Abstract
In bulbar and mesencephalic unanesthetized cats, as well as in anesthetized cats with intact brain the role of impulses of different tibial nerve A-fiber subgroups (electrical stimulation at a frequency of 10 S--1) in the reflex changes of arterial pressure was studied. The lowest thresholds were registered in anesthetized cats with intact brain, the highest -- in the bulbar ones. In the former the A-fiber excitation evoked only depressor reflexes. In some of the bulbar and mesencephalic animals only pressure reflexes originated. In this experimental series the reflexes in mesencephalic cats were nearly maximal when the fibers with conduction velocity of over 15 m/s were excited. In bulbar cats it was necessary to excite also the thinner A-fibers for such an effect. Thus, the exclusion of suprabulbar structures in unanesthetized cats lowered the sensitivity of the central mechanism of vasomotor regulation to the impulses from the low-threshold A-fibers. This influence is not apparent in the other group of experiments where depressor reflexes occurred only on stimulation of A-fibers with high conduction velocity. In these experiments stimulation of A-fibers with lower conduction velocity also evoked pressor reflexes, but the difference in their value in bulbar and mesencephalic cats was insignificant.
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