Reordering of scratch generator efferent activity produced by stimulating hindlimb skin afferents in decerebrate immobilized cat

Reordering of the parameters of motor activity produced in the scratch generator by regular electrical stimulation of the ipsilateral hindlimb muscle nerve during different limb positions was investigated in decerebrate immobilized cats. Brief short latency inhibition of currently occurring motor activity was produced in response to stimulation, which did not cause an overall shift in the relationship between the intensity of aiming and scratching motion. Changes in cycle duration and intensity of these activities were phase-locked. Speculations were made on the functional role of the phase-locked nature of motor activity remodeling. The possible existence within the scratch generator of a model of the afferent inflow entering the spinal cord during true scratching is suggested.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 382–390, May–June, 1987.     

Correlation between the kinematics of hindlimb movement and efferent activity in the decerebrate cat during scratching

The statistical relationship was investigated between temporal and amplitude parameters of scratching motion performed by the hindlimb and those of muscular activity during naturally-occurring scratching in the course of experiments on decerebrate cats. The factors mainly determining movement parameters, such as amplitude or the speed and duration of a specific phase were found to be the intensity of EMG activity displayed by scratching and aiming muscles and the duration of aiming muscle activity. Findings from experiments involving limb deafferentation showed that the statistical relationship between the parameters of motion and muscular electrical activity reflect certain patterns of scratch generator operation. Certain relationships linking parameters of electrical activity changed due to the effects of afferent signals.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 525–533, July–August.     

Rearrangement of scratch generator efferent activity during electrical activation of descending systems

Effects of signals proceeding along descending pathways on parameters of scratch generator activity were investigated in decerebrate immobilized cats. Certain phase-linked alterations in these parameters were shown to occur under the effects of electrical activation of the main descending systems. The biggest increase in scratch cycle duration under electrical stimulation of Deiter's nucleus, the red nucleus, and pyramidal tract is produced when stimuli are applied during the first half of the aiming stage. Stimulation during the second half of the aiming phase and at the start of the scratching movement hardly affect the scratching cycle. The main increase in length of scratch cycle during electrical stimulation of the reticular gigantocellularis nucleus is noted when stimuli are presented during the second half of the aiming stage. Electrical activation of descending pathways during the latter induces a rise in intensity in this phase and reduced intensity of the actual scratching stage. Activation of the pathways during this scratching motion causes heightened intensity of the motion while hardly affecting intensity of the aiming phase. The principles of suprasegmental rectification of scratch generator operation are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 3, pp. 300–309, May–June, 1990.     

Recording of scratch generator efferent activity produced by cyclic hindlimb movement in decerebrate immobilized cat

The effects were observed on spinal scratch generator activity of the afferent inflow produced in decerebrate immobilized cat by regular passive movement of the hindlimb paw following a trajectory close to that observed during actual scratching. These consisted of substantial alteration in scratch generator efferent activity, which thereby became phase-locked with the afferent flow. Synchronization between efferent scratching activity and passive limb motion has occurred by the first movement cycle and phase-locking was the reverse of that seen during actual scratching.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 443–449, July–August, 1987.     

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.     

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.     

Response of human motor units to spinal and supraspinal inhibition

High-selectivity surface electrodes were used to record the activity of single motor units of the human flexor pollicis brevis muscle and their involvement in the "silent period" and the inhibitory phase of the startle response was compared. In both these situations the degree of inhibition was greater for motor units whose action potential had a smaller amplitude. In cases of spinal inhibition, an independent direct relationship also was discovered between the intensity of the inhibitory response and the mean duration of the prestimulus interspike interval, which was completely absent during supraspinal inhibition. Correlation between the parameters of the inhibitory response of the single motor unit to influences of both types was significantly weaker than correlation between the effects of the spinal rebound phenomenon after both responses. The results suggest that involvement of spinal motoneurons in the inhibitory response is determined by interaction between several relatively independent factors.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 298–306, May–June, 1973.     

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.     

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.     

Limb movement,intensity of integral afferent impulses from limb receptors,and level of primary afferent terminal polarization during locomotion in cats decerebrated at high level

The relationship between parameters of electrical muscle activity, changes at hindlimb joint angles, intensity of integral afferent flow, and dorsal root potential during real-life locomotion was investigated in cats decerebrated at high level. Characteristics of rear limb movements before and after deafferentation were described. It was found that afferent activity during locomotion motion consists, of two components — a tonic and a periodic phasic stage. Three main waves may be distinguished in the latter, each of which gives rise to associated changes in the level of primary afferent terminal polarization. These changes in turn are summated with the effects produced by the central generator. Correlations, between the parameters of these processes were investigated and the mechanisms underlying afferent control of locomotion generator function discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 119–127, January–February, 1988.     

Fictive hindlimb motor patterns evoked by AMPA and NMDA in turtle spinal cord-hindlimb nerve preparations.

Application of the glutamate agonists alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate (AMPA, 5-10 microM), or N-methyl-D-aspartate (NMDA, 50-100 microM) to the turtle spinal cord produced fictive hindlimb motor patterns in low-spinal immobilized animals (in vivo) and in isolated spinal cord-hindlimb nerve preparations (in vitro). For in vivo experiments, drugs were applied onto the dorsal surface of 2-4 adjacent spinal cord segments in and near the anterior hindlimb enlargement. Motor output was recorded unilaterally or bilaterally from hindlimb muscle nerves. AMPA elicited vigorous motor patterns in vivo that included strict hip flexor-extensor and right-left alternation. In most turtles, the monoarticular knee extensor nerve FT-KE was active during the HE phase of AMPA evoked burst cycles, similar to the timing of pocket scratch motor patterns. NMDA was less effective in vivo, typically producing only weak and irregular bursting from hip nerves and little or no knee extensor (KE) discharge. Sensory stimulation of a rostral scratch reflex in vivo could reset an ongoing AMPA-evoked motor rhythm, indicating that cutaneous reflex pathways interact centrally with the chemically activated rhythm generator. Most in vitro preparations consisted of six segments of spinal cord, including the entire 5-segment hindlimb enlargement (D8-S2) and the segment immediately anterior to the enlargement (D7), with attached hindlimb nerves. In contrast to in vivo experiments, in vitro preparations exhibited highly regular, long-lasting motor rhythms when NMDA was superfused over the spinal cord. AMPA also produced rhythmic motor patterns in vitro, but these lasted only a few minutes before they were replaced with tonic discharge. FT-KE timing during in vitro chemically elicited activity was similar to that of sensory-evoked pocket scratch motor patterns. Some NMDA-evoked rhythmicity persisted even in 3-segment (D6-D8) and 1-segment (D8) in vitro preparations, demonstrating that neural mechanisms for chemically activated rhythmogenesis reside even in a single segment of the hindlimb enlargement.     

Dependence of efferent activity parameters on limb position during fictitious scratching in decerebrate cats

The influence of tonic afferent inflow as conditioned by ipsilateral hindlimb position on the efferent activity parameters of the spinal generator governing scratching motion was investigated in immobilized decerebrate cats. A significant correlation was observed between motor activity parameters and ensuing bouts of scratching in the absence of afferent flow (after deafferentation of the limbs). This correlation was less pronounced when afferentation remained intact and declined when the limb was shifted from the "aimed" to either the "overaimed" or "deflecting backwards" placing of the limb. The statistically significant correlations found between the parameters of different stages of motor activity and their dependence on hindlimb positions during actual scratching could be responsible for the stability of intended placing of the limbs during the performance of oscillatory movements. Hindlimb deafferentation would appear closest to "aimed" position judging by the parameters of efferent activity and the nature of correlations between them.A. A. Bogomolets Institute of Physiology. Academy of Sciences of the Ukrainian SSR. Kiev. Translated from Neirofiziologiya, Vol. 15, No. 5, pp. 636–645, September–October, 1986.     

Quantitative changes in efferent activity of the scratch generator produced by eliminating influences from the descending systems

The effects of signals proceeding along descending systems of the spinal cord on the parameters of efferent activity in the scratch generator (i.e., discharges in ventral roots L₅ and L₇) were investigated in decerebrate immobilized cats. It was found that eliminating cerebellar modulatory influences on nuclei of the descending system (decerebellation) leads to an altered ratio between the activity of generator hemicenters, increased instability of generator operation, a reduced statistical relationship between alteration in parameters of hemicenter activity, and raised sensitivity to afferent signals in the generator. Complete elimination of descending system influences (after severing the spinal cord at the anterior boundary of the first cervical segment) produced a reduction in the intensity of efferent activity and in the afferent sensitivity of the scratch generator. The functional significance of descending signals for operation of the scratch generator is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 123–131, January–February, 1990.     

Alterations produced in the quantitative characteristics of efferent activity parameters of the locomotor generator by decerebellation

Changes in the parameters of activity in hindlimb locomotor generators following decerebellation were quantified during experiments on decerebrate immobilized cats. Eliminating modulating cerebellar influences on nuclei of descending systems was found to lead to a slight increase in the length of activity in the flexor generator half-center and less intensive activity, as well as shortening of the period and more intensive activity in the extensor half-center, together with increased instability in generator operation, reduced statistical dependence between alterations in parameters of activity at the hindlimb half-center generators, and finally intensified effects of afferent inputs on generator activity. A comparison is drawn between the functional role of the spino-cerebellar loop in the operation of locomotor and scratch generators.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 142–150, March–April, 1991.     

Study of firing pattern in human soleus motor units in tonic vibration reflex

Tonic vibration reflex was produced in the human soleus muscle by vibrating the tendon at the rate of 30–180 Hz and motor unit potentials were recorded. A correlation was found between the points at which these potentials occurred and vibratory stimuli over lower ranges of vibration rates (of up to 70–80 Hz) in all motor units, indicative of discrete bursts in the synaptic inflow to the motoneuron matching the vibratory stimuli. The correlation disappeared with an increase in vibration rate and manifested at high as well as low vibration rates in voluntarily contracted muscle. Since vibration is known to (presynaptically) depress monosynaptic reflexes induced by activating primary spindle endings, it is suggested and maintained that the correlation found at low vibration rate ranges could result from activating vibrational stimuli of secondary spindle endings which act on motoneurons via short pathways, thus evoking discrete motoneuronal EPSP.Information Transmission Research Institute, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 765–772, November–December, 1989.     

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.     

Effect of direct and transcallosal stimulation on inhibition of unit activity in the cat association cortex

Inhibition of association cortical neurons (in the form of inhibition of spontaneous activity or of IPSPs) during direct and transcallosal stimulation was studied in cats immobilized with muscle relaxants. The duration of inhibition of stimulation and the number of stimuli. With an increase in the strength of stimulation inhibition deepened to a certain level for a particular neuron, after which it could be further lengthened with an increase in the number of stimuli. In the case of repeated stimulation by volleys of stimuli, very prolonged inhibition developed gradually in the neurons, during which spontaneous activity was inhibited for 2–5 sec. The duration of the IPSP depended on the intensity of stimulation and number of stimuli and its amplitude depended on the intensity and frequency of stimulation and on the number of stimuli. In some cases the amplitude of the IPSP continued to rise after a short volley of stimuli, even after the end of stimulation. An increase in the number of stimuli in the volley lengthened the IPSPs, but their amplitude remained constant throughout the period of stimulation. Prolonged inhibition (up to a few seconds) was connected with the development of a hyperpolarization postsynaptic potential in the neurons. It is suggested that neurons exerting a monosynaptic inhibitory influence on cells of the association cortex may be located in the opposite hemisphere.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 133–141, March–April, 1981.     

Changes in the intensity of integral afferent inflow from limb receptors and in primary afferent terminal polarization during scratching in the decerebrate cat

Experiments performed on decerebrate cats showed that afferent activity accompanying scratching consists of two components—one with a tonic and the other with a periodic phase. The first of these is determined by limb position and the second closely related to speed and amplitude of angular changes occurring at the joints. Peak integral afferent activity within the cycle occurred at the end of the scratch phase itself, when aiming muscles are already operating. These two components of afferent activity produce corresponding changes in depolarization at primary afferent terminals (DPA), which are added to those DPA changes brought about by the effects of the central generator. Statistical relationships between the aforementioned processes were investigated. Mechanisms underlying afferent control over the operation of the scratch generator are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 49–57, January–February, 1988.     

Post-Tetanic Repetitive Activity in the Cat Soleus Nerve : Its origin, course, and mechanism of generation

Subsequent to conditioning by a high frequency stimulus axons of the cat soleus nerve respond to single stimuli with brief trains of repetitive action potentials. This phenomenon, post-tetanic repetitive activity (PTR), was studied in individual axons and single motor units of an in situ cat soleus nerve-muscle preparation. The occurrence, intensity, and duration of PTR are principally dependent on the frequency and duration of the conditioning tetanus. PTR occurs synchronously in the axon and muscles of single motor units. An analysis of the temporal relationships of the repetitive nerve and muscle potentials showed that PTR is generated in the motor nerve terminal. It is postulated that PTR is produced by a generator potential which is developed in the post-tetanic period between the unmyelinated nerve terminal and the last node of Ranvier.     

Two patterns of bulbar neuronal response to microstimulation of locomotor and inhibitory brain stem sites

Synaptic responses (postsynaptic potentials and action potentials) were evoked in mesencephalic decerebellated cats by stimulating pontine bulbar locomotor and inhibitory sites (LS and IS, respectively) with a current of not more than 20 µA in "medial" and "lateral" neurons of the medulla. Some neurons even produced a response to presentation of single (actually low — 2–5 Hz — frequency) stimuli. The remaining cells responded to stimulation at a steady rate of 30–60 Hz only. Both groups of medial neurons were more receptive to input from LS. Lateral neurons responding to even single stimuli reacted more commonly to input from LS and those responding to steady stimulation only to input from IS. Many neurons with background activity (whether lateral or medial) produced no stimulus-bound response, but rhythmic stimulation either intensified or inhibited such activity. This response occurs most commonly with LS stimulation. Partial redistribution of target neurons in step with increasing rate of presynaptic input may play a major part in control of motor activity.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 257–266, March–April, 1990.