Parabronchial oxygen extraction in ducks during selective cooling of the spinal cord

Pekin ducks Anas platyrhynchos were chronically equipped with thermodes in the vertebral canal. Metabolic heat production, parabronchial oxygen extraction, vertebral canal temperature and body temperature were measured simultaneously before and during spinal cooling, at ambient temperatures ranging from 6 to 25 degrees C. Lowering vertebral canal temperature from 41.4 +/- 0.2 degrees C to 35.9 +/- 0.6 degrees C gave a mean increase in metabolic heat production of 1.54 +/- 0.26 W kg-1. Even though the spinal cooling had a clear metabolic effect, there was no concomitant change in parabronchial oxygen extraction. It is concluded that the thermosensitive structures residing in the spinal cord are not involved in the regulation of parabronchial gas exchange. The increase in parabronchial oxygen extraction, which is reported during cold exposure in birds, may therefore be induced by thermal inputs from peripheral thermoreceptors.