Respiratory Reflexes in the Dogfish

Abstract

Inflation of the pharynx of a dogfish causes an inhibition of respiration manifested as a reduction in rate and amplitude. Tetanic stimulation of the central end of a cut branchial nerve also inhibits respiration. These inhibitory responses differ in their greater regularity and duration from the transient inhibition arising from stimulation elsewhere in the body. Both normal respiration and inflation cause the discharge of receptors whose impulses pass up the vagus nerve. The pattern of firing of these receptors during an inflation corresponds to the pattern, of inhibition. Brief inflations are more effective in securing inhibition if they arrive at a time when the receptors are not being caused to fire by a normal inspiration. Cutting the branchial branches of the IXth and Xth nerves eliminates the pause between successive respirations and increases the respiratory rate. These pauses can be made to reappear by periodically stimulating the central end of a cut branchial nerve. Section of the brain between the medulla and the mesencephalon increases the sensitivity to inflation. Inhibitory afferents run in all branchial branches of the IXth and Xth nerves and in the pre-spiracular branch of the VIIth nerve. It is suggested that in its response to vagotomy the dogfish resembles a medullary mammal.