Electrocardiographic changes associated with the nasopharyngeal reflex in conscious rabbits: vago-sympathetic co-activation.
Electrocardiographic responses were assessed in conscious rabbits when the nasopharyngeal reflex was elicited by inhalation of formaldehyde vapour. There was a profound fall in heart rate (224+/-5 to 64+/-4 beats per min (bpm)) associated with abnormal or absent P-waves. There were no changes in the QRS complex. The R-T interval (control value 118+/-4 ms) was initially shortened to 107+/-3 ms and then prolonged to 130+/-4 ms. Heart rate and P-wave changes were prevented by muscarinic cholinergic blockade with methylscopolamine. The R-T shortening was reduced by 79+/-4% by beta-adrenergic blockade with propranolol. Methylscopolamine also unmasked small tachycardic responses (5-25 bpm) in 5/7 animals. This tachycardia was prevented by propranolol. Thus both parasympathetic vagal cardiac nerves and sympathetic cardiac nerves are activated during the nasopharyngeal reflex, with increased vagal effects in the sino-atrial node, and increased sympathetic effects in the ventricular myocardium.
Nalivaiko
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Department of Physiology, Centre for Neuroscience, Flinders University, Bedford Park, SA 5042, Australia. eugene.nalivaiko@flinders.edu.au
De Pasquale
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CG
Blessing
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D000818:Animals; D003243:Consciousness / Q000502:physiology; D004347:Drug Interactions; D004562:Electrocardiography / Q000379:methods*; D005404:Fixatives / Q000494:pharmacology; D005557:Formaldehyde / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009305:Nasopharynx / Q000187:drug effects / Q000502:physiology*; D011433:Propranolol / Q000494:pharmacology; D011817:Rabbits; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D012601:Scopolamine / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D013610:Tachycardia / Q000517:prevention & control; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
D005404:Fixatives; D018727:Muscarinic Antagonists; D014665:Vasodilator Agents; D005557:Formaldehyde; D011433:Propranolol; D012601:Scopolamine