Cardiac inotropic, chronotropic, and dromotropic actions of subretrofacial neurons of cat RVLM.
The cardiac actions of microinjecting sodium glutamate (0.5-2 nmol) among sympathetic premotor neurons of the subretrofacial nucleus in the rostral ventrolateral medulla (RVLM) were studied in chloralose-anesthetized cats after bilateral vagotomy, sinoaortic denervation, adrenalectomy, and alpha1-receptor blockade. Glutamate microinjections increased heart rate by 25.9 +/- 1.8 beats/min (17. 5%), systolic rate of rise in left ventricular pressure (LVdP/dt) by 1,443 +/- 110 mmHg/s (119%), and arterial blood pressure by 26.9 +/- 1.7 mmHg (50%), whereas they shortened the electrocardiogram P-R interval in 85 of 103 cases by 7.5 +/- 1.2 ms (11.4%), triggering junctional rhythms on five occasions. The increase in LVdP/dt usually led the rise in blood pressure, and its magnitude greatly exceeded any increase attributable to changes in heart rate, diastolic filling, or afterload. Right-sided microinjections caused significantly greater tachycardias than did left-sided microinjections, but only left-sided microinjections triggered junctional rhythms (5 of 52 vs. 0 of 51; P < 0.05), whereas microinjections on either side raised LVdP/dt equally. Subretrofacial neurons thus drive positive chronotropic, inotropic, and dromotropic actions via the cardiac sympathetic nerves, whereas subsets among them preferentially control different aspects of cardiac function.
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Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria 3052, Australia. rmca@hfi.unimelb.edu.au
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D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002415:Cats; D004562:Electrocardiography; D005154:Facial Nerve / Q000502:physiology*; D005260:Female; D007839:Functional Laterality; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008845:Microinjections; D009200:Myocardial Contraction / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D012970:Sodium Glutamate / Q000494:pharmacology; D017725:Ventricular Pressure / Q000187:drug effects
D012970:Sodium Glutamate