Central nervous control of gill filament muscles in channel catfish

The gills of fish are innervated by cranial nerves IX and X. There have been a number of studies on the characteristics of sensory activity carried by these nerves but remarkably little is known about motor control of the gills. Efferent, motor activity to the first gill arch was recorded from the glossopharyngeal nerve in spontaneously breathing channel catfish, Ictalurus punctatus. This study addressed two objectives. The first objective was to characterize efferent branchial nerve activity in spontaneously breathing fish. Nerve recordings show bursts of activity firing in synchrony with ventilation. These bursts occurred once during either abduction or adduction of the operculum with each breath. The observed patterns of neural activity indicate that it represents motor control of gill filament abductor and adductor muscles. The data show that rhythmic output from a central pattern generator controls filament musculature during the ventilatory cycle. The second objective was to use this efferent branchial nerve activity as an index of ventilation (fictive ventilation) in fish before and after paralysis to determine if feedback from phasic mechanoreceptors affects ventilatory timing. Breath-to-breath intervals measured before and after paralysis with gallamine were not significantly different, demonstrating that rhythmic feedback from phasic mechanoreceptors in the gills and/or ventilatory musculature is not involved in the breath-to-breath timing of the normal ventilatory cycle. During the course of these experiments many fish exhibited coughing. Coughs were characterized by a distinctive pattern of nerve activity that was not altered by paralysis. Overall, the data indicate that phasic mechanoreceptor feedback during normal breathing has no effect on the pattern of central motor control of gill filament muscles.