Search

Data on reorganization of the efferent activity parameters of the forelimb locomotor generators during electrical stimulation of the descending systems were obtained during experiments on immobilized decerebrate cats. It has been found that a generator controlling the forelimb locomotor movement is characterized by existence of such a stable state when total influence of different descending systems on this generator is extremely limited. A conclusion is made that the sense of the activity reorganization in the locomotor generator of a forelimb under the effect of signals from descending systems brings the motor program to such a dynamic relation with a supraspinal inflow which provides sufficiently limitation and balancing of the influences of corresponding descending systems on the interneuronal nets, determining time and phase characteristics of the activity of these generators.

Rearrangement of the locomotor generator activity evoked by phasic electrical stimulation of different descending systems has been investigated on decerebrated immobilized cats. The rearrangement heavily depends on the stimulation phase. A maximal increase of the locomotor cycle duration by electrical stimulation of the Deiters nucleus takes place in the end of an "extensor" phase. Stimulation of the Deiters nucleus during the flexor phase decreases the locomotor cycle duration. A maximal increase of the locomotor cycle duration by electrical stimulation of the red nucleus, pyramidal tract and reticular gigantocellular nucleus takes place in the first half of a "flexor" phase. Electrical activation of these descending pathways during the flexor phase promotes an increase in intensity of this phase and a decrease in intensity of the "extensor" phase. Electrical activation of the Deiters nucleus increases intensity of the extensor phase and decreases that of the "flexor" phase. Possible principles of the suprasegmental correction of the locomotor generator activity are discussed.

Rearrangement of the scratching generator activity evoked by phasic electrical stimulation of different descending systems has been investigated on decerebrated immobilized cats. This rearrangement heavily depends on the stimulation phase. Maximal increase of the scratching cycle duration by electrical stimulation of Deiters' nucleus, red nucleus and pyramidal tract takes place in the first half of an aiming phase. The electrical stimulation of structures mentioned above does not practically change duration of the scratching cycle in the second half of the aiming phase and at the beginning of the scratching phase. A maximal increase of the scratching cycle duration by electrical stimulation of reticular gigantocellular nucleus occurs in the second half of the aiming phase. The electrical activation of descending pathways during the aiming phase increases intensity of this phase and decreases intensity of the scratching phase. The electrical activation of descending pathways during the scratching phase increases its intensity and does not change practically the intensity of the aiming phase. Possible principles of the suprasegmental correction of the scratching generator activity are discussed.

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.

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.

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.

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.

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.

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.

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.