Vagal glucoreceptors in the small intestine of the cat.

Abstract

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.

Changes in activity of vagal bronchopulmonary C fibres by chemical and physical stimuli in the cat.

“…Both vagi were dissected below the diaphragm, then sectioned in order to suppress all the abdominal vagal afferents, since numerous C afferents come from gastro-intestinal receptors (Leek, 1972;Mei, 1978).…”

The effects of alimentary infusions of glucose, amino acids, or neutral fat on meal size in hungry pigs.

“…Recently, the intestine has been considered as a possible site of glucoreceptors (Mei, 1978). Experimental evidence for such glucoreceptors active in the short-term control of food intake in the rabbit (Novin, Sanderson & VanderWeele, 1974) and the rat (Yin & Tsai, 1973;Booth, 1972b;Booth & Jarman, 1976) has been ambiguous and has varied with the experimental procedures.…”

Carbohydrates and feeding: An extension of the glucostatic theory of appetite regulation

“…It was originally suspected that these "glucoreceptors" were located in the CNS and probably in the hypothalamus (Mayer, 1956). As time passed, it was suspected and later demonstrated (Shiota and Magnuson, 2008) that these receptors were in fact located in hepatic circulation (Niijima, 1969;Russek & Grinstein, 1974;Russek, 1981), the gastrointestinal tract (Mei, 1978), the causal hind brain (Ritter, 1981), and more recently the blood brain barrier (BBB) (Coiro, 2004). The decrease or increase in the utilization of glucose described above then in turn stimulates either satiety or hunger respectively along with a variety of other factors.…”