On the Nervous Regulation of Gill Blood Flow in the Dogfish (scyliorhinus Canicula)

The motor innervation of the gill blood vessels of the dogfish Scyliorhinus canicula L. has been investigated by electrical stimulation of (1) the branchial branches of the IXth and Xth cranial nerves in isolated perfused 1st holobranch preparations and (2) both Xth cranial nerves in whole anaesthetized fish. The observed vascular responses to nerve stimulation appear to be entirely due to contraction of the striated muscles of the gill arch and not to any direct motor innervation of the major gill blood vessels since the responses were blocked only by the drug pancuronium, which blocks striated muscle motor end-plates. The specificity of pancuronium for the motor end-plate of striated muscle in the dogfish was established by showing that it did not block nervous transmission across the cardiac ganglia. The results from the nerve stimulation studies have been investigated further by pharmacological studies on isolated perfused gill preparations. Acetylcholine produces an atropine-sensitive increase in resistance to perfusion, while both adrenalin and noradrenalin decrease the resistance to perfusion.