Vagal preganglionic fibres to the alimentary canal

It is generally accepted that the motor fibres to the stomach and oesophagus originate in the dorsal nucleus of the vagus (Kuntz, 1953). Furthermore, attempts have been made to show that the efferent fibres to the stomach and oesophagus are derived from localized groups of cells within the dorsal nucleus. In order to demonstrate such specific topographical grouping of cells, most workers have employed the anatomical method where the vagi are sectioned at various levels and the retrogressive changes in the medullary nuclei studied later. The data available from such studies have been reviewed by Molhant (1910) and more recently by Mohiuddin (1953), the latter commenting on the limitations and contradictions of the method. The verification of these histological findings by physiological methods has been rarely attempted. The single exception seems to be Laughton (1929) who showed that, in the cat, faradic stimulation of the floor of the fourth ventricle overlying the dorsal motor nucleus produced increased gastric motility.The importance of the vagal nerves and medullary reflex centres in the neural control of the reticulum, rumen and oesophagus has often been demonstrated (see Duncan, 1953). It has been suggested that the posterior brain stem contains a 'reticulo-ruminal centre' (Iggo, 1951). This paper gives an account of experiments undertaken to delimit the regions within the medulla oblongata from which contraction of the reticulum, rumen and oesophagus can be obtained by electrical stimulation. METHODSNineteen adult Blackface x Kent sheep were used. The weights varied between 25 and 47 kg, the group included twelve females, the seven males were castrates.Anaesthesia was induced by the injection of thiopentone sodium into the recurrent tarsal vein, about 25 mg/kg initially, with supplements as required. After preparation anaesthesia was maintained with 05 % chloralose. The head was firmly secured in a head holder, the medulla exposed and the cerebellum removed by suction to expose the fourth ventricle. Body temperature was maintained within normal limits.

Section: Effects On the Oesophagusmentioning

confidence: 99%

mentioning

confidence: 99%

Localization of regions in the medulla oblongata of sheep associated with rumination

Bell¹,

Lawn²

1955

“…The paucity of active efferent fibres revealing a modification of discharge associated with reflex bradyeardia, however, as well as the absence of a cardiac rhythm of discharge which has been reported by others, led to our decision to attempt to record directly from the cell bodies of the motor component of the nerve. On the basis of available histological evidence reviewed by Mitchell & Warwick (1955) and supported by recent studies in the cat (Mohiuddin, 1953;Calaresu & Cottle, 1964) vagal efferent fibres to the heart originate * Fellow of the Canadian Heart Foundation.…”

mentioning

confidence: 99%

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

Calaresu¹,

Pearce²

1965

Although there exists an extensive literature on primary vagal afferent discharges of cardiovascular origin (Paintal, 1963) there is a need for characterization of discharge patterns in vagal efferent fibres to the heart. Such information from peripheral nerve recordings might then allow the recognition, by exclusion, of related interneuronal activity in intramedullary recordings and thus aid the study of neural mechanisms of cardiomotor reflexes. Earlier attempts to record cardiomotor activity in cardiac branches of the vagus have yielded discharges of questionable origin because, at this level of the nerve, admixture with sympathetic efferents arising in both the stellate and inferior cervical ganglia (Cannon, Lewis & Britton, 1926) is unavoidable unless all peripheral connexions between the vagus and sympathetic nerves are cut. Relevant accounts do not contain assurance that this precaution was taken

“…According to this hypothesis, the cell body for these fibres is not in the nodose ganglion, but has migrated down, say, the aortic nerve, making a large 'loop' as in Fig. 4 G. Fibres with their cell bodies outside the nodose ganglion may also be the myelinated fibres which do not degenerate after infra-nodose vagotomy (Daly & Evans, 1953;Mohiuddin, 1953;Agostoni, Chinnock, Daly & Murray, 1957;Murray, 1957), although an arrangement such as in Fig. 4H could also account for such a finding.…”

Section: Discussionmentioning

confidence: 99%

Direct nervous pathways between the cervical vagus and the aortic or superior laryngeal nerves traversed by baroreceptor, ‘pulmonary stretch’, and other fibres in the cat

Jewett¹

1964

Only brief reports have appeared concerning carotid sinus baroreceptor fibres which conduct orthodromic impulses peripherally in the aortic nerve (Holmes, 1954;Bianconi & Raschi, 1959) and a vagal cardiac branch (Green, 1959) of the cat. The finding of a similar fibre in the cervical vagus of a dog (Jewett, 1964) led to the study to be described here. In the cat, besides these fibres, other baroreceptor fibres and some 'pulmonary stretch' fibres were found to conduct impulses peripherally in the aortic nerve. Electrical stimulation gave results which might be explained by assuming that these 'sensory' fibres do not pass to the central nervous system. METHODSNineteen cats weighing between 1-6 and 5-5 kg were anaesthetized with intra-peritoneal pentobarbitone sodium, 30-40 mg/kg body wt. With the cat supine the trachea was cannulated low in the neck. To facilitate dissection the block of tissue containing the pretracheal musculature, trachea, oesophagus, larynx, and lower pharynx was removed after nerves and vessels along the sides had been sectioned. To record respiration through changes in intra-thoracic oesophageal pressure, the oesophageal stump was cannulated with a polyethylene catheter inserted far enough to lie within the thorax. An unheated (28-33°C) liquid paraffin pool (sp.gr. 0.850) was formed within supported skin flaps; beneath its surface the vagus could be dissected readily to above the nodose ganglion. The nodose ganglion as well as the aortic nerve was identified by dissecting centrally along the superior laryngeal nerve. All recordings were made from the central segmentst (either at the cut end or along the nerve) of cut whole nerves from which the connective tissue had been removed with fine jeweller's forceps. Recording electrodes were AgCl-coated Ag wire of 0-025 in. diameter and stimulating electrodes were the same or of Pt; electrodes were positioned by Prior manipulators. Each of two square-wave stimulators could be made to fire at any given point on a freerunning oscilloscope sweep; the repetition frequency was usually either 50/sec or 100/sec. Recording electrode potentials were differentially amplified by a battery-powered Tektronix 122 pre-amplifier leading to a Tektronix 502 dual-beam oscilloscope. The high-frequency filters attenuated to half value at 1 kc and low-frequency filter attenuated to more than * Present address: Department of Physiology, University of California Medical Center, San Francisco, California 94122, U.S.A. t The term 'segment' is used to avoid the confusion arising from the usual terminology: a cut nerve has four ends, but only two segments.