Spike Potentials and Cardiac Effects of Mammalian Vagus Nerve

Middleton, Samuel; Middleton, H. H.; Grundfest, Harry

doi:10.1152/ajplegacy.1950.162.3.545

Cited by 48 publications

(27 citation statements)

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“…Although the present study has not addressed the question of whether these vagal C fibres are afferent or efferent, McWilliam & Wooley (1990) provided evidence that at least in the rabbit they are probably efferent, since chronic supranodose vagotomy abolishes the C-fibre bradycardia. Previous studies on cats have suggested that vagal control of heart rate is mediated exclusively (Middleton et al 1950;Kidd & McWilliam, 1982) or mainly (Heinbecker & Bishop, 1935) by the small myelinated efferent fibres, which also appear to mediate the reductions in atrial contraction and slowing of atrio-ventricular conduction evoked by vagal stimulation (Kidd & McWilliam, 1982). There are several problems with these earlier studies.…”

Section: Discussionmentioning

confidence: 99%

“…It has been proposed that the B-fibre group, located in the nucleus ambiguus, control chronotropy whilst the C-fibre group, located in the dorsal vagal motor nucleus, control inotropy (Geis & Wurster, 1980). In support of this argument, a number of studies have suggested that the chronotropic action of the vagus in the cat is mediated by the myelinated B-fibre population (Heinbecker & Bishop, 1935;Middleton, Middleton & Grundfest, 1950;Kidd & McWilliam, 1982). Electrical stimulation of myelinated fibres evoked a profound cardiac slowing and additional recruitment of unmyelinated fibres caused no further cardiac slowing.…”

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confidence: 99%

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Heart rate responses to selective stimulation of cardiac vagal C fibres in anaesthetized cats, rats and rabbits.

Jones

Wang

Jordan

1995

The Journal of Physiology

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1. The contribution of cardiac vagal C fibres to vagal chronotropic control in anaesthetized cats, rats and rabbits was analysed using electrical stimulation of the vagus nerve with a selective anodal block technique. 2. After bilateral vagotomy and pretreatment with atenolol, 10 Hz continuous selective stimulation of unmyelinated fibres in the cut peripheral end of the cervical vagus evoked a bradyeardia in anaesthetized rats, cats and rabbits. With this stimulation protocol the three species exhibited a similar lengthening of the heart period (R-R interval) when expressed as a percentage of their basal cardiac interval. 3. The mechanism of action of the selective blocking technique was analysed by recording eighty-nine single A-(n = 12), B-(n = 22) and C-fibre (n = 55) vagal-projecting neurones in the medulla of the rat. This demonstrated that the technique can selectively block conduction in myelinated fibres and that 'break excitation' is seen mainly in unmyelinated fibres. Although thirty C fibres showed break excitation sixteen did not and this difference could not be correlated with their axonal conduction velocity, chronaxie or initial segment frequency following. 4. Using the anodal block technique the vagal effects on heart rate were reanalysed in the cat by incorporating a collision technique. B fibres were activated orthodromically to evoke cardioinhibition and simultaneously antidromically to collide with errant B-fibre spikes activated at the electrode producing anodal block. With this protocol it was noted that the B-and C-fibre bradycardias were not additive. Using a double anodal block and collision technique, it was demonstrated that this phenomenon was likely to be due to occlusion of the effects of B and C fibres. 5. In conclusion, in addition to the well-defined effects of vagal B fibres on heart rate, selective stimulation of vagal C fibres also had a cardioinhibitory effect in all three species studied. However, since the effects of cardiac C fibres on heart rate was small, these neurones alone cannot account for the cardioinhibition of the pulmonary chemoreflex. It is likely that activation of both B-and C-fibre cardiac vagal preganglionic neurones accounts for this reflex cardioinhibition.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Heart rate responses to selective stimulation of cardiac vagal C fibres in anaesthetized cats, rats and rabbits.

Jones

Wang

Jordan

1995

The Journal of Physiology

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“…In the cat, the bradycardia on electrical stimulation of the vagus nerve has been attributed solely to the effects of small-diameter myelinated efferent fibres, recruitment of non-myelinated fibres having no further effect (Middleton et al 1950;, although in an earlier study a slight negative chronotropic action of non-myelinated fibres was reported (Heinbecker & Bishop, 1935). In the dog non-myelinated fibres are reported to have no action on the heart (Donald, Samueloff & Ferguson, 1967), but in the rat both myelinated and non-myelinated fibres are reported to produce a bradyeardia (Nosaka, Yasunaga & Kawano, 1979).…”

Section: Discussionmentioning

confidence: 99%

The effects of electrical stimulation of myelinated and non‐myelinated vagal fibres on heart rate in the rabbit.

Ford¹,

McWilliam²

1986

The Journal of Physiology

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SUMMARY1. The bradyeardia evoked by electrical stimulation of the peripheral end of the rabbit vagus nerve is mediated by both myelinated and non-myelinated fibres.2. Stimulation of myelinated fibres at 5 Hz for 20 s resulted in a fall in heart rate from a control value of 204 + 1-3 to 182 + 1-2 beats min-1 (means + S.E. of means). On stimulation of both myelinated and non-myelinated fibres, heart rate fell to 169 + 2 1 beats min-1. Heart rate returned rapidly to control value following stimulation of myelinated fibres but only slowly after stimulation of both myelinated and non-myelinated fibres. Thus recruitment of non-myelinated fibres increased both the magnitude and duration of the bradyeardia.3. Atropine abolished all effects ofvagal stimulation on heart rate. Hexamethonium abolished the effect of myelinated fibres on heart rate; however, recruitment of non-myelinated fibres still produced a bradyeardia.4. It is suggested that the prolonged effect following stimulation of non-myelinated fibres may reflect the persistent action of a non-cholinergic excitatory transmitter at the ganglion.

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“…Physiological responses were measured using setup A; MAP recordings were made in the second part of every experiment after cutting the vagus nerve distally (setup B). Figure 2 shows an example of the A, B and C fiber components of the mammalian vagal MAP, as originally described by Heinbecker [8] and Gasser and Grundfest [10,11]. For standardization, all stimulus strengths are quoted as multiples of the threshold of the lowest threshold fibers (A fibers) in the MAP of that animal, designated T. In these experiments, T varied between 0.05 and 0.1 V. The lowest threshold B fibers were recruited at between 2.5 and 5T, while for C fibers, this was between 25 and 67T.…”

Section: Methodsmentioning

confidence: 99%

Calibration of Thresholds for Functional Engagement of Vagal A, B and C Fiber Groups In Vivo

et al. 2017

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Vagal nerve stimulation is widely used therapeutically but the fiber groups activated are often unknown. Aim: To establish a simple protocol to define stimulus thresholds for vagal A, B and C fibers. Methods:The intact left or right cervical vagus was stimulated with 0.1 ms pulses in spontaneously breathing anesthetized rats. Heart and respiratory rate responses to vagal stimulation were recorded. The vagus was subsequently cut distally, and mass action potentials to the same stimuli were recorded. Results: Stimulating at either 50 Hz for 2 s or 2 Hz for 10 s at experimentally determined strengths revealed A, B and C fiber thresholds that were related to respiratory and heart rate changes. Conclusion: Our simple protocol discriminates vagal A, B and C fiber thresholds in vivo.

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Spike Potentials and Cardiac Effects of Mammalian Vagus Nerve

Cited by 48 publications

References 0 publications

Heart rate responses to selective stimulation of cardiac vagal C fibres in anaesthetized cats, rats and rabbits.

Heart rate responses to selective stimulation of cardiac vagal C fibres in anaesthetized cats, rats and rabbits.

The effects of electrical stimulation of myelinated and non‐myelinated vagal fibres on heart rate in the rabbit.

Calibration of Thresholds for Functional Engagement of Vagal A, B and C Fiber Groups In Vivo

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