Afferent control of central pattern generators: experimental analysis of scratching in the decerebrate cat.

Systematic quantitative analysis of changes in the spinal scratching generator motor activity evoked by tonic and phasic peripheral afferent signals during "fictitious" scratching was carried out in the cat. Correlations between the kinematics of hindlimb scratching movement, sensory inflow, and primary afferent depolarization were investigated. Reliable correlations between the parameters of generator motor activity during fictitious scratching were revealed: they depended on tonic peripheral afferent inflow. The functional role of these dependencies consists of providing stability for aiming the hindlimb to the itch site. It was shown that scratching generator reaction to a phasic sensory signal depended significantly on afferent input, signal intensity, and its arrival phase in the cycle of motor activity. Phase correction of "scratching" rhythm was performed by inhibition of the current stage of "scratching" cycle, the inhibition magnitude depending on the intensity of a sensory signal run along high threshold afferent fibers. The moments in the scratching cycle, in which the afferent signal caused no rearrangement in scratching generator activity, were discovered for all investigated afferent inputs. These moments corresponded to the transitions from one scratching cycle phase to another. Integral afferent activity was distributed unevenly in the cycle during real scratching. The main part of it was observed just in that scratching cycle part which included the above mentioned no rearrangement phase points. The data obtained allowed us to conclude that the scratching generator should be considered as a working program for the motor optimal control system containing the intrinsic model of the controlled object dynamics (e.g. hindlimb scratching movement dynamics), which produces an inner analog of peripheral flow. This inner flow interacts with peripheral afferent inflow just as one of the latter components. Centrally originated modulation of primary afferent depolarization is a result of affecting the depolarization generating system by this inner "sensory" activity. It is the model, with the aid of which the generator can work after deafferentation. The functional organization of a central pattern generator is considered.

Afferent control of central pattern generators: experimental analysis of locomotion in the decerebrate cat.

Changes in the motor activity of the spinal locomotor generator evoked by tonic and phasic peripheral afferent signals during fictitious locomotion of both slow and fast rhythms were analysed in the cat. The tonic afferent inflow was conditioned by the position of the hindlimb. The phasic afferent signals were imitated by electrical stimulation of hindlimb nerves. The correlation between the kinematics of hindlimb locomotor movement and sensory inflow was investigated during actual locomotion. Reliable correlations between motor activity parameters during fictitious locomotion were revealed in cases of both slow and fast "locomotor" rhythms. The main difference between these cases was that correlations "duration-intensity" were positive in the first and negative in the second case. The functional role of "locomotor" pattern dependence on tonic sensory inflow consisted of providing stability for planting the hindlimb on the ground. For any investigated afferent input the phase moments in the "locomotor" cycle were found, in which an afferent signal caused no rearrangement in locomotor generator activity. These moments corresponded to the transitions between "flexion" and "extension" phases and to the bursts of integral afferent activity observed during real locomotion. The data obtained are compared with the results previously described for the scratching generator. The character of changes in "locomotor" activity in response to tonic and phasic sensory signals was similar to that of such changes in "scratching" rhythm in the case of fast "locomotion". Intensification of the "flexion" phase caused by phasic high-intensity stimulation of cutaneous afferents during low "locomotor" rhythm was changed to inhibition (such as observed during "scratching") when this rhythm was fast. It is concluded that the main regularities of peripheral afferent control for both the locomotor and scratching generators are the same. Moreover, these central pattern generators are just working regimes of a general spinal motor optimal control system containing the intrinsic model of limb movement dynamics. The consequences of this concept and ways of further research are discussed.

[Changes in the intensity of integral afferent inflow from limb receptors and the level of polarization of primary afferent endings in the decerebrate cat during scratching]. / Izmeneniia intensivnosti integral'nogo afferentnogo pritoka ot retseptorov konechnosti i urovnia poliarizatsii terminalei pervichnykh afferentov u detserebrirovannoi koshki vo vremia chesaniia.

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.

[Changes in the segmental reactions in the decerebrate cat during scratching and locomotion]. / Izmeneniia nekotorykh segmentarnykh reaktsii u detserebrirovannoi koshki vo vremia chesaniia i lokomotsii.

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.

[Interrelation of the kinematics of hindlimb movement and efferent activity in the decerebrate cat during scratching]. / Vzaimosviaz' kinematiki dvizhenii zadnei konechnosti i éfferentnoi aktivnosti u detserebrirovannoi koshki vo vremia chesaniia.

Statistical dependence between parameters of hindlimb scratching movements and muscle electrical activity was studied in decerebrated cat during real scratching. Power of electrical signal to scratching and aiming muscles and duration of aiming muscle activity are determining factors of movement parameters (amplitude, velocity and phase duration). Experiments with limb deafferentation had shown that statistical dependences between movement parameters and muscle electrical activity reflect the peculiarities of the scratch generator functioning. Some investigated statistical dependences change under the afferent signal influence.

[Structural organization and connections of the locomotor strip of the medulla oblongata of the cat]. / Issledovanie strukturnoi organizatsii i sviazei lokomotornoi poloski prodolgovatogo mozga koshki.

The bulbar locomotor strip was studied by means of the horse-radish peroxidase technique. HRP microinjections were carried out under functional control of the evoked treadmill locomotion. The experiments have failed to reveal a special cellular column along the locomotor strip and the existence of such a strip as a separate structural formation is questioned. In fact the bulbar locomotor strip may conceal the spinal trigeminal tract and its nucleus. It is postulated that nonspecific afferent activation of the brainstem reticular formation plays a significant role in the locomotion initiation.

[New locomotor areas of the brain stem of the cat]. / Novye lokomotornye oblasti stvola mozga koshki.

New sites in the brainstem eliciting treadmill locomotion have been revealed in decerebrated cats by means of electrical stimulation. These sites--cochlear nuclei, ventral spinocerebellar tract and resciform body which includes dorsal spinocerebellar tract--are located outside the known locomotor regions. It is suggested that the nonspecific afferent activation of the brainstem reticular formation during electrical stimulation of the mentioned sensory tracts is sufficient for the initiation of the treadmill locomotion.

[Efferent projections of neurons of the mesencephalic locomotor region of the cat brain]. / Efferentnye proektsii neironov mezentsefalicheskoi lokomotornoi oblasti mozga koshki.

Efferent projections of mesencephalic locomotor region neurons were studied by means of horseradish peroxidase technique in cat. Ascending and descending projections of these neurons to different structures of the brain with predominant course to the brainstem reticular formation were traced. Some fibres passed through the bulbar and spinal locomotor strip. Mutual bilateral interconnections of the mesencephalic locomotor regions were observed.

[Depolarization of primary afferents of the lumbosacral division of the spinal cord during real locomotion]. / Depoliarizatsiia pervichnykh afferentov poiasnichno-kresttsovogo otdela spinnogo mozga pri real'noi lokomotsii.

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.

[Depolarization of primary afferents during real scratching in the cat]. / Depoliarizatsiia pervichnykh afferentov vo vremia real'nogo chesaniia u koshki.

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.

[Phase-frequency characteristics of afferent activity and depolarization of primary afferents during passive displacement of the hindlimb of the cat]. / Fazovo-chastotnye kharakteristiki afferentnoi aktivnosti i depoliarizatsii pervichnykh afferentov pri passivnom peremeshchenii zadnei konechnosti koshki.

Frequency response characteristics of afferent activity and primary afferent depolarization (PAD) evoked by this activity were investigated in decerebrated cats during passive movement of hindlimb in ankle joint. At the frequencies of 0.2-1.7 Hz the lead of the level of depolarization was determined by the value of phase changes of afferent activity. Above 1.7 Hz a phase lag of the level of depolarization was observed. This lag was caused by the dynamic properties of PAD generation system.

[Depolarization of primary afferents evoked by cyclically modulated natural activity of proprioceptors of the hindlimb of the cat]. / Depoliarizatsiia pervichnykh afferentov, vyzvannaia tsiklicheski modulirovannoi estestvennoi aktivnost'iu propriotseptorov zadnei konechnosti.

The primary afferent depolarization (PAD) evoked during passive sinusoidal movements of a hindlimb in the ankle joint was investigated in decerebrated cats. The frequency of movements varied within 0.14-5.0 Hz, the amplitude of the joint angle with respect to the axis of the tibia changed from 90 degrees to 130 degrees. The dorsal root potential (DRP) negativity increased both during flexion and during extension of the joint. The amplitude of the evoked DRPs was about 50-100 mV. A strong negative correlation was observed between the latency and rise time of the DRP and the frequency of the joint angle changes. During flexion the latency changed from 650 ms at 0.14-0.16 Hz frequency to 100-110 ms at 2.0 Hz and higher frequencies; during extension at the same frequencies the latency changed from 300 ms to 80-85 ms. The latency and rise time became minimal at 2.0 Hz frequency and practically did not change during the further increase of the oscillation frequency. The cord dorsum potential (CDP) evoked by the cutaneous nerve stimulation was recorded in parallel with the DRP. Periodical changes of the N-component of the CDP were in the opposite phase to changes of the DRP. Mechanisms of the observed changes of the PAD and functional significance of these changes during rhythmical motor acts are discussed.

[Changes in the excitability of central endings of the superior laryngeal nerve following activation of the respiratory center]. / Izmenenie vozbudimosti tsentral'nykh terminalei verkhnegortannogo nerva pri aktivatsii dykhatel'nogo tsentra.

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.