[Effect of tyramine on the spinal cord afferent link of pressor reflexes]. / Deistvie tiramina na spinnomozgovoe afferentnoe zveno pressornykh refleksov.

In anesthetized cats, tyramine application on the dorsal surface of C6-TI spinal cord segments suppressed the pressor components of blood pressure reflexes evoked by radial nerve A sigma or A + C afferent stimulation. Tyramine application on L4-SI spinal cord segments suppressed pressor reflexes to tibial nerve stimulation. Both the degree and the rate of reflex suppression increased with the rise in tyramine concentration from I to 4%. Along with these local effects "distant" tyramine action was demonstrated: pressor reflexes to radial nerve stimulation increased when tyramine was applied on L4-SI segments, but after its application on C6-TI segments pressor reflexes to tibial nerve stimulation increased in some cats, decreased in the other ones, or remained practically unchanged.

[Noradrenaline suppression of the spinal efferent component of the pressor reflexes]. / Ugnetenie noradrenalinom spinal'nogo éfferentnogo zvena pressornykh refleksov.

Noradrenaline applied to the dorsal surface of spinal cord segments C6-T1 suppressed the pressor components of the blood pressure reflexes evoked by stimulation of radial nerve afferents in anesthetized cats. Noradrenaline applied to spinal cord segments L4-S1 suppressed pressor reflexes elicited by stimulation of tibial nerve afferents. The increase in noradrenaline concentration from 0.05 to 0.2% enhanced the duration and intensity of this effect.

[Effect of iontophoretic application of acetylcholine on the discharge rate and action potential shape of pacemaker cells]. / Vliianie iontoforeticheskoi applikatsii atsetilkholina na ritm razriadov i formu potentsiala deistviia kletok peismekera.

A study was made of the action of iontophoretic application of acetylcholine to the limited number of pacemaker cells with a simultaneous recording of the activity of one of them. It was shown that both generalized and strictly localized action of acetylcholine is capable of exerting different chronotropic effects. Acceleration of the rhythm was normally accompanied by an increase in the rate of accretion of slow diastolic depolarization (SDD) and by a decrease in the action potential. The same pacemaker cell was demonstrated to modulate the direction of the chronotropic reaction for an opposite one depending on acetyl-choline concentration. Low concentration of the mediator induced rhythm acceleration and an increase in the accretion rate of SDD whereas high concentration led to rhythm deceleration and SDD lowering.

[Effect of acetylcholine on the firing rate and action potential shape of pacemaker cells]. / Vliianie atsetilkholina na chastotu razriadov i formu potentsialov deistviia kletok peismekera.

A study was made of the action of exogenous acetylcholine on the isolated pacemaker of the Rana temporaria heart. Bioelectrical activity of individual cells and sum total activity of the preparation were recorded. Exogenous acetylcholine was found not only to inhibit, but also to accelerate the rhythm of pacemaker cells' discharge. As a rule, positive chronotropic effects were observed when relatively low acetycholine concentrations were used. Parasympathetic acceleration was accompanied by an increase in the rate of slow diastolic depolarization; this is in favour of the active mechanism of this process. It is suggested that low and high concentrations of acetylcholine could change the transmembrane ionic currents in a different way.

[Changes in the bioelectrical activity of pacemaker cells of the desympathized and reserpinized frog heart under conditions of parasympathetic rhythm acceleration]. / Izmenenie bioélektricheskoi aktivnosti kletok peismekera desimpatizirovannogo serdtsa liagushki v usloviiakh parasimpaticheskogo uchashcheniia ritma.

A study was made of the mechanism of parasympathetic acceleration on Rana temporaria hearts with the preliminarily exhausted catecholamine stores due to desympathization and reserpinization of the animals. Bioelectrical activity of the cells of the isolated pace-maker was recorded. Parasympathetic acceleration was accompanied by an increase in the rate of accretion of slow diastolic depolarization (this indicating an active mechanism of this acceleration), and also a slight hyperpolarization and a decrease of the action potential duration. The acceleration effect and the changes of the form of the action potential were absent after atropine treatment of the preparation, this confirming the cholinergic nature of the parasympathetic acceleration. It is supposed that the parasympathetic system mediator acetylcholine--could decrease potassium or increase sodium permeability of the Pacemaker cell membrane, this leading to increase of the slow diastolic depolarization rate and to discharge acceleration.