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

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Abstract
Electrical stimulation of the abdominal vagi revealed that abdominal vagal fibers are distributed throughout the cervical vagal trunk. Conduction velocities of the main group of abdominal fibers ranged from 0.4-1.5 m .cntdot. s-1. Single afferent fibers [37] with endings in the gastric and intestinal mucosa, were isolated from the cervical vagus of adult rats. Conduction velocities of 18 of these endings ranged from 0.5-2.5 m .cntdot. s-1. Light mechanical stimulation, such as stroking the mucosa, evoked a rapidly adapting response from these endings. Sustained pressure or distension with fluid or air did not excite these endings although stretching of the mucosa excited 3 units. Balloon distension usually evoked an on-off response due to phasic stimulation of the mucosa by the balloon during inflation and deflation. These same endings also functioned as non-specific, slowly adapting chemoreceptors responding to various organic and inorganic acids, tap water and distilled water, alcohol, hypertonic saline, NaOH, NH4Cl, CuSO4, casein hydrolysate, mustard powder and cayenne pepper. Hypertonic glucose and guinea-pig bile were ineffective as stimuli. In the presence of an excess of Cl ions the effectiveness of acids in stimulating these endings was in part determined by the pK of the acid. pH per se was not the basic determining factor, but rather the molecular size of the acid.