The effects on respiration in the cat of the sudden excitation of cerebral vascular nociceptors by carbon dioxide.
1. Injection of CO2-saturated saline in a distal direction into either a vertebral artery or an internal maxillary artery in pentobarbitone-anaesthetized cats produced abrupt changes in respiration. Vertebral-artery injections produced a transient inhibition of respiration, followed by a stimulation of it. Internal-maxillary-artery injections produced only the inhibition. 2. Injections during inspiration usually shortened that inspiration, reduced its volume and prolonged the following expiration. In the first 30% of an expiration they prolonged that expiration, but given in the next 50% they shortened it. In the last 20% of expiration internal-maxillary-artery injections again slightly prolonged the expiration. 3. Phenyl diguanide injected into either a vertebral or an internal maxillary artery also produced abrupt effects on respiration. 4. The effects of CO2-saturated saline were abolished by intravenous acetazolamide, suggesting that nociceptors may be affected by a change in local pH. 5. The effects may arise from the excitation of vascular nociceptors, and our observations may suggest a way of studying in animals the receptors responsible for headache.
D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001645:Biguanides / Q000494:pharmacology; D002245:Carbon Dioxide / Q000494:pharmacology*; D002415:Cats; D002536:Cerebral Arteries / Q000294:innervation*; D005260:Female; D006863:Hydrogen-Ion Concentration; D008297:Male; D008438:Maxillary Artery / Q000294:innervation; D009619:Nociceptors / Q000502:physiology*; D012119:Respiration / Q000187:drug effects*; D012965:Sodium Chloride / Q000494:pharmacology; D014711:Vertebral Artery / Q000294:innervation
D001645:Biguanides; D002245:Carbon Dioxide; D012965:Sodium Chloride; D000086:Acetazolamide; C008846:phenyl biguanide