Effects of repetitive stimulation of the locus coeruleus on spinal inhibitory responses to suprasegmental stimulation in cats

Effects of repetitive stimulation of the locus coeruleus on spinal responses to activation of cortico-, reticulo-, and vestibulospinal tracts were studied in decerebellate cats anesthetized with chloralose. Descending influences of these structures were assessed from changes in amplitude of extensor and flexor monosynaptic discharges or from the magnitude of postsynaptic potentials recorded from the corresponding motoneurons. Stimulation of the motor cortex or modullary reticular formation as a rule evoked two-component inhibitory responses in extensor motoneurons and excitatory-inhibitory responses in flexor motoneurons. Stimulation of locus coeruleus effectively depressed the amplitude of the late component and, to a lesser degree, that of the early component of inhibition arising after stimulation of the cerebral cortex or reticular formation. During stimulation of the locus coeruleus no marked changes were found in inhibitory responses evoked by vestibulospinal influences in flexor motoneurons, and also in excitatory responses arising after stimulation of the above-mentioned descending pathways in both groups of motoneurons.     

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.     

Age-related parameters of spinal inhibition of skeletal muscles in regulation of voluntary movements in men

Age-related features of spinal inhibition in the regulation of voluntary movements in men were studied. It was found that presynaptic and nonreciprocal and reciprocal inhibitions of the flexor of toes during voluntary movements were less intense than inhibition during relative muscle rest in subjects of all age groups. This results from the age-related features of supraspinal excitatory and inhibitory effects on Ia and Ib spinal interneurons, which change the mechanism of spinal inhibition of voluntary movements as the organism develops. In boys 9–12 years of age, execution of voluntary movements is accompanied by the lowest presynaptic inhibition of Ia afferents and the most pronounced increase in nonreciprocal and reciprocal inhibition of α-motoneurons in the flexor of toes, compared to the other age groups. Execution of voluntary movements by boys 14–15 years of age leads to an increase in presynaptic inhibition of Ia afferents and the most pronounced decrease in reciprocal and nonreciprocal inhibition of spinal α-motoneurons of the flexor of toes. By the age of 17–18 years, the mechanism of nonreciprocal inhibition of α-motoneurons of the flexor of toes during voluntary movements is similar to that in adolescents aged 14–15 years. The definitive level of presynaptic inhibition of Ia afferents and reciprocal inhibition of α-motoneurons of the flexor of toes during voluntary movements is reached by 17–18 years.     

Changes in postsynaptic responses in spinal motoneurons during repetitive stimulation of the locus coeruleus

Experiments on cats anesthetized with chloralose showed that repetitive stimulation of the locus coeruleus is accompanied by a decrease in IPSPs evoked by stimulation of flexor reflex afferents in extensor motoneurons. The effect appeared 600 msec after the beginning of stimulation and reached its maximum after 1500–2000 msec. Repetitive stimulation of the locus coeruleus did not change the membrane potential and did not affect EPSPs or IPSPs evoked by stimulation of low-threshold muscle afferents; EPSPs due to activation of high-threshold cutaneous and muscle afferents likewise remained unchanged. Repetitive stimulation of more central regions of the brain stem was accompanied not only by a decrease in IPSPs evoked by stimulation of flexor reflex afferents in extensor motoneurons, but also by a decrease in amplitude of EPSPs arising in response to stimulation of these same afferents in flexor motoneurons. These effects were not connected with activation of monoaminergic structures, for unlike effects arising during stimulation of the locus coeruleus, they were also found in previously reserpinized animals.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 51–59, January–February, 1982.     

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.     

Proprioceptive regulation of locomotion

Recent investigations of proprioreceptors in the walking systems of cats, insects and crustaceans have identified reflex pathways that regulate the timing of the transition from stance to swing, and control the magnitude of ongoing motoneuronal activity. An important finding in the cat is that during locomotor activity, the influence of feedback from the Golgi tendon organs in extensor muscles onto extensor motoneurons is reversed from inhibition to excitation. The excitatory action of tendon organs during stance ensures that stance is maintained while extensor muscles are loaded, and may regulate the magnitude of extensor activity according to the load carried by the leg. Afferents from primary and secondary spindles in extensor and flexor muscles have also been found to influence the timing of the locomotor rhythm in a functionally relevant manner. Recent studies indicate that reflex reversals and the regulation of timing by multiple proprioceptive systems are also features of walking systems in arthropods.     

Changes in segmental reflex responses during stimulation of locus coeruleus and potentiation of the action of catecholamines

Repetitive stimulation of the locus coeruleus (up to 150 µA in strength) was accompanied by marked weakening of the inhibitory action of flexor reflex afferents and of the reciprocal inhibitory action on extensor motoneurons. Meanwhile stimulation of this sort had no significant effect on direct inhibition of flexor and extensor motoneurons, on the facilitatory action of flexor reflex afferents and the reciprocal inhibitory action on flexor motoneurons and also on dorsal root potentials. Intravenously injected pyrogallol had a similar action, but its effect was much weaker after spinalization of the animals or blocking of spinal cord conduction by cold. Enhancement of the monosynaptic reflex, which also was observed after injection of pyrogallol, was characterized by different temporal parameters; the intensity of this effect was unaffected both by spinalization and by cold block. These data, and also the results of experiments with partial divisions of the spinal cord, suggest that the effects of stimulation of the locus coeruleus are the result of activity of a descending coerulo-spinal tract, running in the ventral quadrant of the spinal cord.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 39–47, January–February, 1981.     

Comparative neurophysiological characteristics of shivering and caudate tremor

Two models of postural tremor — induced by cold (shivering) and by injection of oxotremorine into the caudate nucleus (caudate tremor) — were compared in experiments on cats. Both models shared the same electromyographic picture of tremor; the frequency of activity of motor units working independently was 4–12 spikes/sec. Both types of tremor were potentiated by cold stimulation of temperature receptors and were inhibited by electrical stimulation of the medial preoptic region of the hypothalamus and by intravenous injection of cholinomimetics. Caudate tremor, unlike shivering, ceased after intravenous injection of scopolamine (an antiparkinsonism drug). On the basis of data on motoneuron function it is concluded that both types of tremor are analogs of physiological postural tremor. The selective inhibitory action of scopolamine on caudate tremor reflects only the mediator organization of structures in the caudate nucleus and cannot therefore serve as the basis for the conclusion that this disturbance of motor activity is a model of pathological postural tremor.O. V. Kuusinen Petrozavodsk State University. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 257–263, May–June, 1981.     

Ia presynaptic inhibition in human wrist extensor muscles: effects of motor task and cutaneous afferent activity.

The task-dependence of the presynaptic inhibition of the muscle spindle primary afferents in human forearm muscles was studied, focusing in particular on the modulation associated with the co-contraction of antagonist muscles and the activation of cutaneous afferents. The changes known to affect the motoneuron proprioceptive assistance during antagonist muscle co-activation in human leg and arm muscles were compared. The evidence available so far that these changes might reflect changes in the presynaptic inhibition of the muscle spindle afferent is briefly reviewed. The possible reasons for changes in presynaptic inhibition during the antagonist muscle co-contraction are discussed. Some new experiments on the wrist extensor muscles are briefly described. The results showed that the changes in the Ia presynaptic inhibition occurring during the co-contraction of the wrist flexor and extensor muscles while the hand cutaneous receptors were being activated (the subject's hand was clenched around a manipulandum) could be mimicked by contracting the wrist extensor muscles alone while applying extraneous stimulation to the hand cutaneous receptors. It is concluded that besides the possible contribution of inputs generated by the co-contraction of antagonist muscles and by supraspinal pathways, cutaneous inputs may play a major role in modulating the proprioceptive assistance during manipulatory movements.     

Influence of forelimb afferents on the activity of lumbar spinal-cord motoneurons

Experiments were conducted on anesthetized cats with microelectrode recording to study the synaptic responses that develop in the lumbar motoneurons on stimulation of the afferent fibers of groups II and III in the nerves of the ipsilateral and contralateral forelegs. Stimulation of these afferents evoked predominantly inhibitory postsynaptic potentials (IPSP) in the extensor motoneurons and excitatory postsynaptic potentials (EPSP) in the flexor motoneurons. A basically inhibitory change in the rhythmic background activity developed under the influence of descending impulsation. The duration of the total inhibition of "spontaneous" motoneuron activity corresponded to the duration of the inhibitory influences exerted by the forelimb flexor-reflex afferents (FRA) on the interneurons. The interaction of the descending and segmental PSP resulted in inhibition and facilitation of the segmental responses in the motoneurons. The ultimate result of this interaction was determined by the shifts in the membrane potential of the motoneuron and by the effects created in the interneurons.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 58–67, January–February, 1971.     

Types of activity of skeletal muscle motor units during cold tremor in cats

Discharges of 184 motor units of the sartorius muscle functioning during cold tremor were investigated in acute experiments on anesthetized cats. Units whose discharges correlated with respiration cycles and units functionally independent of the rhythm of respiration were discovered. Discharges of both types of motor units possessed the same mean frequency (4–12 spikes/sec) and the same low variability of interspike intervals. Additional temperature stimulation of the vascular temperature receptors and changes in the frequency and depth of the respiratory excursions during cold tremor evoked identical responses in the two types of units. It is concluded that both types of motor units have similar thresholds and are of the slow, phasic type.O. V. Kuusinen State University, Petrozavodsk. Translated from Neirofiziologiya, Vol. 11, No. 4, pp. 355–361, July–August, 1979.     

Neural circuits for jumping in the locust

The locust jump consists of three distinct phases: Cocking: a rapid flexion of both hindleg tibia and locking of both tibia in full flexion. Co-contraction: simultaneous contractions in hindleg flexor and extensor muscles lasting about 0.5 s resulting in the storage of energy for the jump in elastic elements of the legs and muscles. Triggering: a sudden inhibition of flexor activity to allow the shortening of the contracted extensors and the release of the energy stored during the co-contraction phase. The neural circuitry controlling these three phases is now reasonably well understood. Some of its major features are: (1) pairs of large identifiable interneurons in the thoracic ganglia for evoking the cocking response (C-neurons) and for triggering the jump (M-neurons), (2) a central excitatory pathway from extensor to flexor tibiae motoneurons to ensure simultaneous activation of extensor and flexor motoneurons during the initial part of the co-contraction phase, (3) a positive feedback pathway from cuticular receptors to extensor motoneurons for maintaining extensor activity during the co-contraction phase, (4) proprioceptive feedback to the trigger interneurons for increasing their excitability during the co-contraction phase and thereby allowing a variety of external stimuli to activate the trigger neurons and evoke a jump, (5) presynaptic inhibition of visual pathways to the trigger neurons to ensure that the trigger neurons are not activated by the simultaneous occurrence of visual and auditory stimuli in the absence of proprioceptive input, and (6) a pair of multifunctional visual movement detecting neurons which can initiate cocking or trigger the jump depending on the animal's state.     

Comparative characteristics of cold- and fever-induced tremor

Experiments were conducted on anesthetized and unanesthetized cats. On the basis of identity of distribution of cold and fever tremor in the muscle groups, its electromyographic picture and the same sensitivity to neurotropic agents a conclusion was drawn that in the cooling of the organism and during fever the same mechanism of the shivering thermogenesis regulation was activated.     

Features of stepping pattern formation in decerebrated cats under epidural spinal cord stimulation

The mechanisms of stepping pattern formation initiated by epidural spinal cord stimulation in decerebrated cats, were investigated. It is shown that the ability to produce the stepping pattern involve the L3-L5 segments. In flexor muscle, the formation of stepping pattern under optimal stimulation frequency (5-10 Hz) of these segments is provided by polysynaptic activity with the latency 80-110 ms. In extensor muscle, this process is realized through interaction of monosynaptic reflex and polysynaptic activity. The stepping pattern under epidural stimulation is determined by spinal structures with modulation influence of the peripheral feedback.     

Synaptic effects of contralateral somatic afferents on spinal motoneurons

Electrical activity of flexor and extensor alpha-motoneurons of the lumbar segments of cat's spinal cord as recorded intracellularly during electric stimulation of afferents of the contralateral posterior limb. Contralateral postsynaptic potentials (PSP) were shown to be evoked by activation of cutaneous and high-threshold muscle afferents. The high-threshold afferents of various muscle nerves participate to varying degrees in the generation of contralateral PSP. Contralateral inhibitory postsynaptic potentials (IPSP) were recorded in both flexor and extensor motoneurons along with contralateral excitatory postsynaptic potentials (EPSP). There are no fundamental differences in their distribution between flexor and extensor neurons. Inhibitory influences as a rule are predominant in both during the first 20 msec, and EPSP are predominant in the interval between 20 and 100 msec. The balance of excitatory and inhibitory pathway activity was found to be not as stable as that of the homolateral pathways.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 418–425, July–August, 1971.     

The Effect of Transcutaneous Electrical Spinal Cord Stimulation on the Functional Activity of Spinal Inhibition in the System of Synergistic Muscles of the Lower Leg in Humans

Human Physiology - The effect of 20-minute transcutaneous electrical spinal cord stimulation (tESCS) on the severity of nonreciprocal and recurrent inhibition of spinal α-motoneurons in humans...     

Central program of hind limb interaction during locomotion in cats

The central program for interaction between the hind limbs, expressed as the time structure of motor discharges in the nerves to the various muscles, was studied in immobilized decerebrate spinal cats during fictitious locomotion. The program of hind limb interaction (alternating or inphase) in the decerebrate cats was shown to be determined by the relations between the flexor hemicenters. The activity of the latter is either antiphased or cophased. The character of activity of the extensor hemicenters is determined secondarily on account of alternating interaction of each of them with the ipsilateral flexor hemicenter. After injection of dopa into the animals the cophased program of hind limb interaction may be determined by the cophased working of the extensor center.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 1, pp. 65–73, January–February, 1979.     

Effect of repetitive stimulation of the locus coeruleus on spinal inhibition evoked in cats by activation of flexor reflex afferents

Repetitive stimulation of the locus coeruleus with a frequency of 40 Hz and strength of 50–150 µA in decerebellated cats anesthetized with chloralose was accompanied by a decrease in the inhibitory action of flexor reflex afferents (FRA) on the extensor monosynaptic reflex. This effect, which appeared after 600 msec, reached a maximum 1500–1700 msec after the beginning of repetitive stimulation. A minimum of 7–10 stimuli was needed to evoke the effect. After the end of stimulation the inhibitory action of FRA was not fully restored until after 2–3 sec. During application of a single stimulus or a short high-frequency series of stimuli of the same strength to the locus coeruleus no such effect was found. An increase in the strength of stimulation in that case was accompanied by activation of adjacent more rapidly conducting structures. The advantage of repetitive stimulation for detecting effects of slowly-conducting brain structures is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 187–195, March–April, 1981.     

Unit responses in the cat auditory cortex to electrical stimulation of nerve fibers innervating receptor cells in different parts of the organ of corti

Responses of 200 primary auditory cortical neurons to electrical stimulation of nerve fibers in different receptor zones of the cochlea were studied in cats anesthetized with pentobarbital. Under the influence of paired stimulation, after the response to the conditioning stimulus a state of prolonged (from 4 to 200 msec) refractiveness to the second stimulus developed in all the neurons tested. This long-lasting inhibition of unit activity was due to inhibition developing in the thalamus and the auditory cortex itself. The intensity and duration of excitation and inhibition in the cortical projection focus were maximal when the center of the receptive field was stimulated and decreased when the stimulus shifted from the center to the periphery. The region of the receptor surface of the cochlea to stimulation of which the auditory cortical neurons respond by an action potential is much narrower than the region whose electrical stimulation depresses the discharge of these neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 418–425, July–August, 1982.     

Primary afferent depolarization in the cervical enlargement of cats evoked by activation of cervical sensory nerves

Depolarization of primary afferent terminals in the cervical enlargement of the spinal cord evoked by activation of sensory nerves of the upper cervical segments (C₂) was studied in cats anesthetized with pentobarbital. It was shown that low-threshold muscular and high-threshold cutaneous afferents of nerves of the forelimb were depolarized most strongly. Parallel with this depolarization, prolonged (over 0.5 sec) inhibition of the monosynaptic and polysynaptic flexor reflex developed. It is suggested that these influences are transmitted via pathways running in the posterior and lateral white columns. The results are discussed in connection with regulation of postural motor activity in vertebrates.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 190–197, March–April, 1982.