INTRINSIC MECHANISMS CONTROLLING CARDIAC STOMACH VOLUME OF THE RAINBOW TROUT (ONCORHYNCHUS MYKISS) FOLLOWING GASTRIC DISTENSION

Author:

GROVE DAVID J.1,HOLMGREN SUSANNE2

Affiliation:

1. Marine Science Laboratories Menai Bridge, LL59 5EY Wales, UK

2. Comparative Neuroscience Unit, Department of Zoophysiology, University of Göteborg Box 250 59, S-400 31 Goteborg, Sweden

Abstract

1. Inflation of the cardiac stomach of the rainbow trout induced reflex muscular contractions. The stomach then slowly relaxed asymptotically towards its maximum volume. Continued distension caused the stomach to become compliant and this was irreversible within the time course of each experiment (8h). Repeated periods of rest and distension revealed a short-term inhibition of reflex contractions which recovered as resting periods were extended. Sectioning the vagosympathetic trunk did not influence the response to distension. Similar responses occurred in isolated, perfused stomachs. 2. Both tetrodotoxin and atropine plus methysergide induced immediate compliance, suggesting that it was caused by the blockade of enteric excitatory neurones. Atropine alone primarily reduced reflex contractions whilst methysergide completed this suppression and induced profound gastric relaxation. 3. Somatostatin reversibly suppressed reflex contractions whilst vasoactive intestinal polypeptide (VIP) induced gastric relaxation. 4. A model is proposed in which distension initially causes reflex activity via cholinergic and serotonergic nerves, whilst gastric tone remains high. Somatostatin then suppresses rhythmic contractions, whilst VIP suppresses the tryptaminergic mechanisms that maintain gastric tone. 5. The rainbow trout stomach possesses intrinsic mechanisms that mimic the extrinsic, nerve-controlled ‘receptive relaxation’ or ‘accommodation’ that follows feeding in higher vertebrates.

Publisher

The Company of Biologists

Subject

Insect Science,Molecular Biology,Animal Science and Zoology,Aquatic Science,Physiology,Ecology, Evolution, Behavior and Systematics

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