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.     

Responsiveness of the H reflex to loading and posture in patients following stroke

The objective of the research was to examine the effects of loading and posture on motoneuronal excitability of the triceps surae (TS) for patients with hemiplegia. Twelve healthy subjects and 12 patient subjects with post-stroke hemiparesis (onset period: 3–60 months) were enrolled in this study. The subjects were instructed to remain in quiet sitting with the test knee straight and three standing conditions of different superincumbent loads by shifting body weight to the test leg (10%, 50%, and 90% of body weight), while the H reflexes and M waves of the TS were measured. The results clearly indicated that H reflex amplitudes were not affected by different loading conditions in standing for both healthy subjects and patients who had a previous stroke. In addition, the H reflex amplitude in quiet standing for healthy subjects was significantly downward modulated relative to that in relaxed sitting with the test knee straight, but this posturally driven modulation was impaired in patients following stroke. Current electrophysiological findings imply that body weight as a means for rehabilitation facilitation had little immediate effect on paretic TS, and absence in postural gating of reflex excitability appeared to be an incentive for postural instability resulting from post-stroke hemiparesis.     

Abnormal Control of Orbicularis Oculi Reflex Excitability in Multiple Sclerosis

Brain lesions in patients with multiple sclerosis may lead to abnormal excitability of brainstem reflex circuits because of impairment of descending control pathways. We hypothesized that such abnormality should show in the analysis of blink reflex responses in the form of asymmetries in response size. The study was done in 20 patients with relapsing-remitting multiple sclerosis and 12 matched healthy subjects. We identified first patients with latency abnormalities (AbLat). Then, we analyzed response size by calculating the R2c/R2 ratio to stimulation of either side and the mean area of the R2 responses obtained in the same side. Patients with significantly larger response size with respect to healthy subjects in at least one side were considered to have abnormal response excitability (AbEx). We also examined the blink reflex excitability recovery (BRER) and prepulse inhibition (BRIP) of either side in search for additional indices of asymmetry in response excitability. Neurophysiological data were correlated with MRI-determined brain lesion-load and volume. Eight patients were identified as AbLat (median Expanded Disability Status Scale–EDSS = 2.75) and 7 of them had ponto-medullary lesions. Nine patients were identified as AbEx (EDSS = 1.5) and only 2 of them, who also were AbLat, had ponto-medullary lesions. In AbEx patients, the abnormalities in response size were confined to one side, with a similar tendency in most variables (significantly asymmetric R1 amplitude, BRER index and BRIP percentage). AbEx patients had asymmetric distribution of hemispheral lesions, in contrast with the symmetric pattern observed in AbLat. The brainstem lesion load was significantly lower in AbEx than in AbLat patients (p = 0.04). Asymmetric abnormalities in blink reflex response excitability in patients with multiple sclerosis are associated with lesser disability and lower tissue loss than abnormalities in response latency. Testing response excitability could provide a reliable neurophysiological index of dysfunction in early stages of multiple sclerosis.     

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.     

Modifications of the EEG activity upon activation of peripheral thermoreceptors in humans

In 12 tested subjects, we studied changes in the frequency-amplitude EEG characteristics evoked by thermostimulation of the left palm (its immersion in a pool of water with a changing temperature); temperatures of 24 and 42°C provided cooling and heating stimulations. Cooling of the palm resulted in an increase of the power of fast EEG oscillations, especially in the parietal and occipital regions and in the right temporal zone. Heating of the palm skin evoked an increase in the power of α- and θ-waves, and the latter component was most noticeably intensified in the frontal and right temporal regions. Possible mechanisms responsible for EEG modifications under conditions of thermostimulation of the skin are discussed.     

Changes in the excitability of and synaptic effects on motoneurons during formation of the scratch motion generator in the cat

Studies on immobilized decerebrate (at intracollicular level) cats in which the scratch generator had been set up following bicuculline application to the upper cervical segments of the spinal cord, showed that the state of the segmental apparatus of the lumbosacral section of the spinal cord differs substantially from that seen in the spinal animal. Direct excitability of motoneurons of the "aiming" and "scratching" muscles rises, while recurrent and reciprocal Ia inhibition of motoneurons intensifies and the influence of Ib afferents on motoneurons declines. Afferents of the flexor reflex exert a primarily inhibitory influence on motoneurons of the "aiming" muscles. This influence becomes predominantly excitatory following spinalization, while the inhibitory effects of these afferents on motoneurons of the "scratch" muscles declines. The functional significance of the changes discovered in generation of scratch routine is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 244–250, March–April, 1987.     

Modulation of soleus H-reflex during dorsal and plantar flexions in the human ankle joint

Recording of the H-reflex was used to study the changes in the reflex excitability of soleus motoneurons during dorsal and plantar flexions of the ipsilateral and contralateral feet performed with different strengths by 15 healthy subjects. The dorsiflexion of the ipsilateral foot was accompanied by the “classic” reciprocal inhibition of the soleus motoneurons, the degree of the inhibition being directly proportional to the strength of the contraction of pretibial muscles and depending on the presence of foot support. The plantar flexion of the ipsilateral foot was accompanied by changes in reflex excitability, which were inversely proportional to the strength of the flexion. This was apparently related to the activation of a mechanism protecting the muscle against excessive contraction. The dorsal and plantar flexions of the contralateral foot were accompanied by similar changes in the reflex excitability of soleus motoneurons, namely, an increase in the case of weak contraction and a decrease in the case of strong contraction. However, the increase in reflex excitability during contralateral dorsiflexion was smaller and its decrease began at a weaker contraction than in the case of contralateral plantar flexion. The changes in the reflex excitability of soleus motoneurons during movements of the contralateral foot, which were also strength-dependent, confirmed the presence of cross-projections that are likely to be part of the generator of the central pattern of lower limb movement coordination.     

Changes in the reflex excitability of the soleus spinal center in humans performing various motor tasks

The reflex excitability of the soleus spinal motoneurons was assessed in healthy subjects performing different types of motor tasks: voluntary contraction of the flexor (dorsal flexion) and extensor (plantar flexion) muscles of the foot. The effect of the contraction strength of these muscles was also evaluated. During dorsal flexion of the ipsi-and contralateral feet, changes in the reflex ecitability of the soleus motoneurons were unidirectional: the excitability decreased. The decrease in the reflex excitability was more profound during dorsal flexion with the maximum strength than with the half-maximum strength. During the plantar flexion of the ipsi-and contralateral feet, the excitability of the soleus motoneurons changed in opposite directions: in some subjects it increased, while in the others it decreased. The reflex excitability of the soleus motoneurons changed to a greater extent during dorsal or plantar flexion of the ipsilateral foot. In the case of plantar flexion, the soleus motor center is possibly affected by a broader spectrum of influences than in the case of dorsal flexion, which can explain the variations in the reflex excitability changes during plantar flexion.     

Descending modulation of reflex reactions in spinal motoneurons produced by spinal cord injury in man

A study was made of changes in the amplitude of H-reflexes in m. gastrocnemius and the intensity of Ia inhibition in healthy subjects versus patients with midthoracic injury to the spinal cord before, during, and after voluntary tensing of the masticatory, cervical, and finger muscles. Tensing these muscles brought about facilitation of H-reflex and reduced intensity of Ia response in healthy subjects and patients with paraparesis but produced the opposite effect on paraplegics (or had no influence on reactions). This leads to a discussion of the relationship between the changes observed in reflex reactions and posttrauma damage to structure and function of the spinal cord.A. A. Bogomolets Institute, of Physiology, Academy of Sciences of the Ukrainian SSR. Kiev. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 105–113, January–February, 1988.     

Inhibition of spinal reflex responses in the last period of embryogenesis

Some characteristics of spinal reflex reaction inhibition were studied in cat fetuses during the last three weeks of antenatal development. The experiments were conducted on fetuses with intact placental circulation. Restoration of the excitability of the spinal reflex arcs was very slow after stimulation of the dorsal root by a single stimulus. In embryos studied 20 days before birth the full inhibition of reflex responses lasted about 500 msec. Even 2–3 sec after a single stimulation of the afferent fibers the amplitude of the reflex response to the second stimulus was only 30–40% of the control value. It was determined that such long postactivation depression is unrelated to refractoriness or antidromic inhibition. The presence of a prolonged intense depolarization of afferent terminal fibers at these stages suggests a presynaptic inhibition as one of the most probable reasons for the prolonged postactivation depression. Another important factor in the appearance of postactivation depression is probably the morphologic and functional immaturity of synaptic structures. A reciprocal inhibition was observed in cat fetuses on the 10–12th antenatal day. On the basis of these data it is suggested that in embryogenesis presynaptic inhibition considerably precedes that of postsynaptic fibers.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 68–75, January–February, 1971.     

Effect of peripheral heating and cooling on spinal reflex activity

The effects of heating and cooling the skin of the thigh and leg on the character of changes in monosynaptic and polysynaptic reflexes and of the first negative wave (N_`) of the dorsal cord potential was studied in acute experiments on lightly anesthetized cats. During cooling of the skin the amplitude of the monosynaptic reflex and N₁-wave was increased while the polysynaptic reflex was inhibited; during heating the amplitude of the monosynaptic reflex and N₁-wave was reduced while the polysynaptic reflex was increased. After de-efferentation the cooling effect was reduced, and after division of the spinal cord responses to cooling of the skin were considerably inhibited. The mechanism of the selective action of cooling and heating of the skin on monosynaptic and polysynaptic reflexes are discussed.Institute of Physiology, Academy of Sciences of the Kazakh SSR, Alma-Ata. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 181–185, March–April, 1973.     

Scratch reflex evoked by strychnine applied to the spinal cord

Effective facilitation of the scratch reflex was observed in experiments on recently decerebrated and spinal cats in response to application of strychnine solution to the dorsal surface of the spinal cord. The receptive fields of the scratch reflex in this case depended on the segments to which the strychnine was applied. The receptive fields of a scratch reflex evoked by D-tubocurarine coincided with those of the intact adult animals, but the receptive fields for strychnine application were wider and corresponded to those of the scratch reflex in kittens [1, 10]. It is suggested that strychnine application abolishes the inhibition of the afferent inputs of the scratch reflex in the lower cervical segments of the spinal cord which has developed during ontogeny.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 622–625, November–December, 1978.     

Effects of partial bulbar section on inhibition of jaw-opening reflexes induced by central gray matter stimulation in the cat

The effects of severing the spinal trigeminal tract and its caudal nucleus on high-threshold jaw-opening reflex elicited by tooth pulp stimulation were investigated during experiments on cats under chloralose-Nembutal anesthesia. Low-threshold jaw-opening reflex produced by stimulating the A--infraorbital nerve at an intensity 2–3 thresholds in relation to the most excitable fibers on this nerve was also observed, as well as suppression of these reflexes induced by central gray matter stimulation. It was found that spinal trigeminal tract section produces a 8–52% increase in high-threshold reflex. The amplitude of low-threshold reflex either remained unchanged or showed a slight tendency to rise or fall. Brief stimulation of the central gray matter produced a 100% decrease in high-threshold reflex in intact animals compared with a 40–60% decrease after section of the trigeminal tract. Protracted stimulation of the central gray brought about an 80% decline in high-threshold reflex in intact animals as against 25–30% after section. The degree to which brief stimulation of the central gray produced depression of low-threshold stimulation remained unchanged by trigeminal tract section. Protracted stimulation of the central gray matter brought about a 25–50% reduction in low-threshold reflex in intact animals and a reduction of 75% in three animals and 15–20% in four animals. This implied that the caudal nucleus of the spinal trigeminal tract exerts a more substantial influence on the process of high- than low-threshold reflex inhibition when the central gray matter is stimulated.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 362–368, May–June, 1987.     

Direct cortical response in the cat motor cortex during summation

Summation was studied by a procedure close to that used in producing a conditioned reflex. Subthreshold electrical stimulation, which gave rise to a dominant focus in the cat motor cortex, was applied after photic stimulation. Under these conditions, summation occurred both when the two stimuli were applied simultaneously and when the weaker stimulus preceded the stronger one by a very short interval (tens of milliseconds). Increased excitability was characteristic of the dominant focus. An excessive increase in excitability weakened the summation reflex. Electrographically, this type of conditioning was reflected in an increase in amplitude of the primary negative wave of the direct cortical response, recorded in the motor area at a distance of 2–3 mm from the stimulation point. It is concluded from analysis of this electrophysiological phenomenon and comparison of the results with data in the literature that different mechanisms are involved in the summation process during different sequences of stimulation ("photic+electrical" and "electrical+photic").Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 293–302, November–December, 1969.     

Altered excitability of and synaptic effects of motoneurons during the establishing of a locomotor generation in the cat

Research was performed on spinal cats injected with DOPA and decorticate (decerebrated at level A 13) and spinal cats. It was found that formation (activation) of the spinal locomotor generator is accompanied by heightened excitability in the extensor and the reverse trend in the flexor motoneurons, by an increase in the efficacy of recurrent and reciprocal Ia inhibition of -motoneurons, and by a weakening of the influence of Ib afferents and extensor reflex afferents on these same motoneurons. The likely functional role of these changes in tuning of the spinal segmental apparatus in the generation of locomotor rhythm is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 679–687, September–October, 1986.     

Effect of substances potentiating or inhibiting unit activity in the locus coeruleus on some types of spinal inhibition in cats

Microinjections of aspartic acid and chlorpromazine into the region of the locus coeruleus, which strengthen spontaneous unit activity in that structure, in decerebellate cats anesthetized with chloralose, led to depression of the inhibitory influence of flexor reflex afferents on extensor discharges, but did not change the facilitatory action of these afferents on flexor monosynaptic discharges and had no effect on recurrent inhibition of extensor discharges or reduced it. Microinjection of noradrenalin into this region, which depresses spontaneous unit activity in the locus coeruleus, or of procaine, which blocks action potential generation in neurons, led to potentiation of the inhibitory action of flexor reflex afferents on extensor discharges and to strengthening of recurrent inhibition, but did not affect the facilitatory action of these afferents on flexor discharges. The role of tonic descending influences of the locus coeruleus in the control of spinal inhibition evoked by flexor reflex afferents is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 247–256, May–June, 1981.     

Responses of motor cortex neurons of the cat to auditory stimulation and their role in the instrumental food reflex

The responses of motor cortex neurons in the cat to the presentation of a single auditory click and a series of 10 clicks presented with 1,000/sec frequency were studied under conditions of chronic experiments before and after the development of an instrumental food reflex. After reflex development a single presentation of a positive conditioned stimulus (single click) markedly influenced for 7 sec the appearance of instrumental movements. At the same time, the immediate responses of motor cortex neurons to presentation of the conditioned auditory stimulus had no impact on the appearance in the motor cortex of discharges leading to the realization of instrumental movements. Consequently, motor cortex neurons do not require activation from afferent sensory inputs for the generation of such discharges. The immediate neuronal responses to conditioned stimulation did not inhibit the realization of the instrumental reflex. It is proposed that they are associated with the realization of motor function in the unconditioned defensive response evoked by the presentation of an auditory stimulus. The presence or absence of responses to auditory conditioned stimulation was dependent upon the signal meaning of the stimulus, its physical parameters, and the degree of excitability of the animal.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 539–550, July–August, 1985.     

Thermostimulation-Induced Modulation of Conditioned Reflex Movement-Related Reactions of Cortical Neurons of the Cat

In awake cats trained to perform a food-procuring conditioned operant reflex (placing movement), we studied impulse reactions of 86 neurons of the motor cortex (field 4) related to realization of the above movements. As conditioning stimuli (CS) initiating the reflex, we used either non-noxious electrocutaneous stimulation (ECS) of the contralateral forelimb or an acoustic stimulus (sound click). Impulsation of cortical neurons was recorded under conditions of (i) isolated presentation of the CS (control), (ii) presentation of the CS (either ECS or acoustic stimulus) combined with thermostimulation (heating with a miniature electric bulb) of the skin of the working forelimb, and (iii) the same, but with stimulation of the resting forelimb. When we recorded spike activity of neurons within the projection motor zone of the resting limb subjected to ESC, alternating thermostimulation of both forelimbs resulted in considerable intensification and an increase in the duration of neuronal responses, especially in cases where thermostimulation was applied to the working limb ipsilateral to the recording site (a two- to threefold increase). When spike reactions were recorded within the motor cortex of the working forelimb, thermostimulation resulted in a considerable increase in the intensity of these reactions and a decrease in their latency, but only when such stimulation was applied to the working forelimb. Thermostimulation of the resting (ipsilateral, subjected to ESC) limb evoked opposite effects (the intensity of neuronal reactions dropped). In both situations, placing movements remained within the control limits. When sound click was used as a distant CS, thermostimulation of the working limb enhanced neuronal responses, increased their duration by 50-100%, and also increased the time of forestalling of the movement initiation by spike neuronal reactions. Thermostimulation of the resting forelimb in this situation also suppressed neuronal reactions. We conclude that foreign stimulations directed toward modifications of the receptor model of the operant reflex experimental situation formed in the animal result in a decrease in the intensity of the spike responses of field-4 neurons and prolongation of the latencies of these responses, while stimulations promoting the inflow of afferent information to the cortical projection of the working limb evoke opposite effects, an increase in the intensity of neuronal spike responses and a decrease in their latencies.     

Effect of noradrenalin and serotonin on synaptic transmission in the rat spinal cord

Experiments on superfused isolated spinal cord preparations from rats aged 8–13 days showed that noradrenal in and serotonin have only a weak effect on monosynaptic reflex discharges but a substantial effect on polysynaptic motoneuronal discharges: noradrenalin potentiates whereas serotonin inhibits them. Both amines inhibit dorsal root potentials evoked by stimulation of high-threshold afferents. Potentiation of polysynaptic motoneuronal discharges induced by noradrenalin is connected with hyperpolarization of high-threshold afferents due to inhibition of the function of neurons in the substantia gelatinosa, and with increased excitability of interneurons participating in the generation of motoneuronal discharges. Serotonin inhibits polysynaptic motoneuronal discharges through its direct depolarizing effect on terminals of high-threshold afferents and depression of interneuron activity responsible for these discharges. Adrenergic and serotonin receptors, mediating these effects of noradrenalin and serotonin, were subjected to pharmacologic analysis.A. M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 241–247, May–June, 1982.     

The investigation of locomotor activity control system in humans under the air-stepping conditions during passive and voluntary leg movements

The degree of activation of the central stepping program during passive leg movement was studied in healthy subjects under unloading conditions; the excitability of spinal motoneurons was studied during passive and voluntary stepping movements. Passive stepping movements with characteristics maximally close to those during voluntary stepping were accomplished by the experimenter. The bursts of muscular activity during voluntary and imposed stepping movements were compared. In addition, the influence on the leg movement of artificially created loading onto the foot was studied. The excitability of spinal motoneurons was estimated by the amplitude of modulation of the m. soleus H reflex. Changes in the H reflex (Hoffmann’s reflex) after fixation of the knee and hip joints were also studied. In most subjects, passive movements were accompanied by bursts of electromyographic (EMG) activity in the hip muscles (sometimes in shank muscles); the timing of the EMG burst during the step cycle coincided with the burst’s timing during voluntary stepping. In many cases, the bursts in EMG activity exceeded the activity of homonymous muscles during voluntary stepping. Simulation of foot loading influenced significantly the distal part of the moving extremity during both voluntary and passive movements, which was expressed in the appearance of movements in the ankle joint and an increase in the phasic EMG activity of the shank muscles. The excitability of motoneurons during passive movements was higher than during voluntary movements. Changes and modulation of the H reflex throughout the step cycle were similar without restriction of joint mobility and without hip joint mobility. Fixation of the knee joint was of great importance. It is supposed that imposed movements activate the same mechanisms of rhythm generation as supraspinal commands during voluntary movements. During passive movements, presynaptic inhibition depends mostly on the afferent influences from the moving leg rather than on the central commands. Under the conditions of “air-stepping,” the afferent influences from the foot pressure receptors are likely to interact actively with the central program of stepping and to determine the final activity pattern irrespective of the movement type (voluntary or passive).