Mechanosensitive properties of gastric vagal afferent fibers in the rat

Single, teased fiber recordings were made from the decentralized right cerv ical vagus nerve (hyponodal) of the rat. A total of 67 afferent fibers that responded to gastric distension (GD) were studied: 9 fibers were stimulate d by phasic balloon GD, 58 by more natural fluid GD. All balloon GD-respons ive fibers had resting activity (3.1 imp/s), and 57/58 fluid GD responsive fibers had resting activity (1.3 imp/s). All balloon GD-responsive fibers e xhibited a dynamic response to phasic distension followed by slow adaptatio n, whereas fluid GD-responsive fibers exhibited increasing responses as int ragastric pressure increased, followed typically by slow adaptation. Respon ses to graded GD were studied in all fibers, and all gave increasing respon ses to increasing pressures (5-60 mmHg). Thresholds for response varied bet ween 0 and 18 mmHg. Mean response thresholds for two durations of fluid GD (30 and 60 s) were 5.6 and 3.9 mmHg; the mean response threshold to phasic balloon GD (30 s duration) was 5.3 mmHg. The potential sensitizing effect o f platelet activating factor (PAF, 50 or 100 ng . kg(-1) . min(-1) for 20 m in) infused into the gastric artery was studied in 20 fibers. Fifteen fiber s exhibited an increase in spontaneous activity; intragastric pressure also slightly increased during PAF infusion. The increase in activity produced by PAF was attenuated in the presence of the PAF receptor antagonist WEB 20 86. After PAF-induced acute inflammation of the stomach, three of five fibe rs studied did not exhibit any change in response to graded GD. The present study characterized distension-sensitive afferent fibers in the right cerv ical vagus innervating the stomach of the rat by balloon GD and fluid GD. T he results document that all distension-sensitive gastric vagal afferent fi bers encoded the intensity of GD, but none had response thresholds in what might be considered the noxious rang. PAF infusion activated mechanosensiti ve gastric vagal afferent fibers, but acute inflammation produced by PAF di d not sensitize responses to GD.