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Afferent nervous pathways involved in the neural intergration of the respiratory and circlatory systems in fish Smith, John Clegg


By superimposing an artificial water flow over the gills out of phase with the natural breathing movements of the fish, it has been possible to demonstrate that bradycardia and cardiorespiratory synchrony develop in response to decreased peripheral oxygen levels. Further evidence that peripheral and not central receptors are involved was furnished by injecting deoxygenated blood into the dorsal aorta; no effect on heart rate or breathing was observed. Bradycardia still develops in response to hypoxia at the respiratory surface even during the absence of branchial blood flow demonstrating that the circulatory system is not involved in this reflex. Numerous tastebud-like receptors have been found lining the anterior faces of the gill bars. These are innervated by the branchial branches of the vagus nerve. Stimulation of the cut central ends of these nerves results in responses similar to those obtained when environmental oxygen levels are decreased. It is suggested that these tastebud-like organs are the receptors and that the branchial branches of the vagus nerve form one afferent pathway for reflex bradycardia and cardiorespiratory synchrony. Other possible afferent pathways are suggested and the functional significance of the reflex is discussed.

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