title: The effects of asphyxia on afferent activity recorded from the cervical vagus in the duck.
abstract: Recordings were made of nervous activity from duck arterial chemoreceptors, arterial baroreceptors and pulmonary receptors during steady-state conditions (normoxic normocapnia, hypoxia, and hypercapnia) and apnoeic asphyxia. Arterial chemoreceptors were stimulated by hypoxia and intra-arterial KCN injection and showed an increasing discharge throughout asphyxia. During the first 2 min of asphyxia the time course of the development of asphyxic bradycardia paralleled that of the increase in arterial chemoreceptor discharge. Arterial baroreceptors discharged at a constant latency from the heart beat when mean arterial pressure was constant, while a drug-induced increase in mean arterial pressure was associated with a reduced latency and increased baroreceptor activity per heart-beat. During asphyxia mean arterial pressure often rose so that, despite the effect of bradycardia, baroreceptor activity per heart-beat and activity per unit time increased. Pulmonary receptors showed a linear relationship (negative slope) between discharge rate and % CO2 in inspired air and usually stopped firing in apnoeic asphyxia. The initiation and maintenance of diving bradycardia are discussed in terms of these results.
mesh_terms: D000818:Animals; D001237:Asphyxia; D002628:Chemoreceptor Cells / Q000502:physiology; D004242:Diving; D004372:Ducks / Q000502:physiology*; D004594:Electrophysiology; D006339:Heart Rate; D011311:Pressoreceptors / Q000502:physiology; D011661:Pulmonary Stretch Receptors / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology*