Effects of Sectioning Cranial Nerves IX and X on Cardiovascular and Ventilatory Reflex Responses to Hypoxia and Nacn In Channel Catfish

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Abstract
The afferent pathways mediating cardiovascular and ventilatory hypoxic reflexes were identified in anaesthetized, spontaneously breathing (ASB) channel catfish, Ictalurus pimctatus (Rafinesque), by bilateral section of cranial nerve IX and branchial branches of cranial nerve X to the four gill arches (Xb1-Xb4). Cardiovascular and ventilatory responses to hypoxia and NaCN were attenuated by partial denervation of the gills. There were no significant cardiovascular or ventilatory reflex responses to either hypoxia or NaCN after total branchial denervation. This suggests that hypoxic reflexes in channel catfish are mediated by O2-sensitive chemoreceptors located peripherally in the gills and innervated bycranial nerves IX and X.