Bulbar Vasomotor Center Research Articles

Serotoninergic and Nitroxidergic Neurons in the Nuclei of the Medulla Oblongata in the Rat

The aim of the present work was to undertake topochemical mapping of serotoninergic and nitroxidergic neurons in eight medulla oblongata nuclei of the so-called “bulbar vasomotor center” in 12 Wistar rats. The proportion of serotoninergic neurons in the projections of these nuclei was found to average 12–15%, compared with 31–43% in the nuclei of the posterior cervical group. Nitroxidergic neurons were distributed more uniformly, the proportions in the different nuclei ranging from 19% to 49%. Some 2–6% of neurons were located between nuclei and between nuclei and conducting pathways, these cells presumably performing integrative functions in the regulation of hemodynamics.

Nitroxidergic Neurons in Nuclei of the Medulla Oblongata in Hypertensive and Normotensive Rats

Distribution of nitroxidergic neurons and neuronal NO-synthase activity in certain medulla oblongata nuclei were studied in normotensive and hypertensive rats with different types of arterial hypertension. In rats with renovascular hypertension, neuronal NO-synthase activity markedly decreased in most nuclei 2 weeks after surgery, while the number of NO-positive cells did not change significantly; after 4 weeks, the percentage of NO-positive neuron markedly decreased and neuronal NO-synthase activity also slightly decreased. No further decrease in neuronal NO-synthase activity was observed 8 week after intervention, but the percentage of NO-neurons decreased compared to that in normotensive rats. In spontaneously hypertensive rats, changes in most nuclei were directed similarly to those observed in 8-week renovascular hypertension, but motor nuclei demonstrated less differentiated reaction to hypertension. In all cases, changes in the parameters observed in sensory nucleus (n. solitarius) appeared earlier and were more pronounced than in nuclei of the reticular formation related to bulbar vasomotor center.

NO-Positive Neurons in Some Nuclei of Human Bulbar Vasomotor Center in Arterial Hypertension

The distribution of nitroxidergic neurons and activities of neuronal NO synthase in them in some nuclei of the bulbar vasomotor center were studied in patients with early forms of arterial hypertension. Activity of neuronal NO synthase is reduced significantly in the majority of nuclei in patients with early forms of arterial hypertension, while the content of NO-positive cells was only slightly changed. More pronounced changes in this parameter were detected in the solitary tract nuclei in comparison with the reticular formation nuclei, which had efferent relationships with the intermediate lateral spinal nucleus.

Electrophysiological study of sympathoexcitatory structures of the bulbar ventrolateral surface as related to vasomotor regulation

The responses in T3–4, T10–11 and L2–3 white rami to stimulation of different zones of the bulbar ventrolateral surface were maximal when the region of about 4 mm laterally to the midline was stimulated. A weak surface stimulation of all these zones elicited only a long latency response consisting of three waves. A short latency response appeared when supramaximal stimuli were applied only to the intermediate zone—the region up to 6 mm rostrally to the hypoglossal nerve root level (zone S and caudal part of zone M). The data presented show that long and short latency responses are conducted from the intermediate zone to the spinal cord via dorsolateral funiculus fibres with a conduction velocity of about 5.6 ± 0.6m/s. In addition, a special descending sympathoexcitatory pathway oriented to T2 preganglionic neurons with a conduction velocity of about 12.3 ± 3.2m/s was demonstrated. Antidromic discharges of the output sympathoexcitatory neurons elicited by dorsolateral funiculus stimulation were found in the intermediate zone only at a depth of about 400–2000 μ M. Stimuli applied to different regions of the ipsilateral bulbar ventrolateral surface activate at least two groups of surface fibres (conduction velocities 6.7–8.0 and 2–3.2m/s) which, in turn, activate the output neurons with a rather constant delay of about 20 ms equal to a difference between the latencies of long and short latency white rami responses. The mechanism of delay formation seems to be concentrated in the intermediate zone and formed probably by a chain of interneurons. A possible scheme of neuronal organization of the bulbar ventrolateral sympathoexcitatory structures is presented and discussed. The descending tonic activation of spinal vasomotor neurons is formed by spontaneous discharges of antidromically identified output neurons with a mean firing rate of about 14.4 imp./s. Some neurons are reflexly activated within the time limits of the late somatosympathetic reflex response. Coagulation of the intermediate zone resulted in a profound fall of blood pressure, disappearance of pressor and late somatosympathetic reflexes, whereas the spinobulbospinal somatosomatic reflex remains unchanged. The baroreceptor inhibition is partly realized through the elements of sympathoexcitatory intermediate zone because the preferable inhibition of the long latency white rami response was demonstrated in the middle of R-R interval and during a sharp increase in the arterial pressure induced by vasoconstrictor drugs. Thus, the structures of the intermediate zone seem to play a key role in supporting of blood pressure level and organization of pressure reflexes. They are suggested to be the actual elements of the bulbar vasomotor center.

Effect of controlled halothane anaesthesia on splanchnic blood flow and cardiac output in the dog.

Effects of halothane anaesthesia on aplanchnic blood flow and cardiac output were studied in six dogs. Blood flows in the hepatic artery, the superior mesenteric artery and the portal vein were measured electromagnetically. Cardiac output was measured by thermodilution. Depth of anaesthesia, ventilation, acid-base state and body temperature were controlled. Cardiac output and blood flows in the hepatic artery, the superior mesenteric artery and the portal vein decreased significantly to 73%, 54%, 59% and 60% of control values, respectively. Total peripheral vascular resistance decreased significantly, while mesenteric and portal resistance remained essentially unchanged and hepatic arterial resistance showed a significant increase. It is suggested that the difference between the various vascular responses may be caused by a differentiated release from baroreceptor inhibition in various parts of the bulbar vasomotor center.

Local morphophysiological organization of the bulbar vasomotor center

Local morphophysiological organization of the bulbar vasomotor center

Hemodynamic changes to direct stimulation of the bulbar vasomotor center by acetylcholine

1. After injection of acetylcholine directly into the region of the gigantocellular reticular nucleus of the brainstem marked changes are observed in the minute and systolic blood volumes, total peripheral resistance of the vessels and systemic arterial pressure. 2. Pressor neurons of the bulbar vasomotor center and also structures of the central nuclei of the vagus nerve system are evidently responsible for these changes. 3. The experimental results raise the question of a possible selective effect of acetylcholine on structures of the bulbar vasomotor center.

Decreased blood pressure due to brain septal stimulation: Parameters of stimulation, bradycardia, baroreceptor reflex

Abstract Effects of varying the pulse length, frequency and duration of the electrical stimulus applied to the septal area of the chloralosed cat were studied. The degree of the blood pressure fall was taken as an index of the efficiency of the stimulation. Unidirectional pulses of 0.1,1,5,10, and 15 msec were tested. Pulse duration of 10 msec was generally the most effective. Frequencies of 15–50 and 80 cps were used, the frequency of 50 c/s was the most efficient. Stimulation time prolonged to 28.5 min showed that the septal area is very resistant to fatigue. Bradycardia was also studied and it was observed that eserine enhance the bradycardic effect of septal stimulation. Sometimes bradycardia was still present after vagotomy thus suggesting a diminution of cardiac sympathetic tone. The baroreceptor reflex was blocked by the hypotension due to septal stimulation; the possibility is advanced of a partial inhibition of the bulbar vasomotor center by impulses originating in the septal area.

The effect of anesthetics on the bulbar and spinal vasomotor formations

Vascular response to local stimulation of various components of the bulbar vasomotor center and of the lateral spinal cord horns (Th7–Th8) were recorded in decerebrated and spinal cats. Histological control was carried out in all the experiments. Depression of the vascular responses by

Functional organization of the bulbar vasomotor center. Activity of the neurons of the pressor zone during carotid reflexes

Functional organization of the bulbar vasomotor center. Activity of the neurons of the pressor zone during carotid reflexes

Functional organization of the bulbar vasomotor center

Experiments were carried out on cats under urethane anesthesia. A study was made of pressor and depressor “points” in the reticular formations of medulla oblongata. The vasomotor effects were recorded by local stimulation with electric current with different parameters of retangular impulse. The data obtained show the following: 1) there was no strict space division between the groups of neuronal elements with pressor and depressor function: both of them were present in all the formations studied; however, the pressor ones were more frequently encountered in the rostrolateral, whereas depressor — in the mediocaudal formations; 2) both types of neuronal elements, some of which when stimulated provoked only a pressor, while others - only a depressor effect, possess different specialized functions and their excitability in response to the parameters of the stimulating current differed: diverse frequency optimums, length of the current impulse, and intensity thresholds. Neuronal elements within each type also differed by their excitability; 3) alteration of the functional state of the neuronal elements by local polarization and reflexly led to changes of their excitability, which could have different directions in the neuronal elements with pressor and depressor function.

TONIC AND REFLEX FUNCTIONS OF MEDULLARY SYMPATHETIC CARDIOVASCULAR CENTERS

TONIC AND REFLEX FUNCTIONS OF MEDULLARY SYMPATHETIC CARDIOVASCULAR CENTERS