Respiratory responses to stimulation of branchial vagus nerve ganglia of a teleost fish.

The effects of electrical stimulation of epibranchial vagus ganglia upon respiration of the carp were investigated. Single shocks evoked fast twitch responses in a number of respiratory muscles with latencies around 18 msec to the beginning and 30-35 msec to the peak of activity. Shocks given during abduction decreased the respiratory cycle duration by shortening abduction and accelerating adduction. Stimuli given throughout most of adduction also shortened the respiratory cycle, accelerating the adduction only. These responses are similar to vagally mediated lung receptor reflexes of mammals. Stimulation with short trains of pulses produced a rapid expansion-contraction movement. This movement resembles in all respects (shape, time in the respiratory cycle, muscle coordination) the intermediate expansion of a normal coughing movement. Continual stimulation at frequencies close to the normal respiratory rate had a synchronising influence upon respiration, speeding up or slowing down its rate. HRP applied to the third vagal ganglion showed that there is a small projection of this ganglion to the nucleus intermedius facialis, although the majority of sensory fibres terminate in the vagal lobe. The nucleus intermedius facialis is already known to connect directly with the respiratory motor centres and thus might provide a pathway for the fast twitch response. A projection was also found to the nucleus ambiguus; in mammals this nucleus plays an important role in the regulation of respiratory movements.