Splanchnic slowly adapting mechanoreceptors with punctate receptive fields in the mesentery and gastrointestinal tract of the cat.

1. A class of slowly adapting mechanoreceptors with A-delta and C fibres running in the splanchnic nerves of cats is described.2. The mechanoreceptors have punctate regions of mechanical sensitivity at macroscopic vascular branching points and have been found in the lesser omentum, the mesentery of the gall-bladder, porta hepatis, portal vein, pancreas, spleen and the duodenum, jejunum, ileum, colon and their mesenteries.3. The receptive fields of these mechanoreceptors vary considerably in size in the different regions. The largest receptive fields were found in the small intestinal mesentery and consisted of up to seven points of mechanical sensitivity at vascular divisions, each separated by distances of a few up to about 40 mm. The smallest receptive fields were single or double points of mechanical sensitivity which were most commonly found in relation to the portal vein in the root of the mesentery.4. Maintained stretch of the receptive field elicited a train of impulses which had phasic and tonic components. The tonic discharge was sometimes maintained for more than 1 min.5. Distension of a neighbouring viscus often caused a discharge which had a phasic component and a variable tonic component. The occurrence of the latter appeared to depend on the relative positions of the bowel and mesentery, and was probably associated with a change in tension on the mesentery.6. Occlusion of the portal vein resulted in some units in a discharge which began soon after the start of the occlusion.7. The receptors do not appear to be affected by acid, hypoxia or hypercapnia.