Sensitive control of heart rate in monkeys using burst stimulation of the vagus nerve

Burst vagus stimulation led to synchronization of the cardiac and vagal rhythms at certain frequency ranges. The increase of the number of impulses in a burst from 1 to 16 extended the range of synchronization and shifted it towards lower frequencies forming a total range of exact regulation of the heart rate within 85--40% of the initial rate. It was suggested that vagal effect consists of tonic and synchronizing components.     

Controlled sinus arrhythmia during burst stimulation of the vagus nerve

In experiments on anesthesized cats and rats the desynchronization of the heart rate and burst stimulation of the vagus brought about severe sinus arrhythmia. Analysis of the functional dependence between the P--S interval (atrial wave of the ECG--moment of vagus stimulation) and the P--P interval showed periodical alterations in pacemaker sensitivity to the effect of the vagus during each cardiac cycle. It is supposed that natural vagus arrhythmia is the result of discoordination between heart automacy and efferent vagus bursts of central origin.     

Effect of the sympathetic nervous system in regulating heart rhythm during burst stimulation of the vagus nerve

In cat experiments, the right inferior cardiac nerve was stimulated at a frequency of 2 and 4 Hz and the right vagus by bursts of 1, 2, 4, 8 and 16 impulses. Stimulation of the inferior cardiac nerve shifted the ranges of the heart rate control up the frequency scale. The shift of the range boundaries was mainly determined by the intensity of sympathetic regulation and by the number of impulses in a burst which stimulates the vagus nerve.     

电刺激迷走神经对蟾蜍心率和心率变异的影响

目的:观察不同频率迷走神经刺激对蟾蜍离体心脏的心率及心率变异的影响。方法:将蟾蜍心脏和右侧迷走交感干离体后,以不同频率电刺激神经,记录心电图曲线并作心率变异性(HRV)分析。结果:交感神经阻断后,电刺激迷走交感干,心率(HR)显著下降(P0.01),全部正常心动周期的标准差(SDNN)和相邻正常心动周期差值的均方根(RMSSD)显著升高(P0.01),不同频率刺激组之间没有明显差异;与对照组相比,各指标变化较大;给药组0.2Hz时高频(HF)显著升高(P0.01),低频/高频比值(LF/HF)明显降低(P0.05),0.8Hz时HF和LF/HF接近刺激前水平。结论:一定范围内增加刺激频率,迷走神经降低心率的作用增强;没有交感神经调节条件下的迷走神经对心率和心率变异的调节可能存在不同的机制。     

迷走神经刺激对记忆的影响

迷走神经刺激(vagus nerve stimulation, VNS)用于终止癫痫发作已经有二十年的历史.期间VNS也用于难治性抑郁的治疗.在治疗过程中研究者发现VNS 对癫痫、抑郁患者的学习和记忆能力有改善作用,这种改善作用在一些动物和人体实验中也得到证实.但VNS在记忆形成的哪个阶段起作用以及如何起作用的具体机制尚不十分清楚.因此,进一步了解VNS对记忆的影响及作用机制有利于探讨记忆形成的生理机制,也为临床治疗特异性记忆障碍和相关神经精神疾病提供新的思路和有益补充.本文综述了近十几年来VNS对记忆的影响及相关机制.     

Reaction of the hypothalamo-hypophyseal system of cats to stimulation of the cervical sympathetic nerve and the afferent fibers of the vagus nerve]

Data are presented on the functional morphology of the hypothalamo-hypophysial neurosecretory system of cats in stimulation of the cervical sympathetic nerve and of the afferent fibers of the vagus. Stimulation of the sympathetic nerve selectively activated the supraoptic nucleus and caused the discharge of the neurohormones from the posterior lobe of the hypophysis, whereas its infundibular portion contained much neurosecretory material. In response to the stimulation of the vagus all the portions of the neurohypophysis were released of the Gomori-positive substance; both the supraoptic and the paraventricular nucleus were activated.     

Effect of stimulating the auricular branch of the vagus nerve on the heart rate in patients with severe chronic heart failure

A study was made to evaluate the prospects of improving the cardiac function by electrical stimulation of the auricular branch of the vagus nerve in patients with severe chronic heart failure (CHF). Sympathetic hyperactivity and the cardiac function were evaluated by 24-hour ECG monitoring, echocardiography, and a 6-min walk test. At the time of enrollment into the study, patients had a heart rate (HR) of more than 60 bpm, a left ventricular (LV) ejection fraction (EF) of less than 40%, and CHF NYHA functional class (FC) III or IV even with well tolerated medications. Control-group patients (n = 7) did not show significant changes in the functional state of the heart after sham treatment. In the test group (n = 44), a significant increase in LV EF and a decrease in end-systolic volume were induced by electrical pulse stimulation of the auricular branch. A decrease in HR was documented in 34 patients; CHF FC decreased by one or two grades in 40 patients. The changes were assumed to reflect new balance achieved in the autonomic regulation of the heart to contribute to sustaining competence of the myocardium. Electrical pulse stimulation of the auricular branch of the vagus nerve was concluded to provide a safe and efficacious addition to drug therapy in patients with severe CHF.     

Histopathologic features of the vagus nerve after electrical stimulation in swine

This paper describes the histological features of the vagus nerve after its stimulation with an electrostimulation system that is being developed for morbid obesity treatment. An electrostimulation system was implanted laparoscopically around the ventral vagal trunk of five Large White female pigs (49.63+/-1.94 kg.). Vagal nerve stimulation was performed by continuous constant voltage current pulses. Thoracic samples of both ventral and dorsal vagal trunks were obtained thoracoscopically one month after implantation. Animals were sacrificed one month after thoracoscopic vaguectomy. Tissue samples were then harvested from the vagal nerve at the implantation site, 1cm cranial to it, thoracic portion of ventral and dorsal vagal trunks, sub-diaphragmatic dorsal vagal trunk, left and right vagus nerves. Specimens were analysed with light microscope. The severity of the lesions was graded from 0 to 4 (0: no lesion, 1: mild, 2: moderate, 3: severe and 4: extremely severe), taking into account fibrosis, vascularization, necrosis, fiber degeneration and inflammation. Electrode implantation resulted in thickened epineurium and endoneural connective tissue. The greatest lesion score was evidenced at the leads implantation site in the ventral vagal trunk, followed by, in order of decreasing lesion severity, left vagus nerve, thoracic portion of ventral vagal trunk, subdiaphragmatic dorsal vagal trunk, thoracic portion of dorsal vagal trunk and right vagus nerve. The stimulation device used in this study caused connective tissue growth, greatest in the samples located closer to the implantation site. However, there was no sign of altered vascularization in any studied specimen.     

Differential blood pressure and heart rate responses to supramedullary brain stimulation in cats

The purpose of this study was to compare the cardiovascular responses to electrical stimulation of different supramedullary brain regions. Arterial blood pressure (BP) and heart rate (HR) effects were elicited by electrical stimulation of the lateral hypothalamus (LH), mamillary bodies (Mm), substantia nigra (SN), globus pallidus (GP), and the subthalamic nucleus (Sub) in conscious, freely moving cats. Pressor responses were obtained from all of these regions. The higher intensity of stimulation the higher increase in BP and HR was obtained. However, clear-cut differences occurred in the effects both during and after the termination of stimulations. Namely, a continuous increase in BP and HR was obtained from the LH and SN. In contrast, the initial increase in BP and HR was followed by a reduction compared to the peak value of the effects of stimulation in the GP and the Sub. However, the BP and HR never reduced to the pre-stimulaion level during the stimulation. Also the changes following the cessation of stimulation at the different brain loci were dissimilar. The BP and HR either returned gradually to the pre-stimulation level, or long-lasting oscillation occurred. The electrical activity of the nucleus of the solitary tract (NTS) and the vagus nerve co-varied with the changes in BP and HR. It is concluded that the supramedullary stimulations produce differential cardiovascular effects, and these effects are modified by the baroreflexes that are activated by the electrically elicited rise in blood pressure.     

Origin and the functional role of adrenergic fibers of the vagus nerve in cats

Origin of adrenergic fibres of vagus is studied. They are shown to appear in the thoracic vagus through caudal anastomosis introduction. The observations indicated that axons of spinal neurons and neurons of the ganglion stellate passed through caudal anastomosis and entered a thoracic vagus nerve. Stimulation of the thoracic vagus in cats after atropine sulphate injection increases the heart rate.