Avian arterial chemoreceptor responses to steps of CO2 and O2

The responses of avian arterial chemoreceptor preparations to 44-sec steps of inspired CO2 and O2 were quantified. Anesthetized ducks were unidirectionally ventilated, arterial pH was recorded with a fast responding indwelling electrode, and neural activity was recorded from 28 preparations consisting of dissected filaments of the vagus nerve (23 single-fibered, 5 few-fibered). We analyzed responses using cycle-triggered stimulus histograms of neural discharge, cross correlation analysis, and analysis of variance. Average responses of the chemoreceptor preparations to PaCO2 steps from 24 +/- 1 to 38 +/- 1 Torr were larger (per Torr), occurred faster, and appeared more rate sensitive than the responses to PaO2 steps from 101 +/- 3 to 56 +/- 2 Torr. Average responses to CO2 steps usually appeared more rate sensitive when measured during arterial hypoxia than during arterial normoxia. These characteristics are very much like those reported for mammalian arterial chemoreceptors, except that responses of avian chemoreceptor preparations to repetitive CO2 steps were highly variable according to statistical analysis.