Intrapulmonary CO 2 receptors in the duck: II. Comparison with mechanoreceptors

Abstract

Single-unit recordings from vagal afferents exhibiting discharge patterns in phase with pump ventilation were made in domestic ducks to determine if receptors, other than intrapulmonary CO 2 receptors, discharge in phase with the pump. After identification of the units during pump ventilation, the units were tested during unidirectional ventilation for their response to changes in inspired CO 2 concentration (F i CO 2 ) and to changes in mechanical distortion resulting from increases in intrapulmonary pressure (Pip). Two types of receptors with distinct differences in discharge pattern were encountered: (1) Receptors which responded rapidly to changes in F I CO 2 but which were insensitive to mechanical deformation (18 receptors out of 22). These receptors were located in the lung and were similar to those described by Fedde et al. (1974). (2) Receptors that were insensitive to changes in F I CO 2 but increased their discharge frequency parallel to increases in Pip (4 receptors out of 22). These receptors appear to be slowly adapting mechanoreceptors. Their location could not be determined. The results suggest that with cyclic ventilation, spontaneous or artificial, only two types of receptors with vagal afferents are stimulated, both of which are highly stimulus-specific. Whereas the intrapulmonary CO 2 receptors are very likely to be involved in control of breathing, the role played by mechano-receptors is unknown.