Control of movements of the stomach and spiral intestine of Raja and Scyliorhinus

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Abstract
The extrinsic nerves of the stomach of dogfish and skates regulate the frequency and amplitude of contraction by inhibition followed by rebounds. By contrast the nerves of the spiral intestine are excitatory.Stimulation of the vagus nerve of the ray produced slight reduction in the amplitude of spontaneous contractions of the cardiac stomach. Much greater inhibition was produced by stimulation of the sympathetic nerves and was followed by large rebound contractions. These effects were imitated by adrenalin and serotonin which altered the frequency and amplitude of contraction in various ways. These actions were not blocked by either propranalol (1–5 × 10−5 M) or phentolamine (2 × 10−5 M) and indeed were often increased. The excitatory response to adrenalin was not blocked by TTX even after this had blocked the response to the nerve. Responses both to the nerve and adrenaline were blocked by trazodone. Acetyl choline caused some contraction of the stomach but only at high concentration.Muscles of the spiral intestine of Raja or Scyliorhinus were activated by stimulation of their sympathetic nerves and by adrenalin. These responses were not blocked by phentolamine and only reduced by propranalol They were blocked by trazodone. The response to adrenalin continued after the nerve was blocked by TTX. Acetyl choline had very little effect on the spiral intestine.The striking differences between the responses of the stomach and intestine are probably related to the fact that the plexus in the latter contains no nerve cells. The neurons in the stomach are therefore presumbly connected with the inhibition and large rebound contractions.