Abstract
Openings of paleopulmonic parabronchi in paralyzed, unidirectionally ventilated geese were photographed through small holes in the bird's mediodorsal secondary bronchi during single-unit recording from intrapulmonary CO 2 receptors. Changes in the discharge frequency of the receptors as fractional CO 2 concentration of ventilating gas was alternated between 0 and 0.05 were compared with the changes in cross-sectional areas of randomly selected parabronchial lumina. Intrapulmonary CO 2 receptors, similar to those found in other avian species, are also present in geese. Changes in intrapulmonary CO 2 concentration greatly influenced the discharge of these receptors but did not induce movement of parabronchial smooth muscle in this region of the lung. If most of the receptors are located in the paleopulmonic parabronchi, as currently appears to be the case, we must conclude that changes in receptor discharge in response to changes in intrapulmonary CO 2 concentration do not result from mechanical distortion of the receptors induced by smooth muscle contraction; intrapulmonary CO 2 receptors appear to be true chemoreceptors.
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