Afferent neural activity from pseudobranch of teleosts. Effects of Po2, pH, osmotic pressure and Na+ ions

Morphological study of the pseudobranch of teleosts has established the presence of a rich, sensory innervation composed of several types of receptors which are associated with the “true” pseudo- branchial cells and the blood vessels. Using in vitro perfused preparations of the rainbow trout (Salmo gairdnerii) pseudobranch, we have tried to establish the existence of a sensitivity to chemical factors in the plasma. Analysis of the electric activity in the pseudobranchial nerve revealed two types of impulses: 1.1. Abrupt changes in hydrostatic pressure resulted in a burst of large amplitude impulses. For similar types of impulses, increase in the concentration of Na+ ions in the perfusing solutions brought about an average increment of frequency of more than 3% per meq. L−1 above 125 meq. L−1.2.2. The frequency of small amplitude impulses is influenced mainly by the PO2 and osmotic pressure. The average increment of frequency is greater than 1% per torr below PO2 = 100 torr and more than 2% per mOsm below 269 mOsrn.L−1.It was concluded that there are at least three types of receptors: this is in good agreement with the morphological findings. It follows that the function of the pseudobranch, still unknown, might have to do with ion and ventilatory regulation mechanisms.