Sensory receptors in the first gill arch of rainbow trout.

Afferent neural activity was recorded from sensory receptors innervated by the glossopharyngeal nerve (cranial nerve IX) in isolated, perfused first gill arch preparations from rainbow trout. The present study demonstrates the presence of every major type of peripheral cardio-respiratory receptor described in fish in this preparation. Oxygen-sensitive chemoreceptors responsive to internal and/or external hypoxia and cyanide were present. Qualitatively these receptors behaved in an identical fashion which was also similar to that described for mammalian carotid body chemoreceptors. About 5% of the sensory receptors examined were O2-sensitive. proprioceptors were the most numerous receptor type identified and were sensitive to mechanical stimulation of the arch, rakers or filaments. Finally, baroreceptors, the least numerous class of receptor identified, were also present with activity that was altered in response to changes in perfusion pressure. While the reflex responses elicited by the stimulation of these receptors were not addressed in this study, it is likely that these receptors contribute to the reflex cardio-respiratory responses to changes in gill perfusion, gill deflection and hypoxia (environmental or internal) described in fishes. These data thus support suggestions concerning homologies between the first gill arch of teleosts and the carotid bodies of mammals and the importance of the first gill arch in trout in cardio-respiratory control.