A HERING-BREUER-TYPE REFLEX FROM THE GILL ARCHES OF A TELEOST FISH

Publisher Summary The chapter presents experiments that were conducted on a teleost fish, that is, the carp, Cyprinus carpio, in which vagal input was modified by electrical stimulation at different phases of the normal respiratory cycle. In fishes anaesthetized with MS 222 (30–40 mg/l), the ganglia of the second and third branchial branches of the vagus were exposed. Stimulation was carried out with bipolar stainless steel needle electrodes insulated to the tips and implanted in the ganglion about 0.5 mm apart. The stimuli were phase locked to the respiratory cycle and were either single shocks or short trains. Respiration was monitored by recording the electromyograms of important respiratory muscles, together with the movement of an operculum. The stimulus pulses could be delivered at predetermined phases of the respiratory cycle by triggering the stimulator from the mechanoreceptor output via an adjustable delay circuit. It was found that single shocks delivered to the vagus result in a reflex action in various respiratory muscles with a latency of about 20–30 ms. The effect is highly variable and habituates or adapts rapidly even to stimuli presented many seconds apart.