TRIGEMINALLY-MEDIATED ALTERATION OF CARDIORESPIRATORY RHYTHMS DURING NASAL APPLICATION OF CARBON-DIOXIDE IN THE RAT

Stimulation of the upper respiratory tract with air-borne irritants ca n result in dramatic alterations of cardiorespiratory rhythms that inc lude apnea, bradycardia and selective peripheral vasoconstriction. Sin ce carbon dioxide can stimulate receptors in the nasal passages, we wa nted to determine if this odorless gas can induce the same autonomic c hanges as air-borne irritants. Passing 100% carbon dioxide through the nasal passages of rats anesthetized with chloralose-urethane produced apnea, a vagally-mediated bradycardia and a sympathetically-mediated increase in mean arterial blood pressure. Application of atropine bloc ked the bradycardia without affecting respiratory or blood pressure ch anges, while injection of prazosin eliminated blood pressure responses but did not affect heart rare or apnea. There were no significant aut onomic responses to nasal application of 10, 25 or 50% carbon dioxide. The responses were mediated through the trigeminal innervation of the nasal mucosa since they could be blocked when the anesthetic procaine was applied to the nasal cavity. We conclude that these cardiorespira tory responses are due to stimulation of trigeminal nociceptors locate d within the nasal mucosa.