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The dorsal cord and dorsal root potentials were recorded in immobilized thalamic cats during fictitious scratching evoked by mechanical stimulation of the ear. Depolarization of primary afferents was shown to be simulated by the central scratching generator. Antidromic spike discharges appeared at the peak of the primary afferent depolarization waves in certain afferent fibers. Similar discharges arise in the resting state in response to stimulation of limb mechanoreceptors. It is suggested that during real scratching primary afferent depolarization and antidromic spikes evoked by it may effectively modulate the level of the afferent flow to spinal neurons.

The cord dorsum and dorsal root potentials were recorded during fictious scratching in L6 segment of the thalamic cats. It is shown that primary afferent depolrization (PAD) can be modulated by the central generator of scratching. In some afferent fibres antidromic spikes appear on the top of PAD-waves. Antidromic spikes can be also evoked in the period of "rest" by mechanical stimulation of hindlimb receptors. It is supposed that PAD and resulting antidromic spikes which appear during real scratching may effectively control the level of afferent inflow to the spinal neurons.

Impulse activity of lumbosacral interneurons was recorded extracellularly during fictitious scratching in decerebrated immobilized cats. Most neurons whose activity was modulated during fictitious scratching were revealed in the lateral intermediate zone and in the lateral ventral horn. These neurons were divided into some groups differing in the type of activity modulation during fictitious scratching. Neurons whose activity did not change during fictitious scratching were mainly located dorsally in the gray matter. Cells showing wide convergence of excitatory influences from high threshold cutaneous and muscle afferents referred mainly to "aiming" neurons. In contrast to "aiming" neurons, most cells with inputs from only low threshold cutaneous or high threshold muscle afferents belonged to "scratching" neurons. The neuronal activity in different groups is shown to depend on the limb position. The neuronal organization of the spinal scratching generator is discussed on the basis of the obtained data.

Changes in polarization of central afferent terminals of the superior laryngeal nerve with variations in the level of the respiratory generator activity evoked by a short (up to 1 min) asphyxia were investigated in experiments on anesthetized and paralyzed rabbits using Wall's method. Antidromic responses decreased up to 5-20% of the control level during activation of the respiratory generator with an increase in frequency and amplitude of rhythmic discharges in the phrenic nerve evoked by a short asphyxia. It is supposed that the primary afferent polarization depends not only on the level of afferent inflow but also on the activity of the central respiratory generator.

Primary afferent depolarization (PAD) in the lumbosacral enlargement of the spinal cord evoked by selective activation of propriospinal (PS) pathways was studied in anesthetized cats. Activation of PS pathways in the lateral funiculus was more effective for PAD generation than that in the ventral funiculi. Excitation of PS pathways evoked PAD in terminals of cutaneous and muscle fibres including Ia muscle fibres. Neuronal mechanisms of intersegmental distribution of PAD and its possible functions are discussed.

Segmental reflex responses of the lumbosacral spinal cord to peripheral afferent stimulation were investigated in immobilized decorticated cats before and during fictitious locomotion. Appearance of fictitious locomotion was accompanied by an increase of the N1 component of the dorsal cord potential and of the dorsal root potential. Modulation of these responses depending on the phase of fictitious locomotion was observed against a background of their tonic increase. The N1 component and dorsal root potential had larger amplitudes when they appear at the end of the "extensor" phase and at the beginning of the "flexor" phase and smaller amplitudes when they were evoked at the end of the "flexor" phase and at the beginning of the "extensor" phase. Poly- and monosynaptic reflex responses of motoneurons revealed the same phase dependence during fictitious locomotion. Mechanisms and physiological significance of the revealed retuning of segmental reflex responses are discussed on the basis of the obtained data.

The sequence of discharges in nerves to 22 hindlimb muscles during fictitious locomotion was investigated on immobilized thalamic cats. It is shown that for most hindlimb muscles the central locomotor program is rather simple and consists of alternating activation of flexors and extensors. A conclusion is made on the existence of interneuronal flexor and extensor centres in each half of the spinal cord, working in turns during locomotion. More complex discharges were recorded from the nerves to Edb and Per. tert. and also from the nerves to biarticular muscles (St, P. bic., Ten.). It is suggested that motoneurons of these muscles are connected to the flexor and extensor centres in a more complex way.

Changes in depolarization of primary afferents and their correlation with afferent impulsation and limb movement were studied in the lumbar spinal cord during real scratching of decerebrated cats. Two components in rhythmic dorsal root potential were observed. First--centrally evoked, retained during fictitive scratching after immobilization; second--evoked by afferent discharge, coming to the spinal cord during the scratching phase of the limb movement.

Impulse activity of lumbar interneurons was recorded extracellularly during fictious locomotion of thalamic cats. Neurons whose activity was modulated in the rhythm of fictitious locomotion were revealed in the lateral intermediate zone and in the lateral ventral born. 41.2% of these neurons were mainly activated at the phase of "flexion", 48.5%--at the phase of "extension" and 10.3%--at both phases. Neurons with tonically increasing or decreasing activity during rhythmic efferent discharges and neurons whose activity did not change during fictitious locomotion were also observed. All these types of neurons were similarly activated during late discharges in efferent nerves. But in this case the depth of modulation of neuronal activity was lower than during fictitious locomotion. Afferent inputs to the recorded interneurons were also investigated. The neuronal organization of the spinal locomotor generator is discussed on the basis of the obtained data.

Segmental reflex responses of the lumbosacral spinal cord to peripheral afferent stimulation were investigated in immobilized decerebrated cats before and after d-tubocurarine or bicuculline application to the upper cervical segments and during fictitious scratching evoked by mechanical stimulation of the pinna. Application of these drugs led to a decrease of N1 component of the cord dorsum potential, dorsal root potential and polysynaptic responses in efferent nerves. The appearance of fictitious scratching was accompanied by additional tonic inhibition of these reactions and against its background the modulation of amplitudes of segmental reactions depending on the fictitious scratching phase was observed. Modulation of monosynaptic reflexes was also observed during fictitious scratching. Mechanisms and physiological significance of retuning of segmental reflex responses during activation of a spinal scratching generator are discussed on the basis of the data obtained.

Isolated cells from the spinal cord of chick embryo were investigated under conditions of intracellular perfusion and voltage clamp using the method of rapid application of extracellular solutions. Two components were found in the L-glutamate-activated current: a fast-inactivating component and a steady one. The dose-response relationship demonstrated one-to-one interaction between L-glutamate and membrane receptor with Kd values about 0.75 X 10(-5) mol/l for the steady component and 3.2 X 10(-5) mol/l for the fast one.

Ionic currents induced by application of L-3, 4-dihydroxyphenylalanine (L-DOPA) and acidic amino acids: L-glutamate, kainate, N-methyl-D-aspartate (NMDA) were investigated in experiments on isolated spinal cord neurons of the lamprey by means of whole-cell recording and concentration clamp methods. L-DOPA was found to activate glycine, but not excitatory amino acid receptors.

The influence of tonic afferent inflow conditioned by ipsilateral hindlimb position on the spinal generator of scratching efferent activity parameters was investigated in immobilized decerebrated cats. When the afferent inflow was absent (after the hindlimb deafferentation) strong correlation between the motor activity parameters of successive "scratch" cycles was observed. In case of the intact afferentation this correlation was somewhat weaker and decreased with shifting the hindlimb from the aimed position to overaimed or deflecting backward. The discovered statistically significant correlations between the parameters of different motor activity phases and their dependence on the hindlimb position are organized in such a way that they can provide stability of the aimed position of the hindlimb carrying out oscillatory movements. According to the parameters of the efferent activity and their correlation type, the hindlimb deafferentation is most similar to the aimed position of the hindlimb.

Spontaneous rhythmic discharges (fictitious locomotion) were recorded in motor hindlimb nerves of decerebrated animals with intact caudal hypothalamic region. Stimulation of this region led to the appearance of fictitious locomotion. Spontaneous discharges did no-appear after decerebration at lower levels and in spinalized cats. A conclusion is made on the presence of structures in the caudal hypothalamus which are necessary for the activation of lower locomotor centres and the production of spontaneous rhythmic discharges in motor nerves.

Impulse activity of lumbar interneurons was recorded extracellularly during the late long-lasting discharges in efferent nerves of immobilized thalamic animals. 70% of investigated neurons changed their activity during the late discharges. The activity of 35% of neurons increased, during late discharges in flexor nerves, while during activity in extensor nerves it was inhibited. 27% of neurons had the opposite reaction. Neurons, whose activity correspondingly increased (5%) or decreased (3%) during the late discharges both in flexor and extensor nerves were also observed. Most interneurons, changing their activity during late discharges, were located in the lateral parts of intermediate zone and in the lateral ventral horn at the depth of 2.8 mm. Certain dependence between the character of afferent inputs to the neuron and correlation of its activity with late efferent discharges was revealed. Neurons whose activity did not change during late discharges (40%) were mainly located somewhat dorsally, at the depth of about 2.0 mm. Possible role of described interneurons in generation of late discharges is discussed.

Transient and steady-state L-glutamate-activated membrane currents were investigated by means of intracellular perfusion, voltage clamp techniques and concentration clamp in spinal cord neurons of 6-11 day chick embryos. The Hill coefficient was found to equal 1 for transient and 2 for steady-state components. Concentration of L-glutamate evoking half effect decreased during development more than 10 times for the steady-state component whereas it remained constant for the transient component. Existence of two types of glutamate-activated receptors in the membrane of spinal cord neurons at early stages of embryonic development is supposed.

Correlations between parameters of electrical muscle activity, changes of joint angles of the hindlimb, intensity of afferent inflow and dorsal root potential during real locomotion were studied in highly decerebrate cats. Characteristics of the hindlimb movements before and after deafferentation were described. It has been shown that during locomotion the afferent activity consisted of two components: tonic and periodic phase ones. In the latter one three principal waves can be distinguished, each inducing appropriate changes in primary afferent terminals polarization level. These changes in their turn, were summated with those elicited by central generator. Correlation dependences between parameters of the above mentioned processes were investigated. Mechanisms of afferent control of the locomotor generator function are discussed.

Rebuildings of the scratching generator activity caused by phasic electrical stimulation of ipsilateral hindlimb muscle nerves during different hindlimb positions were studied in decerebrated immobilized cats. Strong dependence of these rebuildings on the stimulation phase was observed. The character of the "scratch" cycle duration rebuilding was formed by the scratching generator tendency to bring efferent activity into such correlation with the stimulus that the stimulation moment coincided with the moment of efferent activity phase triggering. Phasic altering of the efferent activity intensity rebuilding was observed against a background of "aiming" and "scratching" activity correlation shift in the direction of strengthening activation of muscles innervated by the stimulated nerve. This rebuilding was intensified when the hindlimb deflects from the aimed position in the direction of corresponding muscles stretching. Physiological sense of "rebuilding absence phases" is discussed. It is postulated that absence of the duration and intensity changes can be achieved simultaneously only with definite correlation between phase and intensity of the afferent impulsation burst.

The statistical analysis of the neuronal impulse activity of spinal locomotor centres was performed at rest and during generation of efferent discharges in thalamic immobilized cats. The activation of the spinal locomotor generator was accompanied by shortening of interspike intervals in neuronal spike trains and reduction of their fluctuations. During this process the interspike interval histograms became more symmetrical and the quantity of neurons which had regular oscillations in autocorrelation histograms increased considerably. At rest neuronal spike trains were characterized by dependence of successive intervals. This dependence increased during generation of efferent discharges. Possible mechanisms of the reconstruction of time organization of the neuronal impulse activity of spinal locomotor centres during their activation are discussed.

The quantity of impulses which is necessary to be registered for detecting a reliable correlation between spike trains of synaptically connected neurons was estimated using a mathematical model. This quantity of impulses was studied as dependent on the weight of connection between neurons (the amplitude of EPSP evoked by a single impulse of an input neuron in an output one), on the intensity of total background excitatory influences upon the output neuron and on its own parameters. The necessary quantity of impulses was 10(7)-10(8) for cells with connection weights, parameters and characteristics of background activity similar to those of real spinal neurons. An increase in the amplitude of unitary EPSP and a decrease in the intensity of the input background impulse train and in duration and amplitude of interspike hyperpolarization of the postsynaptic neuron led to a decrease in the quantity of impulses necessary for detecting a reliable correlation. The possible principles of the construction of the spinal locomotor generator are discussed on the basis of those data.

The experiments performed on decerebrated cats have shown that afferent activity during scratching consisted of two components--tonic and periodic phasic ones. The first component was determined by the limb position, the second was closely related to the amplitude and velocity of joint angle changes. Maximum of integral afferent activity in the cycle coincided with the scratching jerk phase. These two components of afferent activity evoked corresponding depolarization changes in primary afferent terminals and these changes added to those elicited by central generator. Statistical correlations between the aforementioned parameters were studied. The afferent control mechanisms of scratching generator are under discussion.

In immobilized intercollicularly decerebrated cats tonic underthreshold activation of the spinal scratching generator (after application of tubocurarine or bicuculline on C1-C2 segments) is accompanied by an increase in primary different terminal depolarization, decrease in N1-component of cord dorsum potential evoked by stimulation of cutaneous afferents, decrease in the amplitude of DRP and early polysynaptic responses of motoneurons evoked by stimulation of cutaneous and muscle afferents; a respective rise and reduction in activity of intermediate nucleus interneurons which are mono- and di (oligo)-synaptically connected with afferent terminals. Spinalization of animal led to reverse changes. Injection of DOPA into spinal animals allowed comparing changes in the state of lumbar segmental apparatus during tonic underthreshold activation of spinal scratching and locomotor generators.

Central program of interaction of hindlimbs during fictitious locomotion expressed in the time structure of motor discharges in nerves to different muscles was investigated in decerebrated and spinal immobilized cats. It was shown that in the decerebrated animals the program of interaction of hindlimbs (alternative or synphase) is determined by interaction of the flexor half-centres. The latter work either in-phase or out-of-phase. The character of activity of extensor half-centres is determined secondarily by alternating interaction of each of them with homolateral flexor half-centre. After injection of DOPA the central program of interaction of hindlimbs can be determined by synchronous work of extensor half-centres.

Experiments on the isolated spinal cord have shown that even in early chicken embryogenesis, when first signs of the locomotor activity appeared, modulation of the presynaptic inhibition by the locomotor generator was present. Only few spinal cord segments are able to generate the locomotor rhythm.

Effects of inhibitory mediators on the membranes of isolated lamprey spinal cord neurones were investigated by means of whole-cell recording and concentration clamp techniques. Glycine and γ-aminobutyric acid (GABA) applications evoked desensitizing chloride currents. The concentrations at half-maximum effects were 16 μM for glycine- and 1.5 mM for GABA-activated currents. Ionic responses to applications of both amino acids demonstrated full cross-desensitization. Strychnine and bicuculline suppressed both glycine- and GABA-activated conductances to the same degree. We suggest that in the membranes of lamprey spinal cord neurones glycine and GABA act on the same receptor-channel complexes.

Changes in electric polarization of lumbosacral primary afferent terminals were studied during fictious locomotion of immobilized decorticated and spinal cats. Fictitious locomotion was accompanied by a stable hyperpolarization of afferent terminals. In the presence of hyperpolarization a periodic depolarization took place with the rhythm of efferent activity. These tonic and phasic changes were observed in the terminals of all the studied groups of afferent fibres (cutaneous and muscle Ia and Ib). Periodic depolarization was in-phase indifferent ipsilateral lumbosacral segments. During fictitious gallop the changes in depolarization of primary afferent terminals were in-phase on different sides; during fictitious walking these periodic changes were of out-of-phase character. Physiological significance of changes in electric polarization of primary afferent terminals by the spinal locomotor generator is discussed on the basis of the data obtained.

It is shown on unanesthetized immobilized decorticated cats that spinalization of the animal leads to depolarization of the central afferent terminals, decrease of early polysynaptic responses in motoneurons and dorsal root potentials (DRP) evoked by stimulation of the low-threshold cutaneous and muscle afferents, increase of early polysynaptic responses and DRP evoked by stimulation of high-threshold muscle afferents, reduction in the activity of intermediate nucleus interneurons mono- and polysynaptically connected with primary afferents, rise of the activity of interneurons di- and oligosynaptically connected with primary afferents. Injection of DOPA into spinal animals leads to opposite changes. Dependence between changes in the state of segmental neuronal apparatus and the level of spinal locomotor generator activity are discussed on the basis of the data obtained.

Descending projections of brain cortex and basal ganglia to the hypothalamic locomotor region were demonstrated in cat with horseradish peroxidase technique. Neurons projecting directly to the functionally identified locomotor region are dispersed in different gyri with predominance in areas 4 and 6 of the motor cortex. Such neurons are also located in entopeduncular nucleus. Massive cortico-and pallido-hypothalamic projections as a rule do not reach the most caudal hypothalamic divisions where the locomotor region is localized.

The changes in densities of L-glutamate- and glycine-activated currents through the membrane of spinal neurons were investigated in 6-11 day chick embryos using enzymatic isolation of cells and voltage clamp technique. General tendency of the current density increase during cell differentiation was found. A considerable decrease of the glycine-activated current density against a background of such an increase was observed on the 9th day of incubation. Reciprocal relation between L-glutamate- and glycine-activated current densities was found for a single neuron. Functional significance of the revealed density changes is discussed in connection with the development of the locomotor function of the spinal cord.

Experiments on the isolated spinal cord of 16-20 day old chick embryos using brain sections have shown that rhythm of the spontaneous motility was generated by the dorsal horn network.

It is shown on decorticated (high-decerebrated) and spinal cats and on spinal cats injected with DOPA that the activation of the spinal locomotor generator is accompanied by an increase of the extensor and a decrease of the flexor motoneurons' excitability, an increase of the recurrent and reciprocal Ia inhibition, a decrease of Ib and flexor reflex afferent influences on motoneurons. The possible physiological role of changes in tuning of the spinal segmental apparatus in the generation of the locomotor rhythm is discussed.

Electrical activity in nerves of different hindlimb muscles was investigated during fictitious scratching in decerebrated and decapitated cats. Phases of motor discharges could be distinguished corresponding to the phases of real scratching: aiming (flexion in the thigh and ankle joints and extension in the knee joint) and scratching (opposite movements in the same joints). According to the pattern of the discharges the hindlimb muscles were divided into three groups. In the nerves to the muscles of the 1st group the activity was observed during "initial aiming" period and during rhythmic "aiming phases". It was reciprocal to the activity in the nerves to the muscles of the 2nd group appearing during "scratching phases". In the nerves to the muscles of the 3d group the activity was observed both in "initial aiming" period and in rhythmic "aiming and scratching phases". Passive forward deflexion of the limb intensified the "scratching phases" and decreased the intensity of the discharges during "initial aiming" and "aiming phases". Physiological significance of such an organization of central program and structure of spinal scratching generator are discussed.

Kinetics of lumbar primary afferent depolarization was investigated during fictitious scratching of decerebrated and decapitated cats. Fictitious scratching was accompanied by tonic and phasic primary afferent depolarization. Periodic depolarization of primary afferents was synphasic in different segments of the lumbosacral spinal cord. Tonic depolarization was observed in the terminals of all the investigated groups of fibres (low-threshold cutaneous and of groups 1a and 1b). Phasic changes took place in terminals of low-threshold cutaneous fibres and fibres of group 1b. Physiological significance of modulation of primary afferent depolarization by the spinal scratching generator is discussed on the basis of the data obtained.

It is shown that the state of the segmental apparatus of the lumbal spinal cord of immobilized intercollicularly decerebrated cats during formation of a scratching generator is essentially different from that of a spinal animal. The excitability of "aiming" and "scratching" motoneurons increases, recurrent and reciprocal Ia inhibition of motoneurons becomes stronger and influence of Ib afferents weaker. The flexor reflex afferents exert inhibitory influences on "aiming" motoneurons. After spinalization these influences become excitatory, and the inhibitory influences on "scratching" motoneurons become weaker. The functional role of described changes is discussed.

Experiments on decerebrate cats have shown that N1 component potential of dorsal surface and dorsal root potential elicited by electrical stimulation of paw plantar surface tonically decrease during locomotion and scratching. Phase changes occur against a background of tonic changes in the rhythm of limb movements. The dynamics of the observed changes correlates well with that of primary afferent depolarization during these movements. It is concluded that presynaptic inhibition underlies the changes in segmental reactions.

Changes of polarization of central afferent terminals during evoked locomotion of mesencephalic cats were studied in lumbar spinal cord. Significant part of primary afferent depolarization was shown to be evoked by afferent impulsation; intensity of such impulsation increased during limb flexion and decreased during extension.

The paper presents data obtained in experiments on the study of primary afferent depolarization and retuning of segmental reactions to afferent signals during fictitious locomotion and fictitious scratching in immobilized decorticated, decerebrated and spinal cats. Fictitious locomotion was accompanied by sustained hyperpolarization, while fictitious scratching--by sustained depolarization of primary afferent central terminals. On the background of tonic changes periodic waves of primary afferent depolarization coinciding with the rhythm of efferent activity were observed. In different ipsilateral lumbosacral segments these periodic waves occurred in phase. The data are presented about the groups of afferent fibres in which central endings display tonic and phasic changes of primary afferent depolarization. Fictitious locomotion led to tonic increase and fictitious scratching--to tonic decrease in a number of evoked segmental reflex reactions. These tonic changes served as the background on which segmental reactions were modulated with the rhythm of locomotor and scratching generators. It is shown that the modulation of polarization of central primary endings by locomotor and scratching generators is the reason for many changes in reflex reactions. The conclusion is made that due to modulation of presynaptic inhibition the generators perform an active tonic and phase-dependent selection of afferent information. The role of such active selection in the peripheral correction of the function of locomotor and scratching generators is discussed.

Rebuildings of the scratching generator efferent activity caused by the phasic electrical stimulation of ipsilateral hindlimb skin nerves during different hindlimb positions were studied in decerebrated immobilized cats. Stimulation was followed by short latency inhibition of the efferent activity. Stimulation did not cause correlation shifts in the common "aiming" and "scratching" activity. Changes in the efferent activity cycle duration and intensity depended on the stimulation phase. Inversion of intensity changes occurred with transition from the middle-force to strong stimulation. A functional role of the dependence of the efferent activity rebuilding on the stimulation phase is considered. The scratching generator is supposed to contain a model of the afferent inflow which enters the spinal cord during real scratching.

Dorsal root and cord dorsum potentials were recorded in lumbar segments L6, L7 during fictitious locomotion of thalamic immobilized cats. Negative waves in the dorsal root potential and respectively positive waves in the cord dorsum potential appeared during periodic discharges in the ankle flexor nerve. The conclusion is made that central locomotor generator activity modulates the level of primary afferent depolarization.

Dorsal root and cord dorsum potentials were recorded in lumbar segments L6, L7 during fictitious locomotion of thalamic immobilized cats. Negative waves in the dorsal root potential and respectively positive waves in the cord dorsum potential appeared during periodic discharges in the ankle flexor nerve. The conclusion is made that central locomotor generator activity modulates the level of primary afferent depolarization.