Electrical activity of efferent vagal fibres and dorsal nucleus of the vagus during reflex bradycardia in the cat

108

SUMMARY1. Action potentials were recorded from seventy-four single and twentynine small multifibre nerve strands efferent to the trachea and lungs of cats and dogs. From the pathway (vagal or sympathetic), spontaneous activity, conduction velocity and responses to various interventions the efferent fibres were classified in the following way.2. Group I, vagal. These had a mean conduction velocity of 9-7 m/sec, and had a respiratory but seldom a cardiac rhythm. Their discharge was inhibited during hypertension caused by injections of adrenaline and during inflation of the lungs, but was increased during tracheal occlusion, stimulation of peripheral chemoreceptors and irritation of the larynx. The fibres are thought to be constrictor to the airways.3. Group II, sympathetic. These had a mean conduction velocity of 0O85 m/sec and usually had inspiratory and cardiac rhythms. Their discharge usually responded qualitatively as that of group I fibres to the various interventions, but with clear quantitative differences. They are divided into three subgroups on the basis of their responses to injections of adrenaline and to asphyxial stimuli.4. Group III, vagal and sympathetic. These had a mean conduction velocity of 9 0 m/sec, very slow discharge rates and often an expiratory and cardiac modulation. They were activated during hypertension due to adrenaline and often by tracheal occlusion, chemoreceptor stimulation, laryngeal irritation and lung inflation. Their motor action is unknown.5. Group IV, vagal and sympathetic. These had conspicuous cardiac rhythms resembling those of vascular baroreceptors, but their discharge could not be correlated with arterial blood pressure. Their mean conduction velocity was 6-6 m/sec. Some were active after combined vagotomy and * Present address: University Laboratory of Physiology, Oxford.

Section: Group I Vagal Fibresmentioning

confidence: 96%

mentioning

confidence: 99%

Action potentials in parasympathetic and sympathetic efferent fibres to the trachea and lungs of dogs and cats

Widdicombe¹

1966

108

“…The thickness of the nucleus ranges from 0.1 to 0 5 mm dorsoventrally, and the width ranges from 0-2 to 0-7 mm. As accurate anatomical localization of the electrode tip could not be obtained from stereotaxic co-ordinates, iron deposits were placed at the sites of stimulation, and revealed histologically by a method previously described (Calaresu & Pearce, 1965a).…”

Section: Methodsmentioning

confidence: 99%

The mechanism of the cardio‐acceleration elicited by electrical stimulation of the parahypoglossal area in the cat

Calaresu¹,

Henry²

1970

Self Cite

SUMMARY1. In chloralosed and in decerebrated cats localized electrical stimulation of a discrete parahypoglossal area (including the nucleus intercalatus and a discrete neighbouring region ventrolateral to the hypoglossal nucleus) elicited cardio-acceleration and arterial hypertension, either singly or together.2. The cardio-acceleratory response was decreased by intravenous administration of propranolol (2 mg/kg). In another group of experiments the response was abolished by acute bilateral cervical vagotomy but it was observed to return partially when stimulation was applied one or more hours after vagotomy. The hypertensive response was not affected by propranolol or by vagotomy.3. Evoked electrical activity with a latency of 3-10 msec was recorded from pre-and post-ganglionic sympathetic cardio-acceleratory nerves during stimulation of this region.4. These findings demonstrate the existence of a discrete medullary area which controls heart rate by activation of a sympathetic pathway and inhibition of a parasympathetic pathway.

“…The paramedian reticular nucleus was found to extend from about 0 5 to 3-0 mm rostral to the obex, from 0 5 to 1-2 mm lateral to the mid line and from 1-7 to 3-5 mm from the dorsal surface of the medulla. To obtain accurate anatomical localization of the electrode tip iron deposits were placed at the site of stimulation and revealed histologically by a method previously described (Calaresu & Pearce, 1965a).…”

Section: Methodsmentioning

confidence: 99%

The function of the paramedian reticular nucleus in the control of heart rate in the cat

Calaresu¹,

Thomas²

1971

Self Cite

SUMMARY1. Selective electrical stimulation of the paramedian reticular nucleus (PRN) in anaesthetized and decerebrate-anaesthetized cats elicited cardiac slowing which was shown to be due to inhibition of the sympathetic input to the heart.2. In decerebrate preparations stimulation of the PRN elicited cardioacceleration which was abolished by bilateral vagotomy.3. It is suggested that these changes in heart rate in opposite directions can be accounted for by an inhibitory influence of the PRN on both neural inputs to the heart. In the absence of vagal activity, demonstrated in anaesthetized and decerebrate-anaesthetized preparations, the response to stimulation of the PRN resulted in cardiac slowing. In contrast, when both sympathetic and parasympathetic pathways were active (decerebrate preparation) stimulation of the PRN resulted in cardio-acceleration, due to simultaneous inhibition of the two neural inputs to the heart. 4. It is concluded that the two inhibitory functions of the PRN are probably mediated by two different populations of neurones and that the PRN plays an integrative role in the medullary control of heart rate.