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In experiments on immobilized decerebrate cats, data about reorganization of efferent activity parameters of the forelimb and hindlimb locomotor generators evoked by electrical stimulation of descending systems were obtained. The generators controlling both forelimb and hindlimb locomotor movements were found to be characterized by the existence of stable states at which total influence of different descending systems on these generators was extremely limited. These data enable us to conclude that the sense of activity reorganization in locomotor generators of both forelimb and hindlimb under the influence of descending system signals is in bringing the motor program to a dynamic relation with supraspinal inflow, where a sufficient degree of limitation and balancing of the influences of corresponding descending systems on the interneuronal nets, determining time and phase characteristics of these generators, is ensured. Possible mechanisms of realization of this interaction between descending signals and locomotor activity generators are discussed.

Whole-cell glycine-activated currents were investigated in chick spinal cord neurons cultivated for up to three weeks. Based on the morphological and electrophysiological characteristics of neurons, two different types of nerve cells were distinguished during the first few days in culture. The first type consisted of “mature” nerve cells which appear to be motoneurons. They died by five to seven days in vitro . Immature neurons or neuroblasts constituted another type of nerve cell. They developed in culture and became differentiated neurons. Glycine-activated currents were elicited in both types of neurons during different periods in vitro . Sensitivity to glycine of “mature” neurons decreased from two to five days in vitro : ed 50 for agonist action increased from 0.4 to 1.3 mM. The sensitivity of neuroblasts to this transmitter increased during differentiation: ed 50 decreased from 1.4 to 0.12 mM on three to 14 days in vitro , respectively. Changes in glycine-activated conductance of these developing neurons were investigated later on. The conductance in differentiated neurons was markedly sensitive to membrane potential, while neuroblasts did not show such dependence. Voltage sensitivity was due to voltage-dependent kinetics of the ion channel. Desensitization kinetics of the glycine-activated currents were double-exponential. The time constant for the slow desensitizing component was dependent on glycine concentration, which was not the case for the fast component. The increase in glycine sensitivity of the neuroblasts was accompanied by deceleration of desensitization kinetics of the agonist-activated currents. A remarkable feature of the currents elicited in neuroblasts was their extremely long time course after rapid agonist removal from the cells. The properties of these long-term currents suggest that a large fraction of the receptors are desensitized, even during quite short applications of the transmitter. The presence of glycine in the culture medium did not affect the increase of neuronal sensitivity to the agonist. The block of spontaneous bioelectric activity by adding tetrodotoxin to the culture medium abolished developmental changes in glycine-activated conductance. Possible mechanisms for the changes in transmitter sensitivity of the neurons are considered.

The influences of signals in descending systems on the parameters of scratching generator activity were studied on decerebrate immobilized cats. It was shown that phasic electric stimulation of descending systems evoked certain phase-dependent reorganization of the parameters of scratching generator efferent activity. Maximum increase in scratching cycle duration during electric stimulation of Deiters' nucleus, red nucleus and pyramidal tract is observed during stimulation in the first half of aiming phase. Stimulation in the second half of aiming phase and at the beginning of scratching jerk phase virtually does not change the scratching cycle duration. Maximum increase in scratching cycle duration during electric stimulation of the nucleus reticularis gigantocellularis is observed in the second half of aiming phase. Electric activation of descending pathways during aiming phase increases its intensity and decreases the intensity of scratching jerk phase. Activation of descending pathways during scratching jerk phase increases its intensity and virtually does not change the aiming phase intensity. Influences of electric activation of descending systems on scratching generator work reveal dependence on limb position. They are increased when the limb is deflected to the rear and are decreased during over-aimed position. Decerebellation leads to a decrease of scratching generator activity parameters rearrangement under influence of electric stimulation of the red nucleus and nucleus reticularis gigantocellularis, and to its increase during Deiters' nucleus stimulation. On the basis of these results the principles of supraspinal correction of scratching generator work are discussed.

Pheochromocytoma PC12 cells incubated with and without nerve growth factor were investigated using the patch-clamp technique in the whole-cell recording mode, and the concentration clamp method in the rat. On the fourth day of incubation with nerve growth factor, sodium potential-activated ionic currents appeared in the membranes of the most morphologically differentiated cells. At the same period a three-fold increase of acetylcholine-activated current density, compared with the cells incubated without nerve growth factor, was observed. Thus, the qualitative and quantitative changes in membrane properties can be a result of metabolic reorganization in PC12 cells induced by nerve growth factor and accompanied by morphological differentiation according to neuronal phenotype.

The action of glycine and GABA on isolated lamprey spinal cord neurons was investigated by means of intracellular perfusion and concentration clamp techniques. These amino acids activated desensitizing chloride ionic conductances. The concentrations of agonists evoking half-maximum effects (ED50) were equal to 16 microM and 1.5 mM for glycine- and GABA-activated currents, respectively. Increase in the transmitter concentration led to a decrease in the time constant of desensitization. Current-voltage relationships of glycine- and GABA-activated currents were strongly dose-dependent. At low agonist concentrations the time constant of activation decreased with membrane hyperpolarization. Glycine- and GABA-activated currents exhibited complete cross-desensitization. The specific glycine antagonist, strychnine, suppressed both glycine- and GABA-activated currents to the same degree. Selective antagonists of GABA receptors, bicuculline and picrotoxin, produced equal blocking effects on glycine- as well as GABA-evoked responses. In the cells studied, taurine activated desensitizing ionic conductance. Responses evoked by taurine and glycine applications demonstrated complete cross-desensitization. Taurine-activated currents were sensitive to strychnine, bicuculline and picrotoxin. These results suggest the existence of one receptor-channel complex for the main inhibitory transmitters in lamprey spinal cord neurons. 3,4-Dioxy-L-beta-phenylalanine evoked desensitizing strychnine-sensitive ionic responses which exhibited cross-desensitization with glycine-activated currents.

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.