Retuning of segmental responses to peripheral stimulation in cats during fictitious locomotion

Segmental responses of the lumbosacral region of the spinal cord to peripheral afferent stimulation were studied in decorticated, immobilized cats before and during fictitious locomotion. The appearance of fictitious locomotion was accompanied by a tonic increase in the N₁-component of the dorsal cord potential and dorsal root potential. Against the background of this tonic increase, modulation of these responses depending on the phase of fictitious locomotion was observed. When the N₁-component and dorsal root potential were evoked at the end of the "extension" phase and at the beginning of the "flexion" phase their amplitude was greater, but when they were evoked at the end of the "flexion" phase and the beginning of the "extension" phase it was smaller. Polysynaptic and monosynaptic reflex response of motoneurons exhibited the same phase dependence during fictitious locomotion. The mechanisms and physiological importance of this retuning of segmental responses are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 283–291, May–June, 1981.     

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.     

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.     

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.     

Kinematics of different types of locomotor movements in the deafferented rat

The kinematics of rat hindlimb movements were assessed and compared pre- and post-deafferentation during swimming, forelimb treadmill locomotion plus hindlimb swimming motion, and walking using all four limbs. All types of locomotion were characterized by an increase in the frequency of locomotor rhythm and reduced amplitude of motion at the hindlimb joints following deafferentation. The reduced change observed in the angle of the coxofemoral joint, indicative of a horizontal component in locomotor motion, was mainly brought about by less marked extension. This would confirm evidence indicating that increased load on the extremities, with its ensuing naturally-occurring afferent outflow, is accompanied by a reduced locomotor motion rate and a rise in the amplitude of the latter due to intensified extension of the limb. The increased forward carriage of the hind limb seen during the transition to four-legged locomotion persisted after deafferentation; this may be considered a sign of coordination amongst the limbs. Deafferentation led to a reduction in the MEG of muscle activity, which was found to be lowest in swimming and highest during walking. The role of the afferent inflow in shaping different types of locomotor motion is evaluated.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 520–525, July–August, 1987.     

Phase-dependent changes in dorsal root potential during actual locomotion in rats

Fluctuations in dorsal root potential (DRP) were investigated in trials on white rats during two types of locomotion, differing in the intensity of afferent flow (swimming and walking). Two negative waves of DRP were observed corresponding to the stance (or propulsive) phase and the swing (or transfer) phase within a single locomotor cycle. Whereas DRP had risen primarily during the stroke phase with increased intensity during swimming, it increased during the standing phase in walking. A relationship was revealed between the amplitude of DRP and the intensity of afferent flow apparent during passive displacement of the limb, as well as locomotion. It is concluded that DRP waves are mainly due to influences from peripheral afferents during actual locomotion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 3, pp. 333–340, May–June, 1988.     

Influence of adequate vestibular stimulation on locomotor activity in the guinea pig forelimb muscles. Tilting in relation to the longitudinal axis

The influence of adequate vestibular stimulation occurring as the animal tilted around longitudinal axis on locomotor activity of the forelimb muscles was investigated during experiments on guinea pigs decerebrated at precollicular level. Locomotor activity was produced by electrical stimulation of the mesencephalic locomotor region. An increase in extensor EMG activity was observed when the animal shifted its weight onto the limb ipsilateral to the tilt during the "standing" phase and a reduction in flexor activity during the swing phase. The reverse of these changes was seen in the activity of antagonist muscles in the contralateral limb. It was found that changes in muscular locomotor activity exceeded those observed during animal movements by 60–40° in the extensors and 40–20° in the flexors during cyclic sinusoidal tilting in the 0.02–0.4 Hz range. The mechanisms underlying vestibular control of locomotor activity are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 534–541, July–August, 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.     

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.     

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.     

Importance of preswing rectus femoris activity in stiff-knee gait

Stiff-knee gait is characterized by diminished and delayed knee flexion during swing. Rectus femoris transfer surgery, a common treatment for stiff-knee gait, is often recommended when a patient exhibits prolonged activity of the rectus femoris muscle during swing. Treatment outcomes are inconsistent, in part, due to limited understanding of the biomechanical factors contributing to stiff-knee gait. This study used a combination of gait analysis and dynamic simulation to examine how activity of the rectus femoris during swing, and prior to swing, contribute to knee flexion. A group of muscle-actuated dynamic simulations was created that accurately reproduced the gait dynamics of ten subjects with stiff-knee gait. These simulations were used to examine the effects of rectus femoris activity on knee motion by eliminating rectus femoris activity during preswing and separately during early swing. The increase in peak knee flexion by eliminating rectus femoris activity during preswing (7.5+/-3.1 degrees ) was significantly greater on average (paired t-test, p=0.035) than during early swing (4.7+/-3.6 degrees ). These results suggest that preswing rectus femoris activity is at least as influential as early swing activity in limiting the knee flexion of persons with stiff-knee gait. In evaluating rectus femoris activity for treatment of stiff-knee gait, preswing as well as early swing activity should be examined.     

Frequency potentiation in the neonatal rabbit hippocampus

The formation of properties of frequency potentiation in the entorhinal afferent pathway of the hippocampus was studied in unanesthetized rabbits aged from 1 to 15 days. In areas CA₁ and CA₃ of the dorsal hippocampus in newborn rabbits repetitive (1–20 Hz) electrical stimulation of the perforant path led to an increase in amplitude of the slow wave of the field potential by 20–100% compared with the control and to an increase in the probability of response discharges from the neurons from 0–0.5 in the control to 0.8–1.0 during tetanization. In rabbits aged 2–3 days potentiation was more marked at a frequency of 4–6 Hz, whereas depression of the responses developed rapidly to a higher frequency of stimulation. The frequency optimum of 4–15 Hz was established on the 5th day. Potentiation of the first component of the field potential was observed starting from the 8th–10th day of life. The experimental results show that the property of frequency potentiation in the cortical afferent connections of the hippocampus is found in rabbits actually at birth, and it acquires the adult form at the beginning of the second week of life.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 533–539, November–December, 1979.     

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.     

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.     

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.     

Organization of the afferent input in the rabbit superior colliculus

The organization of the afferent input into the superior colliculus was investigated in unanesthetized curarized rabbits. The afferent signal reaches the rabbit superior colliculus via at least two groups of fibers with mean conduction velocities of 3 and 6 m/sec. The components C₁ and C₂ of the evoked potential reflect postsynaptic unit activity arising after the arrival of impulses along these groups of fibers. This is confirmed by investigation of the shape of the evoked potential after stimulation of different points of the afferent pathway, data on conduction velocities, and comparison of single unit activity with the phases of evoked potential. The presence of components of this potential with short latent periods is evidence of predominance of the direct retinotectal input in the rabbit, a fact which may be connected with the lissencephalic type of brain development.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 281–289, May–June, 1977.     

Variations in UV-induced lethality and "petite" mutagenesis in synchronous culture of Saccharomyces cerevisiae. II. Responses of radiosensitive mutants to lethal damage

Summary A UV sensitive mutant of Saccharomyces cerevisiae, rad _1–3, considered to be blocked in a repair process of the excision-resynthesis type, exhibited in synchronized cultures, cyclic variations to UV-induced lethality comparable to those of the wild type strain. That is, the G1 phase was the most radiosensitive and G2 the most radioresistant.A mutant which is deficient in UV-induced intragenic recombination (rec ₅), also exhibited cyclic variations in radiosensitivity although the pattern of the response was strongly modified as compared to that of its original wild type: there was a progressive increase in radiosensitivity during the G1 phase which is never observed in a wild type strain.The double mutant rec ₅, rad _1–3 also exhibited the same type of cyclic responses in radiosensitivity as rad _1–3 and wild type strains, but the magnitude on the fluctuations was diminished due to a decrease in resistance during the G2 phase.Our results show that the repair process of the excision-resynthesis type, which is blocked in rad _1–3, would act very efficiently on UV-induced lesions and constantly throughout the cell cycle. The repair mechanism involved in intragenic mitotic recombination (rec ₅ strain) would mainly act during S and G2 phases.The response of rec ₅ rad _1–3 mutant showed that the two repair mechanisms refered to would not be the sole mechanisms involved in the expression of cyclic variations in lethality.     

Effect of dalargin,a synthetic leu-enkephalin analogue on synaptic transmission in the Lorenzini ampullae of rays

Effects of dalargin, a synthetic leu-enkephalin analogue and its antagonist naloxone on synaptic transmission in afferent synapses of ray electroreceptors were investigated using an isolated preparation of Lorenzini ampullae from Black sea rays. It was shown that dalargin (10^–6–10^–10 mole liter) both decreased background activity and evoked activity of an afferent fiber in a dose-dependent manner. Naloxone (10^–5 mole/liter) also inhibited afferent impulsation and completely blocked responses of the Lorenzini ampullae to dalargin application. L-glutamate-induced excitatory responses were reduced in the presence of dalargin. It is suggested that the modulatory action of dalargin on glutamatergic synaptic transmission in the Lorenzini ampullae is exerted via specific opiate receptors.Translated from Neirofiziologiya, Vol. 25, No. 1, pp. 18–21, January–February, 1993.     

Gibberellin induces endopeptidase activity in detached cotyledons of Pisum sativum

Endopeptidase activity in cotyledons of 5-day seedlings of Pisum sativum increased rapidly during germination. However, the increase of the activity in detached cotyledons was depressed. We examined whether a growth regulator can be substituted for the embryonic axis on the development of endopeptidase activity. As monitored by an assay with azoalbumin, the development of endopeptidase activity from crude extracts of detached cotyledons appeared to be slightly accelerated by incubation with 10^–5 M GA₃. However, the pattern after gelatin-polyacrylamide gel suggested that the activity induced in detached cotyledons during a 5-d incubation at 10^–7 M GA₃ was the same as that in attached ones during germination for 5 days and an even greater increase in activity was obtained with 10^–5 M GA₃. These results suggest that GA₃ from the embryonic axis induces endopeptidase activity in attached cotyledons at the first stage of germination.Abbreviations ABA abscisic acid - IAA indole-3-acetic acid - GA gibberellic acid