1988 Volume 156 Issue Suppl Pages 75-81
We evaluated rapid and transient changes in phrenic (PN) and internal intercostal (IIC) activities when 0.5 ml of saline saturated with 100% CO2 was injected into the vertebral artery at the C1 level before and after cisternal administration of carbonic anhydrase inhibitor (acetazolamide) in decerebrated, spontaneously breathing cats. Before acetazolamide administration, the injections evoked an initial, transient inhibition of ongoing PN or IIC activity, followed by excitation of subsequent respiratory activities with a short onset latency of less than 3 sec. On the other hand, cisternal administration of acetazolamide abolished both the initial inhibition and the subsequent rapid excitation of respiratory activities, although there still existed a delayed, weak and prolonged excitation of respiration. These results indicated that hydration of CO2 accelerated by carbonic anhydrase within the brain would be essential for the rapid changes in respiratory activity mediated by the central chemoreceptors.