Gastric Mucosal Chemoreceptors With Vagal Afferent Fibres in the Cat

Abstract

Electrical activity was recorded in 19 single fibres, with very slow conduction velocities, dissected from the cervical vagi of 10 cats. The nerve endings of these fibres were in the gastric mucosa and were destroyed when the mucosa was scraped away. A brief burst of impulses was recorded when the mucosa was stroked firmly with a smooth rod but there was no response when the stomach was made to contract, when it was compressed firmly between finger and thumb, or when it was lightly distended. Over-distension excited 3 of the mucosal nerve endings. The mucosal nerve endings were specifically sensitive to either acid or alkaline solutions on the mucosa. The discharge of impulses in the afferent fibre persisted for as long as the stronger solutions used (0-1 N-NaOH or 0-1 N-HCR) remained on the mucosa. The threshold of the acid receptors was pH 3 or lower and of the alkali receptors was pH 8 or above. The endings were not affected by hypotonic or hypertonic solutions or by any other chemicals that were tried. A clear distinction is made between the gastric mucosal nerve endings described in the paper and the tension and "stretch" receptors which are found in the deeper layers of the gastric wall. It is concluded that the mucosal nerve endings probably function as slowly-adapting chemoreceptors.A low-threshold gastric "stretch" receptor is described.Both mechanical and chemical stimulation of the gastric mucosa elicit a variety of sensations and reflex responses. Carlson and Braafladt [1915] and Wolf and Wolff [1947] found that there was a sensation of pressure or an undifferentiated awareness when the normal gastric mucosa of their subjects was rubbed or squeezed; touch, however, was not perceived. Gastric movements in sheep and goats may be enhanced by acidification of the gastric contents [Titchen, 1953] or by mechanical stimulation of the gastric mucosa [see Habel, 1956, for review]. There does not seem to have been any previous electrophysiological account of afferent fibres with endings in the mucosa. The gastric afferent fibres already described came from tension and "stretch" receptors Iggo, 1955. The endings of these fibres were in the outer layers of the gastric wall.The present study is part of a wider investigation of small afferent fibres. It was begun when a gastric afferent fibre was found which did not fit into the category described previously. The ending of the fibre was destroyed when the gastric mucosa was removed. This paper describes the response of similar fibres to mechanical and chemical stimulation. A preliminary account of this work has already appeared [Iggo, 1957 b].

Proceedings of the Physiological Society, 18–19 January 1974, St.Thomas's Hospital Meeting: Communications

“…This first peristaltic wave has a velocity of 28 + 2 cm/sec. Iggo (1957) and Davison (1972). These units in the rat more closely resemble the reticulo-epithelial and abomasal endings described recently in the sheep (Harding & Leek, 1972a, b).…”

Mucosal receptors in the gastric antrum and small intestine of the rat with afferent fibres in the cervical vagus.

“…In only a small proportion of such studies has an attempt been made to investigate the chemosensitivity of afferent nerve endings. Iggo (1957) and Davison (1972b) have described mucosal endings of single vagal fibres in the stomach and small intestine of the cat which respond to mechanical and chemical stimulation of the mucosa. Harding & Leek (1972a, b) and Leek (1972) have isolated vagal afferent units with chemosensitive endings in the abomasum and reticulum of the sheep and further details are provided in recent reviews (Leek, 1977;Leek & Harding, 1975).…”

Gastric emptying of organic acids in the dog.

“…From first principles it is likely that the volume receptor is located in the stomach and that other receptors are located in the duodenum. Previous observations also favour this assumption (Iggo, 1955(Iggo, , 1957Paintal, 1954;Meeroff, Go and Phillips, 1975). In order to test this hypothesis, proximal gastric vagotomy (PGV) was performed, and emptying experiments were repeated after this procedure.…”