Effects of Carotid Chemoreceptor Stimulating and Depressing Agents on Internal Intercostal Muscle Activity in the Rabbit

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The effects of carotid chemoreceptor stimulating and depressing agents on internal intercostal muscle activity (IIMA) were studied before and after surgical denervation of the carotid sinus nerve (CSN) in the rabbit. An intracarotid injection of 30μg of sodium cyanide (NaCN) during inspiration caused an increase in both IIMA and respiratory rate (RR). In contrast, intracarotid administration of 10μg of dopamine (DA) during inspiration resulted in a decrease in both IIMA and RR. The NaCN- and DA-induced characteristic responses in IIMA were abolished by the section of the CSN. The results indicate that the excitatory and inhibitory responses of IIMA to intracarotid injections of NaCN and DA are mainly mediated through carotid chemoreflexes.