The first fibers to become excited were C-fibers, followed in turn by A-fibers, a group of slowly-conducting A-fibers, and a group of fast-conducting A-fibers. The latent period of excitation of the C-fibers remained unchanged whatever the rate of skin cooling, whereas in A-fibers it increased with slowing of the rate of fall of temperature. The level of maximal activity neither in A- nor in C-fibers depended on the gradient of skin cooling, but in all the groups of fibers mentioned the time taken to reach the maximum of activity decreased with an increase in the rate of cooling.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii State University, Gor'kii. Translated from Neirofiziologiya, Vol. 12, No. 4, pp. 405–412, July–August, 1980.