Effects of sectioning cranial nerves IX and X on the cardiac response to hypoxia in the coho salmon, Oncorhynchus kisutch

We have shown that oxygen receptors located in the first gill arches of coho salmon, and responsible for hypoxic bradycardia, may be innervated by branches of the glossopharyngeal nerve (cranial IX). Bilateral section of these branches produced a reduction in the cardiac response to rapidly induced hypoxia. Branches of the vagus nerve (cranial X) also innervate the first gill arches in salmon; when both vagal and glossopharyngeal branches to the first gill arches were sectioned, hypoxic bradycardia was reduced by the same degree as was observed when the glossopharyngeal branches alone were sectioned. The surgical procedures involved in denervation appeared to have no effect on the cardiac response to hypoxia. The pattern of innervation of oxygen receptors causing hypoxic bradycardia in salmonids is compared with the more diffuse pattern found in elasmobranchs.