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SUMMARY1. In anaesthetized cats, the unitary activity of seventy-eight sensory vagal neurones was recorded in nodose ganglia by means of extracellular glass microelectrodes.2. These neurones were stimulated by perfusion of the small intestine (duodenum and first part of jejunum) with glucose or other different carbohydrates at concentrations of 1-20 g/l. (i.e. 55-1100 m-osmole/l.).3. The neurones were slowly adapting to stimulation and their discharge frequency was always low (1-30 Hz).4. The activity of these neurones depended on the particular carbohydrate used and on its concentration: the discharge frequency generally increased when the concentration rose.5. The neurones were of the C type (conduction velocities: 0*8-1-4 m/sec; mean, 1.1 m/sec).6. In contrast with the known neurones connected to the gastro-intestinal tension receptors, they were not obviously activated by intestinal contractions or distensions.7. In the same way, the stimuli which produced the response of other known endings, i.e. the mucosal receptors, were not effective; these stimuli included in particular stroking of the mucosa, over-distension of the bowel, intestinal perfusion with alkaline or acid solutions. On the other hand, the use of substances other than glucose (KCl and NaCl of the same osmolarity) showed that the osmotic pressure was not directly related to the receptor activation.8. Therefore it is proposed to call the endings corresponding to these neurones 'glucoreceptors'.9. The effect of glycaemia and intestinal motility were also studied. These variables acted presumably by changing the intestinal absorption rate.10. The functional characteristics of the glucoreceptors (in particular the short latency of their response) strongly suggested that they were located close to the intestinal epithelium.11. An ultrastructural study was performed in an attempt to identify the histological site of the receptors. Many non-medullated fibres were observed in the villi, especially beneath the epithelial layer. They gave complex branchings with abundant swellings. Some of them, at least, belonged to the vagal sensory component, because they were less numerous after unilateral selective sensory vagotomy. Therefore these complex endings could serve as the vagal glucoreceptors.

The number and caliber of myelinated and non-myelinated fibers of entire and sensory vagal nerves of cats were studied by means of light and electron miscroscopy. The results obtained with electron microscopy show that the non-myelinated component is particularly rich (about 40,000 elements at the cervical level), with clearly higher numbers of fibers than demonstrated thus far with light microscopy. The ratio of myelinated to non-myelinated fibers is on the average 1:4 for the total vagi and only 1:8 for the sensory vaga component. The comparison of the nerve above and below the level of the nodose ganglion shows that (1) mean fiber diameter is usually greater at the infranodose than at the supranodose level, and (2) some myelinated fibers of small diameter occurring below the nodose ganglion become non-myelinated above it. Additionally, the number of non-myelinated fibers per Schwann cell is greater at the supranodose than at the infranodose level; this speaks in favor of a reorganization of the C-fiber population from one level to the other.

SUMMARY1. In anaesthetized cats, sixty-two vagal sensory units with afferent endings in the lower oesophageal sphincter were recorded by means of extracellular glass micro-electrodes implanted in the nodose ganglion.2. All the receptors had non-medullated fibres, with conduction velocities ranging from 0O8 to 1-2 m/s. From the direct stimulation of the lower oesophageal sphincter, three types of mechanoreceptors were identified. 3. Thirty-one were activated by natural stimuli: tonic contraction of the sphincter and distension elicited by the passage of a bolus. Artificial stimulation effected by digital compression was also effective. These receptors were similar to muscular endings already described in the-digestive tract. Their main characteristic, i.e. their slow adaptation, suggests that they act as sensors of sphincter opening and closure. This was corroborated by observations obtained during distension of the cervical or thoracic oesophagus; a maximum decrease occurred in the lower oesophageal sphincter mechanoreceptor discharge when the distension was produced between 9 and 12 cm from the lower oesophageal sphincter.4. Twenty-nine endings were found in the superficial layers mucosaee). Contrary to the muscular receptors, the mucosal receptors were not affected by normal contractions or distensions of the lower oesophageal sphincter. They were activated only by strong stimuli like digital compression or distension achieved with a balloon. In addition, mucosal stroking was a potent stimulus. Whatever the stimulus used, the mucosal receptors showed rather rapidly adapting discharges. These receptors should be considered to be sensors of bolus consistency.5. Two mechanoreceptors, located in the serous membrane ofthe lower oesophageal sphincter, were identified by touching or by stretching. Their discharges showed that they belonged to the rapidly adapting type.6. A comparison of the three types of receptors found in the lower oesophageal sphincter is made with known digestive endings and their possible role is discussed.

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