Gastric motility patterns for digestion and vomiting evoked by sympathetic nerve stimulation and 5-hydroxytryptamine in the dogfish Scyliorhinus canicula

Abstract

The sympathetic control of motor activity in the stomach of the dogfish Scyliorhinus canicula and its pharmacology was studied in freshly killed animals with the abdominal viscera superfused in situ with elasmobranch Ringer by recording gastric pressure and by quantitative analysis of video-tape recordings of the activity. Little spontaneous activity was seen in the stomach, although in two animals retrograde contractions occurred in the spiral intestine. The effects of electrical stimulation of the splanchnic (sympathetic) nerves varied markedly with frequency. At 4 Hz after a latency of about 1 min there was a slight increase in the overall level of contractile activity in both cardiac and pyloric regions of the stomach, which persisted throughout the stimulation period (5-7 min). At 16 Hz a contraction was visible in the pyloric region within 10 s of the start of stimulation. Over the next 30 s this contraction proceeded cranially becoming more powerful as it swept into the cardiac region. This contraction returned the contents of the pyloric stomach to the cardiac stomach past the valve-like junction between them. This contraction continued into the cardiac stomach and in some animals propelled the contents into the oesophagus. About 2 min after the start of stimulation there followed a series of contractions in both gastric regions, predominantly in the circular muscle. In the cardiac region these contractions occurred alternately in the proximal and distal regions. Occasionally a large contraction passed a bolus of material from the cardiac to the pyloric region. No movements or pressure changes were observed in the stomach after stimulation of the vagus, although contractions were readily induced in the oesophagus. It is proposed that the initial large retrograde contraction provides a mechanism by which the animal can vomit indigestible or accidentally ingested material. In contrast the later motor patterns suggest that this type of activity is involved in more normal digestive functions of mixing food with gastric secretions, trituration and gastric emptying. Evidence is presented which implicates 5-hydroxytryptamine as a principal neurotransmitter involved in the genesis of the retrograde contraction by the splanchnic nerve.