Bengt ÖBerg

Cardiovascular effects elicited from the ventral surface of medulla oblongata in the cat

Cardiovascular adjustments induced by topical application of drugs on a restricted area on the ventral surface of the medulla oblongata, corresponding to the caudal part of the rostral chemoreceptor area and the intermediate area, have been studied in chloralose-anesthetized cats. Topical application of GABA or glycine on these structures resulted in blood pressure fall, bradycardia, vasodilatation in the kidney and the skeletal muscles and also depression of respiration. Similar responses except for a slight tachycardia occurred with application of physostigmine. Application of GABA resulted in a marked attenuation of the reflex vasoconstrictor responses to removal of arterial baroreceptor restraint (carotid occlusion), particularly in the kidney, and to disappearance of the reflex renal vasodilatation to baroreceptor stimulation. The findings suggest that GABA application leads to a general diminution of the tonic vasomotor neuron activity, and with regard to renal vasomotor neurons a virtual cessation. Atropine methylnitrate application induced blood pressure rise, increased peripheral resistance in both skeletal muscle and kidney and a strongly potentiated renal vasoconstrictor response to carotid occlusion. The results indicate that the studied superficial medullary structures play an important role for the maintenance of tonic vasomotor neuron activity, especially renal.

The effect of stimulus pattern on the pressure response to electrical stimulation of the carotid sinus nerve of cats.

Summary The resultant effect of CSN stimulation, as well as depending on the stimulus strength or duration, also depends upon the pattern of the stimulation. Intermittent stimuli have been shown in these experiments to produce a fall in blood pressure, whereas, stimuli with identical parameters produced a rise in pressure when applied continuously. Similarly, it has been shown that when the stimulus parameters were such that depressor effects were seen to continuous stimulation, grouping the stimuli produced equivalent or greater depressor responses with 10% or less of the total number of stimuli per second. This observation may be of relevance in the design of baropacers for the treatment of certain types of hypertension.