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.     

Effects of adequate vestibular stimulation on locomotor activity in fore- and hindlimb muscles in the guinea pig. Movement along a vertical axis

The effects of applying adequate vestibular stimulation to the mesencephalic locomotor region on locomotor activity in fore- and hindlimb muscles was investigated during experiments on decerebrate guinea pigs. This stimulation was produced by linear sinusoidal shifting of the animal along a vertical axis at rates of 0.08, 0.2, 0.4, and 0.8 Hz (with peak accelerations of 0.010, 0.063, 0.252, and 1.010 m·sec^–2 respectively). A downwards shift was found to increase electromyographic extensor muscle activity in fore- and hindlimbs occurring during the swing phase of the locomotor cycle. An upwards movement was accompanied by the opposite changes in muscle activity. Minimum acceleration required to produce an alteration in muscle activity equaled 0.063 m·sec^–2 (0.006g). These alterations were characterized by cyclical delay in relation to linear (active) acceleration. Phase lags in the activity of fore- and hindlimb extensor muscles at the rate of 0.8 Hz reached 63° and 86° respectively. Changes in flexor muscle activity ran counterphasically to these; phasic delay equalled 264° and 275° respectively. The part played by the vestibular system in control over locomotor activity in vertebrate muscles is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 192–197, March–April, 1989.     

Influence of the efferent vestibular system on vestibulo-spinal reflexes in the guinea pig

The influence of the efferent vestibular system on vestibulo-spinal activity was investigated during experiments on guinea pigs decerebrated and following cerebellar extirpation at precollincular level. Efferent vestibular neurons forming compact groups ventromedially to the vestibular nuclei were excited by means of electrical stimulation. Electromyographic activity in the triceps brachii extensor muscles of the right and left forelimbs was adopted as a test reaction (crossed extensor reflex and locomotor activity produced by stimulating the mesencephalic locomotor region). Adequate stimulation of the vestibular apparatus was accomplished by static tilting and cyclic shifting of the animal around its longitudinal axis at angles of ±20°. The efferent vestibular system was found to exert a bilateral inhibitory action on vestibulo-spinal activity. Vestibular efferent stimulation produced a reduction in the intensity of vestibulo-fugal influences: it does not change the dynamics of vestibulo-spinal reflex effects, however. Mechanisms of vestibular efferent action on vestibular control of spinal motor activity are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 78–86, January–February, 1989.     

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 evoked rhythmic activity in the forelimb nerves of immobilized guinea pigs

The effects of adequate vestibular stimulation, achieved by turning the animal around its longitudinal axis, on intensity of rhythmic activity in forelimb muscle nerves were investigated during experiments on immobilized decerebrate guinea pigs. This activity was produced by electrical stimulation of the mesencephalic locomotor region, following the action of DOPA administered i.v. Rhythmic activity arises mainly in the flexor muscle nerve under these circumstances. The intensity of such activity alters as the body was tilted, diminishing and increasing as the body is tilted to the ipsi- and contralateral side, respectively. Alterations in activity are characterized by an acceleration-related phase lag of –110 to –150° during cyclic tilting at the rate of 0.02–0.4 Hz.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 223–227, March–April, 1990.     

Neuronal activity of the lateral vestibular nucleus of the guinea pig evoked by tilting the animal about the longitudinal axis during locomotion

In experiments on decerebrate guinea pigs, the impulse activity of neurons of the lateral vestibular nucleus evoked by tilting the animal about the longitudinal axis was investigated under conditions of spontaneous and mesencephalon stimulation-evoked locomotor activity. In most investigated neurons, locomotor activity led to changes in their responses to adequate vestibular stimulation. The dominant reaction was intensification of such responses, which was observed in almost all vestibulospinal neurons and in 2/3 of cells not having descending projections. Responses were suppressed only in 1/4 of the neurons not projecting to the spinal cord. The changes in the evoked responses had an amplitude character; the lag of the changes in the discharge frequency relative to the acceleration that caused them was constant. It is suggested that intensification of dynamic reactions of vestibular neurons during locomotion provides maintenance of the animal's equilibrium during movements in space by various gaits and along different trajectories.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 541–549, September–October, 1991.     

Study of different kinds of locomotor movements in rats

The kinematics and electromyographic activity of the hind limb muscles of intact rats fixed in a special frame were investigated during locomotor movements of different kinds. A change in the external conditions determining the degree of limb loading (the presence or absence of support, and so on) was shown to lead to changes in the pattern and (or) amplitude of the movements. Six types of locomotion were distinguished, and in accordance with the kinematics of the hind limb movements these can be divided into two types: swimming and stepping. The analysis showed marked variability of the parameters (frequency, duration of the swing phase and of the support phase) of the different locomotor movements.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 183–189, March–April, 1985.     

The rhombencephalic "locomotor region" in turtles

Electrical stimulation (10–20 µA, 20–30 Hz) of the rhombencephalon in decerebrate turtles can induce cyclic coordinated limb movemnts. The "locomotor region" is a strip, oriented in the rostro-caudal direction, which coincides in its location with the lateral reticular formation. Both in the medial and in the lateral reticular formation extracellular ipsilateral and contralateral synaptic responses of single neurons evoked by stimulation of the "locomotor region," (10–30 µA, 2 Hz), were recorded. Usually these responses had latent periods of between 3 and 12 msec (mode 5–6 msec). Excitation of the "locomotor region" thus leads to extensive spread of activity in the rhombencephalon. The possible mechanisms of this spread are discussed.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 12, No. 4, pp. 382–390, July–August, 1980.     

Modulation of segmental reflex reactions during actual locomotion in rats

High- and low-threshold reflex segmental reflex reactions produced by stimulating the dorsal root at different stages of the locomotor cycle were investigated during locomotor swimming motions in white rats. Findings show respectively considerable inhibition of and a pronounced increase in extensor and flexor lowthreshold reflex reactions during the absence and presence of activity in the associated muscles. Low-threshold stimulation produced no outstanding effect on the shaping of the muscles' own activity and hence failed to affect time course or amplitude parameters of locomotor movements. Changes in reflex reactions to high-threshold stimulation during the locomotor cycle largely resembled changes in these responses to low-threshold stimulation, although development of highthreshold reactions differed from that of low-threshold response in affecting the parameters of locomotor activity in the associated muscle, while likewise altering frequency parameters of the locomotor rhythm. The physiological significance and mechanisms possibly underlying modulations in the efficacy of afferent peripheral influences during locomotion are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 3, pp. 326–333, May–June, 1988.     

Reordering of scratch generator efferent activity produced by stimulating hindlimb muscle afferents in decerebrate immobilized cats

Reorganization of the parameters of efferent activity produced in the spinal generator by electrical stimulation of the ipsilateral hindlimb muscle nerves during different limb positions were investigated in decerebrate immobilized cats. A direct relationship was found between this reordering and the stage at which stimuli were applied. The rearranged duration of the scratch cycle showed a tendency to bring motor activity into phase with stimuli so that the stimulus falls due at the onset of the motor activity phase. This phasically collated rearrangement was observed where a shift had occurred in the relationship between "aiming" and "scratch" motion tending towards intensified activity in the muscles innervated by the stimulated nerve. Rearrangement became more evident when the hindlimb deflected from the target position in accordance with the direction of muscle stretching. The physiological significance of the interposition of the "no rearrangement" phase is discussed. It is deduced that this absence of change in duration and intensity can only be produced simultaneously when a certain relationship is achieved between the phase of afferent signal reception in the scratch cycle and signal intensity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 372–382, May–June, 1987.     

Role of afferent activity in the generation of stepping movements

Efferent fibers of the hind limbs were divided and electrical activity of a filament from the ventral root of S1 was recorded in experiments on mesencephalic cats capable of locomotion in response to stimulation of the "locomotor region" of the midbrain. In response to weak stimulation of the locomotor region, when the forelimbs were not performing stepping movements, regular waves of activity appeared in the filament with a period close to the duration of the step during walking (0.5–1.0 sec). This periodic process was largely dependent on the tonic afferent inflow: various extero- and interoceptive stimuli applied to the hind limb could change the period of generation or abolish it. Active stepping movements of the forelimbs as well as passive movements of the hind limbs led to synchronization of activity in the filament with these movements. After division of the afferent fibers to the hind limbs the animals performed one or two steps in response to stimulation of the dorsal root of S1 by a short series of pulses. They could also perform independent stepping movements of the hind limb if 15–30% of the fibers in the dorsal root of L7 remained intact.M. V. Lomonosov Moscow State University. Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 401–409, 1972.     

Unit responses in the "locomotor strip" of the cat hindbrain to microstimulation

Synaptic responses of single units in the "locomotor strip" of the hindbrain were recorded extracellularly. Short-latency responses appeared in neurons of the rostral part of the strip to stimulation of the "locomotor region" of the mesencephalon. Neurons of the caudal part of the strip responded to microstimulation of its other regions, including rostral. If the distance between the neuron and point of stimulation was under 2–3 mm, short-latency (1.2–1.6 msec) responses could be observed. The thresholds and latent periods of the responses increased when the distance apart increased. Polysynaptic responses with a latent period of 3–4 msec could be potentiated by an increase in the frequency of stimulation up to 30–40 Hz. It is suggested that axons of the "locomotor strip" are oriented in the rostrocaudal direction for a distance of 2–3 mm and give off collaterals which run toward neighboring neurons. The strip may be an integrative center, "intercalated" between the rostral portions of the brain stem and spinal cord.Deceased.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 510–518, September–October, 1978.     

Rearrangement of efferent activity of the locomotor generator under electrical activation of descending systems in immobilized cats

The effects of signals travelling through vestibulo-, rubro-, reticulo-, and corticospinal systems on the parameters of locomotor generator activity were investigated in decerebrate immobilized cats. Certain phase-linked alterations in these parameters were found to occur under the effects of electrical stimulation applied to these systems (brief trains of stimuli). The biggest increase in locomotor cycle length was produced by electrical stimulation of Deiter's nucleus — stimulus presentation at the end of the extension phase; stimulation at the flexor stage leads to a shortening of this cycle. Maximum increase in locomotor cycle length produced by electrical stimulation of the red nucleus and nucleus gigantocellaris reticularis together with the pyramidal tract takes place during the first half of the flexion phase. Electrical activation of these descending pathways during the flexion phase induces intensification of this phase and reduced intensity of the extension phase. Activation of the vestibulospinal tract produces increased and reduced intensification of the extension phase respectively. Principles of suprasegmental correction of locomotor and scratch generators are compared.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 151–160, March–April, 1991.     

Transformation of the afferent tactile signal into a motor command in the cat motor cortex

Activity of 112 neurons of the precruciate motor cortex in cats was studied during a forelimb placing reaction to tactile stimulation of its distal parts. The latent period of response of the limb to tactile stimulation was: for flexors of the elbow (biceps brachii) 30–40 msec, for the earliest reponses of cortical motor neurons about 20 msec. The biceps response was observed 5–10 msec after the end of stimulation of the cortex with a series of pulses lasting 25 msec. Two types of excitatory responses of the neurons were identified: responses of sensory type observed to each tactile stimulation of the limb and independent of the presence or absence of motion, and responses of motor type, which developed parallel with the motor response of the limb and were not observed in the absence of motion. The minimal latent period of the responses of motor type was equal to the latent period of the sensory responses to tactile stimulation (20±10 msec). Stimulation of the cortex through the recording microelectrode at the site of derivation of unit activity, which increased during active flexion of the forelimb at the elbow (11 stimuli at intervals of 2.5 msec, current not exceeding 25 µA), in 70% of cases evoked an electrical response in the flexor muscle of the elbow.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 115–123, March–April, 1977.     

The role of skin afferent in regulation of locomotion evoked by electrical epidural stimulation of spinal cord in decerebrated cats

The role of hindpaw skin afferent input in the locomotor pattern formation induced by epidural spinal cord stimulation was investigated in decerebrated cats. Locomotor activity was evoked by continuous 3-5Hz stimulation of dorsal surface of L4-L5 spinal segments. Kinematic and electromyographic activity (EMG) of m. Quadriceps, m. Semitendinosus, m. Tibialis anterior an m. Gastrocnemius lateralis before and after blocking of skin receptors in one hind limb were recorded. In addition, reflex responses in the hind limb muscles to epidural stimulation with frequency 0.5 Hz were analysed. Blocking of skin receptors of the foot with chlorothane paw irrigation or 2 % lidocaine administrated into the hind paw was performed. After blocking of skin receptors of the foot the stepping pattern changed. Stepping with dorsal foot placement and dragging during swing phase was observed. Duration of stance phase significantly decreased. Inhibition of polysynaptic activity of proximal and distal extensor muscles and distal flexor muscles of hind paw during locomotion was found. Monosynaptic responses after blocking of skin receptors of the foot changed insignificantly.     

Tonic inhibitory influences of locus coeruleus on the response gain of limb extensors to sinusoidal labyrinth and neck stimulations

Previous experiments had shown that in decerebrate cats activation of limb extensor motoneurons during side-down roll tilt of the animal or side-up neck rotation depends on both an increased discharge of excitatory vestibulospinal (VS) neurons and a reduced discharge of inhibitory reticulospinal (RS) neurons of the medulla, thus leading to disinhibition of limb extensor motoneurons. The present experiments were performed to find out whether the locus coeruleus (LC) complex keeps under its tonic inhibitory control the medullary inhibitory RS neurons and, if so, whether this structure intervenes in the gain regulation of the vestibular and neck reflexes acting on the limb extensor musculature. In precollicular decerebrate cats with good postural rigidity of the four limbs, the amplitude of modulation and thus the response gain of the first harmonic component of multiunit EMG responses of limb extensors to sinusoidal stimulation of labyrinth and neck receptors (at 0.15 Hz, +/- 10 degrees) were quite small in forelimb muscles (triceps brachii) and almost negligible or absent in hindlimb muscles (triceps surae). Electrolytic lesion limited to the LC complex decreased the tonic contraction of limb extensors, but greatly increased in the forelimbs (and brought to the light in the hindlimbs) the response modulation of extensor muscles to the same parameters of labyrinth or neck stimulation. Correspondingly, the response gain increased, but no change in the phase angle of the responses was observed. Both changes in posture, as well as in response gain of the limb extensors to labyrinth and neck stimulation, fully developed some time after the LC lesion. This increase in response gain of the vestibular and neck reflexes acting on the limb extensor muscles did not depend on the decrease in postural activity following the LC lesion, since it was still obtained when an increased static stretch of the extensor muscle following passive flexion of the limb compensated for the reduced EMG activity. Moreover, the slope of the regression line relating the gain of the multiunit EMG response of the triceps brachii to animal tilt with the base frequency greatly increased following lesioning of the LC, thus indicating that for the same background discharge of the muscle the amplitude of modulation, and thus the response gain, increased significantly. The effects described above involved mainly, but not exclusively, the limbs ipsilateral to the side of the lesion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Convergence of reticulo-, vestibulo-, and rubrospinal influences on cervical spinal motoneurons in cats

Intracellular recordings were made of synaptic responses of 93 motoneurons in the cervical region of the cat spinal cord to stimulation of the medial longitudinal bundle, the brain-stem reticular formation, the lateral vestibular nucleus of Deiters, and the red nucleus. In response to stimulation of the medial longitudinal bundle and the vestibular nucleus responses in the motoneurons of the distal groups of muscles of the forelimb were predominantly excitatory, whereas in motoneurons of the proximal extensor muscles they were predominantly inhibitory. During stimulation of the red nucleus, excitatory and inhibitory responses were recorded in almost equal numbers of cells regardless of their functional class. Monosynaptic EPSPs appeared in one-fifth of motoneurons in response to stimulation of the medial longitudinal bundle and, in a few cases, to stimulation of the vestibular and red nuclei. Otherwise, during stimulation of these structures polysynaptic responses were recorded in the motoneurons. In 62% of cases postsynaptic potentials arising in response to stimulation of the various suprasegmental structures tested were identical in direction in the same motoneurons. A mutually facilitatory effect was observed during stimulation of different suprasegmental inputs. The results are evidence that interaction between influences of the structures tested takes place largely at the level of spinal interneurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 4, pp. 391–399, July–August, 1978.     

Responses of upper cervical spinal neurons in cats to stimulation of the brain-stem locomotor region at different frequencies

Synaptic responses of neurons in segments C₂ and C₃ to stimulation of locomotor points in the medulla or midbrain were recorded extracellularly in mesencephalic cats. Neurons generating responses with an index of 0.4–0.6 to stimulation with a frequency of 2 Hz maintained this same index at frequencies of 20–60 Hz. The discharge index of many neurons during stimulation at 2 Hz was low, and it increased to 0.4–0.6 when high-frequency stimulation was used. More than half of the cells were excited by stimulation of both ipsilateral and contralateral locomotor points; one-quarter of the neurons responded to stimulation of locomotor points in both medulla and midbrain. The cells studied were located 1.8–4.2 mm from the dorsal surface of the spinal cord. The mean latencies of responses with an index of not less than 0.5 lay within the range 2–30 msec, with a mode of 2–8 msec. Considerable fluctuations of latent period were observed for long-latency responses. The possibility that the neurons studied may participate in the transmission of activity from the locomotor region of the brain stem to stepping generators in the spinal cord is discussed.Institute for Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 355–361, July–August, 1983.     

Primary afferent depolarization induced by cyclically modulated natural hind limb proprioceptor activity in cats

Primary afferent depolarization (PAD), developing during passive movements of the ankle with a frequency of 0.14–5.0 Hz was investigated in decerebrate cats. An increase in the dorsal root potential, the amplitude of which was used to judge the intensity of PAD, was observed during both extension and flexion of the joint. Parallel with waves of the dorsal root potential, changes in amplitude of the N component of the dorsal cord potential in response to stimulation of a cutaneous nerve during different phases of the limb movement cycle were recorded. These changes were periodic in character and opposite in phase to oscillations of dorsal root potential. The mechanisms of the observed changes in the PAD level and also the functional significance of these changes during cyclic motor acts are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 372–380, May–June, 1985.     

Rearrangement of parameters of efferent activity in generators of cyclic motor response produced by electrical stimulation of cerebellar inputs in cats

Rearrangement of the parameters of scratch and locomotor generators produced by electrical stimulation of the inferior olive and nucleus reticularis lateralis as well as the cerebellar fastigial nucleus and nucleus interpositus was investigated in decerebrate immobilized cats. Results showed that a comparable rearrangement of the time course of activity in both locomotor and scratch generators was produced by altering the nature of signals proceeding along mossy and climbing fibers alike. Maximum rearrangement of scratch and locomotor generator activity, as induced by electrical activation of the inferior olive and lateral reticular nucleus, is observed during the first half of flexor half-center operation in these generators. The scratch (unlike the locomotor) generator typically shows considerably rearranged efferent activity following electrical activation of nuclei of the cerebellum and cerebellar afferents. The article discusses mechanisms of cerebellar origin which may be responsible for exerting a corrective action on scratch and locomotor generators during change in the phase and amplitude parameters of cerebellar input signals.A. A. Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 24, No. 2, pp. 131–140, March–April, 1992.